Impedance plethysmography revisited

Abstract

Noninvasive techniques for measuring blood flow have recently been of great interest in cardiovascular psychophysiology. Among these, impedance plethysmography is often used for measuring stroke volume and cardiac output (=stroke volume × heart rate) and sometimes used for measuring forearm blood flow. This review describes the basic principles and techniques of blood flow measurement by use of impedance plethysmography in the thoracic and forearm regions. On the basis of the so-called “parallel conductor model” (by J. Nyboer), the equation estimating stroke volume and forearm blood flow is uniformly derived. The importance of obtaining blood pressure is noticed because this enables the calculation of peripheral vascular resistance (=mean blood pressure/cardiac output) and forearm vascular resistance (=mean blood pressure/forearm blood flow). This review is also concerned with systolic time intervals (pre-ejection period, left ventricular ejection time, QS2 or electro-mechanical systole, QT/QS2) : the by-products of impedance plethysmography and the parameters that seem to indicate beta-adrenergic activity. Validities and some controversial problems, as well as the limitations, in relation to these matters are discussed.