Effect of long-term anemia and retransfusion on central circulation during exercise

The purpose of this study was to evaluate the effect of long-term anemia and subsequent retransfusion of erythrocytes on various circulatory parameters. Anemia was induced in nine healthy male subjects by repeated venesections. The stored blood was retransfused after 9 wk (range 8-11 wk). Exercise tests were performed before venesection in the control state (C), in the anemic state (A), and 48 h after retransfusion (R). Hemoglobin concentration levels were 146 +/- 10 g/l in C, 110 +/- 7 g/l in A, and 145 +/- 9 g/l in R. Maximal O2 uptake was 4.55 +/- 0.6, 3.74 +/- 0.7, and 4.45 +/- 0.6 l/min in C, A, and R, respectively. A decrease in heart rate of 7 beats/min (P less than 0.01) and in cardiac output of 2 l/min (P less than 0.05) at maximal exercise occurred in the anemic state compared with control values. These decreases were not reversed but, rather, were further accentuated after retransfusion. The adaptive response to submaximal exercise (cycling at 150-175 W) in anemia was mediated to the amount of 50% by an increase in cardiac output (mainly an increase in heart rate) and 50% was due to increased O2 extraction in the peripheral tissue. In conclusion, long-term anemia was found to decrease the heart rate and cardiac output at maximal exercise. Furthermore the close correlation between hemoglobin concentration and maximal O2 uptake in humans is confirmed.