Influence of size of emboli on extravascular lung water

We examined the influence of the size of emboli on the vascular volume (QL) and extravascular volume (Qev) accessible to 3HOH during a single pass through an isolated dog lung lobe using the double indicator-dilution method with 125I-human serum albumin as the vascular indicator. As successively more beads of a given diameter (58, 548, or 3,175 microns) were introduced into a lung lobe, a linear relationship between QL and Qev was obtained as they both decreased. The slope of the graph of QL vs. Qev with progressive embolism was directly proportional to the bead diameter. This suggested an approach for estimating the total vascular volume in vessels smaller than the diameter of the beads before embolization, referred to as Qm. If it is assumed that most of the transvascular diffusional exchange of 3HOH occurs in vessels smaller than the smallest beads (mainly capillaries) and that vessel obstruction does not change the ratio of Qev to the perfused capillary volume, the slope of the plot of QL vs. Qev is an estimate of the fraction, Qm/QL, of the total vascular volume in vessels smaller than the bead diameter. In the dog lung lobes studied, Qm/QL was approximately 0.64 for 58-microns vessels, 0.75 for 548-microns vessels, and 0.82 for 3,175-microns vessels. The results suggest that, with occlusion of vessels greater than or equal to 58 microns, 3HOH does not diffuse significantly into unperfused regions.(ABSTRACT TRUNCATED AT 250 WORDS)