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Vasodilator Therapy in Microembolic Porcine Pulmonary Hypertension

Received from the Division of Critical Care Medicine, Department of Anesthesia, Stanford University Medical Center, Stanford, California.

Abstract

The hemodynamic effects of prostaglandin E₁, sodium nitroprusside (SNP), nitroglycerin, and hydralazine were studied in a porcine model of elevated pulmonary vascular resistance (PVR) due to glass bead microembolization (60–150-µm diameter).

Each animal received all four drugs. Each drug was titrated to produce a 30% reduction in mean systemic arterial pressure. Although all four drugs decreased PVR, distinct differences in the hemodynamic profiles of the four drugs were evident. Prostaglandin E₁ produced the largest reduction in mean pulmonary artery pressure (from 41 ± 1 to 32 ± 9 mm Hg, mean ± sem) and PVR (25 ± 3 to 18 ± 2 mm Hg·L^–1·min^–1), and did not affect the ratio of PVR to systemic vascular resistance (PVR/SVR). Sodium nitroprusside and nitroglycerin produced moderate decreases in PVR (nitroglycerin 21 ± 2 to 18 ± 2 mm Hg·L^–1·min^–1, SNP 22 ± 2 to 19 ± 2 mm Hg·L^–1 min^–1) and in mean pulmonary artey pressure (nitroglycerin 39 ± 1 to 35 ± 1; SNP 40 ± 1 to 36 ± 2 mm Hg). Both drugs significantly increased the PVR/SVR ratio. Hydralazine was the only drug that significantly increased cardiac output (1.6 ± 0.2 to 1.9 ± 0.3 L/min). Hydralazine had no significant effect on mean pulmonary artey pressure, reduced PVR to the smallest extent (11%), and resulted in the largest increase in the PVR/SVR ratio (from 0.52 ± 0.04 to 0.80 ± 0.08).

In this model of increased pulmonary vasculature resistance prostaglandin E₁ caused an equivalent amount of pulmonay and systemic vasodilation, as expressed by the PVR/SVR ratio. Hydralazine caused the least amount of pulmonary vasodilation for a given amount of systemic vasodilation. Nitroglycerin and SNP were intermediate in their effects between prostaglandin E₁ and hydralazine.

Key Words: EMBOLISM pulmonary—vasodilator therapy. • LUNG embolism—Vasodilator therapy.

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