Energy expenditure in obstructive sleep apnea

Abstract

Patients with obstructive sleep apnea (OSA) are often obese and, in common with obese patients generally, find it difficult to lose weight. Obstructive sleep apnea may be associated with changes in total daily energy expenditure that could contribute to obesity and complicate its management. To determine whether resting metabolic rate and the thermogenic effect of food are reduced in OSA, we have compared postabsorptive resting energy expenditure (REE) and dietary thermogenesis (DT) in 14 patients with moderate to severe symptomatic OSA and 14 control subjects matched for obesity. Anthropometrics, body composition analysis using bioelectrical impedance and indirect calorimetry using a metabolic can and canopy system were performed in all subjects. Dietary thermogenesis after a liquid meal equivalent to 35% of REE was measured in 13 patients and 8 control subjects. Measurements were repeated after chronic (mean ± SD 12 ± 5 weeks) nasal continuous positive airway pressure (CPAP) therapy in 10 patients with OSA. Energy expenditure was expressed in terms of metabolic body size. The patients with OSA were heavier and had larger necks and a larger lean body mass (LBM) than controls, but the two groups were well matched for body mass index (BMI) and percent body fat. REE was greater in OSA patients than controls, but when corrected for LBM there was no difference between the two groups (27 ± 3 vs. 28 ± 4 kcal/kg). DT was similar in patients and controls (17 ± 6 vs. 15 ± 10%). REE/LBM was quite consistent among patients with OSA, regardless of body weight. REE and DT did not change following chronic nasal CPAP therapy. Resting energy expenditure was related to LBM (r = 0.76; p < 0.001) but not apnea ± hypopnea index (r = 0.11). We conclude that REE and DT are not reduced in obese patients with moderate to severe symptomatic OSA. These findings suggest that patients with OSA have a pattern of obesity characterized by energy homeostasis at an elevated body weight set-point.