Abstract

Reduction of packed cell volume has been recommended as a therapeutic procedure in patients with polycythaemia secondary to hypoxic lung disease. We have investigated the effects of this policy on blood flow and oxygen carriage to the calf in 12 such patients. Packed cell volume was decreased from 0.61 to 0.51 (mean) by isovolaemic haemodilution on a cell separator, with significant reductions in blood viscosity at high and low shear rates. Resting calf blood flow was unchanged but peak flow during reactive hyperaemia increased by 17% and 21% one and seven days after the procedure. Oxygen carriage to the calf at rest was initially unchanged but had fallen by 20% at seven days. During reactive hyperaemia oxygen carriage was not impaired by the reduction in packed cell volume since the rise in blood flow offset any reduction in arterial oxygen content. This study has shown that when blood flow is stressed during reactive hyperaemia oxygen carriage is not compromised by a therapeutic reduction in packed cell volume.