Evaluation of cardiac parameters using electrical impedance plethysmography

Impedance plethysmography is a method for determining changes in body tissue volumes, based on the measurement of electric impedance at the body surface. Because it is a non-invasive and cost-effective method to measure and analyze hemodynamics, it would bring to physiologists very important diagnostic information for the continuous care of critical patients with hemodynamic disorders.

This study aimed at acquiring non-invasively and at analyzing plethysmografic waves by measuring the electrical impedance. For measurements we built a device that was designed as an injection module with a microcontroller, a programmable waveform generator, and a voltage controlled current source which generates a sinusoidal pulse with adjustable frequency (10-200 kHz) and adjustable intensity. In output, the device delivers an analogical signal representing the variation of the impedance of the explored section. The acquisition of the bioimpedance signal on PC was made easier by the use of a national instrument data acquisition device, the NI USB 6009.

The bioimpedance signal processing, the user interface and the display were managed by MATLAB. Sample impedance data for a test subject are presented. From the experimental results, it is shown that the proposed bioimpedance measuring system could provide good performance over the frequency range for central or peripheral territory.

The clinical importance of these findings is that this method can measure vascular parameters noninvasively, continuously and more conveniently in humans.