Effects of Vasodilators on Gas Exchange in Acute Canine Embolic Pulmonary Hypertension

Open Access
Publisher Website
Google Scholar
Abstract
Pulmonary vascular tone was investigated by construction of pulmonary arterial pressure (PAP)/cardiac output .ovrhdot.Q plots, and gas exchange, by the multiple inert elimination technique, in 24 anesthetized dogs before and after pulmonary embolization of autologous clots. Three PAP/.ovrhdot.Q plots were obtained by a manipulation of venous return at baseline and 60 min and 110 min after embolization. Before the third PAP/.ovrhdot.Q plot, the dogs randomly allocated to one of the following iv treatments: 1) placebo (n = 6); 2) prostaglandin E1 (PGE1) 0.4 .mu.g.cntdot.kg-1.cntdot.min-1 (n = 6); 3) hydralazine 2 mg/kg (n = 6); and 4) nitroprusside 10 .mu.g.kg-1.cntdot.min-1 (n = 6). These vasodilators decreased systemic arterial pressure by a mean of 44%. Ventilation-perfusion (.ovrhdot.VA/.ovrhdot.Q) distributions were determined at the same .ovrhdot.Q (2.4 .+-. 0.1 l.cntdot.min1-.cntdot.m-2 .+-. SE) of each PAP/.ovrhdot.Q plot. Embolization increased the intercept and the slope of the PAP/.ovrhdot.Q plots (P < 0.002). Distributions of .ovrhdot.VA/.ovrhdot.Q were only moderately impaired, with an increased dispersion of both .ovrhdot.VA and .ovrhdot.Q and a shift of .ovrhdot.VA distributions to higher .ovrhdot.VA/.ovrhdot.Q. PaO2 changed from 208 .+-. 5 to 172 .+-. 8 mmHg (P < 0.01) (fraction of inspired O2 was 0.4). None of the treatments had any effect on .ovrhdot.VA/.ovrhdot.Q distributions. Placebo and PGE1 had no effect on PAP/.ovrhdot.Q plots. Hydralazine and nitroprusside reduced the slope of the PAP/.ovrhdot.Q Q plots. Thus, in this canine model of acute pulmonary embolism: 1) .ovrhdot.VA/.ovrhdot.Q distributions were moderately impaired accounting for only slight hypoxemia, and 2) pulmonary hypertension was partially reversible by hydralazine and by nitroprusside without associated non-flow-dependent change in .ovrhdot.VA/.ovrhdot.Q distributions and arterial oxygenation.