Studies on haematocrit in peripheral arterial disease.

Haematocrit is often elevated in peripheral arterial disease, and is an important determinant of blood viscosity and of platelet behaviour. We have studied the relationships of haematocrit to claudication, smoking habit, calf blood flow, platelet aggregation in whole blood, and the late complications of aortic bifurcation grafts. In 31 claudicants, blood viscosity, haematocrit and fibrinogen levels were significantly higher compared to 50 controls (p less than 0.01). However this was largely explained by a higher prevalence in claudicants of cigarette-smoking, which is associated with increased blood viscosity, haematocrit and fibrinogen levels. In 8 stable claudicants with high-normal haematocrit (mean 0.50), venesection reduced haematocrit to low-normal levels (mean 0.44). Resting calf blood flow was unchanged: peak flow increased slightly (17%) but oxygen delivery (peak flow X haemoglobin concentration) was unchanged. Spontaneous platelet aggregation in whole blood was studied using a single platelet counting method: the increase in haematocrit in patients with claudication was not associated with a significant increase in aggregation, and a negative association of haematocrit and aggregation was observed. In a preliminary retrospective study of patients with late complications of aortic bifurcation grafts, significantly higher haematocrits prior to operative were found compared to controls who had not returned to the clinic. Further prospective studies are required to assess the significance of haematocrit in peripheral arterial disease, and to determine whether any adverse effects are due to associations with smoking, rheology or platelet behaviour.