Ørjan Grøttem Martinsen

• Laeng, Bruno; Zambrana, Imac; Hou, Jie; Martinsen, Ørjan Grøttem & Holm, Kristiane (2026). Machine learning classification of emotional videos via autonomic arousal based on pupil diameters, electrodermal activity and heart rate. International Journal of Psychophysiology. ISSN 0167-8760. s. 113455–113455. doi: 10.1016/j.ijpsycho.2026.113455. Fulltekst i vitenarkiv Vis sammendrag

  We evaluated the ability of Electrodermal Activity (EDA), Heart Rate Variability (HRV), and Pupil Diameter (PD) to detect emotional states via machine learning to determine whether simple arousal metrics can distinguish complex emotional labels: Amusement, Awe, Disgust, Nurturant Love, and Sadness. In a laboratory session, participants (N = 47) selected the most appropriate emotional label out of five immediately after viewing 10 short videos. Classifications relied solely on the three psychophysiological measures and by applying three machine learning models: Support Vector Machine (SVM/SVC), Random Forest (RF), and Extreme Gradient Boosting (XGBoost). Features included baseline-corrected average pupil diameter (PD) and electrodermal activity (EDA) peaks. Noisy heart rate variability (HRV) data were excluded to prevent signal-to-noise ratio degradation. PD reflects sympathetic noradrenergic activation and reciprocal coupling within the Autonomic Nervous System (ANS), providing a stable state estimate. In the core ‘affect circumplex’, SVC achieved peak accuracy, and PD achieved the highest feature importance score across architectures. Results revealed a many-to-one mapping where discrete valence states produced indistinguishable physiological signatures: high-arousal states (Amusement, Sadness) and low-arousal states (Awe, Disgust) were conflated. Notably, Awe triggered PD constriction, mirroring Disgust's profile. Tactical removal of the cardiovascular features significantly improved RF and XGBoost performance. These findings suggest that simple arousal metrics, and specifically pupillometry, can classify affect without using complex time-series analysis. Non-invasive sensors may facilitate the development of sensitive computerized systems calibrated to objective physiological data.

• Aldosky, Haval Y. Yacoob; Bari, Dindar S. & Martinsen, Ørjan Grøttem (2026). Correlations of multifrequency impedance components with water conductivity. Physics and chemistry of liquids (Print). ISSN 0031-9104. doi: 10.1080/00319104.2026.2704203. Fulltekst i vitenarkiv
• Youssif, Ardawan A.; Bari, Dindar S.; Girgis, Shanaz D.; Abdulkarim, Rawaz A.; Farouk, Ayat L. & Aldosky, Haval Y.Yacoob [Vis alle 7 forfattere av denne artikkelen] (2026). Effects of seasonal changes on the skin surface electrical susceptance. Biomedical Engineering & Physics Express. 12(2). doi: 10.1088/2057-1976/ae4df1. Fulltekst i vitenarkiv
• Hou, Jie; Ali, Abdulkadir Hassen & Martinsen, Ørjan Grøttem (2025). Using neuromorphic computing in prediction of GABA concentration – a pilot study. Journal of Electrical Bioimpedance. 16(1), s. 146–149. doi: 10.2478/joeb-2025-0019. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Neuromorphic computing has the potential to facilitate detection of GABA concentration levels in the brain, and offers energy-efficient, real-time machine learning processing possibilities. To study whether neuromorphic computing can be used for GABA concentration detection, dielectric relaxation spectroscopy was used to acquire permittivity data of different concentrations of GABA solution. Thereafter, two different machine learning models were compared (Feedforward neural network (FFNN) and convolutional neural network (CNN)) for accuracy in prediction of GABA concentration from dielectric properties. The CNN model was then converted to spiking Neural Networks (SNNs), which showed promising results for energy efficiency and real-time processing capabilities. The system incorporates Tkinter, a Python interface to the Tcl/Tk GUI toolkit for seamless data transfer between the neuromorphic chip and the measurement system, ensuring flexibility and scalability in a user-friendly system.

• Nøvik, Steffen; Hirayama-Shoji, Kayoko; Combriat, Thomas; Sakalys, Domantas; Aashamar, Erik & Louch, William E. [Vis alle 9 forfattere av denne artikkelen] (2025). Bioimpedance and electrophysiology measurements of engineered heart tissues outside the culture medium. Biosensors and Bioelectronics. ISSN 0956-5663. 287, s. 117634–117634. doi: 10.1016/j.bios.2025.117634. Fulltekst i vitenarkiv
• Pabst, Oliver; Schülke, Christin; Balasingham, Ilangko; Krauss, Stefan Johannes Karl; Glover, Joel Clinton & Martinsen, Ørjan Grøttem (2025). Recording and modeling of pinched hysteresis loops, the fingerprint of a memristor, in neurons. Scientific Reports. 15. doi: 10.1038/s41598-025-21035-0. Fulltekst i vitenarkiv Vis sammendrag

  A variant of the Hodgkin-Huxley model has been proposed in which time-varying Na+ and K+ ion conductances are replaced by memristors, based on the proposal that ion channels are memristors. This hypothesis predicts that current-voltage plots of neurons subjected to sinusoidal stimulation should exhibit a pinched hysteresis loop, the fingerprint of a memristor. We tested this using whole-cell patch clamp recordings from human neurons derived from neural progenitor cells and observed pinched hysteresis loops in 16% of all recorded neurons. Recordings with current clamp and voltage clamp with a holding potential of 0 mV yielded a higher success rate than voltage clamp recordings with a holding potential of around − 60 mV. In addition, more neurons exhibited pinched hysteresis loops when the applied voltage or current amplitude was high, and the frequency was low. The recording of pinched hysteresis loops in neurons gives evidence that these contain memristors and this is the first time to be shown experimentally. This is not just an indication that the memristor-based Hodgkin-Huxley model is valid; it also demonstrates that models of neurons based on memristors actually resemble nature. We then subjected simulated neurons expressing Hodgkin-Huxley voltage-gated Na+ and K+ channels to sinusoidal membrane potential oscillations and found that the presence of pinched hysteresis loops depended strongly on the density of voltage-gated K+ channels and on the membrane capacitance but not on the presence of voltage-gated Na+ channels. Because Na+ channels are expected to be largely inactivated in neurons at a holding potential of 0 mV, these findings together suggest that it is the presence of voltage-gated K+ channels that is critical for the observed memristive behavior.

• Fagerland, Steffen Knut Maude; Løve, Andreas; Helliesen, Tord K.; Martinsen, Ørjan Grøttem; Rootwelt-Revheim, Mona-Elisabeth & Endestad, Tor (2025). Method for Using Functional Near-Infrared Spectroscopy (fNIRS) to Explore Music-Induced Brain Activation in Orchestral Musicians in Concert. Sensors. 25(6). doi: 10.3390/s25061807. Fulltekst i vitenarkiv
• Rozynek, Zbigniew Jerzy; Harkavyi, Y.; Martinsen, Ørjan Grøttem & Giżyński, K. (2025). Fabrication of a new type of electrically conductive micro-tracks via mechanical compression of beaded structures. Materials & design. ISSN 0264-1275. 253. doi: 10.1016/j.matdes.2025.113985. Fulltekst i vitenarkiv Vis sammendrag

  In recent years, the importance of critical raw materials for global economic development has become increasingly evident, especially in electronics. A challenge in this industry is replacing traditional, unsustainable silver nanoparticle-based conductive pastes used for creating conductive paths. This paper presents an approach to fabricating conductive micro-tracks from preassembled bead-like chains of microparticles. These single-particle-thick structures achieve high conductivity through a straightforward post-processing method — mechanical compression — offering a sustainable alternative to complex nanoparticle pastes. Our study explores the effects of uniaxial compression on malleable microparticles deposited additively on substrates, examining particle deformation, interparticle contact area changes, and their impact on conductivity. Through comprehensive numerical simulations, closely aligned with experimental observations, we establish a quantitative relationship between compressive strain (ɛ), compressive force (FN), the contact area between the compressing plate and the ball (A1), interparticle contact area (A2), and the electrical resistance (R) of the particle chain. We studied linear structures of monodisperse microparticles and investigated the effects of polydispersity and deviations from linearity. Furthermore, we studied the influence of compression force and process temperature on the stability of the substrate on which beaded structures are formed. This research presents a sustainable alternative to traditional nanoparticle pastes, offering a bottom-up method for developing optimized conductive paths.

• Cunha, André; Schülke, Christin; Mesri, Alireza; Ruud, Simen Kristoffer; Aizenshtadt, Aleksandra & Ferrari, Giorgio [Vis alle 16 forfattere av denne artikkelen] (2024). Development of a Smart Wireless Multisensor Platform for an Optogenetic Brain Implant. Sensors. 24(2). doi: 10.3390/s24020575. Fulltekst i vitenarkiv Vis sammendrag

  Implantable cell replacement therapies promise to completely restore the function of neural structures, possibly changing how we currently perceive the onset of neurodegenerative diseases. One of the major clinical hurdles for the routine implementation of stem cell therapies is poor cell retention and survival, demanding the need to better understand these mechanisms while providing precise and scalable approaches to monitor these cell-based therapies in both pre-clinical and clinical scenarios. This poses significant multidisciplinary challenges regarding planning, defining the methodology and requirements, prototyping and different stages of testing. Aiming toward an optogenetic neural stem cell implant controlled by a smart wireless electronic frontend, we show how an iterative development methodology coupled with a modular design philosophy can mitigate some of these challenges. In this study, we present a miniaturized, wireless-controlled, modular multisensor platform with fully interfaced electronics featuring three different modules: an impedance analyzer, a potentiostat and an optical stimulator. We show the application of the platform for electrical impedance spectroscopy-based cell monitoring, optical stimulation to induce dopamine release from optogenetically modified neurons and a potentiostat for cyclic voltammetry and amperometric detection of dopamine release. The multisensor platform is designed to be used as an opto-electric headstage for future in vivo animal experiments.

• Bari, Dindar S.; Rammoo, Mohammed Noor S.; Youssif, Ardawan A.; Najman, Hoger M.; Aldosky, Haval Y. Yacoob & Tronstad, Christian [Vis alle 8 forfattere av denne artikkelen] (2024). Electrodermal Activity for Quantitative Assessment of Dental Anxiety. Journal of Sensor and Actuator Networks. 13(6). doi: 10.3390/jsan13060088. Fulltekst i vitenarkiv Vis sammendrag

  In spite of the development in technology and the recent innovations in dentistry, dental anxiety remains a common issue, and accurately assessing it is challenging due to reliance on patients’ self-reports, which are often biased. Hence, this study was undertaken to determine whether dental anxiety can be quantified objectively using the EDA parameters. EDA (skin conductance (SC), skin susceptance (SS), and skin potential (SP)) parameters and heart rate (HR) were recorded from 40 participants during two different sessions (baseline and anxiety). In addition, the Modified Dental Anxiety Scale (MDAS) scale was also used to record the level of anxiety. The physiological data from EDA and HR were compared with the subjective self-reports of anxiety provided on the MDAS to show whether higher EDA and HR readings correspond to higher scores on the MDAS. To elicit dental anxiety, participants were exposed to several film clips associated with dental treatment. EDA signals were compared between the two sessions for all clips and all EDA scores. SC and HR significantly (p < 0.05) increased during the anxiety session compared to the baseline session. The number of fluctuations per minute in the SC, SS, and SP notably increased during the anxiety session. The MDAS results revealed that the participants had dental anxiety when they were exposed to video clips of dental procedures. The study results imply that EDA parameters could be used as a useful tool to monitor dental anxiety, in particular in young children and non-verbal patients or those with intellectual disabilities, which may aid the dentist in the successful management of dental anxiety during treatment. The moment-to-moment EDA data on a patient’s anxiety levels throughout particular dental operations provides a clearer picture of anxiety variations than pre- or post-appointment surveys alone, in addition to offering unbiased tracking of dental anxiety levels over self-reports. This study seeks to encourage further research into the most effective EDA parameters for improving the management of dental anxiety.

