• Simon A Joosten, Scott A Sands, Bradley A Edwards, Kais Hamza, Anthony Turton, Kenneth K Lau, Marcus Crossett, Philip J Berger, and Garun S Hamilton.
• Monash Lung and Sleep, Monash Health, Monash Medical Centre, Melbourne, Australia.
• Respirology. 2015 Jul 1; 20 (5): 819-27.

Background And ObjectiveThis study aimed to evaluate the involvement of airway cross-sectional area and shape, and functional residual capacity (FRC), in the genesis of obstructive sleep apnoea (OSA) in patients with supine-predominant OSA.MethodsThree groups were recruited: (i) supine OSA, defined as a supine apnoea-hyponoea index (AHI) at least twice that of the non-supine AHI; (ii) rapid eye movement (REM) OSA, defined as REM AHI at least twice the non-REM AHI and also selected to have supine AHI less than twice that of the non-supine AHI (i.e. to be non-positional); and (iii) no OSA, defined as an AHI less than five events per hour. The groups were matched for age, gender and body mass index. Patients underwent four-dimensional computed tomography scanning of the upper airway in the supine and lateral decubitus positions. FRC was measured in the seated, supine and lateral decubitus positions.ResultsPatients with supine OSA demonstrated a significant decrease in FRC of 340 mL (P = 0.026) when moving from the lateral to supine position compared to controls with no OSA, and REM OSA patients. We found no differences between groups in upper airway size and shape. However, all groups showed a significant change in airway shape with the velopharyngeal airway adopting a more elliptoid shape (with the long axis laterally oriented), with reduced anteroposterior diameter in the supine position.ConclusionsA fall in FRC when moving lateral to supine in supine OSA patients may be an important triggering factor in the generation of OSA in this patient group.© 2015 Asian Pacific Society of Respirology.

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