Deep-Tissue Hemodynamic Sensing: Comparing Impedance and Photoplethysmography for Wearable Blood Pressure Estimation

A study with 261 participants (130 with high blood pressure, 131 without) compared two technologies for cuffless blood pressure measurement. Researchers analyzed over 150,000 cardiac cycles using a custom dual-modality sensor. Impedance plethysmography (IPG) penetrated deeper into tissues and revealed up to three distinct morphological patterns per participant, while photoplethysmography (PPG) showed uniform profiles. The IPG signal on the ventral forearm showed a significant effect on blood pressure status (p = 0.024), which was absent in the PPG signal. Increasing body mass index (BMI) significantly reduced the prevalence of steep-upstroke archetypes in IPG (p = 0.035), indicating a damping effect of adipose tissue. The results suggest that bioimpedance captures rich hemodynamic signatures that are invisible to optical sensors.