Vasomotion Influences Airflow in Peripheral Airways

Abstract

The purpose of this study was to test the hypothesis that blood flow, by its effect on blood volume, influences airflow resistance in peripheral airways. In conscious ewes, forced sinusoidal flow oscillations (5 Hz) were applied through a balloon-tipped, dual-channel fiberoptic bronchoscope placed in a segmental bronchus, and peripheral airflow resistance (Rp) was determined from flow and bronchial pressure. Drugs with predominant vascular or airway muscle effects were administered locally through the bronchscope. Nitroglycerin (NTG) produced a dose-dependent increase in mean Rp (+288% at 1,000 .mu.g), which was blocked by methylene blue (p < 0.05) and not reversed by atropine. Carbachol (CARB) also increased mean Rp in a dose-dependent manner (+605% at 400 .mu.g); this effect was not blocked by methylene blue, but it was reversed by atropine (p < 0.05). The increase in mean Rp after a single dose of NTG (250 .mu.g) was sustained for at least 20 min and transiently reversed by vasopressin (0.2 units, p < 0.05) but not by isoproterenol (100 .mu.g). Conversely, the sustained increase in Rp after a single dose of CARB (50 .mu.g) was transiently reversed by isoproterenol (p < 0.05) but not by vasopressin. We conclude that NTG increased Rp by vasodilation and CARB by bronchoconstriction. This supports the hypothesis that vasodilation limits airflow in the lung periphery, presumably because of vascular congestion.