DIRECT MEASUREMENT OF PULMONARY MICROVASCULAR DISTENSIBILITY

Pulmonary vascular distensibility has an important influence on pulmon ary hemodynamics. Although many measurements of distensibility have be en made on large pulmonary vessels, there is less information on micro vascular distensibility. We have measured the distensibility of the sm allest (<70-mum-diam) precapillary arterioles and postcapillary venule s. Isolated dog lobes, at 2.5 cmH2O transpulmonary pressure, were perf used at low flows, which caused the arteriovenous pressure gradient to be very small and thereby permitted accurate estimation of microvascu lar pressure. As microvascular pressure was systematically varied betw een 0 and 30 mmHg, subpleural microvascular diameters were determined from computer-enhanced images obtained by videomicroscopy. Arteriolar and venular distensibilities were not different from each other. The m icrovascular pressure-diameter relationship was alinear with distensib ility coefficients of 1-3% mmHg-1, values that are of the same order o f magnitude as previously measured distensibilities of 100- to 1,000-m um-diam canine pulmonary vessels.