title: Upper Airway Collapsibility (Pcrit) and Pharyngeal Dilator Muscle Activity are Sleep Stage Dependent.
abstract: OBJECTIVE
  An anatomically narrow/highly collapsible upper airway is the main cause of obstructive sleep apnea (OSA). Upper airway muscle activity contributes to airway patency and, like apnea severity, can be sleep stage dependent. Conversely, existing data derived from a small number of participants suggest that upper airway collapsibility, measured by the passive pharyngeal critical closing pressure (Pcrit) technique, is not sleep stage dependent. This study aimed to determine the effect of sleep stage on Pcrit and upper airway muscle activity in a larger cohort than previously tested.
  
  
  METHODS
  Pcrit and/or muscle data were obtained from 72 adults aged 20-64 y with and without OSA.Pcrit was determined via transient reductions in continuous positive airway pressure (CPAP) during N2, slow wave sleep (SWS) and rapid eye movement (REM) sleep. Genioglossus and tensor palatini muscle activities were measured: (1) awake with and without CPAP, (2) during stable sleep on CPAP, and (3) in response to the CPAP reductions used to quantify Pcrit.
  
  
  RESULTS
  Pcrit was 4.9 ± 1.4 cmH2O higher (more collapsible) during REM versus SWS (P = 0.012), 2.3 ± 0.6 cmH2O higher during REM versus N2 (P < 0.001), and 1.6 ± 0.7 cmH2O higher in N2 versus SWS (P = 0.048). Muscle activity decreased from wakefulness to sleep and from SWS to N2 to REM sleep for genioglossus but not for tensor palatini. Pharyngeal muscle activity increased by ∼50% by breath 5 following CPAP reductions.
  
  
  CONCLUSIONS
  Upper airway collapsibility measured via the Pcrit technique and genioglossus muscle activity vary with sleep stage. These findings should be taken into account when performing and interpreting "passive" Pcrit measurements.
authors.affiliation: Neuroscience Research Australia (NeuRA) and the School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Jayne C
authors.initials: JC
authors.lastname: Carberry
authors.affiliation: Melbourne School of Psychological Sciences, University of Melbourne, Parkville and Institute for Breathing and Sleep, Austin Health, Heidelberg, Victoria, Australia.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Jordan
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: David P
authors.initials: DP
authors.lastname: White
authors.affiliation: Division of Sleep Medicine, Brigham and Women's Hospital and Harvard Medical School, Boston, MA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Wellman
authors.affiliation: Neuroscience Research Australia (NeuRA) and the School of Medical Sciences, University of New South Wales, Sydney, New South Wales, Australia.
authors.forename: Danny J
authors.initials: DJ
authors.lastname: Eckert
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D045422:Continuous Positive Airway Pressure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010609:Pharyngeal Muscles / Q000503:physiopathology*; D010614:Pharynx / Q000503:physiopathology; D011312:Pressure; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D012894:Sleep Stages / Q000502:physiology*; D012895:Sleep, REM; D014059:Tongue / Q000503:physiopathology; D014851:Wakefulness; D055815:Young Adult
keywords: airway anatomy; electromyography; sleep disordered breathing; upper airway physiology