Operational Lung Volumes While Seated, Supine, and During Exercise in Obese and Nonobese Children

Abstract

PURPOSE: The effects of adult obesity on lung function at rest, such as reductions in functional residual capacity and expiratory reserve volume, are well recognized. However, the effects of obesity on operational lung volumes at rest, while lying supine, and during exercise in obese children are unknown but could create meaningful respiratory limitations. METHODS: 11 nonobese (Ht: 143.3±5.2 cm; Wt: 35.8±3.8 kg; BMI percentile: 50±21; Body fat: 27±6%) and 12 obese (Ht: 149.7±6.7 cm; Wt: 65.8±14.4 kg; BMI percentile: 97.5±1.4; Body fat: 46±3%) children underwent dual energy x-ray absorptiometry, pulmonary function testing, and measurement of operational lung volumes when seated upright, while supine, during constant load cycling at 40 W, and during maximal exercise testing. RESULTS: Ratio of forced expiratory volume in the first second and forced vital capacity (FEV1/FVC) was lower in obese compared with nonobese children (83.6±4.1 vs. 88.6±4.1%; P=0.004). Functional residual capacity (FRC) was lower in obese compared with nonobese children when seated upright (38.5±4.8 vs. 49.3±4.0%TLC; P < 0.001) and while supine (35.0±6.4 vs. 45.4±6.5%TLC; P < 0.001). Three children (2 obese) experienced expiratory flow limitation (EFL) while supine. Both end expiratory lung volume (EELV) and end inspiratory lung volumes (EILV) were lower during exercise at 40 W (P < 0.01) and EILV was lower at peak exercise (P=0.048) in obese compared with nonobese children. EELV did not change from rest to exercise at 40 W or peak exercise in nonobese children. In obese children, EELV was higher at peak exercise (44.4±4.7%TLC) compared with rest and exercise at 40 W (40.5±4.1 and 38.7±3.1%TLC, respectively; P < 0.05). None of the nonobese children experienced EFL during exercise. In obese children, one experienced EFL during exercise at 40 W (44%tidal volume; VT) and seven experienced EFL at peak exercise (37±22%VT). Higher levels of fat mass were associated with lower levels of FRC when seated (r=-0.88; P < 0.001) and while supine (r=-0.65; P=0.003), and EELV during exercise at 40 W (r=-0.68; P=0.001). CONCLUSIONS: Obese children demonstrate low lung volume breathing when seated, while supine, and during exercise, which may contribute to an obstructive breathing pattern at rest as well as EFL and dynamic hyperinflation during peak exercise.