• Bari, Dindar S.; Aldosky, Haval Y. Y.; Tronstad, Christian & Martinsen, Ørjan Grøttem (2024). Disturbances in Electrodermal Activity Recordings Due to Different Noises in the Environment. Sensors. 24(16). doi: 10.3390/s24165434. Fulltekst i vitenarkiv Vis sammendrag

  Electrodermal activity (EDA) is a widely used psychophysiological measurement in laboratory-based studies. In recent times, these measurements have seen a transfer from the laboratory to wearable devices due to the simplicity of EDA measurement as well as modern electronics. However, proper conditions for EDA measurement are recommended once wearable devices are used, and the ambient conditions may influence such measurements. It is not completely known how different types of ambient noise impact EDA measurement and how this translates to wearable EDA measurement. Therefore, this study explored the effects of various noise disturbances on the generation of EDA responses using a system for the simultaneous recording of all measures of EDA, i.e., skin conductance responses (SCRs), skin susceptance responses (SSRs), and skin potential responses (SPRs), at the same skin site. The SCRs, SSRs, and SPRs due to five types of noise stimuli at different sound pressure levels (70, 75, 80, 85, and 90 dB) were measured from 40 participants. The obtained results showed that EDA responses were generated at all levels and that the EDA response magnitudes were significantly (p < 0.001) influenced by the increasing noise levels. Different types of environmental noise may elicit EDA responses and influence wearable recordings outside the laboratory, where such noises are more likely than in standardized laboratory tests. Depending on the application, it is recommended to prevent these types of unwanted variation, presenting a challenge for the quality of wearable EDA measurement in real-world conditions. Future developments to shorten the quality gap between standardized laboratory-based and wearable EDA measurements may include adding microphone sensors and algorithms to detect, classify, and process the noise-related EDA.

• Krispel, Thomas; Badeli, Vahid; Jafarinia, Alireza; Reinbacher-Köstinger, Alice; Tronstad, Christian & Ranftl, Sascha [Vis alle 11 forfattere av denne artikkelen] (2024). arterioscope.sim: Enabling Simulations of Blood Flow and Its Impact on Bioimpedance Signals. Bioengineering. 11(12). doi: 10.3390/bioengineering11121273. Fulltekst i vitenarkiv Vis sammendrag

  Objectives: Early detection of cardiovascular diseases and their pre-existing conditions, arteriosclerosis and atherosclerosis, is crucial to increasing a patient’s chance of survival. While imaging technologies and invasive procedures provide a reliable diagnosis, they carry high costs and risks for patients. This study aims to explore impedance plethysmography (IPG) as a non-invasive and affordable alternative for diagnosis. Methods: To address the current lack of large-scale, high-quality impedance data, we introduce arterioscope.sim, a simulation platform that models arterial blood flow and computes the electrical conductivity of blood. The platform simulates bioimpedance measurements on specific body segments using patient-specific parameters. The study investigates how introducing arterial diseases into the simulation affects the bioimpedance signals. Results: The simulation results demonstrate that introducing atherosclerosis and arteriosclerosis leads to significant changes in the computed signals compared to simulations of healthy arteries. Furthermore, simulation of a patient-specific healthy artery strongly correlates with measured signals from a healthy volunteer. Conclusions and significance: arterioscope.sim effectively simulates bioimpedance signals in healthy and diseased arteries and highlights the potential of using these signals for early diagnosis of arterial diseases, offering a non-invasive and cost-effective alternative to traditional diagnostic methods.

• AliAbbasi, Easa; Martinsen, Ørjan Grøttem; Pettersen, Fred-Johan; Colgate, James Edward & Basdogan, Cagatay (2024). Experimental Estimation of Gap Thickness and Electrostatic Forces Between Contacting Surfaces Under Electroadhesion. Advanced Intelligent Systems. doi: 10.1002/aisy.202300618. Fulltekst i vitenarkiv Vis sammendrag

  Electroadhesion (EA) is a promising technology with potential applications in robotics, automation, space missions, textiles, tactile displays, and some other fields where efficient and versatile adhesion is required. However, a comprehensive understanding of the physics behind it is lacking due to the limited development of theoretical models and insufficient experimental data to validate them. This article proposes a new and systematic approach based on electrical impedance measurements to infer the electrostatic forces between two dielectric materials under EA. The proposed approach is applied to tactile displays, where skin and voltage-induced touchscreen impedances are measured and subtracted from the total impedance to obtain the remaining impedance to estimate the electrostatic forces between the finger and the touchscreen. This approach also marks the first instance of experimental estimation of the average air gap thickness between a human finger and a voltage-induced capacitive touchscreen. Moreover, the effect of electrode polarization impedance on EA is investigated. Precise measurements of electrical impedances confirm that electrode polarization impedance exists in parallel with the impedance of the air gap, particularly at low frequencies, giving rise to the commonly observed charge leakage phenomenon in EA.

• Aliabbasi, Easa; Muzammil, Muhammad; Sirin, Omer; Lefevre, Philippe; Martinsen, Ørjan Grøttem & Basdogan, Cagatay (2024). Effect of Finger Moisture on Tactile Perception of Electroadhesion. IEEE Transactions on Haptics. ISSN 1939-1412. 17(4), s. 841–849. doi: 10.1109/TOH.2024.3441670. Fulltekst i vitenarkiv
• Salih, J.M.; Bari, D.S.; Aldosky, H.Y.Y. & Martinsen, Ørjan Grøttem (2023). Influence of sunscreen sun protection factor on moisture, oil and pH of the skin. Fresenius Environmental Bulletin (FEB). ISSN 1018-4619. 32(7), s. 2599–2605. Fulltekst i vitenarkiv
• Huus, C.M.L.; Callesen, H.E.; Darling-Rasmussen, P.; Martinsen, Ørjan Grøttem; Bikic, A. & Storebø, O.J. (2023). The use of external trigeminal nerve stimulation as an initial treatment for ADHD symptoms in children: A qualitative study of case series reports. Psychiatry Research Case Reports. ISSN 2773-0212. 2(2). doi: 10.1016/j.psycr.2023.100154. Fulltekst i vitenarkiv
• Tariverdi, Abbas; Côté-Allard, Ulysse Teller Masao; Mathiassen, Kim; Elle, Ole Jakob; Kalvøy, Håvard & Martinsen, Ørjan Grøttem [Vis alle 7 forfattere av denne artikkelen] (2023). Reinforcement Learning-Based Switching Controller for a Milliscale Robot in a Constrained Environment. IEEE Transactions on Automation Science and Engineering. ISSN 1545-5955. 21(2), s. 2000–2016. doi: 10.1109/TASE.2023.3259905. Fulltekst i vitenarkiv
• Bari, Dindar S.; Rammoo, Mohammed Noor S.; Aldosky, Haval Y. Y.; Jaqsi, Mohammed K. & Martinsen, Ørjan Grøttem (2023). The Five Basic Human Senses Evoke Electrodermal Activity. Sensors. 23(19). doi: 10.3390/s23198181. Fulltekst i vitenarkiv Vis sammendrag

  Electrodermal activity (EDA) usually relates to variations in the electrical properties of palmar or plantar skin sites. EDA responses, namely skin conductance responses (SCRs), skin potential responses (SPRs) and skin susceptance responses (SSRs) are shown to be sensitive indexes of sympathetic nervous system activation and are studied in many research projects. However, the association between EDA responses and the five basic human senses has not been investigated yet. Our study aimed to explore the relationship between the three EDA responses (SCRs, SSRs and SPRs) and the five basic human senses. These three EDA responses were measured simultaneously at the same skin site on each of the 38 volunteers. The tested five senses were sight, hearing, touch, taste and smell. The results showed that the different tested senses led to different degrees of EDA responses due to activation of the sympathetic nervous system and corresponding secretion of sweat. Although a controlled study on the degree of EDA as a function of the strength of each stimulus was not performed, we noted that the largest EDA responses were typically associated with the smell sense test. We conclude that EDA responses could be utilized as measures for examining the sensitivity of the human senses. Hence, EDA devices may have important roles in sensory systems for future clinical applications.

• Hou, Jie; Strand-Amundsen, Runar James & Martinsen, Ørjan Grøttem (2023). Detection of physiological concentrations of GABA using dielectric spectroscopy - A pilot study. Journal of Electrical Bioimpedance. 14(1), s. 47–52. doi: 10.2478/joeb-2023-0006. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter that is present at a relatively low level throughout the normal adult human brain. Abnormal GABA levels are found in people with neurodegenerative disorders such as Parkinson’s disease, epilepsy, schizophrenia, depression, and others. Being able to measure the GABA concentration would be beneficial for patient groups with fluctuating GABA levels for better diagnosis and treatment. In this study, we explore the feasibility of using dielectric relaxation spectroscopy for the detection of GABA concentrations within a physiological range, with the perspective of miniaturization and use during implantation. Utilizing machine learning techniques, we were able to differentiate GABA concentrations down to 5 μm. This work investigates a novel use of dielectric relaxation spectroscopy, to assess if physiological GABA concentrations can be detected through permittivity measurements.

• Dapsance, Florian; Hou, Jie; Dufour, Damien; Boccara, Charlotte; Briand, Nolwenn & Martinsen, Ørjan Grøttem (2023). Adipose Tissue Characterization With Electrical Impedance Spectroscopy and Machine Learning. IEEE Sensors Letters. 7(10). doi: 10.1109/LSENS.2023.3317921. Fulltekst i vitenarkiv Vis sammendrag

  Biological tissues have variable passive electrical properties depending on their cellular constitution. Electrical impedance spectroscopy (EIS) is commonly used to monitor cell and tissue characteristics. By measuring the impedance of a sample at various frequencies, it is possible to collect information regarding cell size and shape, cell membrane properties, or cytoplasm conductivity. From the perspective of longitudinal structural monitoring, bioimpedance measurements outrank traditional tissue analysis methods, such as fixation and slicing, owing to their nondestructive nature. Machine learning can be used to automatically process the impedance data and make real-time classifications of tissue types. Here, we present preliminary results on ex-vivo mouse adipose tissue measurements using EIS and further data processing and classification using machine learning models.

• Tronstad, Christian; Amini, Maryam; Olesen, Eline; Qvigstad, Elisabeth; Pabst, Oliver & Martinsen, Tormod [Vis alle 11 forfattere av denne artikkelen] (2022). Diabetic foot assessment using skin impedance in a custom made sensor-sock. Journal of Electrical Bioimpedance. 13(1), s. 136–142. doi: 10.2478/joeb-2022-0019. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Diabetic peripheral neuropathy (DPN) may lead to several changes in the skin, and some of these may influence the skin impedance spectrum. In the present study we have developed a prototype solution for skin impedance spectroscopy at selected skin sites (big toe pulp, heel and toe ball) that was tested in a pilot study on five patients with DPN and five healthy controls. At the big toe, most of the controls had markedly lower impedance than the DPN group, especially in the range of 1-100 kHz. The separation between the groups seems to be weaker at the heel and weakest at the toeball. The results may indicate that monitoring of the skin impedance spectrum may be a method for detection of skin changes associated with DPN, encouraging further studies with the big toe sensor in particular.

• Nøvik, Steffen; Drageseth, Magnus Flø; Grøndalen, Magnus Børresen; Nilsen, Ola; Krauss, Stefan Johannes Karl & Martinsen, Ørjan Grøttem [Vis alle 7 forfattere av denne artikkelen] (2022). A CMOS Multi-Electrode Array for Four-Electrode Bioimpedance Measurements. IEEE Transactions on Biomedical Circuits and Systems. ISSN 1932-4545. 16(6), s. 1276–1286. doi: 10.1109/TBCAS.2022.3214243. Fulltekst i vitenarkiv Vis sammendrag

  This work demonstrates how a multi-electrode array (MEA) dedicated to four-electrode bioimpedance measurements can be implemented on a complementary metal–oxide–semiconductor (CMOS) chip. As a proof of concept, an 8 × 8 pixel array along with dedicated amplifiers was designed and fabricated in the TSMC 180 nm process. Each pixel in the array contains a circular current carrying (CC) electrode that can act as a current source or sink. In order to measure a differential voltage between the pixels, each CC electrode is surrounded by a ring shaped pick up (PU) electrode. The differential voltages can be measured by an on-board instrumentation amplifier, while the currents can be measured with an on-bard transimpedance amplifier. Openings in the passivation layer exposed the aluminum top metal layer, and a metal stack of zinc, nickel and gold was deposited in an electroless plating process. The chips were then wire bonded to a ceramic package and prepared for wet experiments by encapsulating the bonding wires and pads in the photoresist SU-8. Measurements in liquids with different conductivities were performed to demonstrate the functionality of the chip.

