Electrical Impedance Plethysmography

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Abstract
The quantity of blood measured by this radiofrequency method is defined by its parallel resistive effect. The effective vol. pulse is based on twice the mean height of the excursion during the entire cycle. Its cubic value is derived by substitution of the calculated parallel resistance, Rb, together with data defining the resistivity of the blood, [rho], and the length of the segment, 1 , in the equation for the volume of an electrical conductor, [image]. The quantity of blood displaced from the venous reservoir of a given segment, and the rate of its refilling may also be detd. quantitatively by this method. Data are tabulated showing the effect of 2 and 4 electrode technics of impedance measurement of both arms; the parallel effect of 2 similar body segments on the measurement of the pulse vol.; the physical and physiological effect of covering the skin surface between the electrodes with salt jelly, and then with A1 foil; and the response in pulse volume of the forearm to digital exercise. No clinical data are included in this paper, but it attempts to explain concisely the physical and physiological basis of electrical impedance recording from body segments.

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