EFFECT OF PRESSURE ON AORTIC HYDRAULIC CONDUCTANCE

This study was performed to determine whether the transmural hydraulic conductance (L(p)) of the rabbit aortic wall depends on its distension. In 19 rabbits, the aorta was cannulated in situ and perfused at a given pressure with a physiologically buffered solution containing 4% bovine serum albumin. The output cannula was then occluded to limit fluid flow to that traversing the artery wall. External diameter and transmural fluid flow were measured at three pressures (eight rabbits, group 1) or at four pressures (12 rabbits, group 2) in each vessel. Transmural fluid flow was determined by monitoring the velocity of an air bubble within a buffer-filled tube leading to the input cannula. From group 1 measurements, L(p) values (mean +/- SD) at 50, 100, and 150 mm Hg were calculated to be 3.8 +/- 2.8, 3.5 +/- 1.3, and 4.1 +/- 1.2 x 10(-8) cm/sec/mm Hg, respectively. Group 2 measurements gave values of 4.2 +/- 1.6, 3.8 +/- 1.1, 3.8 +/- 1.1, and 4.2 +/- 1.1 x 10(-8) cm/sec/mm Hg at 75, 100, 125, and 150 mm Hg, respectively. Paired Student's t tests indicated no significant change in L(p) with pressure. However, linear regression analysis demonstrated a weak correlation between L(p) values obtained at 50 and 100 mm Hg (r2 = 0.30) and at 75 and 100 mm Hg (r2 = 0.36). Values of L(p) at 100 and 150 mm Hg and at 125 and 150 mm Hg were closely correlated in each case. These results suggest that between 50 and 100 mm Hg the structural properties of the aortic wall change so as to alter L(p) but not in the same way in each vessel. L(p) may increase or decrease depending on which structural change predominates in a particular vessel.