Viscosity, cerebral blood flow and haematocrit in patients with paraproteinaemia

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Abstract
Blood viscosity may be involved in the control of cerebral blood flow (CBF) (Thomas et al., Humphrey et al.). CBF, using i.v. 133Xe blood viscosity and hematocrit were measured in 21 patients with elevated viscosity due to paraproteinemia. It was the same as in normal subjects. The paraproteinemic patients were anemic with a mean hematocrit of 0.342. This degree of anemia is normally associated with a high CBF. The paraproteinemia patients were compared with a group of 10 anemic patients with matched hematocrits but without paraprotein bands. The whole blood and plasma viscosities were significantly higher in the paraproteinemic patients and the CBF was significantly lower. The hematocrit, and therefore O2 carriage, was similar in the 2 groups. In the anemia of paraproteinemia the expected increase in CBF apparently did not occur because of the limiting factor of increased viscosity. In this instance viscosity rather than O2 carriage apparently is a major determinant in the control of CBF. This is emphasized by the better correlation between CBF and blood viscosity than between CBF and hematocrit. Viscosity and O2 carriage apparently are independent variables in the control of CBF.