Published ahead of print on November 14, 2008, doi:10.1164/rccm.200807-1076OC
© 2009 American Thoracic Society doi: 10.1164/rccm.200807-1076OC
Relationship between Overnight Rostral Fluid Shift and Obstructive Sleep Apnea in Nonobese Men1 Sleep Research Laboratory of the Toronto Rehabilitation Institute; 2 Centre for Sleep Medicine and Circadian Biology, University of Toronto; and 3 Department of Medicine, Toronto General Hospital, University Health Network, Toronto, Ontario, Canada Correspondence and requests for reprints should be addressed to T. Douglas Bradley, M.D., Toronto General Hospital of the University Health Network, 9N-943, 200 Elizabeth Street, Toronto, ON, M5G 2C4 Canada. E-mail: douglas.bradley{at}utoronto.ca Rationale: The cause of increased pharyngeal collapsibility in patients with obstructive sleep apnea is incompletely understood. In awake healthy subjects, we showed that fluid displacement from the legs into the neck induced by lower body positive pressure reduces upper airway size and increases its collapsibility. Prolonged sitting leads to dependent fluid accumulation in the legs. Objectives: To test the hypotheses that the apnea–hypopnea index (AHI) during sleep will be related to the amount of fluid spontaneously displaced from the legs overnight, and that this will, in turn, be related to the time spent sitting the previous day. Methods: In 23 nonobese healthy men referred for sleep studies for suspected obstructive sleep apnea, we assessed the changes in leg fluid volume and in neck circumference from the beginning to the end of the night, and the time spent sitting during the previous day. Measurements and Main Results: The overnight change in leg fluid volume correlated strongly with the AHI (r = –0.773, P < 0.001), the change in neck circumference (r = –0.792, P < 0.001), and the time spent sitting (r = –0.588, P = 0.003). Multivariate analysis showed that the only significant independent correlates of the AHI were the overnight changes in leg fluid volume and neck circumference, which together explained 68% of the variability in the AHI among subjects. Conclusions: These novel findings suggest that overnight rostral fluid displacement from the legs, related to prolonged sitting, may play a previously unrecognized role in the pathogenesis of obstructive sleep apnea in nonobese men that is independent of body weight.
Key Words: pathophysiology • inactivity • fluid distribution
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