Changes in circulating blood volume influence aortic characteristic impedance in awake dogs
Stone, D.N.; Dujardin, J.P.; Klopfenstein, H.S.; Brooks, H.L.; Pieper, H.P.
American Journal of Physiology 246(4 Pt 2): H579-H584
1984
ISSN/ISBN: 0002-9513 PMID: 6720913 Document Number: 221562
Experiments on 5 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 .cntdot. cm-2 (104.5 mm Hg) .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 < 0.01. Volume expansion of 30% was performed 8 times by infusing warm saline. At any given arterial pressure D was always increased and Ep and Zc were always decreased. At 140 kdyn .cntdot. 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 < 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.