AJP - Heart and Circulatory Physiology, Vol 246, Issue 1 1-H7, Copyright © 1984 by American Physiological Society
Changes in smooth muscle tone influence characteristic impedance of the aorta
D. N. Stone and J. P. Dujardin
Experiments were performed on anesthetized dogs to quantitate the effects
of changes in aortic smooth muscle tone on the passive pressure dependence
of the aortic characteristic impedance (Zc). Zc was calculated from the
diastolic pressure-diameter relationship in a wide pressure range induced
by forced slow oscillations in pressure. Changes in aortic smooth muscle
activity were induced by hemorrhage (-15% of the estimated blood volume),
by volume expansion (+15 and +30%), and by alpha-adrenergic blockade.
Curves relating Zc to pressure showed a minimum in the physiological
pressure range and were well described by parabolas under all conditions.
Under control conditions, the minimum Zc pressure was located close to the
mean arterial pressure. Both levels of volume expansion as well as
alpha-blockade reduced Zc at all pressure levels. Hemorrhage increased Zc
at each pressure level and caused the minimum in the Zc vs. pressure curves
to shift to higher values. The observed changes in Zc may play an important
role in the hemodynamic adjustments to hemorrhage and to volume expansion.
