title: An Examination of Methodological Paradigms for Calculating Upper Airway Critical Pressures during Sleep.
abstract: OBJECTIVE
  The goal of this study was to examine different paradigms for determining critical closing pressures (Pcrit). Methods of determining Pcrit were compared, including direct observation of occluded (no flow) breaths versus inferring Pcrit from extrapolated data, and Pcrit generated by aggregating pressure-flow data from multiple runs versus Pcrit averaged across individual pressure-flow runs. The relationship between Pcrit and obstructive sleep apnea (OSA) was examined.
  
  
  METHODS
  A total of 351 participants with and without OSA underwent overnight polysomnography with pressure-flow measurements to determine Pcrit. A series of filters were applied to raw data to provide consistent, objective criteria for determining which data to include in Pcrit calculations. Observed Pcrit values were computed as the mean nasal pressure level at which a subject had at least two breaths with peak inspiratory flow < 50 mL/sec. Extrapolated Pcrit was calculated in two ways: (1) separately for each individual run and then averaged; and (2) using all valid data from individual runs combined into one plot.
  
  
  RESULTS
  Observed Pcrit was calculated in 67% to 69% of participants, a similar or higher proportion of study subjects compared to extrapolated Pcrit values using a ± 3 cm H2O filter. Although raw (unfiltered) extrapolated Pcrit measures were able to be calculated among a greater proportion of participants than filtered, extrapolated Pcrit values, and thus had fewer missing values, they had larger variability. Both extrapolated and observed Pcrit were higher among individuals with OSA compared to those without OSA.
  
  
  CONCLUSIONS
  Observed Pcrit provides a reliable descriptor of hypotonic upper airway collapsibility. Different methods for determining Pcrit were able to distinguish subjects with and without OSA.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: Grace W
authors.initials: GW
authors.lastname: Pien
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: Brendan T
authors.initials: BT
authors.lastname: Keenan
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.|Sleep Center, Children's Hospital of Philadelphia, Philadelphia, PA.
authors.forename: Carole L
authors.initials: CL
authors.lastname: Marcus
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: Bethany
authors.initials: B
authors.lastname: Staley
authors.affiliation: Department of Biostatistics and Epidemiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Ratcliffe
authors.affiliation: Department of Medicine Statistics Core, David Geffen School of Medicine at UCLA, Los Angeles, CA.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Jackson
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: William
authors.initials: W
authors.lastname: Wieland
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Center for Sleep and Circadian Neurobiology, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.|Sleep Medicine Division and Pulmonary and Critical Care Division, Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, PA.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Schwab
mesh_terms: D016022:Case-Control Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010614:Pharynx / Q000503:physiopathology*; D017286:Polysomnography; D011312:Pressure; D012890:Sleep / Q000502:physiology*; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*
keywords: Pcrit; obstructive sleep apnea; pharyngeal collapsibility; sleep-disordered breathing