Fast-CT evaluation of the upper airway during wakefulness in patients with obstructive sleep apnea

Fast-CT scanning was used to study the dynamic changes in the upper airway (UA) during quiet tidal ventilation (VT) in 25 patients with obstructive sleep apnea (OSA). Ten fast-CT scans were sequentially obtained over one respiratory cycle from the level of the hard palate to the hypopharynx with the patients awake in the supine position. The patients were 44 +/- 2 years old, weighed 104 +/- 5 kg, and had moderately severe OSA with an apnea plus hypopnea index (AHI) of 59 +/- 7 per hour. Maximum and minimum UA cross-sectional areas (Amax -Amin) were determined for each UA level and percent reductions in UA size or collapsibility index (CI) were computed as (Amax -Amin)*100/Amax. The lower velo-pharynx was the narrowest (Amin = 80 +/- 12 mm2) and most collapsible segment of the UA (Cl = 55 +/- 5%). Amin was less than 25, 50, or 75 mm2 in 64%, 76%, and 88% of the patients, respectively. Significant narrowing was confined to the proximal segment (levels 1 to 4) in the majority, with the remaining patients having narrowing in both the proximal and distal segments. None of the patients had major narrowing confined to the distal segment alone. Mean UA cross-sectional area (Amean) was generally largest at end-inspiration and smallest at end-expiration. In conclusion, fast-CT has documented substantial changes in UA cross-sectional area during quiet VT in awake supine patients with OSA. The velopharyngeal (retropalatal) segment was the narrowest and most collapsible region. Maximal narrowing was greatest at end-expiration, consistent with relaxation of UA dilator muscle activity.