title: A sigmoidal fit for pressure-volume curves of idiopathic pulmonary fibrosis patients on mechanical ventilation: clinical implications.
abstract: OBJECTIVE
  Respiratory pressure-volume curves fitted to exponential equations have been used to assess disease severity and prognosis in spontaneously breathing patients with idiopathic pulmonary fibrosis. Sigmoidal equations have been used to fit pressure-volume curves for mechanically ventilated patients but not for idiopathic pulmonary fibrosis patients. We compared a sigmoidal model and an exponential model to fit pressure-volume curves from mechanically ventilated patients with idiopathic pulmonary fibrosis.
  
  
  METHODS
  Six idiopathic pulmonary fibrosis patients and five controls underwent inflation pressure-volume curves using the constant-flow technique during general anesthesia prior to open lung biopsy or thymectomy. We identified the lower and upper inflection points and fit the curves with an exponential equation, V = A-B.e-k.P, and a sigmoid equation, V = a+b/(1+e-(P-c)/d).
  
  
  RESULTS
  The mean lower inflection point for idiopathic pulmonary fibrosis patients was significantly higher (10.5 ± 5.7 cm H2O) than that of controls (3.6 ± 2.4 cm H₂O). The sigmoidal equation fit the pressure-volume curves of the fibrotic and control patients well, but the exponential equation fit the data well only when points below 50% of the inspiratory capacity were excluded.
  
  
  CONCLUSIONS
  The elevated lower inflection point and the sigmoidal shape of the pressure-volume curves suggest that respiratory system compliance is decreased close to end-expiratory lung volume in idiopathic pulmonary fibrosis patients under general anesthesia and mechanical ventilation. The sigmoidal fit was superior to the exponential fit for inflation pressure-volume curves of anesthetized patients with idiopathic pulmonary fibrosis and could be useful for guiding mechanical ventilation during general anesthesia in this condition.
authors.affiliation: Divisão de Pneumologia, Instituto do Coração, Faculdade de Medicina, Universidade de São Paulo, Brazil. julianacarvalhoferreira@gmail.com
authors.forename: Juliana C
authors.initials: JC
authors.lastname: Ferreira
authors.forename: Fabio E M
authors.initials: FE
authors.lastname: Benseñor
authors.forename: Marcelo J J
authors.initials: MJ
authors.lastname: Rocha
authors.forename: Joao M
authors.initials: JM
authors.lastname: Salge
authors.forename: R Scott
authors.initials: RS
authors.lastname: Harris
authors.forename: Atul
authors.initials: A
authors.lastname: Malhotra
authors.forename: Ronaldo A
authors.initials: RA
authors.lastname: Kairalla
authors.forename: Robert M
authors.initials: RM
authors.lastname: Kacmarek
authors.forename: Carlos R R
authors.initials: CR
authors.lastname: Carvalho
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D054990:Idiopathic Pulmonary Fibrosis / Q000503:physiopathology*; D008168:Lung / Q000503:physiopathology*; D008176:Lung Volume Measurements / Q000379:methods; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D015656:Respiratory Mechanics / Q000502:physiology*