Roger Hohimer

Physiologic Responses to Chronic Anemia in Fetal Sheep

Publisher Summary This chapter analyzes physiologic responses to chronic anemia in fetal sheep. Fetal sheep made chronically anemic in utero adapt by 30% increase in heart weight, 50% increase in stroke volume and cardiac output, and a fivefold increase in resting coronary blood flow. Angiogenesis occurs as myocardial hypoxia-inducible factor-1, and vascular endothelial growth factor levels also increase. These changes are necessary in order to maintain myocardial and systemic oxygen consumption and function when oxygen content is reduced. Importantly, in fetal sheep that are made anemic, maximal coronary conductance in response to adenosine nearly doubles, increasing from 18.2 to 32.8 ml/min/100 g/mm Hg. Even after adjustment for changes in viscosity and hematocrit, coronary blood flow is 40% greater at normal perfusion pressures. Sheep that are made anemic in late gestation but are transfused prior to birth, thus restoring normocythemia, maintain this relative increase in maximal coronary conductance as adults. Significance of maximal coronary conductance, concepts related to fetal anemia, and the relationship between hematocrit and coronary blood floware discussed . The adult protocol and details about determination of capillary density are alsodescribed.