Resting energy expenditure in OSAS: the impact of a single CPAP application.

Purpose: Data on the impact of obstructive sleep apnea syndrome (OSAS) and its treatment on resting energy expenditure (REE) are currently few and conflicting. The purpose of the present study was to investigate the impact of OSAS on REE, as measured before and after sleep, and the changes in REE after a single continuous positive airway pressure (CPAP) application, for the first time in literature.

Methods: This is a nested case-control study. From the initial study population, two groups were formed, based on the results of nocturnal polysomnography: a group of male OSAS patients and a group of male, age-matched non-OSAS controls. REE was measured in both groups before and after sleep by indirect calorimetry, while patients repeated REE measurements before and after a single nasal CPAP application.

Results: Ninety-two male OSAS patients (45.3 ± 12.8 years old) and 19 male non-OSAS controls (50.8 ± 11.7 years old) were studied. REE/lean body mass (LBM) was higher among patients compared to controls both pre- (29.6 ± 12 vs 22.9 ± 7.9 kcal/kg; p = 0.022, correspondingly) and post-sleep (26.4 ± 9.6 vs 21.6 ± 9 kcal/kg; p = 0.047 correspondingly). REE/LBM decreased significantly after sleep in OSAS patients (p = 0.002), but not in controls; this difference was most evident among patients with more severe disease and higher desaturation. A single nasal CPAP application diminished the pre-post REE/LBM difference (30.3 ± 8.2 vs 28.3 ± 10.3 kcal/kg; p = 0.265), but only among responders.

Conclusions: In OSAS patients, REE values are high and vary significantly before and after sleep. A single nasal CPAP application diminishes this difference among responders, possibly through reversal of nocturnal desaturation.