Quote:Airway collapse during sleep is both dynamic and passive. Dynamic collapse occurs during inspiration. Passive collapse occurs during expiration. Both are the result of a combination of applied forces that collapse and dilate the airway. In a structurally small airway during sleep, when dilating forces that stabilize the airway are greater than the collapsing forces, the airway is obstructed.

Obstruction during sleep is the result of a complex cascade. During inspiration, upper (pharynx) and lower (chest wall and diaphragm) airway muscles are activated. The lower airway muscles create a negative intraluminal force balanced by upper airway muscles that stiffen and dilate the airway. Increases in negative airway pressure or loss of muscle dilation will obstruct the airway. In sleep-disordered breathing both occur. Increased upper airway resistance leads to more negative intraluminal pressure and activation of upper airway dilator muscles is delayed or decreased. During expiration, positive pressure forces dilate the airway, and upper airway muscle tone is reduced. If the balance is unfavorable and the effects of tissue mass are not compensated, collapse and obstruction occur.

The tipping point for apnea is poorly understood, but is likely initiated by passive expiratory collapse. It is this collapse that triggers the dynamic events during inspiration. Without passive airway collapse, the cascade of progressive inspiratory flow limitation, increased negative luminal pressure and increased upper airway resistance may be aborted. If adequate airway size is maintained during expiration, inspiratory obstruction is prevented.

Since during expiration the largest decreases in airway size occur in the hypopharynx, treatment of this segment may be critical for most if not all individuals with sleep-disordered breathing. The tongue suspension procedure was conceived as a means of providing an extraluminal dilating force to the lower pharyngeal airway in contrast to nasal Continuous Positive Airway Pressure (CPAP) which is an intraluminal dilating force. This is accomplished by passing a submucosal suture into the posterior midline tongue. The suture prevents passive collapse while not interfering with anterior and superior tongue movements which are involved with swallowing and speech. Placement is directed towards the level of the foramen cecum.

Quote:Upper airway obstruction during sleep is characteristically attributed to inspiratory narrowing owing to a collapsing subatmospheric pressure against a hypotonic pharyngeal airway. However, several lines of evidence implicate expiratory narrowing as a possible mechanism of the initial narrowing. First, ventilatory motor output is an important determinant of upper airway patency. Oscillation of ventilatory motor output, during the characteristic periodic breathing of OSA, is associated with pharyngeal narrowing or obstruction at the nadir of the motor output, especially in individuals with a highly collapsible airway. Second, an obstructive apnea is often preceded by expiratory narrowing of the upper airway as evidenced by increased expiratory resistance or progressive expiratory narrowing, detected by fiberoptic imaging. Finally, although upper airway narrowing or occlusion occurs during a spontaneous or induced hypocapnic central apnea or induced hypocapnic hypopnea, pharyngeal narrowing during central hypopnea occurs during the expiratory phase only and is associated with increased expiratory upper airway compliance. Therefore upper airway obstruction may occur in either inspiration or expiration. Individuals with a high surrounding tissue pressure may be particularly susceptible to expiratory pharyngeal narrowing during such low ventilatory motor output and driving pressure.