Directional disparity of pulse reflection in the dog.

Local reflection coefficients were experimentally determined in the dog for the first time at the aortoiliac junction using characteristic impedances derived from phase velocity, fluid density, and the vessels' cross-sectional areas. Reflection coefficients were determined for both the normal trifurcation and with the segment of aorta between external and internal iliacs occluded. For the normal case the coefficients were as follows: antegrade, 0.7; retrograde, -0.74. For the occlusion case the coefficients were as follows: antegrade, 0.33; retrograde, -0.67. These results provide experimental support for the concept that the vascular system, at least in this region, favors antegrade and suppresses retrograde pulse transmission. In addition, global reflection coefficients were determined in the femoral artery using a three-point pressure technique. Coefficient magnitudes varied from low (1.6 Hz) to high (9.6 Hz) frequencies, i.e., control, 0.42-0.22; vasoconstriction, 0.65-0.33; vasodilation, less than 0.1 for all frequencies. Discrepancies between results appearing in the literature are evaluated and shown to be associated with the method utilized as well as with system nonlinearities enhanced by tying branches.