Pulmonary arterial dilation by inhaled NO: arterial diameter, NO concentration relationship

The objective of this study was to determine the nitric oxide (NO) concentr ation and vessel diameter dependence of the pulmonary arterial dilation ind uced by inhaled NO. Isolated dog lung lobes were situated between a microfo cal X-ray source and X-ray detector and perfused with either blood or plasm a. Boluses of radiopaque contrast medium were injected into the lobar arter y under control conditions, when the pulmonary arteries were constricted by infusion of serotonin and when the serotonin infusion was accompanied by i nhalation of from 30 to 960 parts/million NO. Arterial diameter measurement s were obtained from X-ray images of vessels having control diameters in th e 300- to 3,400-mum range. Serotonin constricted the vessels throughout the size range studied, with an average decrease in diameter of similar to 20% . The fractional reversal of the serotonin-induced constriction by inhaled NO was directly proportional to inhaled NO concentration, inversely proport ional to vessel size, and greater with plasma than with blood perfusion in vessels as large as 3 mm in diameter. The latter indicates that intravascul ar hemoglobin affected the bronchoalveolar-to-arterial luminal NO concentra tion gradient in fairly large pulmonary arteries. The data provide informat ion regarding pulmonary arterial smooth muscle accessibility to intrapulmon ary gas that should be useful as part of the database for modeling the comm unication between intrapulmonary gas and pulmonary arterial smooth muscle c ells in future studies.