Rationale: Obstructive sleep apnea syndrome (OSAS) is associated with anatomical abnormalities restricting upper airway size and functional factors decreasing pharyngeal dilator activity in sleep. In this study we hypothesized that OSAS is also associated with altered pharyngeal mechanical compliance during wakefulness. Methods: 5 OSAS and 6 control obese girls between 14-18 years of age were studied. All underwent polysomnography, critical closing pressure (Pcrit) studies, and dynamic MRI of the upper airway during awake tidal breathing. Effective airway compliance was defined as the slope of cross-sectional area vs. average pressure between maximum inspiration and maximum expiration along the pharyngeal airway. Pharyngeal pressure fields were calculated using image-based computational fluid dynamics (CFD) and nasal resistance. Spearman correlations were calculated to test associations between AHI, Pcrit, and airway compliance. Results: Effective compliances in the nasopharynx (CNP) and velopharynx (CVP) were lower and negative in OSAS compared to controls: -4.4 vs. 1.9 (mm2/cmH2O, P=0.012), and -2.1 vs. 3.9 (mm2/cmH2O, P=0.021), respectively, suggesting a strong phasic pharyngeal dilator activity during inspiration in OSAS compared to controls. For all subjects CNP and AHI correlated negatively (rS = -0.69, P = 0.02), and passive Pcrit correlated with CNP (rS = -0.76, P=0.006) and with AHI (rS = 0.86, P=0.0006). Conclusions: Pharyngeal mechanics obtained during wakefulness could be used to characterize subjects with OSAS. Moreover, negative effective compliance during wakefulness and its correlation to AHI and Pcrit suggest that phasic dilator activity of the upper pharynx compensates for negative pressure loads in these subjects.
- Airway Compliance
- Dynamic MRI
- Copyright © 2016, Journal of Applied Physiology