Journal of Applied Physiology, Vol 57, Issue 5 1498-1501, Copyright © 1984 by American Physiological Society
Direct effects of nitroprusside do not alter gas exchange in canine oleic acid edema
M. Angle, J. Ducas, U. Schick, L. Girling and R. M. Prewitt
The authors investigated why intrapulmonary shunt (QS/QT) increases with
sodium nitroprusside (SNP) in canine oleic acid pulmonary edema. To
determine the effects of flow alone on QS/QT, a peripheral arteriovenous
fistula with a variable resistor was employed to increase cardiac output
(Q) 26 and 52% above base line in a stepwise fashion (P less than 0.01). To
examine the direct effects of SNP, distinct from changes in flow, the drug
was given to produce matched increments in Q in each dog (P less than
0.01). To control for time, base-line measurements were obtained before and
after each intervention, the sequence of which was alternated. At each
increment in Q, SNP and the arteriovenous fistula increased QS/QT a similar
amount. The mixed venous O2 tension (P-vO2) followed Q similarly in each
group. Pulmonary vascular resistance (PVR) fell more (P less than 0.01)
with SNP than with the arteriovenous fistula at identical Q and P-vO2. The
authors conclude that, in this model, a direct pharmacological effect of
SNP does not contribute to the deterioration in QS/QT. In fact, SNP exerts
a pulmonary vasoactive effect that does not adversely affect gas exchange.
