Regional Hemodynamic Responses to Hypoxia in Polycythemic Dogs.

摘要

Polycythemia increases blood viscosity so that systemic O2 delivery (QO2) decreases and its regional distribution changes. We examined whether hypoxia, by promoting local vasodilation further modified these effects in resting skeletal muscle and gut in anesthetized dogs after hematocrit had been raised to 65%. One group (CON, n=7) served as normoxic controls while another (HH, n=6) was ventilated with 9% N2 for 30 min between periods of normoxia. Polycythemia decreased cardiac output so that QO2 to both regions decreased 50% in both groups. In compensation, O2 extraction fraction increased to 65% in muscle but not in gut. Unlike previously published normocythemic studies, there was no initial hypoxic vasoconstriction in muscle. Metabolic vasodilation during hypoxia was enhanced in muscle when blood in resting muscle. Metabolic vasodilation during hypoxia was enhanced in muscle when blood O2 reserves were first lowered by increased extraction with polycythemia alone. The increase in resting muscle blood flow during hypoxia with no change in cardiac output may have decreased O2 availability to other more vital tissues. In that sense and under these experimental conditions, polycythemia caused a maladaptive response during hypoxic hypoxia. Keywords: Regional blood flow, Regional oxygen delivery, Gut, Skeletal muscle, Reprints, Oxygen deficiency, Erythrocytes, Normoxia, Vasodilation, Anatomy, Medical research. (jg)