Long-term oxygen therapy stops the natural decline of endurance in COPD patients with reversible hypercapnia

Background: Respiratory muscle weakness is one of the most important causes of hypercapnia in patients with COPD. There is evidence that stable hypercapnic patients will benefit from long-term oxygen therapy (LTOT).

Objectives: The prognostic role of reversible hypercapnia in COPD is still unclear. Early implementation of LTOT in these patients may influence endurance time and mortality.

Methods: In this pilot study, we investigated 28 patients (26 males, 49-74 years) with COPD, advanced airflow limitation [forced expiratory volume in 1 s (percentage of predicted value) 40.8 +/- 10.2] and mild hypoxaemia (pO(2) 66.5 +/- 6.3 mm Hg). All patients had developed a moderate reversible hypercapnia during an acute exacerbation or during exercise testing (peak pCO(2) 48.0 +/- 2.5 mm Hg). Patients were allocated randomly to a control group (n = 14) or an LTOT group (n = 14). The two groups were well matched in terms of physiological data. Lung function, endurance time (cycle ergometer), dyspnoea score, blood gases and LTOT compliance were measured at baseline and every 6 months over a period of 3 years.

Results: Endurance time increased from 6.4 +/- 2.7 min at baseline to 7.1 +/- 2.7 min after 1 year in the LTOT group and decreased from 6.1 +/- 3.0 to 4.9 +/- 3.8 min in the controls (p < 0.05). After 1 year, the end-exercise dyspnoea score was significantly lower in the LTOT group (4.5 +/- 1.5) than in the controls (5.7 +/- 1.9).

Conclusion: COPD patients with reversible hypercapnia and mild hypoxaemia benefit from LTOT in terms of endurance time and a reduction of exertional dyspnoea after 1 year.