Effects of Obesity and Sex on Supine Functional Residual Capacity and Expiratory Flow Limitation in Children

Introduction: Childhood obesity is associated with a higher risk of sleep-disordered breathing, but our understanding of the underlying physiologic mechanisms is limited. This study investigated the effects of obesity on lung volumes, expiratory flow limitation (EFL), and respiratory symptoms in the supine position. Methods: Ninety-four children (8–12 years old, n = 58 with obesity and n = 36 without obesity) underwent lung volume and EFL measurements in the seated and supine positions in this repeated-measures cross-sectional study. Children without obesity underwent an additional condition where either a 2.3 kg (n = 26) or 5.0 kg (n = 8) mass was placed on their abdomen to simulate obesity. Ratings of perceived breathlessness (RPB) were recorded. Results: Functional residual capacity (FRC) in the supine when compared with the seated posture decreased more so in children without obesity (43.9 ± 1.0 vs. 34.4 ± 1.0% total lung capacity [TLC]) compared with children with obesity (35.5 ± 0.8 vs. 29.6 ± 0.8% TLC; p = 0.0048 group*posture). EFL in the supine position was present in 17% of children with obesity compared with 6% of children without obesity (p = 0.1218). In children without obesity, mass-loading with 5.0 kg produced further reductions in FRC (seated: 45.0 ± 1.7% TLC; supine: 36.7 ± 1.7% TLC; supine+5.0 kg: 29.4 ± 1.7% TLC; p = 0.0087 seated vs. supine+ and p = 0.0178 supine vs. supine +) and an increase in RPB (seated: 0.38 ± 0.24; supine: 0.42 ± 0.24; supine+5.0 kg: 1.25 ± 0.27; p = 0.0002 seated vs. supine+ and p = 0.0001 supine vs. supine +). Conclusions: Children with obesity breathe at significantly lower lung volumes while supine, increasing the risk of EFL. A better physiologic understanding of the mechanical effects of obesity could potentially improve the management of sleep-related symptoms among children with obesity.