Reactivity of the cerebrovascular bed to carbon dioxide in patients with primary high haematocrit before and after venesection

Abstract

Paired cerebral blood flow measurements at 2 levels of arterial CO2 tension (PaCO2) were made in 10 subjects with an elevated hematocrit and blood viscosity. A value of 32 was obtained for the percent change in flow per kPa [kilopascal] change in PaCO2 (CO2 reactivity). The hematocrit was then lowered by venesection from 0.536 to 0.458 and the measurements were repeated. The post-venesection CO2 reactivity was 29, which was not significantly different from the pre-venesection value. CO2 reactivity is not comprised in patients with low cerebral blood flow secondary to an elevated hematocrit.