Acute oxygen supplementation does not relieve the impairment of respiratory muscle strength in hypoxemic COPD.

STUDY OBJECTIVES

To verify whether hypoxemia affects respiratory muscle strength in the absence of malnutrition and whether such effect, if present, is reversible with an acute oxygen supplementation.

DESIGN

Case series analysis, before-after trial.

SETTING

Outpatient pneumology departments of two university hospitals.

PATIENTS

One hundred twenty patients affected by COPD in stable conditions having actual to ideal body weight ratio of > or =90%.

MEASUREMENTS AND RESULTS

Maximal inspiratory pressure (MIP) was measured at functional residual capacity level in the whole sample of subjects and during oxygen supplementation in 58 patients having a PaO2< or =60 mm Hg when breathing in room air. Predictors of MIP were assessed by a multivariate analysis. MIP values before and after oxygen supplementation were compared by a paired t test. MIP was independently correlated with FVC (p<0.001), PaO2 (p<0.01), and age (p<0.01). In the subgroup of hypoxemic patients, MIP values did not change significantly after oxygen supplementation (3.08+/-1.74 vs 3.03+/-1.91 kPa, t=0.43, not significant).

CONCLUSIONS

Hypoxemia is an important negative correlate of MIP even in well-nourished COPD patients. Its effect is not reversible with an acute oxygen supplementation.