• Tronstad, Christian; Amini, Maryam; Bach, Dominik R. & Martinsen, Ørjan Grøttem (2022). Current trends and opportunities in the methodology of electrodermal activity measurement. Physiological Measurement. ISSN 0967-3334. 43(2). doi: 10.1088/1361-6579/ac5007. Fulltekst i vitenarkiv
• Tariverdi, Abbas; Mathiassen, Kim; Søyseth, Vegard; Kalvøy, Håvard; Elle, Ole Jakob & Tørresen, Jim [Vis alle 8 forfattere av denne artikkelen] (2022). Physics-Based Simulation and Control Framework for Steering a Magnetically-Actuated Guidewire. I Dilger, Lale Canan (Red.), 2022 8th International Conference on Control, Decision and Information Technologies (CoDIT). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781665496070. doi: 10.1109/CoDIT55151.2022.9803963. Fulltekst i vitenarkiv
• Kjølerbakken, Kai Morgan; Miloch, Wojciech Jacek; Martinsen, Ørjan Grøttem; Pabst, Oliver & Røed, Ketil (2022). Numerical Study of Non-Linear Effects for a Swept Bias Langmuir Probe. IEEE Transactions on Plasma Science. ISSN 0093-3813. 50(5), s. 1237–1245. doi: 10.1109/TPS.2022.3164220. Fulltekst i vitenarkiv Vis sammendrag

  We present a numerical study disclosing non-linear effects and hysteresis loops for a swept bias Langmuir probe. A full kinetic particle in cell (PIC) model has been used to study the temporal sheath effects and the probe current. Langmuir "close to steady state" condition is required to characterize the plasma. However, during operations above frequencies normally used, capacitive and non-linear resistive effects are being unveiled. We demonstrate how ion and electron density and temperature change properties of the probe-plasma system. We also show that a swept Langmuir probe exhibits essential properties described as the "fingerprint of memristors" and how a Langmuir probe can be identified as a transversal memristor. Understanding non-linear processes might enable new ways to operate Langmuir probes with higher sampling rates and better accuracy.

• Qasim, Masood S.; Bari, Dindar S. & Martinsen, Ørjan Grøttem (2022). Influence of ambient temperature on tonic and phasic electrodermal activity components. Physiological Measurement. ISSN 0967-3334. 43(6). doi: 10.1088/1361-6579/ac72f4. Fulltekst i vitenarkiv
• Osen, Daniel E.; Abie, Sisay Mebre; Martinsen, Ørjan Grøttem; Egelandsdal, Bjørg & Münch, Daniel (2022). Bioimpedance-based authentication of defrosted versus fresh pork at the end of refrigerated shelf life. Journal of Electrical Bioimpedance. 13(1), s. 125–131. doi: 10.2478/joeb-2022-0017. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Correct food labeling is a legal requirement and helps consumers to make informed purchasing choices. Mislabeling defrosted meat as fresh is illegal in the EU. However, there are no standardized technologies to authenticate fresh versus defrosted meat. We address this by testing if bioimpedance-based measurements can separate defrosted meat from refrigerated-only meat at the end of shelf life, i.e., when also fresh meat shows deterioration. Pork sirloin samples from 20 pigs were first tested at 12 days postmortem (‘fresh group’). This time point was chosen to represent a typical use-by date for refrigerated storage of fresh pork. Then, all samples were transferred to a -24°C freezer for 3 days and thawed for 2 days before final testing (‘frozen-thawed group’). Bioimpedance analyses (BIA) were done in a frequency range of [10 2 -10 6 Hz]. Weight, pH and electrode positioning were assessed to test for potential confounding effects. Statistics for treatment dependent differences were based on the established P y parameter and phase angle, which were extracted from the BI spectra. We found that using bioimpedance testing with tetrapolar electrodes, P y and phase angle allowed almost complete separation of fresh and previously frozen samples. However, within the whole sample population, there was some overlap between the spectra of fresh and frozen samples. Yet, based on P y , only one fresh sample (5% of N total =20) fell in the lowest P y class with all the frozen samples. We used a multifactorial design that allowed to test the effects of potential confounding factors, such as electrode positioning and meat quality parameters. We found a relatively low explained variance for the P y parameter, indicating that confounding effects from other factors or quality defects in fresh pork may affect the detection capacity of bioimpedance-based authentication of fresh pork. Our data, therefore, suggest that reliable fresh-label authentication with bioimpedance testing should be based on testing a small number of samples to represent a specific lot of pork that is to be inspected.

• Hou, Jie; Liavåg, Olav Magnus Ivar; Færden, Ida Høy; Martinsen, Ørjan Grøttem; Tønnessen, Tor Inge & Line, Pål Dag [Vis alle 10 forfattere av denne artikkelen] (2022). Utilization of dielectric properties for assessment of liver ischemia-reperfusion injury in vivo and during machine perfusion. Scientific Reports. 12(1). doi: 10.1038/s41598-022-14817-3. Fulltekst i vitenarkiv Vis sammendrag

  Abstract There is a shortage of donor livers and patients consequently die on waiting lists worldwide. Livers are discarded if they are clinically judged to have a high risk of non-function following transplantation. With the aim of extending the pool of available donor livers, we assessed the condition of porcine livers by monitoring the microwave dielectric properties. A total of 21 livers were divided into three groups: control with no injury (CON), biliary injury by hepatic artery occlusion (AHEP), and overall hepatic injury by static cold storage (SCS). All were monitored for four hours in vivo, followed by ex vivo plurithermic machine perfusion (PMP). Permittivity data was modeled with a two-pole Cole–Cole equation, and dielectric properties from one-hour intervals were analyzed during in vivo and normothermic machine perfusion (NMP). A clear increasing trend in the conductivity was observed in vivo in the AHEP livers compared to the control livers. After four hours of NMP, separations in the conductivity were observed between the three groups. Our results indicate that dielectric relaxation spectroscopy (DRS) can be used to detect and differentiate liver injuries, opening for a standardized and reliable point of evaluation for livers prior to transplantation.

• Tronstad, Christian; Pabst, Oliver; Amini, Maryam; Kleggetveit, Inge Petter; Elvebakk, Ole & Martinsen, Ørjan Grøttem [Vis alle 10 forfattere av denne artikkelen] (2022). Development of a prototype toe sensor for detection of diabetic peripheral small fiber neuropathy. Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC). doi: 10.1109/EMBC48229.2022.9871101. Fulltekst i vitenarkiv
• Hou, Jie; Strand-Amundsen, Runar James; Tronstad, Christian; Tønnessen, Tor Inge; Høgetveit, Jan Olav & Martinsen, Ørjan Grøttem (2022). Small intestinal viability assessment using dielectric relaxation spectroscopy and deep learning. Scientific Reports. 12(1). doi: 10.1038/s41598-022-07140-4. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Intestinal ischemia is a serious condition where the surgeon often has to make important but difficult decisions regarding resections and resection margins. Previous studies have shown that 3 h (hours) of warm full ischemia of the small bowel followed by reperfusion appears to be the upper limit for viability in the porcine mesenteric ischemia model. However, the critical transition between 3 to 4 h of ischemic injury can be nearly impossible to distinguish intraoperatively based on standard clinical methods. In this study, permittivity data from porcine intestine was used to analyze the characteristics of various degrees of ischemia/reperfusion injury. Our results show that dielectric relaxation spectroscopy can be used to assess intestinal viability. The dielectric constant and conductivity showed clear differences between healthy, ischemic and reperfused intestinal segments. This indicates that dielectric parameters can be used to characterize different intestinal conditions. In addition, machine learning models were employed to classify viable and non-viable segments based on frequency dependent dielectric properties of the intestinal tissue, providing a method for fast and accurate intraoperative surgical decision-making. An average classification accuracy of 98.7% was obtained using only permittivity data measured during ischemia, and 96.2% was obtained with data measured during reperfusion. The proposed approach allows the surgeon to get accurate evaluation from the trained machine learning model by performing one single measurement on an intestinal segment where the viability state is questionable.

• Hou, Jie; Ness, Siri Schøne; Tschudi, Jon; O'Farrell, Marion; Veddegjerde, Rune & Martinsen, Ørjan Grøttem [Vis alle 8 forfattere av denne artikkelen] (2022). Assessment of Intestinal Ischemia–Reperfusion Injury Using Diffuse Reflectance VIS-NIR Spectroscopy and Histology. Sensors. 22(23). doi: 10.3390/s22239111. Fulltekst i vitenarkiv Vis sammendrag

  A porcine model was used to investigate the feasibility of using VIS-NIR spectroscopy to differentiate between degrees of ischemia–reperfusion injury in the small intestine. Ten pigs were used in this study and four segments were created in the small intestine of each pig: (1) control, (2) full arterial and venous mesenteric occlusion for 8 h, (3) arterial and venous mesenteric occlusion for 2 h followed by reperfusion for 6 h, and (4) arterial and venous mesenteric occlusion for 4 h followed by reperfusion for 4 h. Two models were built using partial least square discriminant analysis. The first model was able to differentiate between the control, ischemic, and reperfused intestinal segments with an average accuracy of 99.2% with 10-fold cross-validation, and the second model was able to discriminate between the viable versus non-viable intestinal segments with an average accuracy of 96.0% using 10-fold cross-validation. Moreover, histopathology was used to investigate the borderline between viable and non-viable intestinal segments. The VIS-NIR spectroscopy method together with a PLS-DA model showed promising results and appears to be well-suited as a potentially real-time intraoperative method for assessing intestinal ischemia–reperfusion injury, due to its easy-to-use and non-invasive nature.

• Bari, Dindar S.; Aldosky, Haval Y. Yacoob & Martinsen, Ørjan Grøttem (2021). Effects of the long-time wearing of gloves by health care workers managing COVID-19 assessed by electrodermal activity – a pilot study. International Journal of Online and Biomedical Engineering (iJOE). 17(12), s. 177–184. doi: 10.3991/ijoe.v17i12.23439. Fulltekst i vitenarkiv
• Ibba, P.; Tronstad, Christian; Moscetti, R.; Mimmo, T.; Cantarella, G. & Petti, L. [Vis alle 8 forfattere av denne artikkelen] (2021). Supervised binary classification methods for strawberry ripeness discrimination from bioimpedance data. Scientific Reports. 11. doi: 10.1038/s41598-021-90471-5. Fulltekst i vitenarkiv
• Andreasen, N.; Crandall, H.; Brimhall, O.; Miller, B.; Perez-Tamayo, J. & Martinsen, Ørjan Grøttem [Vis alle 8 forfattere av denne artikkelen] (2021). Skin Electrical Resistance as a Diagnostic and Therapeutic Biomarker of Breast Cancer Measuring Lymphatic Regions. IEEE Access. 9, s. 152322–152332. doi: 10.1109/ACCESS.2021.3123569. Fulltekst i vitenarkiv Vis sammendrag

  Skin changes associated with alterations in the interstitial matrix and lymph system might provide significant and measurable effects due to the presence of breast cancer. This study aimed to determine if skin electrical resistance changes could serve as a diagnostic and therapeutic biomarker associated with physiological changes in patients with malignant versus benign breast cancer lesions. Forty-eight women (24 with malignant cancer, 23 with benign lesions) were enrolled in this study. Repeated skin resistance measurements were performed within the same session and 1 week after the first measurement in the breast lymphatic region and non-breast lymphathic regions. Intraclass correlation coefficients were calculated to determine the technique’s intrasession and intersession reproducibility. Data were then normalized as a mean of comparing cross-sectional differences between malignant and benign lesions of the breast. Six months longitudinal data from six patients that received therapy were analyzed to detect the effect of therapy. Standard descriptive statistics were used to compare ratiometric differences between groups. Skin resistance data were used to train a machine learning random forest classification algorithm to diagnose breast cancer lesions. Significant differences between malignant and benign breast lesions were obtained (p<0.01), also pre- and post-treatment (p<0.05). The diagnostic algorithm demonstrated the capability to classify breast cancer with an area under the curve of 0.68, sensitivity of 66.3%, specificity of 78.5%, positive predictive value 70.7% and negative predictive value 75.1%. Measurement of skin resistance in patients with breast cancer may serve as a convenient screening tool for breast cancer and evaluation of therapy. Further work is warranted to improve our approach and further investigate the biophysical mechanisms leading to the observed changes.

