The effect of levarterenol and phentolamine on the hypertensive pulmonary vasculature.

Abstract The pulmonary vascular response to the infusion of levarterenol and phentolamine separately and in various combinations was studied in 6 calves with experimentally produced pulmonary hypertension. Infusion of levarterenol alone increased the pulmonary artery pressure from a mean of 57 to 70 mm. Hg, the left atrial pressure from a mean of 9 to 17 mm. Hg, and the systemic arterial pressure from a mean of 30 to 51 mm. Hg. There was no change in pulmonary vascular resistance or cardiac output. Infusion of phentolamine alone decreased systemic artery pressure from a mean of 101 to 89 mm. Hg. There was no change in pulmonary artery pressure, pulmonary vascular resistance, or cardiac output. When infusion of levarterenol and phentolamine was properly titrated to maintain systemic arterial pressure at the level obtained subsequent to creation of pulmonary hypertension, pulmonary vascular resistance decreased from a mean of 16 to 10 units and cardiac output increased from a mean of 3.2 to 5.0 liters per minute. When levarterenol and phentolamine were improperly titrated, the hemodynamic response corresponded to the effect of the predominant drug. This study demonstrates that levarterenol and phentolamine, properly administered, increase cardiac output and lower pulmonary vascular resistance in calves with experimentally produced pulmonary hypertension.