title: Airway dilator muscle activity and lung volume during stable breathing in obstructive sleep apnea.
abstract: OBJECTIVE
  Many patients with obstructive sleep apnea (OSA) have spontaneous periods of stable flow limited breathing during sleep without respiratory events or arousals. In addition, OSA is often more severe during REM than NREM and more severe during stage 2 than slow wave sleep (SWS). The physiological mechanisms for these observations are unknown. Thus we aimed to determine whether the activity of two upper airway dilator muscles (genioglossus and tensor palatini) or end-expiratory lung volume (EELV) differ between (1) spontaneously occurring stable and cyclical breathing and (2) different sleep stages in OSA.
  
  
  METHODS
  Physiologic observation.
  
  
  METHODS
  Sleep physiology laboratory.
  
  
  METHODS
  15 OSA patients with documented periods of spontaneous stable breathing.
  
  
  METHODS
  Subjects were instrumented with intramuscular electrodes for genioglossus and tensor palatini electromyograms (EMG(GG) and EMG(TP)), chest and abdominal magnetometers (EELV measurement), an epiglottic pressure catheter (respiratory effort), and a mask and pneumotachograph (airflow/ventilation). Patients slept supine overnight without CPAP.
  
  
  RESULTS
  Peak and Tonic EMG(GG) were significantly lower during cyclical (85.4 +/- 2.7 and 94.6 +/- 4.7 % total activity) than stable breathing (109.4 +/- 0.4 and 103 +/- 0.8% total activity, respectively). During respiratory events in REM, tonic EMG(GG) activity was lower than during respiratory events in stage 2 (71.9 +/- 5.1 and 119.6 +/- 5.6% total activity). EMG(GG) did not differ between stable stage 2 and stable SWS (98.9 +/- 3.2 versus 109.7 +/- 4.4% total activity), nor did EMG(TP) or EELV differ in any breathing condition/sleep stage.
  
  
  CONCLUSIONS
  Increased genioglossus muscle tone is associated with spontaneous periods of stable flow limited breathing in the OSA subjects studied. Reductions in genioglossus activity during REM may explain the higher severity of OSA in that stage. Increased lung volume and tensor palatini activity do not appear to be major mechanisms enabling spontaneous stable flow limited breathing periods.
authors.affiliation: Division of Sleep Medicine, Harvard Medical School, Boston, MA, USA. ajordan@rics.bwh.harvard.edu
authors.forename: Amy S
authors.initials: AS
authors.lastname: Jordan
authors.forename: David P
authors.initials: DP
authors.lastname: White
authors.forename: Yu-Lun
authors.initials: YL
authors.lastname: Lo
authors.forename: Andrew
authors.initials: A
authors.lastname: Wellman
authors.forename: Danny J
authors.initials: DJ
authors.lastname: Eckert
authors.forename: Susie
authors.initials: S
authors.lastname: Yim-Yeh
authors.forename: Matthias
authors.initials: M
authors.lastname: Eikermann
authors.forename: Scott A
authors.initials: SA
authors.lastname: Smith
authors.forename: Karen E
authors.initials: KE
authors.lastname: Stevenson
authors.forename: Atul
authors.initials: A
authors.lastname: Malhotra
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology*; D004576:Electromyography; D005105:Expiratory Reserve Volume / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009129:Muscle Tonus / Q000502:physiology; D009130:Muscle, Smooth / Q000503:physiopathology*; D017286:Polysomnography; D012123:Pulmonary Ventilation / Q000502:physiology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*; D012895:Sleep, REM / Q000502:physiology*