To Örebro University

Background: Previous studies have indicated that patients with obstructive sleep apnoea (OSA) have altered ventilation and lung volumes awake and the results suggest that this may be a determinant of severity of desaturations during sleep. However, little is known about regional lung aeration during sleep in patients with OSA.

Methods: Twelve patients with OSA were included in the study. Computed tomography was used to study regional lung aeration during wakefulness and sleep. Lung aeration was calculated in ml gas/g lung tissue in four different regions of interest (ROI(1-4)), along the border of the lung from ventral to dorsal.

Results: Lung aeration in the dorsal (dependent) lung region (ROI(4)) was lower during sleep compared to wakefulness 0.78 +/- 0.19 versus 0.88 +/- 0.19 (mean +/- SD) ml gas/g lung tissue (P = 0.005). Associations were found between awake expiratory reserve volume and change in lung aeration from wakefulness to sleep in ROI(4) (r = -0.69; P = 0.012). In addition, the change in lung aeration in the dorsal region correlated to sleep time (r = 0.69; P = 0.014) but not to time in supine position. The difference in lung aeration between inspiration and expiration (i.e. ventilation), was larger in the ventral lung region when expressed as ml gas per g lung tissue. In two patients it was noted that, during on-going obstructive apnoea, lung aeration tended to be increased rather than decreased.

Conclusions: Aeration in the dorsal lung region is reduced during sleep in patients with OSA. The decrease is related to lung volume awake and to sleep time.