Upper airway function and arousability to ventilatory challenge in slow wave versus stage 2 sleep in obstructive sleep apnoea

Abstract

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, mean6SD apnoeaehypopnoea index (AHI) 49.7616.5 events/h with reduced OSA frequency during SWS (SWS AHI 18.9614.0 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), p¼0.006. During SWS occlusions, time to arousal (mean6SEM) was prolonged (23.062.6 vs 17.161.7 s, p¼0.02). Inspiratory effort developed more rapidly (À1.060.2 vs À0.660.1 cm H 2 O/s, p¼0.019) and was more negative (À28.762.7 vs À20.361.6 cm H 2 O, 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.

Influence of pharyngeal muscle activity on inspiratory negative effort dependence in the human upper airway

“…However, a potential mechanism that could lead to an increased phasic EMG GG activity during Stage 3 would be by an increased tolerance to negative pharyngeal pressure (higher arousal threshold) and, consequently, larger reflex muscle activation. (Ratnavadivel, et al, 2010). By matching analyzed breaths for CPAP level and epiglottic pressure, we believe that sleep stage differences in EMG GG were minimized.…”

Reply: Arousal Threshold in Obstructive Sleep Apnea

“…However, caution is warranted, as current treatments for OSA in both children and adults are often incompletely effective in mitigating sleep-disordered breathing and its consequences, particularly when CPAP compliance is considered. Elevated arousal thresholds in OSA may also be protective via preservation of sleep and facilitation of upper airway muscle activity (8)(9)(10). Thus, it is unclear if elevated arousal thresholds in some patients with OSA are a consequence/adaptive response or a contributor to the disorder.…”

Stable breathing through deeper sleeping

“…In this issue of Thorax , Ratnavadival et al 21 provide an important insight into several critical questions ( see page ). The authors have observed an increase in arousal threshold to respiratory stimuli in slow wave sleep (SWS) compared with stage 2 non-REM sleep.…”