AJP - Heart and Circulatory Physiology, Vol 241, Issue 6 789-H794, Copyright © 1981 by American Physiological Society
Reflex control of canine hindlimb resistance under different modes of perfusion
R. H. Cox and R. J. Bagshaw
The carotid sinus control of hindlimb hemodynamics was determined in
halothane-anesthetized vagotomized dogs. The carotid sinuses were
bilaterally isolated and perfused under controlled conditions. The hindlimb
was perfused under conditions of 1) physiological inflow, 2) constant
pressure, and 3) constant flow. The variation of hindlimb resistance with
mean carotid sinus perfusion pressure was largest under conditions of
constant-pressure perfusion and smallest with physiological inflow. Values
for constant-flow perfusion were intermediate. The effects of different
values of constant-flow perfusion on the carotid sinus control of hindlimb
hemodynamics was also determined. Values of hindlimb resistance increased
with decreasing flow rate as did the variation with carotid sinus perfusion
pressure. No evidence of a contribution of local control mechanisms related
to changes in perfusion pressure or bed inflow could be demonstrated. The
differences in the variation of hindlimb resistance with carotid sinus
pressure under the various perfusion conditions can be explained on the
basis of the mechanics of vascular smooth muscle. The amount of lumen
constriction associated with changes in degree of activation depends on the
conditions under which shortening occurs as well as upon the initial muscle
length. It appears that local factors do not contribute to the control of
hindlimb hemodynamics under the conditions in which these studies were
performed.
