title: Response of genioglossus muscle to increasing chemical drive in sleeping obstructive apnea patients.
abstract: OBJECTIVE
  Subjects with a collapsible upper airway must activate their pharyngeal dilators sufficiently in response to increasing chemical drive if they are to maintain airway patency without arousal from sleep. Little is known about the response of pharyngeal dilators to increasing chemical drive in these subjects. We wished to determine, in obstructive apnea patients, the response of the genioglossus to increasing chemical drive and the contribution of mechanoreceptor feedback to this response.
  
  
  METHODS
  Physiological study.
  
  
  METHODS
  University-based sleep laboratory.
  
  
  METHODS
  20 patients with obstructive apnea.
  
  
  METHODS
  Genioglossus activity was monitored during overnight polysomnography on optimal continuous positive airway pressure (CPAP). Intermittently, inspired gases were altered to produce different levels of ventilatory stimulation. CPAP was then briefly reduced to 1.0 cm H(2)O (dial-down), inducing an obstruction.
  
  
  RESULTS
  Without mechanoreceptor feedback (i.e., on CPAP) the increase in genioglossus activity as ventilation increased from 6.1 ± 1.4 to 16.1 ± 4.8 L/min was modest (ΔTonic activity 0.3% ± 0.5%maximum; ΔPhasic activity 1.7% ± 3.4%maximum). Genioglossus activity increased immediately upon dial-down, reflecting mechanoreceptor feedback, but only when ventilation before dial-down exceeded a threshold value. This threshold varied among patients and, once surpassed, genioglossus activity increased briskly with further increases in chemical drive (1.1% ± 0.84%GG(MAX) per L/min increase in V(E)).
  
  
  CONCLUSIONS
  In sleeping obstructive apnea patients: (1) Mechanoreceptor feedback is responsible for most of the genioglossus response to chemical drive. (2) Mechanoreceptor feedback is effective only above a threshold chemical drive, which varies greatly among patients. These findings account in part for the highly variable relation between pharyngeal mechanical abnormalities and apnea severity.
authors.affiliation: Sleep Center, Foothills Medical Centre, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Andrea H S
authors.initials: AH
authors.lastname: Loewen
authors.forename: Michele
authors.initials: M
authors.lastname: Ostrowski
authors.forename: John
authors.initials: J
authors.lastname: Laprairie
authors.forename: Frances
authors.initials: F
authors.lastname: Maturino
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Hanly
authors.forename: Magdy
authors.initials: M
authors.lastname: Younes
mesh_terms: D000328:Adult; D000402:Airway Obstruction / Q000503:physiopathology*; D053961:Azabicyclo Compounds / Q000008:administration & dosage; D002245:Carbon Dioxide / Q000008:administration & dosage; D045422:Continuous Positive Airway Pressure / Q000379:methods; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000008:administration & dosage; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000008:administration & dosage; D010609:Pharyngeal Muscles / Q000503:physiopathology*; D010879:Piperazines / Q000008:administration & dosage; D017286:Polysomnography / Q000379:methods / Q000706:statistics & numerical data; D012123:Pulmonary Ventilation / Q000187:drug effects; D012137:Respiratory System / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D013268:Stimulation, Chemical
chemical_list: D053961:Azabicyclo Compounds; D006993:Hypnotics and Sedatives; D010879:Piperazines; C515050:zopiclone; D002245:Carbon Dioxide; D010100:Oxygen