Lung aeration during sleep in patients with obstructive sleep apnoea Jonas Appelberg 1 , Christer Janson 2 , Eva Lindberg 2 , Tatjana Pavlenko 3 and Go ¨ran Hedenstierna 4 1 Department of Clinical Physiology, Sundsvall Hospital, Sundsvall, 2 Department of Medical Sciences: Respiratory Medicine and Allergology, Uppsala University, Uppsala, 3 Department of Statistics, Stockholm University, Stockholm, and 4 Department of Medical Sciences: Clinical Physiology, Uppsala University, Uppsala, Sweden Correspondence Jonas Appelberg, Department of Clinical Physiology, Sundsvall Hospital, SE-851 86 Sundsvall, Sweden E-mails: jonas.ap@telia.com; jonas.appelberg@ lvn.se Grants This study was supported by grants from the Swedish Medical research council (no 5315), the Swedish Heart and Lung Foundation, Uppsala County Association Against Heart and Lung Diseases, Swedish Sleep Research Society and from Mid SwedenÕs Research and Development Center. Accepted for publication Received 16 September 2009; accepted 16 April 2010 Key words computed tomography; lung aeration; lung volume; obstructive sleep apnoea; sleep; ventilation Summary 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 0Æ78 ± 0Æ19 versus 0Æ88 ± 0Æ19 (mean ± SD) ml gas ⁄ g lung tissue (P =0Æ005). Associations were found between awake expiratory reserve volume and change in lung aeration from wakefulness to sleep in ROI 4 (r = )0Æ69; P =0Æ012). In addition, the change in lung aeration in the dorsal region correlated to sleep time (r =0Æ69; P =0Æ014) 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. Introduction Several previous reports have indicated that respiration and ventilation is altered in patients with obstructive sleep apnoea (OSA). Both hypoventilation (Jones et al., 1985), altered ventilatory response to CO 2 (Garay et al., 1981; Sullivan et al., 1990; Appelberg & Sundstro ¨m, 1997), and reduced lung volume (O ¨ nal et al., 1985; Se ´rie `s et al., 1989) has been reported in these patients. Obesity, a common feature in patients with OSA, is one important factor responsible for changes in lung volume. These changes, mainly presented as a reduction in functional residual capacity (FRC) and expiratory reserve volume (ERV), has been shown to affect the ventilatory drive (Appelberg & Sundstro ¨m, 1997), nocturnal apnoea and desat- uration frequency (Appelberg et al., 2000) and arterial satura- tion in patients with OSA (Se ´rie `s et al., 1989). Even if the significance of a reduced lung volume seems well established the mechanisms are unclear. One consequence of reduced lung volume could be that closure of peripheral airways occur during normal breathing, a phenomenon that is even more pronounced in the supine position and possibly during sleep when lung volume is further reduced (Hudgel & Devadatta, 1984; Ballard et al., 1990). Closure of peripheral airways may affect regional aeration within the lung and we have recently found in healthy subjects that aeration in the dependent lung region is lower during sleep in comparison with wakefulness (Appelberg et al., 2007). Although the change in FRC and lung aeration probably is too small to cause significant desaturations during sleep in healthy subjects, the effect in obese subjects with obstructed breathing might be different. The aim of the present study was accordingly to analyse regional lung aeration during sleep in patients with OSA. Subjects and methods Subjects The study population consisted of 11 men and one woman who had been referred to the Department of Clinical Physiology, Sundsvall Hospital, for investigation of snoring and daytime Clin Physiol Funct Imaging (2010) 30, pp301–307 doi: 10.1111/j.1475-097X.2010.00941.x Ó 2010 The Authors Journal compilation Ó 2010 Scandinavian Society of Clinical Physiology and Nuclear Medicine 30, 4, 301–307 301