• Abie, Sisay Mebre; Münch, Daniel; Egelandsdal, Bjørg; Bjerke, Frøydis; Wergeland, Ivar & Martinsen, Ørjan Grøttem (2021). Combined 0.2 T static magnetic field and 20 kHz, 2 V/cm square wave electric field do not affect supercooling and freezing time of saline solution and meat samples. Journal of Food Engineering. ISSN 0260-8774. 311. doi: 10.1016/j.jfoodeng.2021.110710. Fulltekst i vitenarkiv Vis sammendrag

  Previous studies proposed that electric and magnetic fields can affect the freezing of biological tissues, including meat. Yet, improved freezing through sole magnetic or combined electro-magnetic field exposure is disputed. Also, as previous studies typically tested very small sample dimensions, it is unclear if the reported effects are transferrable to larger product sizes that are relevant to commercial food freezing. Here we aimed at reassessing previous findings by constructing and testing a scaled-up setup for applying electric and magnetic fields during freezing. Importantly, our setup replicates key technical aspects of previous electro-magnetic freezer designs. We modeled and measured the spatial distribution of electric and magnetic fields generated by this setup. We then studied possible effects of field exposure on freezing of two different volumes of saline water and of meat. We tested four different field treatments: sole magnetic and electric field exposure, a combination of both and a control without altered field exposure. We show that the 20 kHz square wave electric field was largely homogenous, while the static 0.2 T magnetic field was not. We found that none of the field treatments altered freezing dynamics of the three tested sample types. Our findings, hence, do not support previous data obtained with similar electro-magnetic field freezer setups. We discuss how our study that uses very distinct field parameters, may inform the general discussion on the effectiveness of electro-magnetic field exposure during food freezing.

• Jacobsen, Fredrik Alstad; Hafli, Ellen Wold; Tronstad, Christian & Martinsen, Ørjan Grøttem (2021). Classification of emotions based on electrodermal activity and transfer learning - a pilot study. Journal of Electrical Bioimpedance. 12(1), s. 178–183. doi: 10.2478/joeb-2021-0021. Fulltekst i vitenarkiv Vis sammendrag

  Abstract This paper describes the development, execution and results of an experiment assessing emotions with electrodermal response measurements and machine learning. With ten participants, the study was carried out by eliciting emotions through film clips. The data was gathered with the Sudologger 3 and processed with continuous wavelet transformation. A machine learning algorithm was used to classify the data with the use of transfer learning and random forest classification. The results showed that the experiment lays a foundation for further exploration in the field. The addition of augmented data strengthened the classification and proved that more data would benefit the machine learning algorithm. The pilot study brought to light several areas to help with the expansion of the study for larger scale assessment of emotions with electrodermal response measurements and machine learning for the benefit of fields like psychology.

• Singstad, Bjørn Jostein; Azulay, Naomi; Bjurstedt, Andreas; Bjørndal, Simen Chill; Drageseth, Magnus Flø & Austdal, Lars Peter Engeset [Vis alle 21 forfattere av denne artikkelen] (2021). Estimation of heart rate variability from finger photoplethysmography during rest, mild exercise and mild mental stress. Journal of Electrical Bioimpedance. 12(1), s. 89–102. doi: 10.2478/joeb-2021-0012. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Due to the possibilities in miniaturization and wearability, photoplethysmography (PPG) has recently gained a large interest not only for heart rate measurement, but also for estimating heart rate variability, which is derived from ECG by convention. The agreement between PPG and ECG-based HRV has been assessed in several studies, but the feasibility of PPG-based HRV estimation is still largely unknown for many conditions. In this study, we assess the feasibility of HRV estimation based on finger PPG during rest, mild physical exercise and mild mental stress. In addition, we compare different variants of signal processing methods including selection of fiducial point and outlier correction. Based on five minutes synchronous recordings of PPG and ECG from 15 healthy participants during each of these three conditions, the PPG-based HRV estimation was assessed for the SDNN and RMSSD parameters, calculated based on two different fiducial points (foot point and maximum slope), with and without outlier correction. The results show that HRV estimation based on finger PPG is feasible during rest and mild mental stress, but can give large errors during mild physical exercise. A good estimation is very dependent on outlier correction and fiducial point selection, and SDNN seems to be a more robust parameter compared to RMSSD for PPG-based HRV estimation.

• Hou, Jie; Strand-Amundsen, Runar James; Tronstad, Christian; Høgetveit, Jan Olav; Martinsen, Ørjan Grøttem & Tønnessen, Tor Inge (2021). Automatic prediction of ischemia-reperfusion injury of small intestine using convolutional neural networks: A pilot study. Sensors. 21(19). doi: 10.3390/s21196691. Fulltekst i vitenarkiv Vis sammendrag

  Acute intestinal ischemia is a life-threatening condition. The current gold standard, with evaluation based on visual and tactile sensation, has low specificity. In this study, we explore the feasibility of using machine learning models on images of the intestine, to assess small intestinal viability. A digital microscope was used to acquire images of the jejunum in 10 pigs. Ischemic segments were created by local clamping (approximately 30 cm in width) of small arteries and veins in the mesentery and reperfusion was initiated by releasing the clamps. A series of images were acquired once an hour on the surface of each of the segments. The convolutional neural network (CNN) has previously been used to classify medical images, while knowledge is lacking whether CNNs have potential to classify ischemia-reperfusion injury on the small intestine. We compared how different deep learning models perform for this task. Moreover, the Shapley additive explanations (SHAP) method within explainable artificial intelligence (AI) was used to identify features that the model utilizes as important in classification of different ischemic injury degrees. To be able to assess to what extent we can trust our deep learning model decisions is critical in a clinical setting. A probabilistic model Bayesian CNN was implemented to estimate the model uncertainty which provides a confidence measure of our model decisions.

• Tariverdi, Abbas; Venkiteswaran, Venkatasubramanian Kalpathy; Richter, Michiel; Elle, Ole Jakob; Tørresen, Jim & Mathiassen, Kim [Vis alle 8 forfattere av denne artikkelen] (2021). A Recurrent Neural-Network-Based Real-Time Dynamic Model for Soft Continuum Manipulators. Frontiers in Robotics and AI. doi: 10.3389/frobt.2021.631303. Fulltekst i vitenarkiv Vis sammendrag

  This paper introduces and validates a real-time dynamic predictive model based on a neural network approach for soft continuum manipulators. The presented model provides a real-time prediction framework using neural-network-based strategies and continuum mechanics principles. A time-space integration scheme is employed to discretize the continuous dynamics and decouple the dynamic equations for translation and rotation for each node of a soft continuum manipulator. Then the resulting architecture is used to develop distributed prediction algorithms using recurrent neural networks. The proposed RNN-based parallel predictive scheme does not rely on computationally intensive algorithms; therefore, it is useful in real-time applications. Furthermore, simulations are shown to illustrate the approach performance on soft continuum elastica, and the approach is also validated through an experiment on a magnetically-actuated soft continuum manipulator. The results demonstrate that the presented model can outperform classical modeling approaches such as the Cosserat rod model while also shows possibilities for being used in practice.

• Abie, Sisay Mebre; Martinsen, Ørjan Grøttem; Egelandsdal, Bjørg; Hou, Jie; Bjerke, Frøydis & Mason, Alex [Vis alle 7 forfattere av denne artikkelen] (2021). Feasibility of using electrical impedance spectroscopy for assessing biological cell damage during freezing and thawing. Sensors. 21(12). doi: 10.3390/s21124129. Fulltekst i vitenarkiv Vis sammendrag

  This study was performed to test bioimpedance as a tool to detect the effect of different thawing methods on meat quality to aid in the eventual creation of an electric impedance-based food quality monitoring system. The electric impedance was measured for fresh pork, thawed pork, and during quick and slow thawing. A clear difference was observed between fresh and thawed samples for both impedance parameters. Impedance was different between the fresh and the frozen-thawed samples, but there were no impedance differences between frozen-thawed samples and the ones that were frozen-thawed and then stored at +3 °C for an additional 16 h after thawing. The phase angle was also different between fresh and the frozen-thawed samples. At high frequency, there were small, but clear phase angle differences between frozen-thawed samples and the samples that were frozen-thawed and subsequently stored for more than 16 h at +3 °C. Furthermore, the deep learning model LSTM-RNN (long short-term memory recurrent neural network) was found to be a promising way to classify the different methods of thawing.

• Nøvik, Steffen; Drageseth, Magnus Flø; Martinsen, Ørjan Grøttem & Häfliger, Philipp Dominik (2021). Four Electrode Bioimpedance Sensor System on CMOS Chip. I Salem, Fathi (Red.), Proceedings 2021 Midwest Symposium on Circuits and Systems. IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781665424615. doi: 10.1109/MWSCAS47672.2021.9531741. Fulltekst i vitenarkiv
• Holm, Sverre; Holm, Thomas & Martinsen, Ørjan Grøttem (2021). Simple circuit equivalents for the constant phase element. PLOS ONE. 16(3). doi: 10.1371/journal.pone.0248786. Fulltekst i vitenarkiv Vis sammendrag

  The constant phase element (CPE) is a capacitive element with a frequency-independent negative phase between current and voltage which interpolates between a capacitor and a resistor. It is used extensively to model the complexity of the physics in e.g. the bioimpedance and electrochemistry fields. There is also a similar element with a positive phase angle, and both the capacitive and inductive CPEs are members of the family of fractional circuit elements or fractance. The physical meaning of the CPE is only partially understood and many consider it an idealized circuit element. The goal here is to provide alternative equivalent circuits, which may give rise to better interpretations of the fractance. Both the capacitive and the inductive CPEs can be interpreted in the time-domain, where the impulse and step responses are temporal power laws. Here we show that the current impulse responses of the capacitive CPE is the same as that of a simple time-varying series RL-circuit where the inductor’s value increases linearly with time. Similarly, the voltage response of the inductive CPE corresponds to that of a simple parallel RC circuit where the capacitor’s value increases linearly with time. We use the Micro-Cap circuit simulation program, which can handle time-varying circuits, for independent verification. The simulation corresponds exactly to the expected response from the proposed equivalents within 0.1% error. The realization with time-varying components correlates with known time-varying properties in applications, and may lead to a better understanding of the link between CPE and applications.

• Hou, Jie; Abie, Sisay Mebre; Strand-Amundsen, Runar James; Galperin, Yuri; Bergli, Joakim & Schuelke, Christin [Vis alle 8 forfattere av denne artikkelen] (2021). Temperature dependence of the microwave dielectric properties of γ -aminobutyric acid. Scientific Reports. 11(1). doi: 10.1038/s41598-021-97178-7. Fulltekst i vitenarkiv Vis sammendrag

  The GABA molecule is the major inhibitory neurotransmitter in the mammalian central nervous system. Through binding to post-synaptic neurons, GABA reduces the neuronal excitability by hyperpolarization. Correct binding between the GABA molecules and its receptors relies on molecular recognition. Earlier studies suggest that recognition is determined by the geometries of the molecule and its receptor. We employed dielectric relaxation spectroscopy (DRS) to study the conformation and dielectric properties of the GABA molecule under physiologically relevant laboratory conditions. The dielectric properties of GABA investigated have given us new insights about the GABA molecule, such as how they interact with each other and with water molecules at different temperatures (22°C and 37.5°C). Higher temperature leads to lower viscosity, thus lower relaxation time. The change in the GABA relaxation time due to concentration change is more associated with the solution viscosity than with the GABA dipole moment. A resonance behavior was observed with high GABA concentrations at physiological temperature, where there might be a phase transition at a certain temperature for a given GABA concentration that leads to a sudden change of the dielectric properties.

