DYNAMIC UPPER AIRWAY IMAGING DURING AWAKE RESPIRATION IN NORMAL SUBJECTS AND PATIENTS WITH SLEEP-DISORDERED BREATHING

The effects of respiration on upper airway caliber were studied using cine computed tomography (CT) in 15 normal subjects, 14 snorer/mildly apneic subjects, and 13 patients with obstructive sleep apnea. All subjects were scanned in the supine position during awake nasal breathing. Eight-millimeter-thick axial slices were obtained at four anatomic levels from the nasopharynx to the retroglossal region every 0.4 s during a respiratory cycle. Tidal volume measured from an integrated pneumotachograph signal was correlated with slice acquisition during inspiration and expiration to generate loops comparing upper airway area and tidal volume. In all three' subject groups and at all anatomic levels studied, there were significant dimensional changes in upper airway caliber during the respiratory cycle. The major findings in this investigation include: (1) the upper airway was significantly smaller in apneic than normal subjects, especially at the retropalatal low and retroglossal anatomic levels; in apneic patients the airway had an anterior-posterior configuration unlike the normal airway, which had a horizontal configuration with the major axis in the lateral direction; (2) in all three subject groups, little airway narrowing occurred in inspiration, suggesting that the action of the upper airway dilator muscles balanced the effects of negative intraluminal pressure. In apneic patients there was more enlargement of the airway in early inspiration, presumably reflecting increased upper airway muscle dilator activity; (3) in expiration, positive airway pressure resulted in expansion of the airway; this expansion was largest in the apneic patients, indicating that the apneic airway was more distensible than the normal airway; (4) at the end of expiration the upper airway narrowed significantly, especially in the apneic patients. Thus the airway in apneic patients may be heading toward a closed position at end-expiration.