Effect of CPAP on intrinsic PEEP, inspiratory effort, and lung volume in severe stable COPD

Background: Intrinsic positive end expiratory pressure (PEEPi) constitutes an inspiratory threshold load on the respiratory muscles, increasing work of breathing. The role of continuous positive airway pressure (CPAP) in alleviating PEEN in patients with severe stable chronic obstructive pulmonary disease is uncertain, This study examined the effect of CPAP on the inspiratory threshold load, muscle effort, and lung volume in this patient group. Methods: Nine patients were studied at baseline and with CPAP increasing in increments of 1 cm H2O to a maximum of 10 cm H2O. Breathing pattern and minute ventilation ((V)over dotI), dynamic PEEN, expiratory muscle activity, diaphragmatic (PTPdi/min) and oesophageal (PTPoes/min) pressure-time product minute, integrated diaphragmatic (EMGdi) and intercostal EMG (EMGic) and end expiratory lung volume (EELV) were measured. Results: Expiratory muscle activity was present at baseline in one subject. In the remaining eight, PEEN was reduced from a mean (SE) of 2.9 (0.6) cm H2O to 0.9 (0.1) cm H2O (p<0.05). In two subjects expiratory muscle activity contributed to PEEN at higher pressures. There were no changes in -tory pattern but Vi increased from 9.2 (0.6) l/min to 10.7 (1.1) l/min (p<0.05). EMGdi remained stable while EMGic increased significantly. PTPoes/min decreased, although this did not reach -cal significance. PTPdi/min decreased significantly from 242.1 (32.1) cm H2O.s/min to 112.9 (21.7) cm H2O.s/min). EELV increased by 1.1 (0.3) 1 (p<0.01). Conclusion: High levels of CPAP reduce PEEN and indices of muscle effort in patients with severe stable COPD, but only at the expense of substantial increases in lung volume.