ENERGY-EXPENDITURE IN OBSTRUCTIVE SLEEP-APNEA

Patients with obstructive sleep apnea (OSA) are often obese and, in co mmon 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 therm ogenic effect of food are reduced in OSA, we have compared postabsorpt ive resting energy expenditure (REE) and dietary thermogenesis (DT) in 14 patients with moderate to severe symptomatic OSA and 14 control su bjects matched for obesity. Anthropometrics, body composition analysis using bioelectrical impedance and indirect calorimetry using a metabo lic cart and canopy system were performed in all subjects. Dietary the rmogenesis after a liquid meal equivalent to 35% of REE was measured i n 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 w as expressed in terms of metabolic body size. The patients with OSA we re 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 (B MI) and percent body fat. REE was greater in OSA patients than control s, 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 amon g patients with OSA, regardless of body weight. REE and DT did not cha nge following chronic nasal CPAP therapy. Resting energy expenditure w as 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 pati ents with moderate to severe symptomatic OSA. These findings suggest t hat patients with OSA have a pattern of obesity characterized by energ y homeostasis at an elevated body weight set-point.