Blood volume studies in chronic obstructive non-specific lung disease.

Blood volume studies in chronic hypoxic lung disease have produced conflicting results. Some have demonstrated that the red cell volume-hypoxic relationship is similar to that in normal subjects, whereas others have found that it is subnormal. Plasma volume has not been shown to be related to hypoxia. To elucidate this further, 45 patients with chronic obstructive bronchitis were studied. They were on average hypoxic at rest and on exertion, but mean values of red cell volume, plasma volume, venous haematocrit, red cell count, and haemoglobin concentration were normal. Red cell volume was linearly related to the degree of hypoxia, but the response was subnormal. Arterial oxygen saturation rather than tension was the main determinant of red cell volume, and resting values correlated better than exercise values with red cell volume. The best correlations were obtained when red cell volume was expressed as a function of the lean body mass rather than the total body weight. Red cell volume was also linearly related to arterial Co tension. Plasma volume did not correlate with any of the blood gases. The subnormal polycythaemic response to hypoxia may have been caused partially by latent iron deficiency and chronic infection; but severe hypoxia, hypercapnia, and gastrointestinal bleeding were not aetiological factors. The importance of tissue hypoxia in the regulation of the erythropoietic response and the reasons why previous blood volume studies have produced conflicting results are discussed.