Rg

FIGURE 7 (See color insert.) Volumetric state-dependent airway imaging in a normal subject using magnetic resonance imaging. Airway volume during sleep is smaller in the retropalatal (RP) region but not the retroglossal (RG) region. Such images suggest that the upper airway during sleep does not narrow as a homogenous tube. Source: From Ref. 138.

FIGURE 7 (See color insert.) Volumetric state-dependent airway imaging in a normal subject using magnetic resonance imaging. Airway volume during sleep is smaller in the retropalatal (RP) region but not the retroglossal (RG) region. Such images suggest that the upper airway during sleep does not narrow as a homogenous tube. Source: From Ref. 138.

TIDAL VOLUME (L)

FIGURE 8 Changes in upper airway area as a function of tidal volume during the respiratory cycle. Airway caliber is relatively constant in inspiration. Airway size increases in early expiration and decreases in late expiration. Source: From Ref. 43.

TIDAL VOLUME (L)

FIGURE 8 Changes in upper airway area as a function of tidal volume during the respiratory cycle. Airway caliber is relatively constant in inspiration. Airway size increases in early expiration and decreases in late expiration. Source: From Ref. 43.

at end-expiration, along with other studies demonstrating apneics events during expiration, has led to the conclusion that airway closure can occur in both inspiration and expiration (23,71,72,142,143).

Nasopharyngoscopy combined with a Müller maneuver has provided an awake simulation of an apnea event when a subject is requested to inspire against a closed mouth and occluded nose. Studying airway narrowing at graded negative intraluminal pressures generated by the subject has reaffirmed that airway collapse is not homogeneous (144). More recent work has demonstrated a good correlation between AHI and retropalatal narrowing during a Müller maneuver (80,81).

It appears based on comparisons between apneic patients and controls that the former have greater decrements in airway dimension during a Müller maneuver suggesting an increased compliance in the apneic upper airway (144). In general, studies examining the dynamic behavior of the upper airway have provided a framework for understanding the pathogenesis of airway closure.

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