Simultaneously Capturing Electrocardiography and Impedance Plethysmogram Signals From Human Feet by Capacitive Coupled Electrode System

Abstract

A microprocessor measurement system is developed for simultaneously capturing electrocardiography (ECG) and impedance plethysmogram (IPG) signals. All the measurement electrodes are coupled with human skin in a non-contact capacitive way. A capacitive coupled pickup circuit is used for obtaining the original ECG and IPG signals. Three differences of electrode configurations are experimentally tested for picking up the ECG signals, i.e., from the plantar area of the feet, from the instep area of the feet, and from a single hand and a single foot. Two different configurations (i.e., two-electrode IPG and four-electrode IPG) are tested to get IPG signals. A singular spectrum analysis (SSA)-based algorithm is embedded in a microprocessor system for signal processing. It is found that the original signals, especially the IPG signals, are quite noisy and can only be used after SSA processing. When both the ECG and IPG signals are measured simultaneously, the ECG signal will be severely ruined by the interference from the excitation current signal of IPG measurement. Relatively satisfied signals can only be simultaneously obtained when one ECG electrode is placed in a hand. The time difference between the ECG R-peak and IPG C-peak (the peak point in IPG) is experimentally tested for its potential application in blood pressure measurement.