Direct coextensive plethysmography for non-invasive measurement of systemic pressures and volumes

A method for noninvasive measurement of pressures and fluid volumes of the complete systemic vascular circuit, called direct coextensive plethysmography, is proposed. This includes the pressures of the large veins, small veins, venules, capillaries, arterioles, small arteries, large arteries and nonvascular fluid compartments. It uses a conventional pressure cuff on the outside of the arm, combined with a tetrapolar bioimpedance electrode band to derive a fluid volume indication (impedance) versus pressure profile for the entire system. Determination of state changes in the residual fluid volume versus pressure profile yields physiologic information about the pressures and fluid volumes in the various segments of the vascular circuit and nonvascular fluid compartments. Advanced signal processing techniques have been applied to improve upon early slope change analysis. Initial confirmation of the correlation between the measured large vein pressure and the central venous pressure were made in a small clinical trial with intensive care unit subjects.