title: Comparative study of four sigmoid models of pressure-volume curve in acute lung injury.
abstract: BACKGROUND
  The pressure-volume curve of the respiratory system is a tool to monitor and set mechanical ventilation in acute lung injury. Mathematical models of the static pressure-volume curve of the respiratory system have been proposed to overcome the inter- and intra-observer variability derived from eye-fitting. However, different models have not been compared.
  
  
  METHODS
  The goodness-of-fit and the values of derived parameters (upper asymptote, maximum compliance and points of maximum curvature) in four sigmoid models were compared, using pressure-volume data from 30 mechanically ventilated patients during the early phase of acute lung injury.
  
  
  RESULTS
  All models showed an excellent goodness-of-fit (R2 always above 0.92). There were significant differences between the models in the parameters derived from the inspiratory limb, but not in those derived from the expiratory limb of the curve. The within-case standard deviations of the pressures at the points of maximum curvature ranged from 2.33 to 6.08 cmH2O.
  
  
  CONCLUSIONS
  There are substantial variabilities in relevant parameters obtained from the four different models of the static pressure-volume curve of the respiratory system.
authors.affiliation: Intensive Care Unit, Hospital Universitario Central de Asturias, Oviedo, Spain. guillermo.muniz@sespa.princast.es
authors.forename: Guillermo M
authors.initials: GM
authors.lastname: Albaiceta
authors.forename: Esteban
authors.initials: E
authors.lastname: Garcia
authors.forename: Francisco
authors.initials: F
authors.lastname: Taboada
mesh_terms: D000403:Airway Resistance; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D005260:Female; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011312:Pressure; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000175:diagnosis / Q000503:physiopathology*; D012680:Sensitivity and Specificity