• Jennifer H Walsh, Kathleen J Maddison, Peter R Platt, David R Hillman, and Peter R Eastwood.
• West Australian Sleep Disorders Research Institute, Department of Pulmonary Physiology, Sir Charles Gairdner Hospital, Nedlands, WA, Australia. Jennifer.Walsh@health.wa.gov.au
• Sleep. 2008 Oct 1;31(10):1440-7.

Study ObjectivesTo determine the effect of head posture on upper airway collapsibility and site of collapse of the passive human upper airway.DesignPharyngeal critical closing pressure (Pcrit) and site of airway collapse were assessed during head flexion, extension and rotation in individuals undergoing propofol anesthesia.SettingOperating theatre of major teaching hospital.ParticipantsFifteen healthy volunteers (8 male), including 7 who were undergoing surgery unrelated to the head or neck.Measurements And ResultsApplied upper airway pressure was progressively decreased to induce variable degrees of inspiratory flow limitation and to define Pcrit. Upper airway and oesophageal pressure transducers identified the site of collapse. Genioglossus muscle activity (EMGgg) was assessed using intramuscular fine wire electrodes inserted percutaneously. Data from 3 subjects were excluded from analysis due to persistent EMGgg. In the neutral posture Pcrit was -0.4 +/- 4.4 cm H2O and collapsed most frequently in the velopharyngeal region. Relative to neutral, Pcrit increased to 3.7 +/- 2.9 cm H2O (P < 0.01) and decreased to -9.4 +/- 3.8 cm H2O (P < 0.01) when the head was flexed and extended, respectively but was unchanged by rotation (-2.6 +/- 3.3 cm H2O; n = 10; P = 0.44). The site of collapse varied, in no consistent pattern, with change in head posture in 5 subjects.ConclusionsHead posture has a marked effect on the collapsibility and site of collapse of the passive upper airway (measured by EMGgg) indicating that controlling head posture during sleep or recovery from anesthesia may alter the propensity for airway obstruction. Further, manipulating head posture during propofol sedation may assist with identification of pharyngeal regions vulnerable to collapse during sleep and may be useful for guiding surgical intervention.

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