Evolution of pulmonary haemodynamics in COLD patients under long-term oxygen therapy

The North-American Trial (NOTT) and the British MRC study clearly indicated that long-term oxygen therapy (LTO) increases the survival rate of patients with severe chronic obstructive long disease (COLD), but O2 must be given for more than 15 h/24 h. At present OT is largely prescribed in COLD patients whose (stable) PaO2 less than or equal to 55 mmHg. The pulmonary haemodynamic effects of OT are still a matter of debate. The first studies, in 1967, indicated that continuous O2 for 6-8 weeks could markedly improve pulmonary hypertension (PH). In the MRC study there was no change in pulmonary artery mean pressure (PAP) in patients receiving O2 for more than 15 h/day, whereas patients not receiving O2 exhibited a progressive increase of PH. In the NOTT study there was a modest but significant improvement of PAP after 6 months in those patients receiving "continuous OT" (in fact greater than 18 h/day), but not in patients receiving only nocturnal OT. In our own study, we found that OT could reverse the progression of PH in COLD patients. In 16 carefully studied patients, PAP increased from 23.3 +/- 6.8 to 28.0 +/- 7.4 mmHg (p less than 0.01) before the initiation of OT (mean duration of follow-up = 48 months) and then decreased to 23.9 +/- 6.6 mmHg (p less than 0.05) during OT (mean duration of follow-up = 31 months). The average yearly change in PAP was +1.5 mmHg before OT, and -2.1 mmHg under OT and the difference was highly significant (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)