title: Protective effects of low respiratory frequency in experimental ventilator-associated lung injury.
abstract: OBJECTIVE
  To determine whether ventilator-associated lung hyperinflation injury can be attenuated by a reduction in respiratory frequency.
  
  
  METHODS
  Prospective comparative laboratory investigation.
  
  
  METHODS
  University medical center research laboratory.
  
  
  METHODS
  Male Sprague-Dawley rats.
  
  
  METHODS
  Eight groups of isolated, perfused rat lungs were exposed to cyclic ventilation at different respiratory frequencies and tidal volumes. Each group of six to eight lung preparations was assigned to one of four respiratory frequencies (10, 20, 40, or 80 breaths/min) and one of two tidal volumes (5 or 20 mL.kg). Measurement of capillary filtration coefficient (Kf,c), a sensitive index of lung microvascular permeability and injury, was made at baseline and at 30, 60, and 90 mins of the experimental conditions.
  
  
  RESULTS
  Lungs exposed to 5 mL.kg tidal volume had no elevation in Kf,c at any time point regardless of respiratory frequency. Lungs exposed to 20 mL. kg tidal volume and a respiratory frequency of 80 had significant elevations in Kf,c at all times after baseline compared with lungs exposed to respiratory frequencies of 10, 20, or 40 (0.14 +/- 0.03, 0.16 +/- 0.02, 0.31 +/- 0.05 vs. 0.76 +/- 0.16). Furthermore, the Kf,c at 90 mins was significantly higher than permeability at baseline in this group (1.53 +/- 0.45 vs. 0.12 +/- 0.02 mL.min.cm H2O.100 g of lung tissue).
  
  
  CONCLUSIONS
  Reduction in respiratory frequency to values much lower than normal ameliorated experimental ventilator-induced hyperinflation lung injury as determined by pulmonary capillary filtration coefficient.
authors.affiliation: Department of Emergency Medicine, Louisiana State University Health Sciences Center, 1541 Kings Highway, PO Box 33932, Shreveport, LA 71130-3932, USA. sconrad@lsuhsc.edu
authors.forename: Steven A
authors.initials: SA
authors.lastname: Conrad
authors.forename: Shu
authors.initials: S
authors.lastname: Zhang
authors.forename: Thomas C
authors.initials: TC
authors.lastname: Arnold
authors.forename: L Keith
authors.initials: LK
authors.lastname: Scott
authors.forename: Donna L
authors.initials: DL
authors.lastname: Carden
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D008297:Male; D011175:Positive-Pressure Respiration; D011446:Prospective Studies; D051381:Rats; D017207:Rats, Sprague-Dawley; D012044:Regression Analysis; D012121:Respiration, Artificial / Q000009:adverse effects*; D012128:Respiratory Distress Syndrome / Q000209:etiology* / Q000503:physiopathology / Q000517:prevention & control*; D015656:Respiratory Mechanics; D013990:Tidal Volume