title: Comparison of expiratory isovolume pressure-flow curves with the stop-flow versus the esophageal-balloon method.
abstract: BACKGROUND
  Expiratory isovolume pressure-flow curves allow determination of flow limitation and airway resistance, but obtaining an isovolume pressure-flow curve requires placing an esophageal balloon. The stop-flow method of obtaining isovolume pressure-flow curves is easy and noninvasive.
  
  
  OBJECTIVE
  To compare the stop-flow and esophageal-balloon methods by measuring the differences between the pressures and flows at which flow limitation first occurs.
  
  
  METHODS
  In 5 healthy subjects we used the esophageal-balloon method and the stop-flow method at 25%, 50%, and 75% of vital capacity (VC), and constructed isovolume pressure-flow curves showing the pressure at which the flow became limited during forced expiration.
  
  
  RESULTS
  The mean calculated pleural pressure at flow limitation with the stop-flow method was 2.7 times and 1.6 times that via the esophageal-balloon method at 25% of VC and 50% of VC, respectively. The maximum flow at flow-limitation with the stop-flow technique was 0.7 times and 0.6 times that via the esophageal-balloon method at 25% of VC and 50% of VC, respectively. We also calculated the resistance (the inverse of the slope of the line to the point of flow limitation), but there were large variations in the resistance values, so there was no statistically significant relationship between the stop-flow and esophageal-balloon methods.
  
  
  CONCLUSIONS
  The stop-flow method showed potential to noninvasively obtain isovolume pressure-flow curves.
authors.affiliation: Fischell Department of Bioengineering, University of Maryland, College Park, Maryland 20742, USA. deryacalhan@yahoo.com
authors.forename: Derya C
authors.initials: DC
authors.lastname: Coursey
authors.forename: Steven M
authors.initials: SM
authors.lastname: Scharf
authors.forename: Arthur T
authors.initials: AT
authors.lastname: Johnson
mesh_terms: D000328:Adult; D000403:Airway Resistance; D057785:Catheters; D004947:Esophagus / Q000502:physiology; D006801:Humans; D008176:Lung Volume Measurements / Q000295:instrumentation / Q000379:methods*; D008297:Male; D011312:Pressure; D055815:Young Adult