Thus, the pharyngeal Pcrit has been found to vary along a spectrum from health (in normal subjects or asymptomatic snorers) to disease (in patients with obstructive hypopneas and apneas). These quantitative differences in Pcrit suggest that obstructive sleep apnea is caused by elevations in pharyngeal collapsibility (Pcrit) during sleep. There is now evidence that elevations in Pcrit are caused by a primary underlying anatomic defect in the pharynx, rather than a disturbance in neuromuscular control. Although the precise nature of this defect is not clear, evidence from animal and human studies suggests that it may be caused by a loss of longitudinal tension within the pharyngeal airway. Such reductions in longitudinal tension can account for development of generalized collapse throughout the pharyngeal airway in apneic patients during sleep. Therapeutic strategies that address the loss of longitudinal tension, rather than the loss of dilating forces, should be targeted in future research studies. In the meantime, routine measurements of the pharynx Pcrit should be made during sleep in apneic patients. These measurement can be used to predict which patients are likely to respond to specific existing treatments when applied singly and in combinations.
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