title: Evaluation of work of breathing in spontaneously breathing animals during partial liquid ventilation.
abstract: BACKGROUND
  Partial liquid ventilation improves lung mechanics and gas exchange in paralyzed mechanically ventilated animals.
  
  
  OBJECTIVE
  Examine the work of breathing (WOB) in a spontaneously breathing animal model during partial liquid ventilation with and without the use of pressure-support ventilation (PSV).
  
  
  METHODS
  This was a prospective study including 6 lambs (mean weight 10.9 +/- 1.3 kg). Baseline measurements, including total work of breathing (WOB(T)), elastic work of breathing (WOB(E)), and resistive work of breathing (WOB(R)), were obtained using pressure-controlled synchronized intermittent mandatory ventilation with positive end-expiratory pressure of 5 cm H(2)O at PSV levels of 0, 5, and 10 cm H(2)O. The animals' lungs were filled with perflubron through an endotracheal tube, in 10-20 mL aliquots, until filled, approximately 30 mL/kg or functional residual capacity. Repeat measurements were obtained at 10 mL/kg, 20 mL/kg, and full. Perflubron was then allowed to evaporate from the lungs and repeat measurements were obtained 3 additional times, with at least a 1 hour separation between phases, for up to 7 hours after the lungs were filled.
  
  
  RESULTS
  No differences were detected in WOB(T), WOB(R), or WOB(E) between the gas-filled lung and the lung filled to functional residual capacity with perflubron. However, compared to the gas-filled lung, WOB(T) and WOB(R) were higher during the filling (p < 0.05) and evaporative phases (p < 0.05). The PSV level affected WOB. Work of breathing was least at PSV 10 cm H(2)O.
  
  
  CONCLUSIONS
  In this pilot study of healthy animals breathing spontaneously with perflubron-filled lungs, there was an acceptable amount of WOB, which decreased with the addition of PSV. However, WOB increased when the perflubron level was not maintained at functional residual capacity.
authors.affiliation: Department of Pediatrics, University of Arkansas for Medical Science, Arkansas Children's Hospital, Little Rock AR 72202, USA. heulittmarkj@uams.edu
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Heulitt
authors.forename: Shirley J
authors.initials: SJ
authors.lastname: Holt
authors.forename: Sterling
authors.initials: S
authors.lastname: Wilson
authors.forename: Pippa
authors.initials: P
authors.lastname: Simpson
mesh_terms: D000403:Airway Resistance; D000818:Animals; D004655:Emulsions; D005466:Fluorocarbons / Q000008:administration & dosage; D006842:Hydrocarbons, Brominated; D021061:Liquid Ventilation; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D012119:Respiration; D012756:Sheep; D014939:Work of Breathing
chemical_list: D004655:Emulsions; D005466:Fluorocarbons; D006842:Hydrocarbons, Brominated; C003072:perflubron