Background: The benefits of non-invasive mechanical ventilation (NIMV) in hypercapnic patients with severe stable COPD remain controversial mainly due to their unknown mechanisms.
Aim: To assess the clinical and physiological benefits of a 3 weeks period of intermittent NIMV and their underlying mechanisms in COPD patients.
Patients and methods: Twelve patients (10 male) prospectively recruited (age 65 +/- 3 years, FEV1 27 +/- 2% predicted, PaO2 46 +/- 2 mmHg, PaCO2 55 +/- 2 mmHg) were submitted to NIMV using a commercially available system (BiPAP) 3 h a day, 5 days a week for 3 weeks. Arterial blood gases, 6 min walking distance, dyspnea (Mahler's scale), breathing pattern, PIMax, ventilatory drive (P0.1) and the impedance of the respiratory system (P0.1/V1/T1) were measured before and after NIMV.
Results: A significant improvement in PaO2, PaCO2, PIMax, dyspnea and exercise capacity was observed in addition to a trend for VT to increase and for respiratory rate (RR) to decrease. The impedance of the respiratory system showed a significant reduction. Ventilatory drive, normalized for PaCO2 levels, did not change. Improvement in PaCO2 was related to an increase in Vp whereas a significant association between the reduction in RR and the fall in respiratory system impedance was also found.
Conclusions: Our study supports previous data demonstrating that NIMV improves clinical and physiologic parameters in advanced stable COPD and suggest that the underlying mechanism is a reduction in the inspiratory load. A randomized clinical trial is needed to confirm that this mechanism is operative.