Termination of Respiratory Events with and without Cortical Arousal in Obstructive Sleep Apnea

Abstract

Rationale: A total of 20-30% of respiratory events in obstructive sleep apnea are terminated without clear arousal. Arousals are thought to predispose to further events by promoting hyperventilation, hypocapnia, and upper-airway dilator muscle hypotonia. Therefore, events terminated without arousal may promote stable breathing. Objectives: To compare physiologic changes at respiratory event termination with American Sleep Disorders Association (ASDA) Arousal to No Arousal, and determine whether secondary respiratory events are less common and have higher dilator muscle activity after No Arousal compared with ASDA Arousal. Methods: Patients with obstructive sleep apnea wore sleep staging, genioglossus (EMG GG ), and tensor palatini (EMG TP ) electrodes plus a nasal mask and pneumotachograph. During stable sleep, continuous positive airway pressure (CPAP) was lowered for 3-minute periods to induce respiratory events. Physiologic variables were compared between events terminated with (1) ASDA Arousal, (2) No Arousal, or (3) sudden CPAP increase (CPAPinc, control). Measurements and Main Results: Sixteen subjects had adequate data. EMG GG , EMG TP , and heart rate increased after ASDA Arousal (340 6 57%, 215 6 28%, and 110.7 6 2.3%) and No Arousal (185 6 32%, 167 6 15%, and 108.5 6 1.6%) but not CPAPinc (90 6 10%, 94 6 11%, and 102.1 6 1%). Ventilation increased more after ASDA Arousal than No Arousal and CPAPinc, but not after accounting for the severity of respiratory event. Fewer No Arousals were followed by secondary events than ASDA Arousals. However, low dilator muscle activity did not occur after ASDA Arousal or No Arousal (EMG GG rose from 75 6 5 to 125 6 7%) and secondary events were less severe than initial events (ventilation rose 4 6 0.4 to 5.5 6 0.51 L/min). Conclusions: Respiratory events that were terminated with ASDA Arousal were more severely flow-limited, had enhanced hyperventilation after event termination, and were more often followed by secondary events than No arousal. However, secondary events were not associated with low dilator muscle activity and airflow was improved after both No Arousal and ASDA Arousal.Keywords: pharyngeal muscle activity; upper airway obstruction; genioglossus; tensor palatini; obstructive respiratory event Approximately 20-30% of respiratory events in obstructive sleep apnea (OSA) do not end with clear arousal from sleep (1-4). Whether subcriterion arousals are present or not has been debated in the literature and is not yet resolved (1, 2, 4, 5). However, the presence of cortical arousal results in enhanced hyperventilation on termination of respiratory events (4). This greater hyperventilation is expected to result in hypocapnia and dilator muscle hypotonia on the return to sleep (because dilator muscle activity, and presumably muscle tone, varies proportionately with respiratory drive), predisposing to further airway obstruction. However, whether dilator muscle activity is reduced in this setting has not been assessed.The concept that arousal-induced hyperventilatio...

Arousal Intensity is a Distinct Pathophysiological Trait in Obstructive Sleep Apnea

“…The pattern of changes in minute ventilation and dilator muscle activity following arousal, for both arousal intensity categories, are similar to those previously presented by Jordan and colleagues 9 for ASDA (American Sleep Disorders Association) scored arousals. Increases in ventilation and dilator muscle activity following cortical arousal, according to standard definitions of arousal, have also been reported in other studies.…”

“…2 An unnecessarily large increase in ventilation following arousal can contribute to subsequent hypocapnia, destabilization of the ventilatory control system, and the cyclical breathing pattern that occurs in OSA. 2,8,9 More recently, Azabarzin and colleagues used an…”

Responsiveness of Jaw Motor Activation to Arousals during Sleep in Patients with Obstructive Sleep Apnea Syndrome

“…Moreover, the majority of MAS activations occurred more frequently after respiratory events with arousal response than those without, as previous studies have also reported for the MAS and other craniofacial muscles. [2][3][4]23 Although previous studies have shown that cardiac arousals without visually detectable EEG changes have been detected after respiratory events, 18,21,23,28 these respiratory events were found to be rarely associated with MAS contractions. This is consistent with the findings of the recent studies in which respiratory efforts and electromyography of the tongue muscles were assessed in relation to respiratory events.…”

“…This is consistent with the findings of the recent studies in which respiratory efforts and electromyography of the tongue muscles were assessed in relation to respiratory events. 23,29,30 However, when transient arousals with visually identifiable EEG changes (e.g., mAR, AW) occurred after respiratory events, the MAS was activated. This result supports a previous suggestion of an association between MAS and arousal response.…”

“…[17][18][19][20][21] As there is a hierarchy of arousal responses, 22 motor activation is more frequently observed in response to a higher level of arousals. 14,23 However, the association between MAS contractions and the level of arousals after respiratory events has not been investigated in OSAS patients. In addition, in patients with OSAS, some arousals can be associated with respiratory events, while other arousals are not related to respiratory events.…”