P36 The upper airway is most collapsible during expiration in obstructive sleep apnoea
Osman A[1,2], Butler J[2], Gandevia S[2] and Eckert D[1,2]
- CRC for Alertness, Safety and Productivity, Melbourne. Vic, Australia
- NeurA, Sydney, New South Wales, Australia
Introduction: Upper airway collapsibility is an important contributor to obstructive sleep apnoea (OSA) pathogenesis. Pharyngeal dilator muscle activity varies throughout the respiratory cycle and may contribute to dynamic changes in airway collapsibility. We have recently shown that an awake test of upper airway collapsibility correlates with upper airway collapsibility during sleep (r=0.8, n=34)1 in OSA. However, whether upper airway collapsibility varies throughout the respiratory cycle is unknown. This study aimed to quantify differences in airway collapsibility and pharyngeal muscle activity during different phases of the respiratory cycle.
Methods: 12 people with OSA (2 female) were equipped with standard polysomnography equipment, a nasal mask, pneumotachograph, two fine-wire intramuscular electrodes into the genioglossus muscle plus epiglottic and choanal pressure catheters. The upper airway collapsibility index (UACI) was quantified as: 100* (choanal-epiglottic pressure)/choanal pressure to brief pulses of negative airway pressure (~-11 cmH2O). ~15 pulses were delivered every 2-8 breaths during each of the following 4 conditions: 1) early-inspiration, 2) mid-inspiration, 3) early-expiration and 4) mid-expiration. Mean genioglossus EMG, 100ms prior to pulse delivery was quantified.
Results: Genioglossus EMG activity varied throughout the respiratory cycle (e.g. mid-expiration was 77±26 whereas mid-inspiration was 126±39% of the early inspiration value, p<0.01). Similarly, upper airway collapsibility changed throughout the respiratory cycle (UACI during early-inspiration=44±26, mid-inspiration=29±18, early-expiration=82±20, mid-expiration=94±13%, <0.01).
Discussion: Upper airway collapsibility varies throughout the respiratory cycle. Indeed, the upper airway is more than 3x more collapsible during mid-expiration compared to mid-inspiration. These findings provide insight into the mechanisms of pharyngeal collapse in OSA.
- Osman A NC, Carberry JC, Burke P, Wijesuriya N, Tong B, Grunstein R, Eckert DJ. Awake upper airway collapsibility is related to airway collapsibility during sleep (Pcrit) in obstructive sleep apnea. Journal of sleep research. 2016;25(2).