Journal of Applied Physiology, Vol 42, Issue 2 196-201, Copyright © 1977 by American Physiological Society
Mechanism of change in pulmonary shunt flow with hemorrhage
P. S. Colley, F. W. Cheney and J. Butler
In the presence of regional atelectasis, hemorrhage increases the pulmonary
shunt fraction (Qs/Qt). We wanted to determine if the increase in Qs/Qt
occurs due to inhibition of hypoxic vasoconstriction or due to hydrostatic
effects associated with a collapsed lung and decrease in cardiac output. We
compared the effects of hemorrhage on flow to a hypoxic lung (Qh) produced
in two ways in anesthetized dogs. In six dogs atelectasis of one lung was
produced by bronchial occlusion and in a second group of six dogs one lung
was ventilated with 100% nitrogen. The other lung in each group was
ventilated with 100% nitrogen. The other lung in each group was ventilated
with 100% O2. Hemorrhage (20 ml/kg) had no effect on Qh/Qt in dogs with a
nitrogen-ventilated lung suggesting that hemorrhage did not inhibit hypoxic
vasoconstriction. In contrast, hemorrhage caused a marked increase in Qh/Qt
in dogs with a collapsed lung because the flow to the inflated ventilated
lung fell, while flow to the collapsed lung did not change. The increase in
Qs/Qt in the dogs with atelectasis can be explained solely on the basis of
mechanical effects produced by the differences in lung heights and alveolar
pressures between ventilated and atelectatic lung.
