Effects of body position on resting lung volume in overweight and mildly to moderately obese subjects

INTRODUCTION: A partial sitting position has been reported to increase functional residual capacity (FRC) in lean subjects, whereas FRC does not change with position in the morbidly obese. The effects of positioning in the subgroup of overweight and mildly to moderately obese subjects have not been examined. We hypothesized that a change in FRC may be related to adipose tissue distribution. METHODS: We investigated the hypotheses that a 30° Fowler's position would increase the FRC and decrease the closing-capacity-to-FRC ratio in subjects with a body mass index in the 25.0-39.9 kg/m² range. We tested whether body fat distribution, measured by waist circumference and waist-to-hip ratio, correlated with the lung-volume changes. RESULTS: The 30° Fowler's position did not improve the FRC, when compared to the supine position (n = 32). The closing-capacity-to-FRC ratio was > 1 in 5 of 7 subjects while sitting, and in all 7 subjects while supine or in the 30° Fowler's position. The waist-to-hip ratio was correlated with closing capacity in all positions, and correlated with closing-capacity-to-FRC ratio in the supine position. CONCLUSIONS: Standard position changes purported to increase FRC are ineffective in the overweight and mildly to moderately obese, a subpopulation represented by almost 67% of Americans. Bedside caregivers may need to modify current practices when the clinical goal is to improve resting lung volumes in sedentary patients.