Upper airway collapsibility and cephalometric variables in patients with obstructive sleep apnea

Increased pharyngeal collapsibility and abnormal anatomic structures have been postulated to contribute to the pathophysiology of obstructive sleep apnea (OSA) syndrome. It is unclear whether the abnormal craniofacial and soft tissue features may affect the pharyngeal collapsibility and contribute to the apnea density. In the present study we examine the relationship between pharyngeal collapsibility and cephalometric variables in a group of 57 male OSA patients. Pharyngeal collapsibility was measured during the night of nasal continuous positive airway pressure (nCPAP) titration by analyzing the pressure-flow relationship. Pharyngeal critical pressure (Pcrit) was calculated as the extrapolated pressure at zero flow. The patients, age 52.0 +/- 9.0 yr, had an average apnea-hypopnea index (AHI) of 72.6 +/- 31.8 and a mean Pcrit of 2.4 +/- 1.0 cm H2O. A significant correlation was found between Pcrit and the soft palate length (SPI) (r = 0.27, p = 0.04), the distance from the hyoid bone to the posterior pharyngeal wall (H-Ph) (r = 0.29, p = 0.03), and the distance from the hyoid bone to posterior nasal space (H-Pns) (r = 0.32 p = 0.02). While in obese patients Pcrit was related to SPI and neck circumference, the distance of the hyoid bone to the mandibular plane (H-MP) affected Pcrit in nonobese patients. Our results show that both pharyngeal soft tissue abnormalities and the lower position of the hyoid bone affect Pcrit in OSA patients, suggesting that an anatomic narrowing contributes to the upper airway collapsibility.