Y.E. Kirpichenko, D.P. Timohin, S.I. Shchukin

Nowadays noninvasive instrumental methods are to be used in medicine. There is an opportunity to study cardiac electrical activity in conjunction with hemodynamics when a method of tetrapolar frequency-division of rheocardiographic and electrocardiographic signals is used. In addition to the traditional transthoracic rheocariographic technique precadiac rheographic signals processing allows to analyze not only comprehensive indicators of hemodynamics, but also all the processes of individual sites of heart (valves, ventricles, cardiac apex). Thus, the precardiac rheocardiogram technique can be considered as an additional tool for ultrasound, or sometimes, even as an independent procedure for heart functionality determination. The essence of precardiac rheography technique is that for measurement purposes we use tetrapolar electrode system. Two electrodes (usually called current electrodes) are used to pass a constant alternating current with a high frequency 100 kHz. amplitude up to 2 mA. The current is imperceptible to the patient and does not cause any physiological reactions. The other two electrodes (usually called measuring electrodes) are placed between the current electrodes and measure the voltage which is caused by the current flowing through the body segment. This voltage corresponds to the impedance of the body segment and changes in blood volume variations. On this basis the blood flow can be measured and analyzed. For data acquisition and subsequent signal analysis we have developed software built in Visual C++ development environment for Windows XP and later. It performs: - Data acquisition, filtration, analyzing; - Modeling impedance distribution by means of layered or spherical models; - Impedance mapping application. For impedance mapping purposes special electrode system has been assembled which allows carrying out impedance mapping procedure less than 20 minutes. Electrode systems are furnished with 8 mm diameter EEG electrodes. This feature provides impedance precision up to 0.1 Om. Electrode system covers most part of the thorax, in that way we can acquire a whole heart projection on the thorax and its changes during cardiac cycle. Software application realizes data registration, processing and other functions. Softweare realize data averaging by 10-12 cardiac cycles and then perform impedance mapping. As a result of impedance mapping we are provided with map of base impedance, map of pulse impedance and map of pulse impedance magnitudes during averaged cardiac cycle. By using all these tools impedance mapping technique has been realized, by which the results of it is possible to recognize borders of heart projection on the thorax, its shifts during cardiac cycle and calculate shifts of ventricle front wall. Also classification of precardiac rheocardiographic signals from different leads has been performed.