Improvement in Upper Airway Function after Weight Loss in Patients with Obstructive Sleep Apnea

Abstract

Overweight patients with obstructive sleep apnea (OSA) are improved by weight reduction, although the underlying mechanisms are not clear. We tested the hypothesis that improvement in OSA after weight loss is associated with improvement in pharyngeal function. Consequently, we measured pharyngeal area at functional residual capacity (AFRC) and at residual volume (ARV), the percent change in pharyngeal area between FRC and RV (.DELTA.Aph%) defined as (AFRC - ARV)/AFRC .times. 100, and the lung volume dependence of phayngeal area (LVD) defined as the difference between AFRC and ARV normalized for the expiratory reserve volume (ERV)-in 12 overweight apneic patients before and after weight loss. We found that after a 26 .+-. 18 kg weight loss, there was a significant reduction in the apnea/hypopnea index from 57 .+-. 29 to 14 .+-. 10 (p < 0.0005) and increase in the lowest nocturnal oxygen saturation from 54 .+-. 20% to 80 .+-. 8% (p < 0.001). This improvement was associated with a significant reduction in .DELTA.Aph% from 25 .+-. 15% to 9 .+-. 18% (p < 0.05) and a significant decrease in LVD from 1.98 .+-. 1.52 cm2/L to 0.16 .+-. 0.88 cm2/L (p < 0.005). There were four patients in whom baseline LVD was low and relatively unchanged after weight loss. Three of these patients exhibited paradoxical inspiratory narrowing of the glottis, which reversed after weight loss; these glottic abnormalities were not present in the rest of the patients with OSA. We conclude that improvement in obstructive sleep apnea after weight loss may be related to improvement in pharyngeal and glottic function.