Haemodynamic effects of haematocrit reduction in patients with polycythaemia secondary to cyanotic congenital heart disease.

Acute reduction in haematocrit (without significant alteration of blood volume) in six patients with severe polycythaemia secondary to cyanotic congenital heart disease resulted in an increase in resting cardiac output without alteration in heart rate. Cardiac output was also increased during a constant-load exercise test after haematocrit reduction, and under these conditions total oxygen uptake was increased with consequent reduction in oxygen debt. These measurements confirm that the subjective improvement in such patients after haematocrit reduction is matched by physiological circulatory changes.