Some Effects of Nitroglycerin upon the Splanchnic, Pulmonary, and Systemic Circulations

Splanchnic, pulmonary, and systemic hemodynamics were studied in 18 patients after the sublingual administration of nitroglycerin. The drug, contrary to expectations, produced an over-all vasoconstrictive effect on the splanchnic circulation rather than vasodilatation. There was no evidence of venous pooling in this bed, and indeed the data may indicate a splanchnic supportive role in augmenting venous return to the heart with disengorgement of its own volume. In contrast, there was vasodilatation and pooling of blood in the pulmonary vascular bed. The systemic circulation probably sustains several effects by nitroglycerin, including arterial vasodilatation. A direct change in large artery distensibility probably explains the modest fall in systolic blood pressure seen. Further decline in arterial pressure may depend on venous pooling of a small or large degree. Probably the fall in systemic and specific organ flows is also linked to decreased venous return and the vascular readjustments provoked thereby. Pulsus alternans was produced by nitroglycerin, a previously unreported effect of the drug, but the mechanism by which it arose could not be defined.