Anatomic and physiologic predictors of apnea severity in morbidly obese subjects

Abstract

Study Objectives: While obesity is the most common risk factor for the development of obstructive sleep apnea, the correlation between measures of obesity and apnea severity is only moderate. We thus attempted to identify anatomic and physiologic predictors of apnea severity. Design: We combined a careful assessment of upper airway anatomy, upper airway physiology, and ventilatory control in a group of obese individuals to identify predictors of apnea severity. Setting: Tertiary care academic medical center. Patients: 14 morbidly obese subjects being evaluated for weight-reduction surgery. Interventions: N/A Measurement and Results: We found no relationship between obesity (weight or body mass index) and apnea severity (respiratory disturbance index, RDI). However, those with severe apnea (RDI > 30) were found to have higher peak genioglossus EMG (GGEMG) (23.5 +/- 1.9 vs. 14.1 +/-3.7 %max, p = 0.05) and greater airway collapsibility during pulses of negative pressure (7.6 +/- 0.9 vs. 4.4 +/-0.7 cmH2O, p =0.02). Airway collapsibility was significantly associated with RDI (r = 0.62, p < 0.01) as was peak GGEMG (r = 0.55, p < 0.05). Of the anatomic variables airway shape (A-P/lateral ratio) and volume change of the pharyngeal airway between total lung capacity and residual volume were different between those with and without severe apnea. Both correlated with RDI (A-P/lateral ratio: r = 0.70, p < 0.01 and volume change: r = 0.77, p < 0.01). Conclusions: We believe these findings suggest that specific anatomic and physiologic properties of the airway interact with obesity to predispose to the development of airway collapse during sleep.