102 ELECTRICAL IMPEDANCE METHODS FOR THE MEASURE- MENT OF STROKE VOLUME IN MAN: STATE OF ART Jüri Vedru Institute of General and Molecular Pathology Group of Biomedical Engineering, Veski 34, EE2400 Tartu, Estonia Abstract  Electrical impedance methods used in practice for stroke volume estimation, though having advantageous features, have their weaknesses, too. In the paper a survey of the methods is given with respect to improvement them using computer simula- tion and advanced signal processing. As well the Kubicek and Sramek methods as the Tischenko method are shown to be con- siderably empirical and unsuitable for such kind of modernisa- tion. Improvement of electrical impedance methods for stroke volume estimation would be realised by using new technique - electrical impedance tomography. Key words  impedance plethysmography, impedance cardiography, impedance tomography, bioimpedance, integral rheography, stroke volume, cardiac output, Kubicek method, Sramek method, Tischenko method Introduction Electrical impedance methods are based on measurement of the electrical impedance (i.e., the modulus of the full complex resistance) of the human body or its parts at sub-high frequency (20...200 kHz). It has been found that the impedance of body pulses in synchronism with the heart. This pulsation is the origin of impedance plethysmogram. Ampli- tude of the impedance plethysmogram comprises about 1/1000 ... 1/100 of the mean value of the observed impedance. Such a phenomenon is explained as a result of an impact of pulsation of blood content in tissues on the electrical resistivity of the tissues (Nyboer et al. 1950). Besides, considerable effect of changing the resistivity of blood itself with its linear velocity is detected (Moskalenko et al. 1959, Liebman et ______________________________________________________ This work was supported by the Estonian Science Foundation grant No. 272.