Upper airway collapsibility measured using a simple wakefulness test closely relates to the pharyngeal critical closing pressure during sleep in obstructive sleep apnea

Study Objectives: A collapsible or crowded pharyngeal airway is the main cause of obstructive sleep apnea (OSA). However, quantification of airway collapsibility during sleep (P_crit) is not clinically feasible. The primary aim of this study was to compare upper airway collapsibility using a simple wakefulness test with P_crit during sleep. Methods: Participants with OSA were instrumented with a nasal mask, pneumotachograph and two pressure sensors, one at the choanae (P_CHO), the other just above the epiglottis (P_EPI). Approximately 60 brief (250 ms) pulses of negative airway pressure (~ -12 cmH₂O at the mask) were delivered in early inspiration during wakefulness to measure the upper airway collapsibility index (UACI). Transient reductions in the continuous positive airway pressure (CPAP) holding pressure were then performed during sleep to determine P_crit. In a subset of participants, the optimal number of replicate trials required to calculate the UACI was assessed. Results: The UACI (39 ± 24 mean ± SD; range = 0%-87%) and P_crit (-0.11 ± 2.5; range: -4 to +5 cmH₂O) were quantified in 34 middle-aged people (9 female) with varying OSA severity (apnea-hypopnea index range = 5-92 events/h). The UACI at a mask pressure of approximately -12 cmH₂O positively correlated with P_crit (r = 0.8; p < 0.001) and could be quantified reliably with as few as 10 replicate trials. The UACI performed well at discriminating individuals with subatmospheric P_crit values [receiver operating characteristic curve analysis area under the curve = 0.9 (0.8-1), p < 0.001]. Conclusions: These findings indicate that a simple wakefulness test may be useful to estimate the extent of upper airway anatomical impairment during sleep in people with OSA to direct targeted non-CPAP therapies for OSA.