title: The supraglottic effect of a reduction in expiratory mask pressure during continuous positive airway pressure.
abstract: OBJECTIVE
  Patients with obstructive sleep apnea may have difficulty exhaling against positive pressure, hence limiting their acceptance of continuous positive airway pressure (CPAP). C-Flex is designed to improve comfort by reducing pressure in the mask during expiration proportionally to expiratory airflow (3 settings correspond to increasing pressure changes). When patients use CPAP, nasal resistance determines how much higher supraglottic pressure is than mask pressure. We hypothesized that increased nasal resistance results in increased expiratory supraglottic pressure swings that could be mitigated by the effects of C-Flex on mask pressure.
  
  
  METHODS
  Cohort study.
  
  
  METHODS
  Sleep center.
  
  
  METHODS
  Seventeen patients with obstructive sleep apnea/hypopnea syndrome and a mechanical model of the upper airway.
  
  
  METHODS
  In patients on fixed CPAP, CPAP with different C-Flex levels was applied multiple times during the night. In the model, 2 different respiratory patterns and resistances were tested.
  
  
  RESULTS
  Airflow, expiratory mask, and supraglottic pressures were measured on CPAP and on C-Flex. Swings in pressure during expiration were determined. On CPAP, higher nasal resistance produced greater expiratory pressure swings in the supraglottis in the patients and in the model, as expected. C-Flex 3 produced expiratory drops in mask pressure (range -0.03 to -2.49 cm H(2)O) but mitigated the expiratory pressure rise in the supraglottis only during a sinusoidal respiratory pattern in the model.
  
  
  CONCLUSIONS
  Expiratory changes in mask pressure induced by C-Flex did not uniformly transmit to the supraglottis in either patients with obstructive sleep apnea on CPAP or in a mechanical model of the upper airway with fixed resistance. Data suggest that the observed lack of expiratory drop in supraglottic pressure swings is related to dynamics of the C-Flex algorithm.
authors.affiliation: Pulmonary Department, Corporacio Sanitaria Parc Tauli, Universitat Autonoma de Barcelona, Sabadell, Barcelona, Spain.
authors.forename: Maria J
authors.initials: MJ
authors.lastname: Masdeu
authors.forename: Amit V
authors.initials: AV
authors.lastname: Patel
authors.forename: Vijay
authors.initials: V
authors.lastname: Seelall
authors.forename: David M
authors.initials: DM
authors.lastname: Rapoport
authors.forename: Indu
authors.initials: I
authors.lastname: Ayappa
mesh_terms: D015331:Cohort Studies; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation* / Q000379:methods; D004867:Equipment Design; D045853:Exhalation; D005260:Female; D006801:Humans; D008297:Male; D008397:Masks; D008875:Middle Aged; D010256:Paranasal Sinuses; D011312:Pressure; D020181:Sleep Apnea, Obstructive / Q000628:therapy*