AJP - Heart and Circulatory Physiology, Vol 246, Issue 4 579-H584, Copyright © 1984 by American Physiological Society
Changes in circulating blood volume influence aortic characteristic impedance in awake dogs
D. N. Stone, J. P. Dujardin, H. S. Klopfenstein, H. L. Brooks and H. P. Pieper
Experiments on five chronically instrumented dogs were performed to study
the effects of changes in circulating blood volume on the aortic smooth
muscle activity in awake animals. The external diameter of the proximal
descending aorta was measured with a sonomicrometer. Aortic pressure was
measured in the same cross-sectional area with a catheter-tip transducer.
Acute hemorrhage of 15% of the estimated blood volume was performed 17
times by quickly withdrawing blood through a jugular cannula. At any given
arterial pressure within the range of overlap the aortic diameter (D) was
always decreased after hemorrhage compared with control, and the
pressure-strain elastic modulus (Ep) and the characteristic impedance (Zc)
were always increased. For example at 140 kdyn X cm-2 (104.5 mmHg) delta D
= -0.61 +/- 0.12 mm or delta D = -3.44 +/- 0.68% of control, delta Ep =
31.0 +/- 8.6%, and delta Zc = 22.6 +/- 4.5%. Each of these changes was
significant with P less than 0.01. Volume expansion of 30% was performed
eight times by infusing warm saline. At any given arterial pressure D was
always increased and Ep and Zc were always decreased. At 140 kdyn X cm-2
delta D = 0.55 +/- 0.15 mm or delta D = 3.12 +/- 0.95% of control, delta Ep
= -12.4 +/- 3.2%, and delta Zc = -12.0 +/- 2.1%. Each of these changes was
significant with P less than 0.01. Since in these awake animals the changes
in circulatory blood volume modified the arterial pressure only slightly,
the contribution of viscoelasticity and myogenicity to the observed
responses was minimal.
