Analytical study of electrical impedance plethysmography in peripheral blood flow

Abstract

The impedance Z, the derivative of Z with respect to time t, dZ/dt, and blood flow F have been measured simultaneously in the central caudal artery of a series of anaesthetised rats. The results of the experiments were expressed in the relationship derived from the Windkessel theory where f(t)=adz(t)/dt+βz(t), in which α and β are constants and f(t) and z(t) express the pulsating fractions in the blood flow F and the impedance Z, respectively. The correlation between the peak-to-peak values of f(t) and of adz(t)/dt+βz(t) was 0·96. The correlation between the mean flow f_o and the peak-to-peak value of f(t) was 0·74. Furthermore, even when the mean flow was zero, adz(t) still existed. The theoretical model was tested against volume flow measurements made using an electromagnetic flowmeter and was found to correlate well. Theoretical estimates of vessel calibre also accord with measured values.