Impedance cardiography a method for non-invasive monitoring of stroke volume: a preliminary study

Impedance cardiography (ICG) is a simple and inexpensive technique for non-invasive and continues measurement of stroke volume. Due to non-invasive nature, ICG is becoming increasingly used in research and clinical applications. With regard to lack of domestic impedance cardiograph and limited similar imported products in the country, an inexpensive and portable prototype of ICG system has been developed through this study. To measure electrical impedance of the thorax area, a constant sin wave current of 50 KHz and 2 mA is injected through two pairs of electrodes and modulated voltage signal with impedance information is picked up by using two other pairs of electrodes. After hardware performance checking, accuracy and efficiency of the system for measurement of the absolute value of SV in comparison with Doppler-echocardiography was evaluated for five patients. Through this study a portable impedance cardiograph was implemented in which could record ICG signal and one-lead ECG signal simultaneously and calculate parameters such as pre-ejection period, left ventricular ejection time, cardiac output, and, thoracic fluid content. After initial test of the system on the five patients, there was a significant correlation (p<0.05) for measurements of SV between ICG and Doppler-echocardiography methods (r = 0.83). ICG has potential to become a simple and reliable technique for non-invasive and continuous measurement of SV. The results of this pilot study demonstrate that there is possibility of manufacturing and development of domestic impedance cardiograph.