• Tronstad, Christian; Martinsen, Tormod; Olsen, Morten; Rosseland, Leiv Arne; Pettersen, Fred-Johan & Martinsen, Ørjan Grøttem [Vis alle 8 forfattere av denne artikkelen] (2020). Splitting one ventilator for multiple patients - a technical assessment. arXiv.org. ISSN 2331-8422. Fulltekst i vitenarkiv
• Amini, Maryam; Niemi, Essi Maria; Hisdal, Jonny; Kalvøy, Håvard; Tronstad, Christian & Scholz, Hanne [Vis alle 8 forfattere av denne artikkelen] (2020). Monitoring the quality of frozen-thawed venous segments using bioimpedance spectroscopy. Physiological Measurement. ISSN 0967-3334. 41(4). doi: 10.1088/1361-6579/ab85b7. Fulltekst i vitenarkiv Vis sammendrag

  Objective: Storage at temperatures as low as −80 °C and below (cryopreservation) is considered a method for long-term preservation of cells and tissues, and especially blood vessel segments, which are to be used for clinical operations such as transplantation. However, the freezing and thawing processes themselves can induce injuries to the cells and tissue by damaging the structure and consequently functionality of the cryopreserved tissue. In addition, the level of damage is dependent on the rate of cooling and warming used during the freezing-thawing process. Current methods for monitoring the viability and integrity of cells and tissues after going through the freezing-thawing cycle are usually invasive and destructive to the cells and tissues. Therefore, employing monitoring methods which are not destructive to the cryopreserved tissues, such as bioimpedance measurement techniques, is necessary. In this study we aimed to design a bioimpedance measurement setup to detect changes in venous segments after freezing-thawing cycles in a noninvasive manner. Approach: A bioimpedance spectroscopy measurement technique with a two-electrode setup was employed to monitor ovine jugular vein segments after each cycle during a process of seven freezing-thawing cycles. Main results: The results demonstrated changes in the impedance spectra of the measured venous segments after each freezing-thawing cycle. Significance: This indicates that bioimpedance spectroscopy has the potential to be developed into a novel method for non-invasive and non-destructive monitoring of the viability of complex tissue after cryopreservation.

• Bari, Dindar S.; Aldosky, Haval Y. Yacoob; Tronstad, Christian & Martinsen, Ørjan Grøttem (2020). The correlations among the skin conductance features responding to physiological stress stimuli. Skin Research and Technology. ISSN 0909-752X. s. 1–7. doi: 10.1111/srt.12989. Fulltekst i vitenarkiv
• Amini, Maryam; Kalvøy, Håvard & Martinsen, Ørjan Grøttem (2020). Finite element simulation of the impedance response of a vascular segment as a function of changes in electrode configuration. Journal of Electrical Bioimpedance. 11(1), s. 112–131. doi: 10.2478/JOEB-2020-0017. Fulltekst i vitenarkiv Vis sammendrag

  Abstract Monitoring a biological tissue as a three dimensional (3D) model is of high importance. Both the measurement technique and the measuring electrode play substantial roles in providing accurate 3D measurements. Bioimpedance spectroscopy has proven to be a noninvasive method providing the possibility of monitoring a 3D construct in a real time manner. On the other hand, advances in electrode fabrication has made it possible to use flexible electrodes with different configurations, which makes 3D measurements possible. However, designing an experimental measurement set-up for monitoring a 3D construct can be costly and time consuming and would require many tissue models. Finite element modeling methods provide a simple alternative for studying the performance of the electrode and the measurement set-up before starting with the experimental measurements. Therefore, in this study we employed the COMSOL Multiphysics finite element modeling method for simulating the effects of changing the electrode configuration on the impedance spectroscopy measurements of a venous segment. For this purpose, the simulations were performed for models with different electrode configurations. The simulation results provided us with the possibility of finding the optimal electrode configuration including the geometry, number and dimensions of the electrodes, which can be later employed in the experimental measurement set-up.

• Bari, Dindar S.; Aldosky, Haval Y. Yacoob & Martinsen, Ørjan Grøttem (2020). Simultaneous measurement of electrodermal activity components correlated with age-related differences. Journal of biological physics (Print). ISSN 0092-0606. 46(2), s. 177–188. doi: 10.1007/s10867-020-09547-4. Fulltekst i vitenarkiv
• Drobnjak, Milena; Hansen, Frederik; Øiestad, Elisabeth Leere; Løvli, Trond; Trones, Roger & Martinsen, Ørjan Grøttem [Vis alle 7 forfattere av denne artikkelen] (2020). Electromembrane extraction with vials of conducting polymer. LC GC North America. ISSN 1527-5949. 38(8), s. 435–439. Fulltekst i vitenarkiv
• Restan, Magnus Saed; Skjærvø, Øystein; Martinsen, Ørjan Grøttem & Pedersen-Bjergaard, Stig (2020). Towards exhaustive electromembrane extraction under stagnant conditions. Analytica Chimica Acta. ISSN 0003-2670. 1104, s. 1–9. doi: 10.1016/j.aca.2020.01.058. Fulltekst i vitenarkiv Vis sammendrag

  Electromembrane extraction (EME) in small, stagnant and chip-like devices has the potential for future in-field operation. Literature briefly discuss such systems, but performance suffered from evaporative losses of sample and acceptor. To address this, the current paper reports electromembrane extraction (EME) of five basic drugs (model analytes) from aqueous buffer solutions and whole blood samples under stagnant conditions in a completely closed system. A laboratory-made polyoxymethylene (POM) well plate served as compartment for the sample solution, while a commercially available well filter plate was used to immobilize 2-nitrophenyl octyl ether (NPOE) as supported liquid membrane (SLM) and as closed compartment for the acceptor solution. Major design parameters (sample compartment and electrode geometry) and operational parameters (sample volume, voltage and extraction time) were investigated and optimized. Electrode geometry was not very critical, but extraction efficiency increased with decreasing sample volume. Extraction from 50 μL aqueous buffer solution for 60 min and with a voltage of 75 V was considered exhaustive (sample was depleted), with recoveries ranging between 75% and 87% for loperamide, haloperidol, methadone, nortriptyline, and pethidine (RSD: 2–12%). Extraction from whole blood samples under optimized conditions yielded slightly lower recoveries, ranging between 57 and 96% (RSD: 3–12%). Stagnant EME was evaluated in combination with liquid chromatography-mass spectrometry (LC-MS) as a highly specific instrumental method, and provided evaluation data on methadone from blood samples in accordance with regulatory requirements (LOD: 0.4 ng/mL, LOQ: 1.4 ng/mL, RSD: 6–20%). This work has improved upon the design of stagnant EME, moving it further towards a viable in-field operation device.

• Sanchez, Benjamin; Martinsen, Ørjan Grøttem; Freeborn, Todd J. & Furse, Cynthia M. (2020). Electrical impedance myography: A critical review and outlook. Clinical Neurophysiology. ISSN 1388-2457. 132(2), s. 338–344. doi: 10.1016/j.clinph.2020.11.014. Fulltekst i vitenarkiv
• Cunha, Andrè Bastos da; Schuelke, Christin; Heiskanen, Arto; Asif, Afia; Hassan, Yasmin M. & Keller, Stephan S. [Vis alle 10 forfattere av denne artikkelen] (2020). Bioimpedance Measurements on Human Neural Stem Cells as a Benchmark for the Development of Smart Mobile Biomedical Applications. International Federation for Medical and Biological Engineering Proceedings. ISSN 1680-0737. 72, s. 38–47. doi: 10.1007/978-981-13-3498-6_6. Fulltekst i vitenarkiv Vis sammendrag

  Over the past 30 years, stem cell technologies matured from an attractive option to investigate neurodegenerative diseases to a possible paradigm shift in their treatment through the development of cell-based regenerative medicine (CRM). Implantable cell replacement therapies promise to completely restore function of neural structures possibly changing how we currently perceive the onset of these conditions. One of the major clinical hurdles facing the routine implementation of stem cell therapy is the limited and inconsistent benefit observed thus far. While unclear, numerous pre-clinical and a handful of clinical cell fate imaging studies point to poor cell retention and survival. Coupling the need to better understand these mechanisms while providing scalable approaches to monitor these treatments in both pre-clinical and clinical scenarios, we show a proof of concept bioimpedance electronic platform for the Agile development of smart and mobile biomedical applications like neural implants or highly portable monitoring devices.

• Tariverdi, Abbas; Venkiteswaran, Venkatasubramanian Kalpathy; Martinsen, Ørjan Grøttem; Elle, Ole Jacob; Tørresen, Jim & Misra, Sarthak (2020). Dynamic modeling of soft continuum manipulators using lie group variational integration. PLOS ONE. 15:e0236121(7), s. 1–29. doi: 10.1371/journal.pone.0236121. Fulltekst i vitenarkiv Vis sammendrag

  This paper presents the derivation and experimental validation of algorithms for modeling and estimation of soft continuum manipulators using Lie group variational integration. Existing approaches are generally limited to static and quasi-static analyses, and are not sufficiently validated for dynamic motion. However, in several applications, models need to consider the dynamical behavior of the continuum manipulators. The proposed modeling and estimation formulation is obtained from a discrete variational principle, and therefore grants outstanding conservation properties to the continuum mechanical model. The main contribution of this article is the experimental validation of the dynamic model of soft continuum manipulators, including external torques and forces (e.g., generated by magnetic fields, friction, and the gravity), by carrying out different experiments with metal rods and polymer-based soft rods. To consider dissipative forces in the validation process, distributed estimation filters are proposed. The experimental and numerical tests also illustrate the algorithm’s performance on a magnetically-actuated soft continuum manipulator. The model demonstrates good agreement with dynamic experiments in estimating the tip position of a Polydimethylsiloxane (PDMS) rod. The experimental results show an average absolute error and maximum error in tip position estimation of 0.13 mm and 0.58 mm, respectively, for a manipulator length of 60.55 mm.

• Amini, Maryam; Hisdal, Jonny; Rosales, Antonio; Kalvøy, Håvard & Martinsen, Ørjan Grøttem (2020). Evaluating the Effects of Cold Storage on Vascular Grafts Using Bioimpedance Measurement Techniques. International Federation for Medical and Biological Engineering Proceedings. ISSN 1680-0737. s. 127–132. doi: 10.1007/978-981-13-3498-6_19. Fulltekst i vitenarkiv
• Pabst, Oliver & Martinsen, Ørjan Grøttem (2019). Simulation based comparison between a transversal and a tangential memristor model with a capacitance in parallel. PLOS ONE. 14(8). doi: 10.1371/journal.pone.0221533. Fulltekst i vitenarkiv Vis sammendrag

  In non-linear measurements, the applied stimulus itself affects the electrical properties of the underlying tissue. If corresponding voltage-current plots exhibit pinched hysteresis loops with pinched point in the origin of coordinates, the tissue can be classified as a memristor. Several organic memristors like human skin, venus flytrap and slime mould memristors have been demonstrated. However, measurements on organic memristors are usually affected by parasitic elements like a capacitance which will influence the appearance of the recorded pinched hysteresis loops. Here we study the parallel connection of two different memristor types, one with tangential and the other with transversal pinched hysteresis loop, and a capacitance by simulations. The simulations are inspired by human skin; beside the sweat ducts that can be modelled as a transversal memristor, the surrounding tissue, the stratum corneum exhibits non-linear electrical properties, as well. Based on a systematic study we suggested that the stratum corneum may be modelled as a tangential memristor. We demonstrate here by simulations that hysteresis loops with two pinched points can be achieved if a tangential memristor model is connected in parallel to a capacitance. Similar results were obtained from the skin recordings of some subjects; examples are presented here. Furthermore, if both the tangential and the transversal memristor models contribute to the simulation, quite asymmetric pinched hysteresis loops are obtained which are similar to recordings of some other test subjects.

