title: The spontaneous breathing pattern and work of breathing of patients with acute respiratory distress syndrome and acute lung injury.
abstract: BACKGROUND
  The spontaneous breathing pattern and its relationship to compliance, resistance, and work of breathing (WOB) has not been examined in patients with acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). Clinically, the ratio of respiratory frequency to tidal volume (f/VT) during spontaneous breathing may reflect adaptation to altered compliance, resistance, and increased WOB. We examined the relationship between f/VT, WOB, and respiratory system mechanics in patients with ARDS/ALI.
  
  
  METHODS
  Data from spontaneous breathing trials were collected from 33 patients (20 with ARDS, 13 with ALI) at various points in their disease course. WOB and respiratory system mechanics were measured with a pulmonary mechanics monitor that incorporates Campbell diagram software. Differences between the patients with ARDS and ALI were assessed with 2-sided unpaired t tests. Multivariate linear regression models were constructed to assess the relationship between f/VT and other pulmonary-related variables.
  
  
  RESULTS
  Patients with ARDS had significantly lower compliance than those with ALI (24 +/- 6 mL/cm H2O vs 40 +/- 13 mL/cm H2O, respectively, p < 0.001), but this did not translate into significant differences in either WOB (1.70 +/- 0.59 J/L vs 1.43 +/- 0.90 J/L, respectively, p = 0.30) or f/VT (137 +/- 82 vs 107 +/- 49, respectively, p = 0.23). Multivariate linear regression modeling revealed that peak negative esophageal pressure, central respiratory drive, duration of ARDS/ALI, minute ventilation deficit between mechanical ventilation and spontaneous breathing, and female gender were the strongest predictors of f/VT.
  
  
  CONCLUSIONS
  The characteristic rapid shallow breathing pattern in patients with ARDS/ALI occurs in the context of markedly diminished compliance, elevated respiratory drive, and increased WOB. That f/VT had a strong, inverse relationship to peak negative esophageal pressure also may reflect the influence of muscle weakness.
authors.affiliation: Critical Care Division, Department of Anesthesia, University of California, San Francisco General Hospital, NH: GA-2, 1001 Potrero Avenue, San Francisco CA 94110, USA. rkallet@sfghsom.ucsf.edu
authors.forename: Richard H
authors.initials: RH
authors.lastname: Kallet
authors.forename: J Claude
authors.initials: JC
authors.lastname: Hemphill
authors.forename: Rochelle A
authors.initials: RA
authors.lastname: Dicker
authors.forename: James A
authors.initials: JA
authors.lastname: Alonso
authors.forename: Andre R
authors.initials: AR
authors.lastname: Campbell
authors.forename: Robert C
authors.initials: RC
authors.lastname: Mackersie
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Katz
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008170:Lung Compliance / Q000502:physiology; D008297:Male; D008451:Maximal Voluntary Ventilation / Q000502:physiology; D008875:Middle Aged; D012119:Respiration; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D013990:Tidal Volume / Q000502:physiology; D014481:United States; D014939:Work of Breathing / Q000502:physiology*