Pressure flow relationships in the isolated altitude acclimatized hindlimb

Prolonged exposure to altitude results in an increased blood volume, vascular capacity, and capillary count. This study investigated the effects of these cardiovascular changes on the pressure flow relationships in the isolated hindlimb. Eleven dogs were exposed to a simulated altitude of 20,000 feet for a period of 16 wk. Hematocrit, hemoglobin, and blood volume all increased significantly during this period. After acclimatization, pressure flow curves were run on the isolated, maximally vasodilated hindlimb. Three sets of curves were run on each hindlimb at hematocrit ratios of 20, 40, and 60%. No difference of statistical significance between normal and acclimatized hindlimbs was observed in the pressure flow relationship at any of the tested hematocrit ratios. These results show that changes in capillary density do not influence significantly the vascular flow patterns in altitude acclimatization. They indicate that normal vasodilation of the existing vessels is responsible for the maintenance of normal pressure and flows irrespective of the increased in vitro blood viscosity.