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Received August 18, 2002
Accepted after revision December 11, 2002
1 Ludwig Engel Centre for Respiratory Research, Westmead Hospital, Westmead, New South Wales, Australia 2145
2 Department of Physics and Astronomy, The University of Leeds, Leeds LS2 9JT, UK
3 Ludwig Engel Centre for Respiratory Research, Westmead Hospital and University of Sydney, New South Wales, Australia, 2145
* To whom correspondence should be addressed. E-mail: jason_kirkness{at}wmi.usyd.edu.au.
The obstructive sleep apnoea syndrome (OSA) is a disorder characterised by repetitive closure and re-opening of the upper airway during sleep. Upper airway luminal patency is influenced by a number of factors including: intraluminal air pressure, upper airway dilator muscle activity, surrounding extraluminal tissue pressure, and also surface forces which can potentially act within the liquid layer lining the upper airway. The aim of the present study was to examine the role of upper airway mucosal lining liquid (UAL) surface tension (
) in the control of upper airway patency. Upper airway opening (PO) and closing pressures (PC) were measured in 25 adult male, supine, tracheostomised, mechanically ventilated, anaesthetised (sodium pentabarbitone), New Zealand White rabbits before (control) and after instillation of 0.5 ml of either 0.9 % saline (n = 9) or an exogenous surfactant (n = 16; Exosurf Neonatal) into the pharyngeal airway. The
of UAL (0.2 µl) was quantified using the 'pull-off' force technique in which
is measured as the force required to separate two curved silica discs bridged by the liquid sample. The
of UAL decreased after instillation of surfactant from 54.1 ± 1.7 mN m-1 (control; mean ± S.E.M.) to 49.2 ± 2.1 mN m-1 (surfactant; P < 0.04). Compared with control, PO increased significantly (P < 0.04; paired t test, n = 9) from 6.2 ± 0.9 to 9.6 ± 1.2 cmH2O with saline, and decreased significantly (P < 0.05, n = 16) from 6.6 ± 0.4 to 5.5 ± 0.6 cmH2O with surfactant instillation. Findings tended to be similar for PC. Change in both PO and PC showed a strong positive correlation with the change
of UAL (both r > 0.70, P < 0.001). In conclusion, the patency of the upper airway in rabbits is partially influenced by the
of UAL. These findings suggest a role for UAL surface properties in the pathophysiology of OSA.
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