Effect of mild hypovolemia and fluid replacement on regional oxygenation, flow, and small vessel blood content in the rabbit heart.

A study was conducted on the effects of mild hemorrhage-induced hypovolemia and subsequent fluid replacement with lactated Ringer's or dextran solution on the hearts of 61 pentobarbital anethetized open-chest New Zealand white rabbits. After a blood loss equivalent to 1.25% of body weight, blood flow in the subepicardial and subendocardial regions of the left ventricular free wall was unaffected, relative tissue PO2 fell, and small vessel blood content, a measure of open capillary density, increased. No regional differences were seen after one hour. With fluid replacement, small vessel blood content returned toward control; coronary blood flow and myocardial relative tissue PO2 were unaltered. These results are best explained by an increased myocardial metabolism and a loss of blood oxygenation in hypovolemia and a return of metabolism toward control with fluid replacement. The lack of regional effects indicated that the subendocardium was no more adversely affected than the subepicardium during the experimentally induced mild hypovolemia.