Comparison of Electrode Configurations for Impedance Plethysmography Based Heart Rate Estimation at the Forearm

Electrical impedance plethysmography (EIP) is a cost effective and power efficient physiological measurement method that could potentially be applied for measuring pulse waves along limbs in ambulatory conditions. The pulse wave information could be utilized to determine the heart rate or other relevant parameters such as heart rate variability or cardiac rhythm. We compared three electrode configurations for EIP at the forearm, with the focus on assessing its utility in a wearable device. The evaluation included EIP measurements with ten healthy participants using adhesive gel electrodes. The evaluated electrode configurations were tetrapolar configuration along the forearm and tetrapolar and bipolar configurations around the wrist. For each electrode configuration, the measurements were performed in stationery condition and during finger movement. The collected data was evaluated for finding out differences in the signal to noise ratio (SNR) between the configurations during the two conditions. The results show that pulse wave signal with adequate SNR for heart rate estimation is obtained from the wrist area while stationary and mostly also during the presence of mild movement. There was no significant difference in the data quality between wrist area and conventional configuration along the limb.