Sunden, L. | Search bioRxiv

bioRxiv2025

Differential Sensitivity of Impedance Plethysmography andPhotoplethysmography Sensors to Temperature-Induced PeripheralVasoconstriction

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 real or fake ice cubes applied to the forearm. PPG signal amplitude significantly decreased with cooling (p < 0.001), indicating sensitivity to capillary blood flow changes. In contrast, IPG signal amplitude remained stable, suggesting it primarily reflects blood flow in larger/deeper vessels. Blood pressure remained stable, while heart rate decreased. These findings suggest IPG is less sensitive to capillary-level changes 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.

physiology↗

bioRxiv2024

What Does Large-scale Electrodermal Sensing Reveal?

Electrodermal activity (EDA) is a physiological measure that is used to index sympathetic arousal in response to stressors and other perturbations. However, EDA is underutilized in real-world, population-level research and clinical practice because of a paucity of remote measurement capabilities on commodity devices. The current study examined the capabilities of continuous remote measurement of EDA at scale to quantify physiological changes in the context of diurnal and circadian rhythms, demographic differences, high arousal contexts such as public holidays and high arousal moments (e.g., the Super Bowl). We first demonstrated the accuracy of a novel EDA sensor developed for the Fitbit Sense 2 wearable device within a controlled, arousal-inducing experiment. We then retrospectively analyzed 10 million hours of continuous EDA data collected from over 16,000 people. We show that continuously sampled in-situ EDA from Sense 2 has similar population-level diurnal patterns as those established from more tightly controlled in-lab experiments. Following this, variation of SCL across day of the week and season are presented. Finally, EDA dynamics occurring in response to commonly held stressful or exciting events such as Thanksgiving and the Super Bowl are described which we interpret as a natural experiment eliciting autonomic arousal.

physiology↗