Thoracic mechanics in COPD patients before and after pulmonary rehabilitation

Background: Patients with COPD have severe breathlessness induced by the increased mechanical work of respiratory muscles in relation to dynamic hyperinflation. Pulmonary rehabilitation programs have been shown to relieve dyspneea, but the mechanism by which they succeed remains controversial. Aim: To evaluate the effect of pulmonary rehabilitation on thoracic mechanics. Method: The association between thoracic hyperinflation measured by plethysmography (functional residual capacity FRC, residual volume RV), respiratory muscle strength (maximal inspiratory pressure MIP, maximal expiratory pressure MEP) and dyspnoea scores (MRC scale) were analyzed in patients with stable COPD before and after pulmonary rehabilitation (outpatient program, 2 months, 3 sessions/week, including daily respiratory muscle training). Results: Twenty patients with COPD stage II-IV GOLD were included. Thoracic hyperinflation was present in all cases: mean FRC 164.9% of the predicted value and RV 209.2% before the rehabilitation program. Mean MIP was 69.6% and mean MEP 105.3%. The severity of dyspnoea before the pulmonary rehabilitation was negatively associated with inspiratory muscle strength (r -0.68) and hyperinflation (r -0.45). Hyperinflation decreased at the end of the rehabilitation program (mean RV decreased with 15.1% and mean FRC with 9.2%), mean MIP increased with 14.3% and the mean dyspnoea score decreased from 3.5 to 2.2. Conclusion: Pulmonary rehabilitation optimized thoracic mechanics in our patients by reducing thoracic hyperinflation and increasing the effectiveness of inspiratory muscles work.