THE 4-ELECTRODE RESISTIVITY TECHNIQUE IN ANISOTROPIC MEDIA - THEORETICAL-ANALYSIS AND APPLICATION ON MYOCARDIAL TISSUE IN-VIVO

Several aspects of the four-electrode resistivity technique were studi ed with special emphasis on the theoretical determination of penetrati on depth and sample volume in anisotropic media such as (cardiac) musc le. Moreover, the presence of a thin disturbing layer on top of the me dium under study was analyzed. A four-electrode sensor was developed f or the measurement of local myocardial resistivity in two orthogonal d irections. The sensor was applied to the epicardium of anesthetized op en chest dogs and, as an example, results are given on the frequency d ependence (5-60 kHz) and the changes during the cardiac cycle of longi tudinal and transverse myocardial resistivity.