Upright body position and weight loss improve respiratory mechanics and daytime oxygenation in obese patients with obstructive sleep apnoea

To determine whether upright body position and weight loss would improve da ytime gas exchange in moderately obese patients with obstructive sleep apno ea (OSAS), 13 patients with mild or moderate OSAS were studied before and a fter weight loss. Pulmonary function tests, arterial blood gases and respir atory gas analysis were measured prior to and after a very low calorie diet (VLCD) period of six weeks. Arterial blood gases were measured in supine a nd standing positions and closing volume in supine and sitting positions be fore and after weight loss. In the upright position, there was a significan t increase in PaO2 (P<0.005) accompanied by a significant decrease in alveo lar-arterial PO2 difference (P<0.005) and closing volume (P<0.05). The medi an weight loss was 11 kg (range 5-18). The number of desaturation episodes (four percentage units or more per hour during sleep) (ODI4) decreased (P<0 .01) after weight loss. The change in PaO2 with weight loss correlated with the decrease in ODI4 (r = 0.73, P<0.01). The increase in expiratory reserv e volume (ERV) was closely related to the amount of weight lost (r = 0.895, P<0.01). The results indicate that weight loss and upright body position i mproved daytime respiratory mechanics and gas exchange in obese patients wi th OSAS. The findings suggest that obesity plays an important role in the p athogenesis of daytime gas exchange disturbances in obese OSAS patients. Th e adoption of a more upright sleep posture might improve nocturnal oxygenat ion in obese patients with OSAS.