• Martinsen, Tormod; Pettersen, Fred-Johan; Kalvøy, Håvard; Tronstad, Christian; Kvarstein, Gunnvald & Bakken, André [Vis alle 10 forfattere av denne artikkelen] (2019). Electrosurgery and temperature increase in tissue with a passive metal implant. Frontiers in Surgery. 6:8, s. 1–8. doi: 10.3389/fsurg.2019.00008. Fulltekst i vitenarkiv Vis sammendrag

  <i>Importance</i>: During monopolar electrosurgery in patients, current paths can be influenced by metal implants, which can cause unintentional tissue heating in proximity to implants. Guidelines concerning electrosurgery and active implants such as pacemakers or implantable cardioverter defibrillators have been published, but most describe interference between electrosurgery and the active implant rather than the risk of unintended tissue heating. Tissue heating in proximity to implants during electrosurgery may cause an increased risk of patient injury.<p> <p><i>Objective</i>: To determine the temperature of tissue close to metal implants during electrosurgery in an <i>in-vitro</i> model.<p> <p><i>Design, Setting, and Participants</i>: Thirty tissue samples (15 with a metal implant placed in center, 15 controls without implant) were placed in an <i>in vitro</i> measurement chamber. Electrosurgery was applied at 5–60 W with the active electrode at three defined distances from the implant while temperatures at four defined distances from the implant were measured using fiber-optic sensors.<p> <p><i>Main Outcomes and Measures</i>: Tissue temperature increase at the four tissue sites was determined for all power levels and each of the electrode-to-implant distances. Based on a linear mixed effects model analysis, the primary outcomes were the difference in temperature increase between implant and control tissue, and the estimated temperature increase per watt per minute.<p> <p><i>Results</i>: Tissues with an implant had higher temperature increases than controls at all power levels after 1 min of applied electrosurgery (mean difference of 0.16°C at 5 W, 0.50°C at 15 W, 1.11°C at 30 W, and 2.22°C at 60 W, all with p < 0.001). Temperature increase close to the implant was estimated to be 0.088°C/W/min (95% CI: 0.078–0.099°C/W/min; p < 0.001). Temperature could increase to above 43°C after 1 min of 60 W. Active electrode position had no significant effect on temperature increases for tissues with implant (p = 0.6).<p> <p><i>Conclusions and Relevance</i>: The temperature of tissue close to a metal implant increases with passing electrosurgery current. There is a significant risk of high tissue temperature when long activation times or high power levels are used.

• Egelandsdal, Bjørg; Abie, Sisay Mebre; Bjarnadottir, Stefania; Zhu, Han; Kolstad, Hilde Raanaas & Bjerke, Frøydis [Vis alle 9 forfattere av denne artikkelen] (2019). Detectability of the degree of freeze damage in meat depends on analytic-tool selection. Meat Science. ISSN 0309-1740. 152, s. 8–19. doi: 10.1016/j.meatsci.2019.02.002. Fulltekst i vitenarkiv Vis sammendrag

  Novel freezing solutions are constantly being developed to reduce quality loss in meat production chains. However, there is limited focus on identifying the sensitive analytical tools needed to directly validate product changes that result from potential improvements in freezing technology. To benchmark analytical tools relevant to meat research and production, we froze pork samples using traditional (−25 °C, −35 °C) and cryogenic freezing (−196 °C). Three classes of analyses were tested for their capacity to separate different freeze treatments: thaw loss testing, bioelectrical spectroscopy (nuclear magnetic resonance, microwave, bioimpedance) and low-temperature microscopy (cryo-SEM). A general effect of freeze treatment was detected with all bioelectrical methods. Yet, only cryo-SEM resolved quality differences between all freeze treatments, not only between cryogenic and traditional freezing. The detection sensitivity with cryo-SEM may be explained by testing meat directly in the frozen state without prior defrosting. We discuss advantages, shortcomings and cost factors in using analytical tools for quality monitoring in the meat sector.

• Pabst, Oliver; Martinsen, Ørjan Grøttem & Chua, Leon (2019). Information can be stored in the human skin memristor which has non-volatile memory. Scientific Reports. 9(1). doi: 10.1038/s41598-019-55749-9. Fulltekst i vitenarkiv Vis sammendrag

  Much is already understood about the anatomical and physiological mechanisms behind the linear, electrical properties of biological tissues. Studying the non-linear electrical properties, however, opens up for the influence from other processes that are driven by the electric field or movement of charges. An electrical measurement that is affected by the applied electrical stimulus is non-linear and reveals the non-linear electrical properties of the underlying (biological) tissue; if it is done with an alternating current (AC) stimulus, the corresponding voltage current plot may exhibit a pinched hysteresis loop which is the fingerprint of a memristor. It has been shown that human skin and other biological tissues are memristors. Here we performed non-linear electrical measurements on human skin with applied direct current (DC) voltage pulses. By doing so, we found that human skin exhibits non-volatile memory and that analogue information can actually be stored inside the skin at least for three minutes. As demonstrated before, human skin actually contains two different memristor types, one that originates from the sweat ducts and one that is based on thermal changes of the surrounding tissue, the stratum corneum; and information storage is possible in both. Finally, assuming that different physiological conditions of the skin can explain the variations in current responses that we observed among the subjects, it follows that non-linear recordings with DC pulses may find use in sensor applications.

• Aria, Shafa; Elfarri, Yassine; Elvegård, Marius; Gottfridsson, Adam; Grønaas, Halvor & Harang, Sigve Smedsrud [Vis alle 25 forfattere av denne artikkelen] (2019). Measuring blood pulse wave velocity with bioimpedance in different age groups. Sensors. 19:850(4), s. 1–10. doi: 10.3390/s19040850. Fulltekst i vitenarkiv Vis sammendrag

  In this project, we have studied the use of electrical impedance cardiography as a possible method for measuring blood pulse wave velocity, and hence be an aid in the assessment of the degree of arteriosclerosis. Using two different four-electrode setups, we measured the timing of the systolic pulse at two locations, the upper arm and the thorax, and found that the pulse wave velocity was in general higher in older volunteers and furthermore that it was also more heart rate dependent for older subjects. We attribute this to the fact that the degree of arteriosclerosis typically increases with age and that stiffening of the arterial wall will make the arteries less able to comply with increased heart rate (and corresponding blood pressure), without leading to increased pulse wave velocity. In view of these findings, we conclude that impedance cardiography seems to be well suited and practical for pulse wave velocity measurements and possibly for the assessment of the degree of arteriosclerosis. However, further studies are needed for comparison between this approach and reference methods for pulse wave velocity and assessment of arteriosclerosis before any firm conclusions can be drawn.

• Elvebakk, Ole; Tronstad, Christian; Birkeland, Kåre I.; Jenssen, Trond Geir; Bjørgaas, Marit Ragnhild Rokne & Gulseth, Hanne Løvdal [Vis alle 9 forfattere av denne artikkelen] (2019). A multiparameter model for non-invasive detection of hypoglycemia. Physiological Measurement. ISSN 0967-3334. 40(8), s. 1–14. doi: 10.1088/1361-6579/ab3676. Fulltekst i vitenarkiv Vis sammendrag

  Objective: Severe hypoglycemia is the most serious acute complication for people with type 1 diabetes (T1D). Approximately 25% of people with T1D have impaired ability to recognize impending hypoglycemia, and nocturnal episodes are feared. Approach: We have investigated the use of non-invasive sensors for detection of hypoglycemia based on a mathematical model which combines several sensor measurements to identify physiological responses to hypoglycemia. Data from randomized single-blinded euglycemic and hypoglycemic glucose clamps in 20 participants with T1D and impaired awareness of hypoglycemia was used in the analyses. Main results: Using a sensor combination of sudomotor activity at three skin sites, ECG-derived heart rate and heart rate corrected QT interval, near-infrared and bioimpedance spectroscopy; physiological responses associated with hypoglycemia could be identified with an F1 score accuracy up to 88%. Significance: We present a novel model for identification of non-invasively measurable physiological responses related to hypoglycemia, showing potential for detection of moderate hypoglycemia using a wearable sensor system

• Tronstad, Christian; Elvebakk, Ole; Staal, Odd Martin; Kalvøy, Håvard; Høgetveit, Jan Olav & Jenssen, Trond Geir [Vis alle 8 forfattere av denne artikkelen] (2019). Non-invasive prediction of blood glucose trends during hypoglycemia. Analytica Chimica Acta. ISSN 0003-2670. 1052, s. 37–48. doi: 10.1016/j.aca.2018.12.009. Fulltekst i vitenarkiv
• Andersen, Jan-Hugo; Bjerke, Olav; Blakaj, Fatos; Flugsrud, Vilde Moe; Jacobsen, Fredrik Alstad & Jonsson, Marius [Vis alle 24 forfattere av denne artikkelen] (2019). Bioimpedance and NIR for non-invasive assessment of blood glucose. Journal of Electrical Bioimpedance. 10, s. 133–138. doi: 10.2478/joeb-2019-0019. Fulltekst i vitenarkiv
• Martinsen, Ørjan Grøttem; Kalvøy, Håvard; Bari, Dindar S. & Tronstad, Christian (2019). A circuit for simultaneous measurements of skin electrical conductance, susceptance, and potential. Journal of Electrical Bioimpedance. 10, s. 110–112. doi: 10.2478/joeb-2019-0016. Fulltekst i vitenarkiv Vis sammendrag

  A circuit is presented that enables measurement of skin electrical conductance, susceptance, and potential simultaneously beneath the same monopolar electrode. Example measurements are shown to confirm the function of the circuit. The measurements are also in accordance with earlier findings that changes in skin conductance and potential do not always correspond and hence contain unique information.

• Strand-Amundsen, Runar James; Tronstad, Christian; Kalvøy, Håvard; Ruud, Tom Erik; Høgetveit, Jan Olav & Martinsen, Ørjan Grøttem [Vis alle 7 forfattere av denne artikkelen] (2018). Small intestinal ischemia and reperfusion - Bioimpedance measurements. Physiological Measurement. ISSN 0967-3334. 39(2). doi: 10.1088/1361-6579/aaa576. Fulltekst i vitenarkiv Vis sammendrag

  Objective: Trans-intestinal bioimpedance measurements have previously been used to investigate changes in electrical parameters during 6h of ischemia in the small intestine. Knowledge is lacking regarding the time course of trans-intestinal bioimpedance parameters during reperfusion. As reperfusion is an important part in the clinical treatment of intestinal ischemia, we need to know how it affects the bioimpedance measurements. Approach: We performed bioimpedance measurements, using a two-electrode setup on selected segments of the jejunum in 15 pigs. A controlled voltage signal was applied while measuring the resulting current. In each pig, five or six 30 cm segments of the jejunum were made ischemic by clamping the mesenteric arteries and veins creating segments with ischemia from 1–16h duration. Reperfusion was initiated at selected time intervals of ischemia, and measured for 5–15h afterwards. Main results: The tan δ parameter (loss tangent) was different (p < 0.016) comparing ischemic and control tissue for the duration of the experiment (16h). Comparing the control tissue 30 cm from the ischemic area with the control tissue 60 cm from the ischemic tissue, we found that the mean tan δ amplitude in the frequency range (3900–6300 Hz) was significantly higher (p < 0.036) in the proximal control after 10h of experiment duration. After reperfusion, the time development of tanδm (loss tangent maximum over a frequency range) amplitude and frequency overlapped and periodically increased above the tanδm in the ischemic intestine. Dependent on the ischemic duration pre-reperfusion, the initial increase in tan δ stabilizes or increases drastically over time, compared to the tan δ amplitude of the ischemic tissue. Significance: As during ischemia, the electrical parameters during reperfusion also follow a characteristic timecourse, depending on the ischemic exposure before pre-reperfusion. The temporal changes in electrical parameters during small intestinal ischemia followed by reperfusion provides important information for assessment of tissue injury.

