Obesity plays an independent worsening modifying effect on nocturnal hypoxia in obstructive sleep apnea

Objective: Obesity's association with obstructive sleep apnea syndrome (OSAS) is well established. The aim of this study was to examine the impact of obesity on nocturnal hypoxia. Methods: Twenty two thousand seven hundred and ninety three patients aged 21-80. years who underwent whole night polysomnography during 2000-2009 were included in the study. For each patient, percent sleep time spent with oxyhemoglobin desaturation lower than 90% was calculated (%NODP). Nocturnal hypoxia was analyzed by gender, age, OSAS severity, and body mass index (BMI) categories. Results: Nocturnal hypoxia was positively correlated with BMI, OSAS severity, and age, but not with gender. The differences in %NODP between the two obese groups and non-obese varied from 0.55% to more than a 20% increase and were correlated with age and OSAS severity. The %NODP ratio between the two obese groups and the non-obese was independent of age and OSAS severity. There was a nearly twofold increase in %NODP in obese patients and a threefold increase in the morbidly obese relative to the non-obese. Conclusions: Our results indicate that obesity plays an independent worsening modifying effect on nocturnal hypoxia in OSAS.