Acetylcholine but not sodium nitroprusside exerts vasodilation in pulmonary hypertension secondary to chronic congestive heart failure

Abstract

Background Reduced endothelium-dependent vasodilation contributes to the development of pulmonary hypertension in chronic congestive heart failure (CHF). We investigated pulmonary endothelium-dependent and independent vasodilation in patients with CHF. Methods We studied 42 patients with CHF (age 55 ± 10, NYHA Classes II–III, left ventricular ejection fraction 27 ± 10%, mean PAP 29 ± 12 mmHg). The endothelial vasodilator capacity of pulmonary resistance vessels was assessed by the infusion of acetylcholine into a pulmonary artery branch while measuring the blood flow velocity with a Doppler flow wire. For comparison endothelium-independent vasodilation was measured with the response to sodium nitroprusside. The conductance vessel diameter (4.4 ± 0.2 mm) was determined by intravascular ultrasound. Acetylcholine was administered at concentrations of 10 −6 to 10 −4 mol/l, sodium nitroprusside was administered at concentrations of 0.125 and 0.25 μg/kg per min. The effects on conductance vessel diameter were investigated in 12 patients by the measurement of diameter and flow velocity following the administration of acetylcholine and sodium nitroprusside. Results Acetylcholine markedly increased blood flow velocity (+39 ± 7% at 10 −4 mol/l; p < .05). This correlated with the baseline PAP ( r = 0.58; p < .05) and pulmonary vascular resistance ( r = 0.58; p < .05). Sodium nitroprusside caused a small increase in the flow velocity (5 ± 2% at 0.125, 12 ± 4% at 0.25 μg/kg per minute; p < .05) that was accompanied by systemic vasodilation. The conductance vessel diameter was unchanged after acetylcholine was administered and was only marginally decreased after the administration of sodium nitroprusside. Conclusions In CHF acetylcholine reveals preserved receptor-mediated endothelial vasodilation, that is positively correlated to pulmonary hypertension, and cannot be reproduced by sodium nitroprusside.