title: Expiratory changes in pressure: flow ratio during sleep in patients with sleep-disordered breathing.
abstract: OBJECTIVE
  The size of the upper airway is smallest during sleep, at the end of expiration. This may favor upper-airway collapse in patients with obstructive sleep apnea. In the respiratory cycles preceding obstructive events during sleep, our hypothesis is that upper-airway resistance (UAR) increased earlier during expiration prior to changes occurring during inspiration.
  
  
  METHODS
  We analyzed the pharyngeal pressure-to-flow ratios in order to determine variations in UAR for both inspiration and expiration during stable respiration and the 4 consecutive breaths preceding upper-airway obstructive events in stage 2 sleep. To assess the variation of resistance throughout the within-breath period during stable respiration and the 4 breaths preceding obstructive events, results were expressed as the instantaneous resistance at fixed points 10%, 30%, 50%, 70%, and 90% of time values of inspiration and expiration. Global inspiratory and expiratory UARs during wakefulness and sleep in stable respiration were expressed by the median of instantaneous UAR values.
  
  
  METHODS
  Tertiary-care academic medical center.
  
  
  METHODS
  Eleven patients with moderate to severe sleep-disordered breathing.
  
  
  METHODS
  None.
  
  
  RESULTS
  During stable respiration, both inspiratory and expiratory resistance increased during sleep, compared to values while awake. The difference between inspiratory and expiratory UAR increased when sleep deepened. During the respiratory cycle, the increase in the end-expiratory UAR occurred earlier than during inspiration; during stable respiration, UAR was much aggravated during the last three breaths preceding an obstructive event.
  
  
  CONCLUSIONS
  Increases in the expiratory UAR occurred earlier than during inspiration in the cycles preceding upper-airway collapse in patients with sleep apnea. This finding suggested an important role of the expiratory phase in promoting upper-airway collapse and is in accordance with the inspiratory pharyngeal instability occurring when lowering the expiratory pressure in patients with obstructive sleep apnea.
authors.affiliation: Sleep Federation, Department of Respiratory Medicine, University Hospital, Nice, France. rtamisie@bidmc.harvard.edu
authors.forename: Renaud
authors.initials: R
authors.lastname: Tamisier
authors.forename: Jean Louis
authors.initials: JL
authors.lastname: Pepin
authors.forename: Bernard
authors.initials: B
authors.lastname: Wuyam
authors.forename: Chrystelle
authors.initials: C
authors.lastname: Deschaux
authors.forename: Patrick
authors.initials: P
authors.lastname: Levy
mesh_terms: D000328:Adult; D000403:Airway Resistance / Q000502:physiology; D045853:Exhalation / Q000502:physiology*; D005260:Female; D006801:Humans; D008176:Lung Volume Measurements; D008297:Male; D017286:Polysomnography; D012720:Severity of Illness Index; D012891:Sleep Apnea Syndromes / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D020181:Sleep Apnea, Obstructive / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D012895:Sleep, REM / Q000502:physiology; D014851:Wakefulness / Q000502:physiology