Benefit from long-term O2 therapy in chronic obstructive pulmonary disease patients.

The Nocturnal Oxygen Therapy Trial (NOTT) and Medical Research Council (MRC) trial have clearly indicated that long-term oxygen therapy (LTO) improved survival in patients with hypoxemic chronic obstructive pulmonary disease (COPD), but the mechanisms accounting for this improved survival could not be established. In particular, there was no link between survival and changes in pulmonary hemodynamics. More recent studies have shown even better results of survival in patients under LTO after at least 5 years. LTO improves the quality of life in these patients by improving their neuropsychological condition, by increasing their walking distance, and by reducing the time spent in hospital. Whether LTO improves pulmonary hemodynamics and right ventricular function is still debated. No significant changes in mean pulmonary artery pressure (PAP) were observed in the MRC study in patients receiving O2 during greater than 15 h/day, whereas a modest but significant fall in PAP was noticed after 6 months in the NOTT patients receiving O2 during greater than 18 h/day. In our own study, confirmed by more recent data from our laboratory, a reversal in the progression of pulmonary hypertension was observed in patients receiving O2 during greater than 16 h/day, but it is not possible to say whether a rather small decrease in PAP and pulmonary vascular resistance will have favorable effects on life expectancy. Presently, we do not know whether LTO can reverse, at least partially, the structural changes in the pulmonary vessels possibly induced by chronic alveolar hypoxia, and we need to perform further studies in this field.