An in vivo study of the total occlusion method for the analysis of forward and backward pressure waves

The arterial pressure wave, Pm, is composed of a forward travelling wave, Pf, and a backward travelling wave, Pb, resulting from partial reflection of PI at the peripheral beds. The magnitude of Pb depends on the degree of vasoconstriction. Total occlusion of the vessel distal to the pressure measurement site results in a wave which is equal to 2Pf. Subtraction of the derived Pf wave from Pm gives Pb, provided there is no re-reflection of Pb by proximal discontinuities. To test the validity of this total occlusion method for the determination of the components of Pm, measurements were carried out in an anaesthetised dog and the results compared with the method of Westerhof et al., (1972). The measurements were made at three arterial sites: 1. in the aorta just proximal to the junction of the renal artery; 2. at the termination of the aorta; and 3. in the femoral artery. The magnitude of Pb was varied by the infusion of vasoactive drugs. There was good agreement between the two methods at site 1 but at the other two sites the agreement was less good. It is shown that this is the result of re-reflection of the backward travelling waves produced by the occlusion at the aortic termination and the renal artery junction.