Pulmonary Diffusing Capacity and Its Subdivisions in Polycythemia Vera

1Polycythemia vera is characterized by a greatly increased red cell mass, and patients with the disease have an increase of both hemoglobin concentration and total blood volume. The purpose of the present study was to observe the effect of these two variables, and their changes with treatment, on pulmonary diffusion. The rate of chemical reaction with hemoglobin is an important factor in the over-all rate of gas uptake from the lung. Roughton and Forster (1) proposed the equation 1/DL = 1/DE + 1/1Vc (Equation 1) and showed that by its use it was possible to subdivide the total diffusing capacity of the lung. DL is the total pulmonary diffusing capacity for CO from the alveolus to the interior of the red cell. Dm is the membrane diffusing capacity and relates to the movement of gas from the alveolus to the surface of the red cell. 9, often referred to as the rate of uptake of CO by the red cells, is actually the product of the rate at which CO replaces 02 in oxyhemoglobin and the concentration of hemoglobin (2). Vc is the pulmonary capillary blood volume at any instant. McNeill, Rankin, and Forster (3) have related these parameters in terms of resistances. 1/DL may be considered as the total resistance to gas uptake, which is composed of the sum of 1/DM, the mem