• Pabst, Oliver; Martinsen, Ørjan Grøttem & Chua, Leon (2018). The non-linear electrical properties of human skin make it a generic memristor. Scientific Reports. 8(1), s. 1–9. doi: 10.1038/s41598-018-34059-6. Fulltekst i vitenarkiv Vis sammendrag

  An electrical measurement is non-linear when the applied stimulus itself affects the electrical properties of the underlying tissue. Corresponding voltage-current plots may exhibit pinched hysteresis loops which is the fingerprint of a memristor (memory resistor). Even though non-linear electrical properties have been demonstrated for different biological tissues like apples, plants and human skin, non-linear measurements as such have not been defined, yet. We are studying the non-linear properties of human skin systematically and initiate non-linear measurements on biological tissues as a field of research in general by introducing applicable recording techniques and parameterization. We found under which voltage stimulus conditions a measurement on human skin is non-linear and show that very low voltage amplitudes are already sufficient. The non-linear properties of human skin originate from the sweat ducts, as well as, from the surrounding tissue, the stratum corneum and we were able to classify the overall skin memristor as a generic memristor. Pinched hysteresis loops vary largely among subjects; an indication for the potential use in biomedical sensor applications.

• Bari, D. S.; Aldosoky, H. Y. Y.; Tronstad, Christian; Kalvøy, Håvard & Martinsen, Ørjan Grøttem (2018). Electrodermal activity responses for quantitative assessment of felt pain. Journal of Electrical Bioimpedance. 9, s. 52–58. doi: 10.2478/joeb-2018-0010. Fulltekst i vitenarkiv Vis sammendrag

  Accurate assessment of experienced pain is a well-known problem in the clinical practices. Therefore, a proper method for pain detection is highly desirable. Electrodermal activity (EDA) is known as a measure of the sympathetic nervous system activity, which changes during various mental stresses. As pain causes mental stress, EDA measures may reflect the felt pain. This study aims to evaluate changes in skin conductance responses (SCRs), skin potential responses (SPRs), and skin susceptance responses (SSRs) simultaneously as a result of sequences of electrical (painful) stimuli with different intensities. EDA responses as results of painful stimuli were recorded from 40 healthy volunteers. The stimuli with three different intensities were produced by using an electrical stimulator. EDA responses significantly changed (increased) with respect to the intensity of the stimuli. Both SCRs and SSRs showed linear relationship with the painful stimuli. It was found that the EDA responses, particularly SCRs (p < 0.001) and SSRs (p = 0.001) were linearly affected by the intensity of the painful stimuli. EDA responses, in particular SCRs, may be used as a useful indicator for assessment of experienced pain in clinical settings.

• Elvebakk, Ole; Tronstad, Christian; Birkeland, Kåre I.; Jenssen, Trond Geir; Bjørgaas, Marit Ragnhild Rokne & Frøslie, Kathrine Frey [Vis alle 10 forfattere av denne artikkelen] (2018). Evaluation of hypoglycaemia with non-invasive sensors in people with type 1 diabetes and impaired awareness of hypoglycaemia. Scientific Reports. 8:14722, s. 1–11. doi: 10.1038/s41598-018-33189-1. Fulltekst i vitenarkiv Vis sammendrag

  People with type 1 diabetes and impaired awareness of hypoglycaemia (IAH) are prone to severe hypoglycaemia. Previous attempts to develop non-invasive hypoglycaemia alarm systems have shown promising results, but it is not known if such alarms can detect severe hypoglycaemia in people with IAH. We aimed to explore whether a combination of non-invasive sensors could reliably evaluate hypoglycaemia (plasma glucose (PG) minimum 2.5 mmol/L) in people with IAH. Twenty participants with type 1 diabetes and IAH underwent randomly ordered, single blinded hyperinsulinemic euglycaemic and hyperinsulinemic hypoglycaemic clamps. Sweating, skin temperature, ECG, counterregulatory hormones and symptoms of hypoglycaemia were assessed. Overall, we were not able to detect clamp-induced hypoglycaemia with sufficient sensitivity and specificity for further clinical use. As a post-hoc analysis, we stratified participants according to their ability to identify hypoglycaemic symptoms during hypoglycaemic clamps. Five out of 20 participants could identify such symptoms. These participants had a significantly higher adrenaline response to hypoglycaemia (p < 0.001) and were reliably identified by sensors. Based on our observations, a non-invasive alarm system based on measurement of sweating responses and ECG changes during hypoglycaemia might provide an alert at a plasma glucose concentration around 2.5 mmol/L if an adequate sympatho-adrenal reaction is elicited.

• Bari, Dindar S.; Aldosky, Haval Y. Yacoob; Tronstad, Christian; Kalvøy, Håvard & Martinsen, Ørjan Grøttem (2018). Influence of relative humidity on electrodermal levels and responses. Skin Pharmacology and Physiology. ISSN 1660-5527. 31, s. 298–307. doi: 10.1159/000492275. Fulltekst i vitenarkiv
• Pabst, Oliver & Martinsen, Ørjan Grøttem (2017). Interpretation of the pinched point position in human skin memristor measurements. International Federation for Medical and Biological Engineering Proceedings. ISSN 1680-0737. 65, s. 430–433. doi: 10.1007/978-981-10-5122-7_108. Fulltekst i vitenarkiv Vis sammendrag

  It is shown that human skin acts like a memristor but systematic studies on skin memristance are not published, yet. If e.g., a low frequency voltage is applied to human skin and the current is measured, a hysteresis loop can be seen in the voltage-current plot. In skin measurements, the pinched point of the hysteresis loop can be shifted from the coordinate origin. In this paper, possible reasons for this observation shall be investigated and interpreted by the use of simulation. Two example measurements on human skin are presented, as well.

• Adamczak, Malgorzata Iwona; Martinsen, Ørjan Grøttem; Smistad, Gro & Hiorth, Marianne (2017). Polymer coated mucoadhesive liposomes intended for the management of xerostomia. International Journal of Pharmaceutics. ISSN 0378-5173. 527(1-2), s. 72–78. doi: 10.1016/j.ijpharm.2017.05.032. Fulltekst i vitenarkiv Vis sammendrag

  The aim of this work was to prepare and test different pharmaceutical formulations in respect of their potential in relieving dry mouth symptom. Since many of the products available on the market provide only temporary relief to the patients, there is need for new formulations able to retain on the oral mucosa. The prolonged moisture protection could be achieved by combining mucoadhesive materials, such as polymers containing hydrogen bonding groups, with vesicles capable of releasing hydration medium from the inner compartment. In this study three different types of liposomes (positively, negatively and neutrally charged) were coated with five different types of polymers: low-methoxylated pectin (LM-pectin), high-methoxylated pectin (HM-pectin), alginate, chitosan and hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC). The particle size and the zeta potential of the obtained carriers were tested by measuring dynamic light scattering (DLS) and electrophoretic mobility. Later on, selected positively charged liposomes were deposited on a negatively charged mica surface and depicted by atomic force microscopy (AFM). The water sorption properties of polymers, uncoated liposomes and polymer-coated liposomes were studied by the means of dynamic vapor sorption (DVS). The experiments were performed within the relative humidity range RH = 95–0–95%, at 35 °C. It was found that coating the liposomes with polymers significantly increased the water sorption capacity of the formulations, making them an attractive choice for hydration of the oral mucosa.

• Schwingenschuh, Simon; Scharfetter, Hermann; Martinsen, Ørjan Grøttem; Boulgaropoulos, Beate; Augustin, Thomas & Tiffner, Katrin [Vis alle 12 forfattere av denne artikkelen] (2017). Assessment of skin permeability to topically applied drugs by skin impedance and admittance. Physiological Measurement. ISSN 0967-3334. 38(11), s. N138–N150. doi: 10.1088/1361-6579/aa904e. Fulltekst i vitenarkiv
• Skjærvø, Øystein; Brandtzaeg, Ole Kristian; Lausund, Kristian Blindheim; Pabst, Oliver; Martinsen, Ørjan Grøttem & Lundanes, Elsa [Vis alle 7 forfattere av denne artikkelen] (2017). Exploring bioimpendance instrumentation for the characterization of open tubular liquid chromatography columns. Journal of Chromatography A. ISSN 0021-9673. 1534, s. 195–200. doi: 10.1016/j.chroma.2017.12.060. Fulltekst i vitenarkiv
• Pabst, Oliver; Tronstad, Christian & Martinsen, Ørjan Grøttem (2017). Instrumentation, electrode choice and challenges in human skin memristor measurement. IEEE Engineering in Medicine and Biology Society. Conference Proceedings. ISSN 1557-170X. s. 1844–1848. doi: 10.1109/EMBC.2017.8037205. Fulltekst i vitenarkiv
• Restan, Magnus Saed; Jensen, Henrik; Shen, Xiantao; Huang, Chuixiu; Martinsen, Ørjan Grøttem & Kubáň, Pavel [Vis alle 8 forfattere av denne artikkelen] (2017). Comprehensive study of buffer systems and local pH effects in electromembrane extraction. Analytica Chimica Acta. ISSN 0003-2670. 984, s. 116–123. doi: 10.1016/j.aca.2017.06.049. Fulltekst i vitenarkiv
• Bari, D. S.; Aldosky, H. Y. Y.; Tronstad, Christian; Kalvøy, Håvard & Martinsen, Ørjan Grøttem (2017). Electrodermal responses to discrete stimuli measured by skin conductance, skin potential, and skin susceptance. Skin Research and Technology. ISSN 0909-752X. 24(1), s. 108–116. doi: 10.1111/srt.12397. Fulltekst i vitenarkiv
• Tronstad, Christian; Elvebakk, Ole; Kalvøy, Håvard; Bjørgaas, Marit Ragnhild Rokne & Martinsen, Ørjan Grøttem (2017). Detection of sympathoadrenal discharge by parameterisation of skin conductance and ECG measurement. IEEE Engineering in Medicine and Biology Society. Conference Proceedings. ISSN 1557-170X. s. 3997–4000. doi: 10.1109/EMBC.2017.8037732. Fulltekst i vitenarkiv
• Strand-Amundsen, Runar James; Reims, Henrik Mikael; Tronstad, Christian; Kalvøy, Håvard; Martinsen, Ørjan Grøttem & Høgetveit, Jan Olav [Vis alle 8 forfattere av denne artikkelen] (2017). Ischemic small intestine - In vivo versus ex vivo bioimpedance measurements. Physiological Measurement. ISSN 0967-3334. 38(5), s. 715–728. doi: 10.1088/1361-6579/aa67b7. Fulltekst i vitenarkiv
• Canali, Chiara; Aristovich, Kirill; Ceccarelli, L.; Larsen, L. B.; Martinsen, Ørjan Grøttem & Wolff, A. [Vis alle 9 forfattere av denne artikkelen] (2016). Electrical impedance tomography methods for miniaturised 3D systems. Journal of Electrical Bioimpedance. 7, s. 59–67. doi: 10.5617/jeb.4084. Fulltekst i vitenarkiv
• Pettersen, Fred Johan; Martinsen, Ørjan Grøttem; Høgetveit, Jan Olav; Kalvøy, Håvard & Odland, Hans Henrik (2016). Bioimpedance spectroscopy of temporal impedance changes in a beating heart. Biomedical Engineering & Physics Express. 2. doi: 10.1088/2057-1976/2/6/065015. Fulltekst i vitenarkiv
• Abie, Sisay Mebre; Bergli, Joakim; Galperin, Yuri & Martinsen, Ørjan Grøttem (2016). Universality of AC conductance in human hair. Biomedical Engineering & Physics Express. 2. doi: 10.1088/2057-1976/2/2/027002. Fulltekst i vitenarkiv
• Strand-Amundsen, Runar James; Tronstad, Christian; Kalvøy, Håvard; Gundersen, Yngvar; Krohn, Claus Danckert & Aasen, Ansgar Oddne [Vis alle 12 forfattere av denne artikkelen] (2016). In vivo characterization of ischemic small intestine using bioimpedance measurements. Physiological Measurement. ISSN 0967-3334. 37(2), s. 257–275. doi: 10.1088/0967-3334/37/2/257. Fulltekst i vitenarkiv Vis sammendrag

