Vasomotion Influences Airflow in Peripheral Airways

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 smooth muscle effects were administered locally through the bronchoscope. Nitroglycerin (NTG) produced a dose-dependent increase in mean Rp (+288% at 1,000 µg), 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 µg); 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 µg) was sustained for at least 20 min and transiently reversed by vasopressin (0.2 units, p < 0...