Pantelopoulos, A. | 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↗

bioRxiv2019

Heart Rate Variability with Photoplethysmography in 8 Million Individuals: Results and Scaling Relations with Age, Gender, and Time of Day

Heart rate variability, or the variation in the time interval between consecutive beats, is a non-invasive dynamic metric of the autonomic nervous system and an independent risk factor for cardiovascular death. Prior limitations of use include requirements for continuous electrocardiography and lack of reference standards. Consumer wrist-worn tracking devices using photoplethysmography now provide the unique potential of continuously measuring surrogates of sympathetic and parasympathetic activity through the analysis of interbeat intervals. Here we leverage wrist-worn trackers to present the largest, to our knowledge, analysis of heart rate variability in humans across the time, frequency, and graphical domains. We derive diurnal parasympathetic and sympathetic measures and provide scaling parameters by age, sex, and time of day. Poincare plots graphically summarize heart rate variability metrics and may detect common arrhythmias. Lastly, we observe a strong dose-dependent correlation between daily steps and optimal heart rate variability metrics. Our results provide the ability to interpret continuous heart rate variability for tens of millions of wrist-worn trackers already in use.

physiology↗