# Differential sensitivity of impedance plethysmography and photoplethysmography sensors to temperature-induced peripheral vasoconstriction

## TL;DR

This study compares how two non-invasive blood flow monitoring techniques respond to changes in temperature.

## Contribution

The study reveals that IPG is less sensitive to superficial blood flow changes compared to PPG.

## Key findings

- PPG signal amplitude significantly decreased with cooling, indicating sensitivity to superficial blood flow changes.
- IPG signal amplitude remained stable during cooling, suggesting it is less affected by superficial blood flow changes.
- Heart rate decreased during cooling, but blood pressure remained stable.

## Abstract

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 (padj = 0.004), indicating sensitivity to superficial blood flow changes. In contrast, IPG signal amplitude remained stable (padj = 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.

The online version contains supplementary material available at 10.1038/s41598-026-36563-6.