title: Low frequency filtering of nasal pressure channel causes loss of flow limitation.
abstract: OBJECTIVE
  The objective of this clinical vignette is to explore whether changes in low filter settings for respiratory waveforms have a clinically significant effect on patient management of obstructive sleep apnea (OSA).
  
  
  METHODS
  This is a case report.
  
  
  METHODS
  We collected data from a continuous positive airway pressure (CPAP) titration polysomnogram (PSG) performed in our university based sleep laboratory. We reviewed the flow signal using low frequency filter settings of 0.0, 0.1, 0.3, and 0.5 Hz.
  
  
  RESULTS
  We noted that a change in the low frequency filter for respiratory flow caused a change in the appearance of an otherwise flattened waveform indicating flow limitation to no longer appear flat.
  
  
  CONCLUSIONS
  We noted that indiscriminate use of the low frequency filter for nasal pressure and flow estimate channels may lead to greater difficulty recognizing respiratory flow limitation.
authors.affiliation: Department of Neurology - Sleep Division, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, USA. robreganw@gmail.com
authors.forename: Robert N
authors.initials: RN
authors.lastname: Walter
authors.forename: Bradley V
authors.initials: BV
authors.lastname: Vaughn
mesh_terms: D045422:Continuous Positive Airway Pressure / Q000379:methods*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009296:Nasal Cavity / Q000502:physiology*; D017286:Polysomnography / Q000379:methods*; D011312:Pressure; D012815:Signal Processing, Computer-Assisted; D020181:Sleep Apnea, Obstructive / Q000503:physiopathology* / Q000628:therapy*