Continuous positive airway pressure increases inspiratory capacity of COPD patients

Background and objective:  Hyperinflation with a decrease in inspiratory capacity (IC) is a common presentation for both unstable and stable COPD patients. As CPAP can reduce inspiratory load, possibly secondary to a reduction in hyperinflation, this study examined whether CPAP would increase IC in stable COPD patients. Methods:  Twenty-one stable COPD patients (nine emphysema, 12 chronic bronchitis) received a trial of CPAP for 5 min at 4, 7 and 11 cmH2O. Fast and slow VC (SVC) were measured before and after each CPAP trial. In patients in whom all three CPAP levels resulted in a decreased IC, an additional trial of CPAP at 2 cmH2O was conducted. For each patient, a ‘best CPAP’ level was defined as the one associated with the greatest IC. This pressure was then applied for an additional 10 min followed by spirometry. Results:  Following application of the ‘best CPAP’, the IC and SVC increased in 15 patients (nine emphysema, six chronic bronchitis). The mean change in IC was 159 mL (95% CI: 80–237 mL) and the mean change in SVC was 240 mL (95% CI: 97–386 mL). Among these patients, those with emphysema demonstrated a mean increase in IC of 216 mL (95% CI: 94–337 mL). Six patients (all with chronic bronchitis) did not demonstrate any improvement in IC. Conclusions:  The best individualized CPAP can increase inspiratory capacity in patients with stable COPD, especially in those with emphysema.