Noninvasive Determination of Central Blood Pressure by Impedance Plethysmography

A new algorithm based on impedance plethysmography provides reliable determinations, on an experimental basis, of arterial blood pressure. Signals over the brachial artery are picked up by four Velcro-type electrodes attached to the skinward side of a regular blood pressure cuff. Mathematical formulas are used to define those impedance pulses that correspond to systolic, diastolic, and mean arterial blood pressure values. The envelope of the impedance pulses recorded during cuff deflation can be defined by linear regressions, function of just one normalized independent variable, which is the ratio between the amplitude of the pulse with maximum amplitude and of the amplitude of the pulses with constant amplitude. These linear regressions are assumed to be universally applicable, the influence of individual anatomic variations having been eliminated by the use of a normalized variable. The results of this study prove that the variable pulse amplitude obtained during a cuff deflation is a quantifiable reaction of the circulatory system to arterial constriction.