title: Tube Law of the Pharyngeal Airway in Sleeping Patients with Obstructive Sleep Apnea.
abstract: OBJECTIVE
  Obstructive sleep apnea (OSA) is characterized by repetitive pharyngeal collapse during sleep. However, the dynamics of pharyngeal narrowing and re-expansion during flow-limited breathing are not well described. The static pharyngeal tube law (end-expiratory area versus luminal pressure) has demonstrated increasing pharyngeal compliance as luminal pressure decreases, indicating that the airway would be sucked closed with sufficient inspiratory effort. On the contrary, the airway is rarely sucked closed during inspiratory flow limitation, suggesting that the airway is getting stiffer. Therefore, we hypothesized that during inspiratory flow limitation, as opposed to static conditions, the pharynx becomes stiffer as luminal pressure decreases.
  
  
  METHODS
  Upper airway endoscopy and simultaneous measurements of airflow and epiglottic pressure were performed during natural nonrapid eye movement sleep. Continuous positive (or negative) airway pressure was used to induce flow limitation. Flow-limited breaths were selected for airway cross-sectional area measurements. Relative airway area was quantified as a percentage of end-expiratory area. Inspiratory airway radial compliance was calculated at each quintile of epiglottic pressure versus airway area plot (tube law).
  
  
  RESULTS
  Eighteen subjects (14 males) with OSA (apnea-hypopnea index = 57 ± 27 events/h), aged 49 ± 8 y, with a body mass index of 35 ± 6 kg/m(2) were studied. A total of 163 flow limited breaths were analyzed (9 ± 3 breaths per subject). Compliances at the fourth (2.0 ± 4.7 % area/cmH2O) and fifth (0.0 ± 1.7 % area/cmH2O) quintiles were significantly lower than the first (12.2 ± 5.5 % area/cmH2O) pressure quintile (P < 0.05).
  
  
  CONCLUSIONS
  The pharyngeal tube law is concave (airway gets stiffer as luminal pressure decreases) during respiratory cycles under inspiratory flow limitation.
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.|Pulmonary Division, Heart Institute (InCor), Hospital das Clínicas, University of São Paulo School of Medicine, São Paulo, Brazil.
authors.forename: Pedro R
authors.initials: PR
authors.lastname: Genta
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.
authors.forename: Bradley A
authors.initials: BA
authors.lastname: Edwards
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.|Department of Allergy Immunology and Respiratory Medicine and Central Clinical School, The Alfred and Monash University, Melbourne, Australia.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Sands
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.
authors.forename: Robert L
authors.initials: RL
authors.lastname: Owens
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.
authors.forename: James P
authors.initials: JP
authors.lastname: Butler
authors.affiliation: Department of Anesthesia, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA.
authors.forename: Stephen H
authors.initials: SH
authors.lastname: Loring
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.
authors.forename: David P
authors.initials: DP
authors.lastname: White
authors.affiliation: Division of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Wellman
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D004825:Epiglottis / Q000503:physiopathology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010614:Pharynx / Q000503:physiopathology*; D011312:Pressure; D012119:Respiration; D012890:Sleep; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology*; D055815:Young Adult
keywords: flow limitation; obstructive sleep apnea; pharyngeal mechanics