(1309) Computer Simulations of Negative Effort Dependence in Obstructive Sleep Apnea

Introduction: Negative Effort Dependence (NED) is a reduction in flow despite increasing breathing effort. Studies in obstructive sleep apnea (OSA) patients suggest that the degree of NED during polysomnography reflects the site of collapse (tongue, soft palate, lateral walls, or epiglottis). The anatomical and physiological factors that regulate NED are poorly understood. This study investigates the relationship between NED and pharyngeal compliance using computer simulations.

Methods: A 3-dimensional model of the pharyngeal airspace and soft tissues was created from magnetic resonance imaging of an OSA patient. Fluid-structure interaction simulations of airway collapse were performed in ANSYS software. Pharyngeal compliance (slope of the area-pressure relationship at the choke point) was varied by varying the modulus of elasticity of the soft tissues. NED was defined as the percent reduction from the peak flow Qmax to the flow Q* at a downstream pressure 2 cmH2O below, namely NED = 100(Qmax-Q*)/Qmax.

Results: Flow initially increased as downstream pressure decreased, but flow reached a peak and started to fall with further reductions in downstream pressure. Pharyngeal compliance increased from 0.05 to 0.1 cm2/cmH2O when the modulus of elasticity changed from 2,500 to 1,000 Pa. This increase in pharyngeal compliance led to a reduction in the maximum flow from 157 to 99 L/min and an increase in NED from 4% to 18%.

Conclusions: Our simulations revealed that NED increases as pharyngeal compliance increases, which is consistent with the in vivo observation that highly compliant anatomical structures (e.g., epiglottis and soft palate) produce more NED than less compliant structures (tongue).