Blood oxygen and carbon dioxide transport in man
The effect of long term domiciliary oxygen therapy on the position and shape of the oxygen dissociation curve, together with other haematologic variables such as 2,3- diphosphoglycerate (2,3-DPG), haemoglobin concentration, packed cell volume, mean corpuscular haemoglobin concentration, and arterial blood gas and pH values, has been studied in patients with chronic bronchitis. Twenty-six patients were randomly allocated to receive either no oxygen therapy or 15 hours per day oxygen therapy. The two groups were initially well matched for age and disablement. Haemoglobin concentration and packed cell volume (P.C.V.) were the only variables to differ significantly between the two groups of patients after start of oxygen treatment, but those patients receiving oxygen therapy showed significant decreases in 2,3-DPG, together with haemoglobin concentration and P.C.V. from the pre-treatment values. The effect of elevated COHb levels, (similar to those encountered in patients who smoke) on exercise tolerance was studied in patients with chronic bronchitis, whose exercise capacity was already limited due to hypoxaemia. Exercise tolerance, assessed by the distance walked in 12 minutes, was lower after elevation of COHb levels, and a significant correlation was established between calculated femoral venous oxygen tensions (assuming A(A-V)02 values of 7 and 10 ml/100 ml blood) and the 12-minute walking distance. (r=0.34, P > 0.01 and r=0.33, P < 0.01).