Chronic intermittent asphyxia impairs rat upper airway muscle responses to acute hypoxia and asphyxia.
BACKGROUND
Obstructive sleep apnea (OSA) is a major clinical disorder that is characterized by multiple episodes of upper airway obstruction due to the failure of the upper airway dilator muscles to maintain upper airway patency. This results in chronic intermittent asphyxia (CIA) due to repetitive apneas, but very little is known about the effects of CIA on upper airway muscle function.


OBJECTIVE
To test the hypothesis that CIA affects upper airway muscle activity and electromyogram (EMG) responses to acute hypoxia and asphyxia.


METHODS
Record upper airway EMG responses to acute hypoxia and asphyxia in control and CIA-treated rats.


METHODS
Department of Physiology, Royal College of Surgeons in Ireland, Dublin, Ireland.


METHODS
Sternohyoid (SH) muscle and diaphragm (DIA) muscle EMG activities were recorded in both groups during normoxia, hypoxia (7.5% O(2) in N(2)), and asphyxia (7.5% O(2) and 3% CO(2)) under pentobarbitone anesthesia.


RESULTS
Baseline SH EMG activity was significantly elevated in the CIA-treated rats compared to the controls, whereas DIA EMG activity was similar in the two groups. In addition, CIA significantly reduced SH EMG but not DIA EMG responses to acute hypoxia and asphyxia.


CONCLUSIONS
The elevated upper airway muscle activity associated with OSA in humans during wakefulness is due at least in part to CIA. We propose that a reduction in the response of upper airway dilator muscles to acute asphyxia following upper airway obstruction is likely to cause further asphyxic insult, leading to a vicious feed-forward cycle exacerbating the condition. Our results suggest that CIA contributes to the pathophysiology of sleep-disordered breathing.
Department of Human Anatomy and Physiology, University College Dublin, Dublin, Ireland. ken.ohalloran@ucl.ie
Ken D
KD
O'Halloran
Michelle
M
McGuire
Turlough
T
O'Hare
Aidan
A
Bradford
D000704:Analysis of Variance; D000818:Animals; D001237:Asphyxia / Q000150:complications / Q000503:physiopathology*; D003964:Diaphragm / Q000502:physiology*; D004576:Electromyography; D000860:Hypoxia / Q000150:complications / Q000503:physiopathology*; D008297:Male; D051381:Rats; D017208:Rats, Wistar; D020181:Sleep Apnea, Obstructive / Q000209:etiology