Collapsibility of the human upper airway: the influence of state, posture and instrumentation

    Research output: ThesisDoctoral Thesis

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    [Truncated] Background. Obstructive sleep apnoea (OSA) is a common condition characterized by recurrent partial or complete collapse of the upper airway (UA) during sleep. Individual predisposition to OSA is quantified by measurement of UA collapsibility. The pharyngeal critical pressure (the pressure at which the UA collapses, Pcrit) is a gold standard measure of this. Pcrit is determined by manipulating applied pressure to induce varying degrees of inspiratory flow-limitation. Ideally, inspiratory flowlimitation is identified using measurement of oesophageal pressure (Pes), which requires a transducer catheter to traverse the UA. However, it is possible that the presence of such a catheter could alter the mechanical behaviour and collapsibility of the UA. Apart from this technical issue, the Pcrit technique is inherently difficult to perform during sleep as altering applied pressure often results in measurementinduced arousals. This is not an issue during general anaesthesia, which provides ideal conditions under which to study UA collapsibility as arousals are suppressed, muscle activation is minimised and other known modifiers, such as head posture, can be controlled while still maintaining spontaneous ventilation. Given these advantages, there is a case for using anaesthesia to characterise an individual’s UA collapsibility. However, it is important to know how such measures equate to those made during sleep. To date this relationship has been inferred by relating easily obtained indirect sleep measures of collapsibility (e.g. apnoea hypopnoea index, AHI) to anaesthesia Pcrit measures. As yet no study has compared UA collapsibility during anaesthesia and sleep using the same metric (i.e. Pcrit). Furthermore while the anaesthesia model has been used to demonstrate the effect of head posture on UA collapsibility, the effect during sleep has yet to be investigated.

    Aims. The aims of the studies described in this thesis were to utilise two distinct states of human consciousness, namely sleep and general anaesthesia, to examine: (i) the effect of Pes monitoring on UA collapsibility; (ii) the mechanisms underlying the state dependent differences in UA collapsibility; and (iii) the effect of head posture on UA collapsibility.

    Original languageEnglish
    QualificationDoctor of Philosophy
    • Walsh, Jen, Supervisor
    • Hillman, David, Supervisor
    • Eastwood, Peter, Supervisor
    Publication statusUnpublished - Apr 2015


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