Obesity is a risk factor for OSA in adults. The relationship between obesity and OSA in childhood is not clear. We reviewed the records of all obese (BMI>85th percentile) children between the ages of 6 and 18, referred for nocturnal polysomnography at our institution. Sleep studies were scored for sleep stages, respiratory events [total apnea/hypopneas, respiratory disturbance index (RDI) and lowest oxygen saturation (OSat)]. Due to age-dependent changes in sleep architecture, data were stratified before comparison to normal values. This study included 153 children (70 female) with a mean BMI of 37.1±1.1 (SEM) and a mean age of 11.9 years. A subset of 20 children were evaluated after at least a 5% reduction in BMI. Analysis of sleep stages revealed paucity of stage 1 (5.7±0.4 v 7.7±0.4%), stage 2 (42.2±1.1 v 51.0±0.6%) and REM (15.6±0.5 v 20.4±0.4%) sleep (p<0.0001 for each). SWS (stages 3&4) was markedly increased in the obese children (36.6±1.1 v 20.6±0.5%; p<0.0001). Apnea occurred in 81% of obese children, and 52% had an RDI>5 events/hour. The mean RDI of 12.8±1.7 was correlated to BMI(p<0.01), but did not differ between blacks and whites, or males and females. The majority of these events (68%) occurred during non-REM sleep. OSat correlated with BMI (p<0.005) and 76% of obese children had an OSat<90% at their nadir. Blacks had a lower OSat than whites(80.6±1.5 v 84.9±1.2%; p=0.03), possibly due to the higher mean BMI in blacks (38.7±1.6 v 34.4±1.5; p=0.05). The minimum OSat increased with weight loss (p<0.05). We conclude that OSA is common in a population of obese children referred for nocturnal polysomnography. In contrast to OSA in adults, the aberrance of sleep architecture in these obese children was characterized by excessive SWS, to the exclusion of REM and other stages. The physiologic significance of this reversal in sleep architecture, and its contribution to OSA in childhood remains unclear. The associations between nocturnal respiratory events (RDI and OSat) and BMI; and the improvement of OSat with weight loss suggests that obesity plays a major role in pediatric OSA.
