• Raphael Heinzer, David P White, Atul Malhotra, Yu L Lo, Louise Dover, Karen E Stevenson, and Amy S Jordan.
• Sleep Medicine Division, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA. rheinzer@post.harvard.edu
• Sleep. 2008 Mar 1; 31 (3): 429-32.

Study ObjectivesWe 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.DesignObservational physiology studyParticipantsWe 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.ResultsThe 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).ConclusionIn OSA patients during sleep, the application of 10 cm H2O EPAP led to prolongation of expiratory time with only marginal increases in FRC. These findings suggest important mechanisms exist to avoid hyperinflation during sleep.

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