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It is widely held that increased blood viscosity due to polycythemia is an important factor contributing to pulmonary hypertension in patients with chronic bronchitis (1-5). An increase in the viscosity factor in -Poiseuille's equation will increase the pressure drop across a vascular bed proportionately, provided volume flow and the dimensions of the vessels remain constant. Roos (6) showed, in the isolated lung of a dog, that increasing packed cell volume is associated with an increase in the pressure drop across the pulmonary vascular bed, blood flow being maintained constant. However, the effects of alterations in blood viscosity upon pulmonary intravascular pressures in man have not been established. Baldwin, Cournand, and Richards (7) noted that the association of polycythemia with chronic bronchitis is rare. It has been shown that red cell volume is often slightly increased in patients with chronic bronchitis who have arterial desaturation (8, 9), but judging by the hematocrit or hemoglobin values in other reports of large numbers of patients (10-12), substantial polycythemia is an uncommon complication. The present investigation is concerned with a highly selected group of patients with chronic bronchitis complicated by marked secondary polycythemia. They were drawn from a large population of patients with chronic bronchitis who were seen in an area where
Segel et al. (1966) studied this question.