Treatment of canine pulmonary hypertension: effects of norepinephrine and isoproterenol on pulmonary vascular pressure-flow characteristics.

Pulmonary vascular flow resistive properties may be described by mean pulmonary arterial pressure (PAP)-cardiac output (CO) plots. The slope of the PAP-CO relationship defines the incremental resistance and the extrapolated pressure intercept defines the effective outflow pressure. We investigated effects of norepinephrine (11 dogs) and isoproterenol (seven dogs) on the pulmonary vascular PAP-CO relationship in a model of pulmonary hypertension produced by injection of autologous blood clots. Multiple PAP-CO coordinates were obtained with and without drug infusion. CO was varied by opening systemic arteriovenous fistulas. PAP-CO relationships were well described by a linear equation (mean r value .964 +/- .032). Isoproterenol increased mean CO by 61% (p less than .01), and calculated pulmonary vascular resistance (PVR) decreased by 31% (p less than .05), corresponding to a 35% decrease (5.1 +/- 2.0 to 3.3 +/- 0.9 mm Hg X liter X min-1; p less than .01) incremental resistance. In the first seven dogs to receive norepinephrine, despite a 25% increase in blood pressure (p less than .01) no significant effects on CO, PAP, PVR, or PAP-CO relationship were observed. In the next four dogs, norepinephrine was infused at a lower dose to increase blood pressure 50% and a higher dose to ensure an increase in CO. In both conditions, calculated PVR fell (p less than .05) compared with that before norepinephrine. However, measured incremental resistance and effective outflow pressure did not change.(ABSTRACT TRUNCATED AT 250 WORDS)