Background: Respiratory and arousal events in sleep are tightly coupled events, with ~80% of respiratory events in obstructive sleep apnoea (OSA) resolving with brief arousal.1 Classic studies show arousals occur at a similar level of peak oesophageal pressure (arousal threshold), independent of the respiratory stimulus (hypoxia, hypercapnia and resistive loads) and despite different time-courses and blood gas status preceding arousal.2 These data strongly support that sensations arising from mechanoreceptor systems and/or increased motor command with augmented breathing effort provide the main stimulus for respiratory arousal in sleep. However, the more precise nature of sensory inputs and the within-breath timing of arousal to increased inspiratory effort remain unclear. This observational study aims to examine the within-breath timing of respiratory arousals and relationships to within-breath changes in inspiratory effort potentially involved in precipitating respiratory arousal in sleep.
Methods: To date, 6 male OSA patients with severe OSA have undergone detailed observational in-laboratory sleep studies. Measurements include conventional sleep signals plus mask/pneumotachograph and oesophageal pressure to assess ventilation and within-breath inspiratory effort breath-by-breath. Following conventional sleep, respiratory and arousal scoring, all apnoea and hypopnoea events associated with arousal from stage 2 sleep were assessed to determine the timing of arousal onset relative to inspiratory effort onset and offset, and the number of arousals commencing in each quartile of inspiratory and expiratory phases of breathing effort.
Results: Arousal onset occurred more frequently during inspiration than expiration at the termination of both apnoea and hypopnoea events (between subject mean±SEM 69.4±14.5%, 172 vs 47 events, Fishers exact test p<0.001 and 72.3 ± 7.1%, 115 vs 73 events, p=0.002 respectively), and occurred most frequently in the first quartile of inspiratory effort (apnoeas; 69/219, 32% Chi² p<0.001, hypopnoeas; 41/188, 22%, p=0.006).
Discussion: These data support that motor output and/or mechanoreceptor inputs stimulated during inspiration provide a key stimulus for respiratory arousal in OSA.