Analysis of critical closing pressure in the perfused rabbit ear

Abstract

Rabbits were pretreated with phenoxybenzamine before removing the ears for perfusion. Under these conditions, where vascular smooth muscle tone is low but not 0, the effect of very low perfusion pressures was studied. With constant-pressure perfusion, perfusion continues at the lowest pressures until effective driving pressure is virtually 0. These observations were made with crystal-loidal and colloidal perfusates. The concept of a critical closing pressure at low vasomotor tone was not supported. This was corroborated by the results of constant-volume perfusions. The pressure tracings resulting from the lowest perfusion volumes were level and did not show evidence of even transient critical closure. The effect of plasma vasotonins on the isolated rabbit ear vessels was demonstrated.