Effect of acute alterations of blood volume on circulatory performance in humans

Six subjects exercised (60% VO2 max) in a 35 degree C environment on the day prior to (C1) and 1 h after withdrawal (PW) of 10% of each subject's blood volume, and 2 wk later on the day prior to (C2) and 1 h after infusion (PI) of the stored blood. Esophageal and mean skin temperatures (Tes and Tsk), forearm blood flow (FBF), cardiac output (Q), heart rate (HR), and blood samples were taken at intervals. Blood withdrawal had no major effect on either Q or stroke volume (SV), as plasma volume was largely restored prior to exercise. Following blood infusion Q and SV during exercise were significantly increased 1.4 1.min-1 and 15 ml.beat-1 above C2 levels and HR was significantly reduced at any Tes. Blood withdrawal decreased the slope of the FBF:Tes relationship. The resulting decrease in cutaneous perfusion caused a significantly greater body heat storage during PW. In contrast during PI, the slope of the FBF:Tes relation was somewhat increased. We conclude that cardiac stroke volume and cutaneous blood flow vary in proportion to changes in absolute blood volume. The rise in body temperature during exercise was significantly greater in hypovolemia but was not significantly reduced following volume expansion.