  The standard clinical method for the assessment of viability in ischemic small intestine is still visual inspection and palpation. This method is non-specific and unreliable, and requires a high level of clinical experience. Consequently, viable tissue might be removed, or irreversibly damaged tissue might be left in the body, which may both slow down patient recovery. Impedance spectroscopy has been used to measure changes in electrical parameters during ischemia in various tissues. The physical changes in the tissue at the cellular and structural levels after the onset of ischemia lead to time-variant changes in the electrical properties. We aimed to investigate the use of bioimpedance measurement to assess if the tissue is ischemic, and to assess the ischemic time duration. Measurements were performed on pigs (n  =  7) using a novel two-electrode setup, with a Solartron 1260/1294 impedance gain-phase analyser. After induction of anaesthesia, an ischemic model with warm, full mesenteric arterial and venous occlusion on 30 cm of the jejunum was implemented. Electrodes were placed on the serosal surface of the ischemic jejunum, applying a constant voltage, and measuring the resulting electrical admittance. As a control, measurements were done on a fully perfused part of the jejunum in the same porcine model. The changes in tan δ (dielectric parameter), measured within a 6 h period of warm, full mesenteric occlusion ischemia in seven pigs, correlates with the onset and duration of ischemia. Tan δ measured in the ischemic part of the jejunum differed significantly from the control tissue, allowing us to determine if the tissue was ischemic or not (P  <  0.0001, F  =  (1,75.13) 188.19). We also found that we could use tan δ to predict ischemic duration. This opens up the possibility of real-time monitoring and assessment of the presence and duration of small intestinal ischemia.

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• Martinsen, Ørjan Grøttem & Heiskanen, Arto (2023). Bioimpedance and bioelectricity basics, 4th edition. Academic Press. ISBN 9780128191071. 631 s. Fulltekst i vitenarkiv
• Mesri, Alireza; Cunha, Andrè Bastos da; Ferrari, Giorgio; Sampietro, Marco & Martinsen, Ørjan Grøttem (2018). A Laser Diode-Based Wireless Optogenetic Headstage. IEEE (Institute of Electrical and Electronics Engineers). ISBN 9781538653876. 4 s. Fulltekst i vitenarkiv

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• Edemann-Callesen, Henriette; Huus, Christel Mie Lykke; Karstoft, Caroline; Bjarnadóttir, Elín; Bikic, Aida & Jeppesen, Pia [Vis alle 13 forfattere av denne artikkelen] (2025). External trigeminal nerve stimulation versus sham stimulation for attention deficit hyperactivity disorder in children and adolescents aged 7–17 years: study protocol for a pilot and feasibility randomized clinical trial. doi: 10.1007/s00787-025-02786-7. Fulltekst i vitenarkiv Vis sammendrag

  External trigeminal nerve stimulation (eTNS) is a non-invasive technique involving external cutaneous stimulation of the trigeminal nerve. In 2019, the Monarch eTNS device was approved as a treatment for children with attention-deficit/hyperactivity disorder (ADHD). The Monarch eTNS device is designed to be applied at home, which offers a certain level of convenience but also necessitates a high degree of compliance and acceptability from the families. To assess the feasibility of – and pilot a larger randomized clinical trial investigating the Monarch eTNS device versus sham for patients aged 7 to 17 years with ADHD. We will conduct a parallel-group, sham-controlled, feasibility randomised clinical trial. We will include 60 children and adolescents (aged 7 to 17 years) diagnosed with ADHD from three clinical sites in Denmark. Patients will be randomised to 4 weeks of active versus sham eTNS. Feasibility outcomes include completion of the trial; the number of eligible participants who consent to inclusion; treatment compliance; acceptability of the intervention and completion. Adverse events will be monitored throughout the trial. Exploratory clinical outcomes include ADHD core symptoms (primary) and several secondary outcomes. Autonomic functions will be evaluated by means of heart rate variability, using a heart rate sensor. This trial will allow us to evaluate the feasibility of conducting a larger randomised clinical trial investigating the use of eTNS as a home-based, non-pharmacological intervention for children and adolescents diagnosed with ADHD.

• Sexton, Alexander Harold; Knaapila, Matti Pekka & Martinsen, Ørjan Grøttem (2024). Monitoring lifetime of thermoplastic composites by combining analytics and machine learning. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Knaapila, Matti Pekka; Martinsen, Ørjan Grøttem; Demchenko, Hanna; Huss-Hansen, Mathias K. & Balzano, Luigi (2023). Simultaneous SAXS/WAXS characterizations of continuous carbon fiber composites subjected to low-velocity-impact. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Martinsen, Ørjan Grøttem; Knaapila, Matti Pekka; Demchenko, Hanna; Balzano, Luigi & Huss-Hansen, Mathias K. (2023). Simultaneous SAXS/WAXS characterizations of continuous carbon fiber composites subjected to low-velocity-impact. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Knaapila, Matti Pekka & Martinsen, Ørjan Grøttem (2023). Monitoring lifetime of thermoplastic composites by combining analytics and machine learning. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Knaapila, Matti Pekka; Fossum, Jon Otto & Martinsen, Ørjan Grøttem (2022). Monitoring lifetime of thermoplastic composites by combining analytics and machine learning. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Knaapila, Matti Pekka & Martinsen, Ørjan Grøttem (2022). Monitoring lifetime of thermoplastic composites by combining analytics and machine learning. Fulltekst i vitenarkiv
• Sexton, Alexander Harold; Knaapila, Matti Pekka & Martinsen, Ørjan Grøttem (2022). Monitoring lifetime of thermoplastic composites by combining analytics and machine learning. Fulltekst i vitenarkiv
• Martinsen, Ørjan Grøttem (2021). Distinguished lecturer message. Journal of Physics: Conference Series (JPCS). ISSN 1742-6588. 2008(1). doi: 10.1088/1742-6596/2008/1/011001. Fulltekst i vitenarkiv
• Schuelke, Christin; Cunha, Andrè Bastos da; Heiskanen, Arto; Asif, Afia; Keller, Stephan S. & Martínez-Serrano, Alberto [Vis alle 8 forfattere av denne artikkelen] (2020). Neural Stem Cell Characterization and Detection of Neurotransmitter release using Bioimpedance and Electrochemistry. Fulltekst i vitenarkiv Vis sammendrag

  The goal of the Training4CRM project is to develop a device for personalized medicine to treat neurodegenerative disorders (Parkinson´s Disease, Huntington´s Disease, and Epilepsy). This future device includes a bioimplant consisting of a 3D scaffold, electronics, a light source and optogenetically modified neuronal cells that will be operated into the patient’s brain to release disease-specific neurotransmitters. The aim of this work is the non-invasive observation of cell proliferation and neuronal differentiation, as well as detection of neurotransmitter release. Electrical Impedance Spectroscopy (EIS) and amperometry provide excellent tools for investigation of various cellular phenomena. EIS can be used to monitor different cellular changes like proliferation, apoptosis, migration, changes in morphology and also (neuronal) differentiation. Compared to most molecular biological methods, bioimpedance measurements are non-invasive and allow for repeated analysis of the same cell population. Human neural stem cells were cultured as monolayer on 2D carbon electrode chips. Bioimpedance measurements were performed every second day to follow the proliferation of hNSCs. Cells impede the flow of current between electrodes. Therefore, an increasing number of cells results in an increased impedance. Amperometry was used to detect the release of neurotransmitters (especially dopamine) after triggered depolarization by stimulation of neurons with a high K+ buffer. Release of oxidizable molecules leads to increased current visible as oxidation peak. This work demonstrates the principle of bioimpedance and electrochemical detection of neurotransmitter release. With EIS, proliferation can be monitored noninvasively over time. With amperometry, detection of repeated depolarization is possible and cells remain active over several days.

• Elvebakk, Ole; Tronstad, Christian; Birkeland, Kåre Inge; Jenssen, Trond Geir; Bjørgaas, Marit Ragnhild Rokne & Frøslie, Kathrine Frey [Vis alle 10 forfattere av denne artikkelen] (2019). Author Correction: Evaluation of Hypoglycaemia with Non-Invasive Sensors in People with Type 1 Diabetes and Impaired Awareness of Hypoglycaemia (Scientific Reports, (2018), 8, 1, (14722), 10.1038/s41598-018-33189-1). Scientific Reports. 9(1). doi: 10.1038/s41598-019-42218-6. Fulltekst i vitenarkiv
• Azumah, Joseph; Hiorth, Marianne; Smistad, Gro & Martinsen, Ørjan Grøttem (2019). Development of alginate and chitosan coated liposomes intended to use in the treatment of xerostomia. Fulltekst i vitenarkiv
• Azumah, Joseph; Hiorth, Marianne; Smistad, Gro & Martinsen, Ørjan Grøttem (2019). Alginate and chitosan coated liposomes intended for treatment of dry mouth. Fulltekst i vitenarkiv
• Azumah, Joseph; Smistad, Gro; Martinsen, Ørjan Grøttem & Hiorth, Marianne (2019). Development of alginate coated liposomes with potential of being used in treatment of dry mouth. Fulltekst i vitenarkiv
• Schuelke, Christin; Cunha, Andrè Bastos da; Heiskanen, Arto; Asif, Afia; Keller, Stephan S. & Kalvøy, Håvard [Vis alle 9 forfattere av denne artikkelen] (2019). Bioimpedance and Electrochemistry for Neural Stem Cell Characterization and Detection of Dopamine Release. IEEE Engineering in Medicine and Biology Society. Conference Proceedings. ISSN 1557-170X. Fulltekst i vitenarkiv Vis sammendrag

  Biophysical measurement methods like electrical impedance spectroscopy and amperometry provide an excellent tool for investigation of various cellular phenomena. In this work, bioimpedance measurements have been performed to assess the proliferation of neural stem cells or PC12 cells. Subsequently, amperometry was used to detect neurotransmitter release from PC12 cells or neurons differentiated from neural stem cells.

• Brandtzaeg, Ole Kristian; Wilson, Steven Ray Haakon; Lundanes, Elsa; Reubsaet, Leon; Krauss, Stefan & Martinsen, Ørjan Grøttem (2018). Online sample Preparation Platforms for Targeted Nano Liquid Chromatography Mass Spectrometry Bioanalysis. Universitetet i Oslo. Fulltekst i vitenarkiv
• Pabst, Oliver; Martinsen, Ørjan Grøttem; Tronstad, Christian & Wilson, Steven Ray Haakon (2018). Electrical properties of human skin: From linear recordings of exogenous electrodermal activity to non-linear memristor measurements. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  This thesis is all about applying an electrical voltage to human skin and measuring the corresponding electrical current. A recording (on any tissue) is non-linear when the electrical properties are affected by the applied signal itself; The measurement is linear otherwise. Non-linear measurements on human skin initiate a very new field of research. Dependent on the polarity of the applied voltage, the sweat inside the ducts is moved towards the skin surface or towards deeper skin layers. Here we confirmed that the sweat ducts are memristors (memory resistor) and found that information can actually be stored inside. If you are a forgetful person, this might be a way to store your bank pin number in the future. A second memristor can be found in the stratum corneum (the tissue in the outer layer of the skin that surrounds the sweat ducts). However, the voltage-current characteristics recorded from human skin vary largely among subjects with potential applications in Diagnostics. Further, we found that human skin can act as a frequency doubler and halve-wave rectifier. An example of linear measurements will be given as an introduction. Changes in sweating due to sympathetic nervous activity are subject of (linear) electrodermal activity (EDA) recordings. Here, the test subjects were asked to do continuous subtractions and deep breaths, to stimulate their sweat activity. By doing so, it was possible to find out that EDA recordings using the alternating current (AC) method are comparable with recordings using the direct current (DC) method.

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