Design and Implementation of a Portable Impedance Cardiograph System for Non-Invasive Stroke Volume Monitoring

Abstract

Measurement of the stroke volume and its changes over time can be very helpful for diagnosis of dysfunctions in the blood circulatory system and monitoring their treatments. Impedance cardiography(ICG)is a simple method of measuring the stroke volume based on changes in the instantaneous mean impedanceof the thorax. This method has received much attention in the last two decades because it is non-invasive, easy to be used, and applicable for continuous monitoring of the stroke volumeas well as otherhemodynamic parameters.The aim of this study was to developa low cost portable ICG system with high accuracy for monitoring stroke volume.The proposed wireless system uses a tetrapolar configuration to measure the impedance of the thorax at 50 kHz. The system consists ofcarefully designed precise voltage-controlled current source,biopotential recorder anddemodulator. The measured impedance was analyzed on the computer to determine the stroke volume. After evaluating the system’s electronic performance, its accuracy was assessed by comparing its measurements with the values obtained from Doppler Echocardiography on 5 participants. An impedance cardiograph was implemented that can noninvasively provide a continuous measure of the stroke volume. The SNR of the system was measured above 50dB. The experiments revealed that a strongcorrelation (r=0.89) exists between the measurements by the developed system and Doppler-echocardiograph (p<0.05). ICG as the sixth vital sign can be measured simply and reliably by the developed system, but more detailed validation studies should be conducted to evaluate the system performance. There is a good promise to upgrade the system to a commercial version domestically for clinical use in the future.