EFFECT OF INCREASED WHOLE-BLOOD VISCOSITY ON REGIONAL BLOOD FLOWS IN CHRONICALLY HYPOXEMIC LAMBS

In chronic hypoxemia blood flow and oxygen supply to vital organs are maintained, but to nonvital organs they are decreased. We measured org an blood flows (microspheres) and whole blood viscosity in 10 chronica lly hypoxemic lambs, with an atrial septal defect and pulmonary stenos is, and in 8 control lambs. Vascular hindrance (resistance/viscosity) was calculated to determine to what extent the effect of increased blo od viscosity on organ blood flow was compensated for by a decrease in vascular tone. Arterial oxygen saturation was decreased (68 +/- 10 vs. 91 +/- 3%, P < 0.001), and both hemoglobin concentration (145 +/- 10 vs. 109 +/- 9 g/l, P < 0.05) and blood viscosity (4.4 +/- 0.6 vs. 3.6 +/- 0.6 mPa.s, P < 0.05) were increased in hypoxemic lambs. Systemic b lood flow, oxygen supply, oxygen uptake, and blood pressures were not significantly different between hypoxemic and control lambs. Myocardia l and cerebral blood flow was maintained in hyperemic lambs, whereas r enal, gastrointestinal, splenic, and thyroidal blood flows were at lea st 30% lower. Vascular hindrance was significantly decreased in the my ocardium and tended to be lower in the brain of hypoxemic lambs, but i n all other organs it was similar to that in control lambs. It is conc luded that blood flow is redistributed in chronic hypoxemia in lambs; myocardial and cerebral blood flow id maintained, whereas blood flow t o splanchnic organs, the kidneys, and the thyroids is decreased. The d ecreased blood flow to organs is a consequence of the increased whole blood viscosity.