Cerebral blood flow in polycythaemia vera.

Haematological variables, cerebral blood flow (CBF) and cardiac index were investigated in 14 patients with polycythaemia vera undergoing venesections. The most important determinant of the CBF was the age of the patients (r = 0.52, p less than 0.05). CBF improved after venesection in the patients in whom the blood volume removed by venesections was over 1000 ml (from 28 to 34 ml/100 g/min; p less than 0.005) and in elderly patients with very low initial CBF (less than or equal to 25 ml/100 g/min) at the haematocrit levels higher than 0.45 (p less than 0.02). Venesections did not change cardiac index. It is suggested that the importance of the haematocrit level as a regulator of CBF increases with age.