Purpose: The effect of the obstructive sleep apnea syndrome on energy expenditure is controversial. The objective of this study was to assess the relationship between 24-hr energy expenditure or sleeping metabolic rate and features of the obstructive sleep apnea.
Methods: Twenty-four apneic men took part in this cross-sectional study and were classified in quartiles of nocturnal desaturation severity, i.e. of percentage total sleep time with SaO2 < 90% determined with polysomnography. 24-hr energy expenditure and sleeping metabolic rate were measured with a whole body indirect calorimetry (respiratory chamber), and body composition by hydrodensitometry. During the stay in the respiratory chamber, urine was collected to assess catecholamine concentration and percentage recording time with SaO2 < 90% (%TRT SaO2 < 90%) was measured with nocturnal oximetry.
Results: Mean fat free mass and fat mass were greater in quartile 4 than in quartile 1 (P < 0.05). %TRT SaO2 < 90% was higher in quartile 4 than in other quartiles (P < 0.0001). 24-hr energy expenditure and sleeping metabolic rate were similar among quartiles. However, when expressed on a per kg body weight basis (kcal/kg), these variables were negatively correlated with the %TRT SaO2 < 90% in the whole group (r = -0.46 and -0.48, respectively, P < 0.05). %TRT SaO2 < 90% was found to be a predictor of sleeping metabolic rate which explained, together with fat mass and fat free mass, 86% of this variance (P < 0.05).
Conclusion: In apneic men energy expenditure relative to body weight decreases with increasing severity of oxygen desaturation which could favour a positive energy balance.