Treatment of pulmonary hypertension in chronic bronchitis and emphysema.

SIR,-We read with interest the leading article by Dr John Rees on the treatment of pulmonary hypertension in patients with chronic bronchitis and emphysema (24 November, p 1398). An appreciable, but unknown, number of patients with hypoxia also develop polycythaemia, and in these cases reducing packed cell volume may help to ameliorate pulmonary hypertension. Blood viscosity rises -exponentially with increasing packed cell volume,' and experimental evidence shows that this produces a significant increase in pulmonary artery pressure and pulmonary vascular resistance,' particularly at packed cell volumes above 0-55. Furthermore, the increased viscosity of polycythaemic blood contributes significantly to the raised pulmonary vascular resistance that occurs in the presence of chronic hypoxia.3 Reducing packed cell volume in patients with polycythaemia secondary to hypoxic cor pulmonale by repeated venesections,4 dextran 40 exchange transfusion,5 or, more recently, erythrapheresis,6 produces significant reductions in pulmonary artery pressure and pulmonary vascular resistance. Erythrapheresis also produces both symptomatic benefit and improvement in work performance.7 Consequently reducing packed cell volume to about 0 50 should be considered as an additional therapeutic option in patients with polycythaemia and pulmonary hypertension secondaryto chronicbronchitis andemphysema.