ACTA M~D1CA PORTUGUESA 1983; Sup. 4:47-53 ORIGINAL CLINICAL SIGNIFICANCE OF HAEMORHEOLOGY

Ischaemia of various organs or tissues is the com monest pathological process in severe and fatal disea ses. It has always been widely assumed that ischaemia is the result of either cardiac failure or narrowing of the arteries. Haemorheology is concerned with the third possibility, that ischaemia may also be due to an abnormality of the flow properties of the blood. Whilst we all accept in everyday life that an increase in the viscosity of a fluid will decrease its flow rate, it is only in the last decade that doctors have begun to accept the analogous possibility in relation to blood. This is despite the fact that as medical students we ha ve all been taught Poiseuille’s famous formula rela ting blood flow to the driving pressure, the fourth po wer of the vessel radius and its viscosity (Figure 1)