title: Abbreviated method for assessing upper airway function in obstructive sleep apnea.
abstract: OBJECTIVE
  Previous studies have shown that the level of flow through the upper airway in patients with obstructive sleep apnea (OSA) is determined by the critical closing pressure (Pcrit) and the upstream resistance (RN). We developed a standardized protocol for delineating quasisteady-state pressure-flow relationships for the upper airway from which these variables could be derived. In addition, we investigated the effect of body position and sleep stage on these variables by determining Pcrit and RN, and their confidence intervals (CIs), for each condition.
  
  
  METHODS
  Pressure-flow relationships were constructed in the supine and lateral recumbent positions (nonrapid eye movement [NREM] sleep, n = 10) and in the supine position (rapid eye movement [REM] sleep, n = 5).
  
  
  METHODS
  University Hospital Antwerp, Belgium.
  
  
  METHODS
  Ten obese patients (body mass index, 32.0+/-5.6 kg/m(2)) with severe OSA (respiratory disturbance index, 63.0+/-14.6 events/h) were studied.
  
  
  METHODS
  Pressure-flow relationships were constructed from breaths obtained during a series of step decreases in nasal pressure (34.1+/-6.5 runs over 3.6+/-1.2 h) in NREM sleep and during 7.8+/-2.2 runs over 0.8+/-0.6 h in REM sleep.
  
  
  RESULTS
  Maximal inspiratory airflow reached a steady state in the third through fifth breaths following a decrease in nasal pressure. Analysis of pressure-flow relationships derived from these breaths showed that Pcrit fell from 1.8 (95% CI, -0.1 to 2.7) cm H(2)O in the supine position to -1.1 cm H(2)O (95% CI, -1.8 to 0.4 cm H(2)O; p = 0.009) in the lateral recumbent position, whereas RN did not change significantly. In contrast, no significant effect of sleep stage was found on either Pcrit or RN.
  
  
  CONCLUSIONS
  Our methods for delineating upper airway pressure-flow relationships during sleep allow for multiple determinations of Pcrit within a single night from which small yet significant differences can be discerned between study conditions.
authors.affiliation: Department of Otorhinolaryngology, University Hospital, Antwerp, Belgium. an.boudewijns@uza.uia.ac.be
authors.forename: A
authors.initials: A
authors.lastname: Boudewyns
authors.forename: N
authors.initials: N
authors.lastname: Punjabi
authors.forename: P H
authors.initials: PH
authors.lastname: Van de Heyning
authors.forename: W A
authors.initials: WA
authors.lastname: De Backer
authors.forename: C P
authors.initials: CP
authors.lastname: O'Donnell
authors.forename: H
authors.initials: H
authors.lastname: Schneider
authors.forename: P L
authors.initials: PL
authors.lastname: Smith
authors.forename: A R
authors.initials: AR
authors.lastname: Schwartz
mesh_terms: D000403:Airway Resistance / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D009765:Obesity / Q000150:complications / Q000503:physiopathology; D010991:Plethysmography; D011187:Posture / Q000502:physiology; D011379:Prognosis; D012720:Severity of Illness Index; D012891:Sleep Apnea Syndromes / Q000150:complications / Q000503:physiopathology*; D012895:Sleep, REM / Q000502:physiology