Effect of expiratory positive airway pressure on sleep disordered breathing

Study Objectives: We sought to determine the effect of expiratory positive airway pressure on end expiratory lung volume (EELV) and sleep disordered breathing in obstructive sleep apnea patients. Design: Observational physiology study Participants: We studied 10 OSA patients during sleep wearing a facial mask. We recorded 1 hour of NREM sleep without treatment (baseline) and 1 hour with 10 cm H₂O EPAP in random order, while measuring EELV and breathing pattern. Results: The mean EELV change between baseline and EPAP was only 13.3 mL (range 2-25 mL). Expiratory time was significantly increased with EPAP compared to baseline 2.64±0.54 vs 2.16±0.64 sec (P = 0.002). Total respiratory time was longer with EPAP than at baseline 4.44±1.47 sec vs 3.73±0.88 sec (P = 0.3), and minute ventilation was lower with EPAP vs baseline 7.9±4.17 L/min vs 9.05±2.85 L/min (P = 0.3). For baseline (no treatment) and EPAP respectively, the mean apnea+hypopnea index (AHI) was 62.6±28.7 and 56.8±30.3 events per hour (P = 0.4). Conclusion: In OSA patients during sleep, the application of 10 cm H ₂O EPAP led to prolongation of expiratory time with only marginal increases in FRC. These findings suggest important mechanisms exist to avoid hyperinflation during sleep.