Hypoxia impairs the arousal response to external resistive loading and airway occlusion during sleep.
OBJECTIVE
Sustained hypoxia is a neurocognitive depressant, which has been shown to impair respiratory load sensation. Hypoxia has also been shown to impair arousal in animal models, but the effects of sustained hypoxia on arousal in humans have not been studied. The aim of this study was to assess the effects of sustained hypoxia on arousal from sleep in normal subjects.


METHODS
Twelve normal male subjects (age, 24.3 +/- 1.2 years; body mass index, 24.8 +/- 1.4 kg/m2) were studied during stable stage 2 non-rapid eye movement sleep on 2 separate nights 1 week apart.


METHODS
Sleep physiology laboratory.


METHODS
Normal healthy volunteers.


METHODS
Arousal responses to external resistive loads (18 cm H2O x L(-1) x sec(-1)) and occlusions were compared during room-air breathing following sustained normoxia and isocapnic hypoxia (SaO2 approximately 85%).


RESULTS
Time to arousal and minimum esophageal pressure preceding arousal were measured. Time to arousal was significantly increased following hypoxia compared with normoxia for resistive loads (24.6 + 4.4 seconds vs. 12.6 +/- 1.9 seconds, p = .007) but not occlusions. Minimum esophageal pressure prior to arousal was more negative following hypoxia for both external loads (-16.8 +/- 1.2 vs. -13.5 +/- 1.3 cm H2O, p = .035) and occlusions (-19.6 +/- 2.2 vs. -15.1 +/- 1.5 cm H2O, p = .029).


CONCLUSIONS
We conclude that sustained isocapnic hypoxia delays arousal to inspiratory loading during sleep and increases the respiratory arousal threshold. This has implications for disorders characterized by sustained nocturnal hypoxia, such as neuromuscular weakness, chronic obstructive pulmonary disease, obesity-hypoventilation syndrome, and severe obstructive sleep apnea.
Hlavac
Michael C
MC
Adelaide Institute for Sleep Health, Repatriation General Hospital, Daw Park, South Australia, Australia. michael.hlavac@cdhb.govt.nz
Catcheside
Peter G
PG
McDonald
Rachel
R
Eckert
Danny J
DJ
Windler
Samantha
S
McEvoy
R Doug
RD
D000328:Adult; D000402:Airway Obstruction / Q000175:diagnosis / Q000453:epidemiology*; D001143:Arousal / Q000502:physiology*; D015992:Body Mass Index; D002245:Carbon Dioxide / Q000378:metabolism; D004569:Electroencephalography; D004947:Esophagus / Q000502:physiology; D006801:Humans; D000860:Hypoxia / Q000175:diagnosis* / Q000503:physiopathology*; D008297:Male; D010100:Oxygen / Q000378:metabolism; D011312:Pressure; D012720:Severity of Illness Index; D012894:Sleep Stages / Q000502:physiology*; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen