A plethysmograph is an instrument or apparatus which provides a graphic means of determining the change in volume of an encased organ or extremity. This book is concerned with the principles and application of electrical resistive or impedance measurements of the body or parts thereof as a static or varying biologic volume conductor of current. Volumetric changes of organs as the lungs or an extremity may be calculated from the electrical resistive plethysmographic changes recorded from externally applied or implanted electrodes.
The author discusses the fundamentals of the electrical measurements of segmental volume conductors by electrical impedance, instruments for measurement of impedance, application of the technique, and vascular flow quantitation by dilution effect on electrical conductivity. The section on the application of electrical plethysmography encompasses concepts of the etiology of impedance pulsation, of gross vascular volume quantitation, of the influence of arterial occlusion on pulse and vascular volume and of