Hypertrophy and coronary and collateral vascularity in dogs with severe chronic anemia.

The purpose of this study was to determine 1) whether a severe hypoxic stimulus could produce an increase in coronary and collateral vascularization and 2) whether minimal coronary resistance, which increases with hypertension-induced hypertrophy, decreases when hypoxia is superimposed on volume load hypertrophy. Data were obtained on 11 dogs rendered anemic to a hematocrit of 11 +/- 0.2 vol% and maintained at this level for 4 wk. Eighteen dogs with a hematocrit of 42 +/- 0.02 vol% were used as controls. After chronic anemia the coronary and collateral flows were quantitated in a beating, vasodilated, isolated heart preparation perfused solely with blood from two normal donor dogs. The following variables were significantly increased in anemia-exposed hearts compared with controls: coronary flow per gram myocardium for the left anterior descending, the circumflex, the right, and the septal arteries; ratio of total coronary flow of each vessel to body weight; and the collateral flows to each coronary vessel. Both the right and left ventricles were hypertrophied. We conclude that severe chronic anemia produces a dissociation between hypertrophy and increased minimal coronary resistance. Severe chronic anemia appears to increase vascularization of both coronary and collateral circulation probably due to tissue hypoxia. In this model coronary collateral vascularity seems to increase in the absence of a pressure difference across collaterals.