Average volume resistivities for thoracic tissues at an exciting frequency of 100 kc. are required for studies of the current flux paths in transthoracie impedance plethysmograph. By using a uniquely designed probe and anesthetized dogs, an average tissue resistivity was found for skeletal muscle to be approximately 400 ohm cm.;heart muscle, 4S0 ohm cm.;lung tissue, 1,200 to 1,500 ohm cm.;kidney and liver, 600 ohm cm.;fat, 1,000 to 2,000 ohm cm.:and for whole canine blood, 150 ohm cm. at a hematocrit of 45. With the exception of whole blood, all values varied significantly between dogs and between individual readings. The values for lung and liver tissues and for fat were noted to have particularly large variations between readings and between animals.nCanine skeletal muscle tissue had a linear electrical resistivity characteristic for excitation current densities up to 80 ma./cm. Representative normal, human skin on the biceps was shown to contribute approximately 4.5 x 10 mhos/cm. of electrode surface area in series with the transthoracie impedance, with possible modifications required for electrode geometry and electrode paste.
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