Comparison of dextran and hematocrit effects in the pulmonary microcirculation.

We have compared the effects of an increase in perfusate viscosity induced by dextran and by hematocrit (Hct) on segmental vascular resistance in the pulmonary circulation and the effect of flow on microvascular resistance in lungs perfused with dextran and red blood cells. We isolated and perfused lungs of 39 neonatal rabbits weighing 670 +/- 250 g. To determine the effect of dextran, group 1 (n = 8) lungs were perfused with both 5% and 20% dextran 70 solutions (Hct, approximately 25%); to determine the effect of Hct, group 2 (n = 5) lungs were perfused alternately with 5% and 40% Hct solutions (5% dextran 70). In group 1 and group 2 lungs, experiments were done at constant flow and pressure. Group 3 and group 4 (each n = 4) lungs were perfused with 5% and 20% dextran 70, respectively (0 Hct); group 5 (n = 5), with 10% dextran 70; group 6 (n = 7), with 5% dextran 500; and group 7 (n = 6), with 20% dextran 70 (Hct, approximately 5%). All lungs were perfused in zone 3; airway and left atrial pressures were 6 and 8 cm H2O, respectively. To partition the circulation, we measured pressures in the pulmonary artery and left atrium continuously and pressures in 20-50-microns arterioles and 20-50-microns venules by micropuncture. We found that an increase in both the concentration and molecular weight of dextran increased perfusate viscosity and the resistance in all three longitudinal vascular segments: arteries, microvessels, and veins.(ABSTRACT TRUNCATED AT 250 WORDS)