title: Short-term potentiation in the control of pharyngeal muscles in obstructive apnea patients.
abstract: OBJECTIVE
  To determine if activation of the genioglossus (GG) muscle during obstructive apnea events involves short-term potentiation (STP) and is followed by sustained activation beyond the obstructive phase (after-discharge).
  
  
  METHODS
  Physiological study.
  
  
  METHODS
  Sleep laboratory in a tertiary hospital.
  
  
  METHODS
  Twenty-one patients with obstructive apnea.
  
  
  METHODS
  Polysomnography on continuous positive airway pressure (CPAP) with measurement of genioglossus activity. Brief dial-downs of CPAP to induce obstructive events.
  
  
  RESULTS
  Peak, phasic, and tonic genioglossus activities were measured breath-by-breath before, during, and following three-breath obstructions. Tonic but not phasic activity increased immediately following the first obstructed breath (4.9 ± 1.6 versus 3.6 ± 1.2 %GGMAX; P = 0.01) under conditions where stimuli to genioglossus activation were likely constant, strongly implicating STP in mediating recruitment of tonic activity. Both phasic and tonic activities declined slowly after relief of obstruction (after-discharge). Decay time constants were systematically shorter for phasic than for tonic activity (7.5 ± 3.8 versus 18.1 ± 8.4 sec; P < 0.001). Decay time-constant of peak activity correlated with tonic, but not phasic, recruitment. Cortical arousal near the end of obstruction resulted in a lower after-discharge (P < 0.01). Contribution of tonic activity to the increase in peak activity (6-65%Peak), as well as the decay constant (6-30 sec), varied considerably among patients.
  
  
  CONCLUSIONS
  Short-term potentiation contributes to recruitment of the genioglossus during obstructive episodes and results in sustained tonic activity beyond the obstructive phase, thereby potentially preventing recurrence of obstruction. Wide response differences among subjects suggest that this mechanism may contribute to severity of the disorder. The after-discharge is inhibited following cortical arousal, potentially explaining arousals' destabilizing effect.
authors.affiliation: Sleep Disorders Centre, Misericordia Health Centre, Winnipeg, Manitoba, Canada ; Sleep Centre, Foothills Medical Centre, University of Calgary, Calgary, Canada.
authors.forename: Magdy
authors.initials: M
authors.lastname: Younes
authors.affiliation: Sleep Centre, Foothills Medical Centre, University of Calgary, Calgary, Canada.
authors.forename: Andrea
authors.initials: A
authors.lastname: Loewen
authors.affiliation: Sleep Centre, Foothills Medical Centre, University of Calgary, Calgary, Canada.
authors.forename: Michele
authors.initials: M
authors.lastname: Ostrowski
authors.affiliation: Sleep Centre, Foothills Medical Centre, University of Calgary, Calgary, Canada.
authors.forename: Patrick
authors.initials: P
authors.lastname: Hanly
mesh_terms: D000328:Adult; D000818:Animals; D001143:Arousal / Q000502:physiology; D002415:Cats; D045422:Continuous Positive Airway Pressure; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D010609:Pharyngeal Muscles / Q000294:innervation* / Q000502:physiology* / Q000503:physiopathology; D017286:Polysomnography; D012123:Pulmonary Ventilation; D012890:Sleep / Q000502:physiology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D013997:Time Factors; D014059:Tongue / Q000502:physiology
keywords: after-discharge; arousal; instability in obstructive apnea; phenotyping