Effect of chronic hypoxia on hemodynamics, organ blood flow and O2 supply in rats.

Aortic blood flow, heart rate, blood pressure and blood flow distribution were measured in 10 chronically hypoxic rats (3 weeks, PB 370-380 Torr) breathing 10% O2 (chronic hypoxia) and after 30 min of breathing air (acute normoxia). Controls were 10 normoxic littermates breathing air (normoxia) and 10% O2 for 30 min (acute hypoxia). Acute hypoxia resulted in increased aortic blood flow and heart rate, and decreased total peripheral resistance. Blood flow and oxygen supply to vital organs increased, indicating that blood flow redistribution plays an important role in oxygen supply. In chronic hypoxia, aortic blood flow and heart rate remained elevated, and total peripheral resistance remained decreased. Blood flow distribution returned towards normoxia levels. Oxygen supply was maintained via increased arterial oxygen concentration. Acute normoxia resulted in decreased aortic blood flow and heart rate, and increased blood pressure and total peripheral resistance. Blood flow distribution was similar to that of chronic hypoxia except skeletal muscles, in which blood flow decreased markedly. Oxygen supply remained unchanged or increased.