Properties of tissues surrounding the upper airway.

The pathogenesis of obstructive sleep apnea (OSA) remains unknown. However, we are beginning to understand the mechanisms leading to sleep apnea by evaluating the structure and function of the upper airway (UA) and the surrounding soft-tissue structures using sophisticated magnetic-resonance-imaging techniques. Knowledge of the morphology and mechanical behavior of the soft-tissue structures is essential for a complete understanding of the physiology of the UA. Although the tongue and soft palate have been considered the most important UA soft-tissue structures, our data have highlighted the importance of the lateral pharyngeal walls in the mediating UA caliber. We have demonstrated that: (1) during wakefulness, the predominant anatomic abnormality underlying UA narrowing in patients with OSA is thickening of the lateral pharyngeal walls; (2) during respiration, there are significant changes in lateral airway dimensions as well as in the thickness of the lateral walls; and (3) incremental levels of continuous positive airway pressure (CPAP) result in progressive thinning of the lateral pharyngeal walls. The dynamic biomechanical behavior of the lateral pharyngeal walls during wakefulness, sleep, and during apneas needs to be investigated.