FLOW-INDUCED VASODILATION IN THE FERRET LUNG

To examine the possibility that shear stress may be a pulmonary vasodi lator stimulus, we studied the effect of changing blood flow on the di ameters of small pulmonary arteries in isolated perfused ferret lung l obes. The arteries studied were in the similar to 0.3- to 1.3-mm-diame ter range, and the diameters were measured by using microfocal X-ray i maging. The diameters were measured at two flow rates, 10 and 40 ml/mi n, with the intravascular pressure in the measured vessels the same at the two flow rates as the result of venous pressure adjustment. The r esponse to a change in flow was studied under both normoxic and hypoxi c conditions. Hypoxia was used to elevate pulmonary arterial tone to i ncrease the likelihood of detecting a vasodilator response. Under norm oxic conditions, changing flow had little effect on the arterial diame ters, but under hypoxic conditions the arteries were consistently larg er at the higher flow than at the lower flow, even though the distendi ng pressure was the same at the two flow rates. The results are consis tent with the hypothesis that shear stress is a pulmonary vasodilator stimulus.