Upper airway distensibility and collapsibility in patients with obstructive sleep apnea

The present study was performed to evaluate the distensibility and collapsibility characteristics of regional segments of the UA in patients with OSA and in normal subjects in response to changes in airway pressure. Seventeen male patients with moderately severe OSA and 13 normal subjects underwent CT of the UA in the supine position while awake. Axial views were obtained from the level of the hard palate to the hypopharynx under conditions of -5, 0, and +10 cm H2O of CAP. The results indicated that the Amin occurred within 20 mm of the hard palate in the retropalatal region of the UA in 16 (94 percent) of the 17 patients and in 12 (92 percent) of the 13 normal subjects. Continuous negative airway pressure of -5 cm H2O failed to significantly decrease either Amin or Amean in either the patients or normal subjects, suggesting good UA load compensation during wakefulness. Continuous positive airway pressure of 10 cm H2O significantly increased Amin and Amean to a similar extent in both groups. The Amin was significantly smaller by 40 percent, 33 percent, and 37 percent in the patients with OSA, compared to the normal subjects, at -5, 0, and +10 cm H2O of CAP, respectively. In contrast, Amean did not differ between the groups. The CT scan criterion of Amin less than or greater than 1.0 cm2 during tidal ventilation of atmospheric pressure correctly categorized patients with OSA and normal subjects with an accuracy of 70 percent. While the behavior of the UA in response to nasal CPAP and CNAP failed to increase the accuracy of CT scan criteria to a level sufficient for clinical use in the diagnosis of OSA, the results clearly indicate that structural changes in the UA contribute to the development of OSA.