Mechanism of change in pulmonary shunt flow with hemorrhage.
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.
D000818:Animals; D004285:Dogs; D006439:Hemodynamics; D006470:Hemorrhage / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008863:Microspheres; D010100:Oxygen / Q000097:blood; D001261:Pulmonary Atelectasis / Q000503:physiopathology*; D011652:Pulmonary Circulation; D014655:Vascular Resistance
D010100:Oxygen