Upper-airway collapsibility: measurements and sleep effects

Abstract

Study objectives: Obstructive sleep apnea (OSA) is characterized by repetitive pharyngeal collapse during sleep. Several techniques have been proposed to assess the collapsibility of the upper airway in awake humans, but sleep-wake comparisons have rarely been attempted and there are few studies comparing OSA patients to control subjects. We sought to compare two collapsibility measurement techniques between normal and apneic subjects, and between wakefulness and sleep.

Design: We conducted three studies. First, we examined whether collapsibility assessed by negative pressure pulses (NPPs) during wakefulness reflected values during sleep in 21 normal subjects. Second, we determined in these normal subjects whether collapsibility during sleep assessed by NPPs was predictive of collapsibility measured by inspiratory resistive loading (IRL). Finally, we compared upper-airway collapsibility between apnea patients (n = 22) and normal volunteers (n = 38) during wakefulness by NPPs.

Setting: Clinical and research laboratories at the Brigham and Women's Hospital.

Participants: Two populations of normal subjects (n = 21 and n = 38) and OSA patients (n = 22).

Measurements and results: Collapsibility during wakefulness, as measured by NPPs, correlated significantly with collapsibility during sleep (r = 0.62; p = 0.003). There was also a significant correlation between the two measures of collapsibility (IRL and NPP) during sleep (r = 0.53; p = 0.04). Both measures revealed a significant increase in pharyngeal collapsibility during sleep as compared to wakefulness. Finally, apnea patients had significantly greater pharyngeal collapsibility than control subjects during wakefulness (p = 0.017).

Conclusions: These data suggest that upper-airway collapsibility measured during wakefulness does provide useful physiologic information about pharyngeal mechanics during sleep and demonstrates clear differences between individuals with and without sleep apnea.

Figure 1

Examples of individual subject's NPP determination of collapsibility. The “collapsible” subject has minimal pressure transmission from the choanae (Cho) to the epiglottis (Epi), whereas in the “noncollapsible” subject, essentially all of the pressure is transmitted from the choanae to the epiglottis.

Figure 2

Comparison of pharyngeal collapsibility during wakefulness between apneic patients and control subjects, all in the supine posture. Pharyngeal collapsibility is calculated as the pressure difference between the choanal and the epiglottic levels (during administration of brief NPPs), as a percentage of applied pressure (see text). The apnea patients had significantly greater collapsibility than control subjects (p < 0.05 between groups). The horizontal line represents the mean value for each group.

Figure 3

Correlation between two different measures of upper-airway collapsibility during sleep in control subjects. The NPP technique uses the pressure drop between the choanae and epiglottis, while the Rph index uses the induced Rph observed during IRL. See text for complete definitions of collapsibility indexes.