title: Determination of respiratory system mechanics during inspiration and expiration by FLow-controlled EXpiration (FLEX): a pilot study in anesthetized pigs.
abstract: BACKGROUND
  Differences between inspiratory and expiratory lung mechanics result in the hysteresis of the pressure volume-loop. While hysteresis area is a global parameter describing the difference between inspiration and expiration in mechanics under quasi-static conditions, a detailed analysis of this difference under the dynamic conditions of mechanical ventilation is feasible once inspiratory and expiratory compliance (Cin/Cex) are determined separately. This requires uncoupling of expiratory flow rate and volume (V).
  
  
  METHODS
  Five piglets were mechanically ventilated at positive end-expiratory pressure (PEEP) levels ranging from 0 to 15 cmH2O. Expiratory flow rate was linearized by a computer-controlled resistor (flow-controlled expiration). The volume-dependent Cin(V) and Cex(V) profiles were calculated from the tracheal pressure volume-loops.
  
  
  RESULTS
  The intratidal curve-progression of Cex(V) was altogether higher with a steeper slope compared to Cin(V). With increasing positive end-expiratory pressure (PEEP) dynamic hysteresis area decreased and Cex(V) tended to run more parallel to Cin(V).
  
  
  CONCLUSIONS
  The relation between inspiratory and expiratory compliance profiles is associated with the hysteresis area and behaves PEEP dependent. Analysing the Cin-Cex-relation might therefore potentially offer a new approach to titrate PEEP and tidal volume.
authors.affiliation: Department of Anesthesiology and Critical Care Medicine, University Medical Centre Freiburg, Freiburg, Germany - stefan.schumann@uniklinik-freiburg.de.
authors.forename: S
authors.initials: S
authors.lastname: Schumann
authors.forename: U
authors.initials: U
authors.lastname: Goebel
authors.forename: J
authors.initials: J
authors.lastname: Haberstroh
authors.forename: L
authors.initials: L
authors.lastname: Vimlati
authors.forename: M
authors.initials: M
authors.lastname: Schneider
authors.forename: M
authors.initials: M
authors.lastname: Lichtwarck-Aschoff
authors.forename: J
authors.initials: J
authors.lastname: Guttmann
mesh_terms: D000771:Anesthesia, Intravenous; D000818:Animals; D004867:Equipment Design; D045853:Exhalation / Q000502:physiology*; D001239:Inhalation / Q000502:physiology*; D007649:Ketamine; D008170:Lung Compliance; D009020:Morphine; D010865:Pilot Projects; D011175:Positive-Pressure Respiration; D011312:Pressure; D012121:Respiration, Artificial / Q000295:instrumentation / Q000379:methods*; D034421:Sus scrofa; D013552:Swine; D013990:Tidal Volume
chemical_list: D007649:Ketamine; D009020:Morphine