Evaluation of the role of lung volume and airway size and shape in supine-predominant obstructive sleep apnoea patients.
OBJECTIVE
This 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.


METHODS
Three 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.


RESULTS
Patients 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.


CONCLUSIONS
A 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.
Monash Lung and Sleep, Monash Health, Monash Medical Centre, Melbourne, Australia.|Ritchie Centre, Monash Institute of Medical Research, Monash University, Melbourne, Australia.
Simon A
SA
Joosten
Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Scott A
SA
Sands
Department of Physiology and School of Psychological Sciences, Monash University, Melbourne, Australia.|Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Bradley A
BA
Edwards
School of Mathematical Sciences, Monash University, Melbourne, Australia.
Kais
K
Hamza
Monash Lung and Sleep, Monash Health, Monash Medical Centre, Melbourne, Australia.
Anthony
A
Turton
Department of Diagnostic Imaging, Monash Health, Melbourne, Australia.
Kenneth K
KK
Lau
Department of Diagnostic Imaging, Monash Health, Melbourne, Australia.
Marcus
M
Crossett
Ritchie Centre, Monash Institute of Medical Research, Monash University, Melbourne, Australia.
Philip J
PJ
Berger
Monash Lung and Sleep, Monash Health, Monash Medical Centre, Melbourne, Australia.|School of Clinical Sciences, Monash University, Melbourne, Australia.
Garun S
GS
Hamilton
D000328:Adult; D000368:Aged; D015992:Body Mass Index; D005260:Female; D005652:Functional Residual Capacity / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D056888:Patient Positioning / Q000379:methods; D012107:Research Design; D012137:Respiratory System / Q000000981:diagnostic imaging / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis / Q000503:physiopathology; D012895:Sleep, REM; D016683:Supine Position; D014057:Tomography, X-Ray Computed / Q000379:methods
apnoea; functional residual capacity; lung volume measurement; sleep; supine position