Peripheral vascular responses during acute anemia

Abstract

Peripheral vascular responses during acute anemia were studied in 19 anesthetized dogs. In one study (n = 9) hindlimb weight and venous pressures were measured prior to and during acute anemia produced by isovolemic dextran-for-blood exchange. In another series of five control and five anemic dogs (hematocrit = 14 ± 1% (mean ± SE)), flow to the limb was occluded and arterial and venous pressure changes in the occluded limb were measured as an index of neurally mediated alterations in limb vasomotor tone. Following reduction of the hematocrit to 14 ± 0.3%, hindlimb weight decreased by an average of 10.0 g (P < 0.01) at 15 min and 12.8 g (P < 0.01) at 30 min of anemia. The decrease in limb weight was associated with a rise (P < 0.01) in limb venous pressure. There was also a relatively greater degree of vasomotor tone in the occluded hindlimb of anemic dogs as compared with control animals. Although both arterial and venous pressures decreased in an occluded hindlimb following the production of anemia, the decreases in vascular pressures were significantly less than those observed in control experiments. It was not possible to distinguish between tone changes in arteries and veins because of the presence of arteriovenous anastomoses. The data show that a peripheral-to-central blood volume translocation occurred in acute anemia which would increase venous return. Further, the results strongly suggest that the volume translocation was a result of an increase in venomotor tone.