Article Text

Upper airway function and arousability to ventilatory challenge in slow wave versus stage 2 sleep in obstructive sleep apnoea
  1. Rajeev Ratnavadivel1,2,
  2. Daniel Stadler1,3,
  3. Samantha Windler1,
  4. Jana Bradley1,
  5. Denzil Paul1,
  6. R Douglas McEvoy1,2,3,
  7. Peter G Catcheside1,2,3
  1. 1Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, Australia
  2. 2School of Medicine, Flinders University of South Australia, Bedford Park, Australia
  3. 3Discipline of Physiology, School of Molecular and Biomedical Science, University of Adelaide, Australia
  1. Correspondence to Dr Peter Catcheside, Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, South Australia 5041, Australia; peter.catcheside{at}


Patients with obstructive sleep apnoea (OSA) have reduced event rates during slow wave sleep (SWS) compared with stage 2 sleep. To explore this phenomenon, ventilatory and arousal timing responses to partial and complete airflow obstruction during SWS versus stage 2 sleep were examined.

Methods Ten patients, mean±SD apnoea–hypopnoea index (AHI) 49.7±16.5 events/h with reduced OSA frequency during SWS (SWS AHI 18.9±14.0 events/h) slept with an epiglottic pressure catheter and nasal mask/pneumotachograph. Patients underwent rapid continuous positive airway pressure (CPAP) dialdowns to three subtherapeutic levels and brief airway occlusions in random order.

Results Post-dialdown, there were marked reductions in peak flow and minute ventilation, and progressive increases in inspiratory effort (p<0.001), but with limited ventilatory recovery and no differences between sleep stages. CPAP versus peak flow relationships on the third and second to last breath pre-arousal were not different between sleep stages. Arousals occurred later and post-dialdown arousal probability was lower during SWS compared with stage 2 sleep, Cox hazard ratio (95% CI) 0.65 (0.48 to 0.88), p=0.006. During SWS occlusions, time to arousal (mean±SEM) was prolonged (23.0±2.6 vs 17.1±1.7 s, p=0.02). Inspiratory effort developed more rapidly (−1.0±0.2 vs −0.6±0.1 cm H2O/s, p=0.019) and was more negative (−28.7±2.7 vs −20.3±1.6 cm H2O, p<0.001) on the breath preceding arousal.

Conclusions Except for a heightened ventilatory drive response during airway occlusion, airway function and ventilatory compensation to ventilatory challenge appear to be similar, but with consistently and substantially delayed arousal responses, in SWS versus stage 2 sleep.

  • Obstructive sleep apnoea
  • sleep stages
  • arousal
  • respiratory physiology
  • continuous positive airway pressure
  • sleep apnoea
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  • See Editorial, p95

  • Supplementary methods are published online only at

  • Linked articles 127860.

  • Funding Lions Medical Research Foundation, Australia (PO Box 253, Greenacres, SA 5086, Australia), National Health and Medical Research Council, Australia (GPO Box 1421, Canberra, ACT, 2601, Australia).

  • Competing interests None.

  • Ethics approval This study was conducted with the approval of the Repatriation General Hospital, Research Ethics Committee.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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