Phenotypes of Velopharyngeal Tube Law in Obstructive Sleep Apnea.

Abstract

The biomechanics of upper airway collapse in obstructive sleep apnea (OSA) remains poorly understood. The goal of this study is to compare the area-pressure relationship (tube law) of the velopharynx at peak inspiration and peak expiration. Cross-sectional. Academic tertiary medical center. The velopharyngeal tube law was quantified in a convenience sample of 20 OSA patients via step reductions in nasal mask pressure during drug induced sleep endoscopy (DISE). The velopharyngeal airspace cross-sectional area was estimated from endoscopy while luminal pressure was recorded with a catheter. The tube law was quantified for nasal mask pressures from 14 to 0 cmH₂O at peak inspiration and at peak expiration in all patients. The tube law was also quantified during the breathing cycle at a constant nasal mask pressure of 4 cmH₂O in 3 patients representing different phenotypes. Velopharyngeal compliance (the slope of the tube law) was not statistically different in the peak inspiration versus peak expiration tube laws. Three phenotypes were observed, namely inspiratory collapse (phenotype 1), expiratory collapse (phenotype 2 = palatal prolapse), and a mostly stable airway during inspiration and expiration that collapsed as CPAP was reduced (phenotype 3). Velopharyngeal compliance is not significantly different at peak inspiration and peak expiration, which suggests that muscle tone is low when luminal pressure is above the closing pressure. Additional studies are needed to investigate how different phenotypes of velopharyngeal collapse may affect therapeutic outcomes.