Seamus Thomson
Seamus Thomson is a Senior Research Scientist at Google, Mountain View, CA, where his research interests include consumer health, wearables, and advanced sensing technologies. He was previously a NASA Postdoctoral Program Fellow at NASA’s Ames Research Center, focusing on science instrumentation for planetary exploration and life-detection missions to the icy moons of Jupiter and Saturn. He received the B.E. (Hons.) and Ph.D. degrees from the School of Aerospace, Mechanical and Mechatronic Engineering at the University of Sydney, where he also earned the B.Med.Sc. degree from the Faculty of Medicine and Health.
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Differential Sensitivity of Impedance Plethysmography and Photoplethysmography Sensors to Temperature-Induced Peripheral Vasoconstriction
Seobin Jung
Alexandros Pantelopoulos
Lindsey Sunden
Pete Richards
Shwetak Patel
Sam Sheng
Scientific Reports (2026)
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Impedance plethysmography (IPG) and photoplethysmography (PPG) are non-invasive techniques for measuring blood volume changes. This study investigated the differential responses of IPG and PPG to temperature-mediated vasoconstriction induced by localized cooling. Twenty-one participants underwent control and treatment conditions, with fake or real ice cubes applied to the forearm. Blood pressure remained stable, while heart rate decreased. PPG signal amplitude significantly decreased with cooling (p_adj = 0.004), indicating sensitivity to superficial blood flow changes. In contrast, IPG signal amplitude remained stable (p_adj = 1.0). No statistically significant differences were observed in timing-derived metrics. These findings suggest IPG is less sensitive to superficial changes in blood flow than PPG, and may be more suitable for monitoring deeper blood flow. This study provides insights into the distinct sensitivities of IPG and PPG, with implications for wearable device development and cardiovascular monitoring.
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This paper presents the first reported measurements of impedance plethysmography (IPG) signals from the human fingertip. The human fingertip serves as a vital non-invasive access point for cardiovascular monitoring, with photoplethysmography (PPG) widely adopted for its assessment of superficial blood flow. However, the optical sensing depth of PPG limits its capacity to fully characterize deeper peripheral hemodynamics. Here, we developed a novel four-electrode fingertip IPG prototype and measurement protocol, enabling the consistent capture of pulsatile impedance waveforms reflecting blood volume changes within the digit. Preliminary data from two participants illustrates clear signal reproducibility, enabling the derivation of key pulse wave metrics including pulse arrival time (PAT). Given IPG’s electrical sensing principle, distinct from PPG’s optical approach, our findings suggest that fingertip IPG offers a complementary “new window” into peripheral circulation. This work establishes fingertip IPG as a significant advancement for non-invasive physiological monitoring, holding promise for both clinical applications and wearable health technologies.
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Evidence of Differences in Diurnal Electrodermal Patterns by Mental Health Status in Free-Living Data
Daniel McDuff
Isaac Galatzer-Levy
Andrew Barakat
Conor Heneghan
Samy Abdel-Ghaffar
Jake Sunshine
Lindsey Sunden
Allen Jiang
Ari Winbush
Benjamin Nelson
Nicholas Allen
medRxiv (2024)
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Electrodermal activity (EDA) is a standardized measure of sympathetic arousal that has been linked to depression in laboratory experiments. However, the inability to measure EDA passively over time and in the real-world has limited conclusions that can be drawn about EDA as an indicator of mental health status outside of a controlled setting. Recent smartwatches have begun to incorporate wrist-worn continuous EDA sensors that enable longitudinal measurement in every-day life. This work presents the first example of passively collected, diurnal variations in EDA present in people with depression, anxiety and perceived stress. Subjects who were depressed had higher tonic EDA and heart rate, despite not engaging in greater physical activity, compared to those that were not depressed. EDA measurements showed differences between groups that were most prominent during the early morning. We did not observe amplitude or phase differences in the diurnal patterns.
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