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Lung volume and collapsibility of the passive pharynx in patients with sleep-disordered breathing

¹Department of Anesthesiology (B1), Graduate School of Medicine, Chiba University, Chuo-ku, Chiba, Japan; and ²Department of Medicine, Faculty of Medicine, University of Calgary, Calagry, Alberta, Canada

Submitted 7 January 2007 ; accepted in final form 22 June 2007

Lung volume dependence of pharyngeal airway patency suggests involvement of lung volume in pathogenesis of obstructive sleep apnea. We examined the structural interaction between passive pharyngeal airway and lung volume independent of neuromuscular factors. Static mechanical properties of the passive pharynx were compared before and during lung inflation in eight anesthetized and paralyzed patients with sleep-disordered breathing. The respiratory system volume was increased by applying negative extrathoracic pressure, thereby leaving the transpharyngeal pressure unchanged. Application of –50-cmH₂O negative extrathoracic pressure produced an increase in lung volume of 0.72 (0.63–0.91) liter [median (25–75 percentile)], resulting in a significant reduction of velopharyngeal closing pressure of 1.22 (0.14–2.03) cmH₂O without significantly changing collapsibility of the oropharyngeal airway. Improvement of the velopharyngeal closing pressure was directly associated with body mass index. We conclude that increase in lung volume structurally improves velopharyngeal collapsibility particularly in obese patients with sleep-disordered breathing.

obstructive sleep apnea; pathophysiology; upper airway; closing pressure

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