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Upper airway collapsibility, dilator muscle activation and resistance in sleep apnoea

¹ Institute for Breathing and Sleep, Austin Health, Heidelberg, ³ School of Behavioural Sciences, University of Melbourne, Parkville and, ⁴ West Australian Institute for Medical Research, University of Western Australia, Nedlands, Australia, ² Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA.

CORRESPONDENCE: R. Pierce, Institute for Breathing and Sleep, Bowen Centre, Austin Hospital, Heidelberg, Victoria 3084, Australia. Fax: 61 394965124. E-mail: r.pierce{at}medicine.unimelb.edu.au

Keywords: Airway mechanics, airways resistance, muscle function, obstructive sleep apnoea, pharynx

Received: May 11, 2006
Accepted April 11, 2007

The calibre of the upper airway is thought to be dependant upon its passive anatomy/collapsibility and the activation of pharyngeal dilator muscles. During awake periods, the more collapsible upper airway in obstructive sleep apnoea (OSA) increases the dilator muscle activity through a negative-pressure reflex.

A direct correlation between the critical closing pressure (P_crit), as a measure of anatomy/collapsability and electromyogram (EMG) activity of genioglossus EMG (GG-EMG) and tensor palatini EMG (TP-EMG), was hypothesised. The relationship between these indices and pharyngeal resistance (R_phar) was also examined.

The study involved eight males with a mean age of 48 (interquartile range 46–52) yrs with OSA, and an apnoea/hypopnoea index of 75 (65–101)·hr^–1 on two nights breathing normally and on nasal continuous positive airway pressure (nCPAP). The P_crit was measured during nonrapid eye movement sleep on nCPAP using brief, incremental reductions in mask pressure. GG-EMG and TP-EMG were measured breath-by-breath, awake, during sleep onset and on nCPAP. R_phar was measured using airway pressures and flow.

Wakeful GG-EMG, early sleep TP-EMG and the sleep decrement in TP-EMG were directly related to P_crit. Muscle activation was negatively correlated with R_phar for TP-EMG awake and GG-EMG early in sleep.

In conclusion these results confirm that dilator muscle activation is directly related to airway narrowing and reduces resistance across patients with obstructive sleep apnoea.

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