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Sleep. 2017 Nov 1;40(11). doi: 10.1093/sleep/zsx160.

The Influence of CO2 on Genioglossus Muscle After-Discharge Following Arousal From Sleep.

Author information

1
Melbourne School of Psychological Sciences, University of Melbourne, Parkville, Victoria, Australia.
2
Institute for Breathing and Sleep and Austin Health, Heidelberg, Victoria, Australia.
3
Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia.

Abstract

Objectives:

Ventilatory after-discharge (sustained elevation of ventilation following stimulus removal) occurs during sleep but not when hypocapnia is present. Genioglossus after-discharge also occurs during sleep, but CO2 effects have not been assessed. The relevance is that postarousal after-discharge may protect against upper airway collapse. This study aimed to determine whether arousal elicits genioglossus after-discharge that persists into sleep, and whether it is influenced by CO2.

Methods:

Twenty-four healthy individuals (6 female) slept with a nasal mask and ventilator. Sleep (EEG, EOG, EMG), ventilation (pneumotachograph), end-tidal CO2 (PETCO2), and intramuscular genioglossus EMG were monitored. NREM eucapnia was determined during 5 minutes on continuous positive airway pressure (4 cmH2O). Inspiratory pressure support was increased until PETCO2 was ≥2 mm Hg below NREM eucapnia. Supplemental CO2 was added to reproduce normocapnia, without changing ventilator settings. Arousals were induced by auditory tones and genioglossus EMG compared during steady-state hypocapnia and normocapnia.

Results:

Eleven participants (4 female) provided data. Prearousal PETCO2 was less (p < .05) during hypocapnia (40.74 ± 2.37) than normocapnia (43.82 ± 2.89), with differences maintained postarousal. After-discharge, defined as an increase in genioglossus activity above prearousal levels, occurred following the return to sleep. For tonic activity, after-discharge lasted four breaths irrespective of CO2 condition. For peak activity, after-discharge lasted one breath during hypocapnia and 6 breaths during normocapnia. However, when peak activity following the return to sleep was compared between CO2 conditions no individual breath differences were observed.

Conclusions:

Postarousal genioglossal after-discharge may protect against upper airway collapse during sleep. Steady-state CO2 levels minimally influence postarousal genioglossus after-discharge.

KEYWORDS:

OSA; OSA-pathogenesis; arousal; breathing control; carbon dioxide; hyperventilation; hypocapnia; normocapnia; pharyngeal muscles; respiratory physiology; upper airway; upper airway collapse

PMID:
29029284
DOI:
10.1093/sleep/zsx160
[Indexed for MEDLINE]

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