title: Physiological mechanisms of upper airway hypotonia during REM sleep.
abstract: OBJECTIVE
  Rapid eye movement (REM)-induced hypotonia of the major upper airway dilating muscle (genioglossus) potentially contributes to the worsening of obstructive sleep apnea that occurs during this stage. No prior human single motor unit (SMU) study of genioglossus has examined this possibility to our knowledge. We hypothesized that genioglossus SMUs would reduce their activity during stable breathing in both tonic and phasic REM compared to stage N2 sleep. Further, we hypothesized that hypopneas occurring in REM would be associated with coincident reductions in genioglossus SMU activity.
  
  
  METHODS
  The activity of genioglossus SMUs was studied in (1) neighboring epochs of stage N2, and tonic and phasic REM; and (2) during hypopneas occurring in REM.
  
  
  METHODS
  Sleep laboratory.
  
  
  METHODS
  29 subjects (38 ± 13 y) (17 male).
  
  
  METHODS
  Natural sleep, including REM sleep and REM hypopneas.
  
  
  RESULTS
  Subjects slept overnight with genioglossus fine-wire intramuscular electrodes and full polysomnography. Forty-two SMUs firing during one or more of stage N2, tonic REM, or phasic REM were sorted. Twenty inspiratory phasic (IP), 17 inspiratory tonic (IT), and five expiratory tonic (ET) SMUs were characterized. Fewer units were active during phasic REM (23) compared to tonic REM (30) and stage N2 (33). During phasic REM sleep, genioglossus IP and IT SMUs discharged at slower rates and for shorter durations than during stage N2. For example, the SMU peak frequency during phasic REM 5.7 ± 6.6 Hz (mean ± standard deviation) was less than both tonic REM 12.3 ± 9.7 Hz and stage N2 16.1 ± 10.0 Hz (P < 0.001). The peak firing frequencies of IP/IT SMUs decreased from the last breath before to the first breath of a REM hypopnea (11.8 ± 10.9 Hz versus 5.7 ± 9.4 Hz; P = 0.001).
  
  
  CONCLUSIONS
  Genioglossus single motor unit activity is significantly reduced in REM sleep, particularly phasic REM. Single motor unit activity decreases abruptly at the onset of REM hypopneas.
authors.affiliation: Sleep Disorders Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA ; Letterkenny General Hospital, Co. Donegal, Ireland.
authors.forename: David G
authors.initials: DG
authors.lastname: McSharry
authors.affiliation: Neuroscience Research Australia and University of New South Wales, Randwick, Sydney, NSW, Australia.
authors.forename: Julian P
authors.initials: JP
authors.lastname: Saboisky
authors.affiliation: Sleep Disorders Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Pam
authors.initials: P
authors.lastname: Deyoung
authors.affiliation: Sleep Laboratory, Psychological Sciences, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Jordan
authors.affiliation: Sleep Laboratory, Psychological Sciences, The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: John
authors.initials: J
authors.lastname: Trinder
authors.affiliation: Sleep Disorders Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Erik
authors.initials: E
authors.lastname: Smales
authors.affiliation: Sleep Disorders Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Lauren
authors.initials: L
authors.lastname: Hess
authors.affiliation: Dept. of Neurology, Harvard Medical School, Boston, MA.
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Chamberlin
authors.affiliation: Sleep Disorders Research Laboratory, Brigham and Women's Hospital and Harvard Medical School, Boston, MA ; Division of Pulmonary and Critical Care, University of California, San Diego, CA.
authors.forename: Atul
authors.initials: A
authors.lastname: Malhotra
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D009123:Muscle Hypotonia / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D017286:Polysomnography; D012119:Respiration; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D012895:Sleep, REM; D014059:Tongue / Q000503:physiopathology
keywords: Obstructive sleep apnea; genioglossus; rapid eye movement sleep; single motor unit; upper airway hypotonia