Effects of arterial ligation and embolization on pulmonary vascular pressure distribution

The effects of embolization on the longitudinal distribution of pulmonary vascular pressures with respect to vascular compliance were determined by the vascular inflow and outflow occlusion technique in isolated blood-perfused pig lungs treated with papaverine to prevent vasomotor responses. Embolization with microspheres having mean diameters of 75, 200, and 550 μm and with barrier beads (2 x 3 x 3.5 mm) significantly increased the pressure gradient across the relatively compliant middle region (ΔPm) without increasing the gradients across the relatively noncompliant regions on the arterial (ΔPa) or venous (ΔPv) ends of the vasculature. In contrast, ligation of several lobar arteries caused ΔPa to increase from 0.9 ± 0.3 to 5.9 ±1.1 mmHg but did not change ΔPm or ΔPv. Assuming that ΔPa and ΔPv measured by vascular occlusion result from cessation of flow through resistances, these data suggest that in isolated pig lungs the vessels at the boundary between the arterial and middle regions defined by the occlusion technique are arteties >2-3 mm diam and smaller than lobar arteries.