title: Repeated blood instillation into the airway of the horse does not cause pulmonary fibrosis.
abstract: BACKGROUND
  Exercise-induced pulmonary haemorrhage (EIPH) occurs in nearly all strenuously exercising horses. Recent studies have attempted to identify the role of free blood within the airspaces, in the lung fibrosis that develops within the lungs of EIPH horses.
  
  
  OBJECTIVE
  Repeated exposure of the equine lung to autologous blood results in lung fibrosis similar to that observed in spontaneous EIPH.
  
  
  METHODS
  Forty ml of autologous blood from the jugular vein was instilled into preselected lung regions of 6 horses one, 2, 3, 4 or 5 times at 2 week intervals, with 40 ml of saline instilled into the contralateral lung serving as a control. The time interval between instillation of the first blood and euthanasia ranged from 2-10 weeks. The lung from each instillation site was harvested, and the histopathology was scored from each region based upon the presence and abundance of blood, haemosiderin and interstitial collagen. Consequently, at the time of euthanasia, the time since instillation of the first blood ranged from 2-10 weeks.
  
  
  RESULTS
  Beyond retention of blood, and the accumulation of haemosiderin, there was no visible increase in perivascular and interstitial collagen within the blood-instilled lung sites. In a small number of regions, there were foci of bronchiolitis obliterans organising pneumonia with collagen accumulation within these foci, but no collagen accumulation with the characteristic perivascular and interstitial histological distribution seen in EIPH.
  
  
  CONCLUSIONS
  Free blood within the airways of horses does not result in a qualitative increase in the amount of interstitial collagen within 8-10 weeks, and is therefore an unlikely aetiological factor in the lung collagen accumulation that occurs in EIPH.
  
  
  CONCLUSIONS
  This study emphasises the efficiency of the equine lung in clearing blood from the airspaces. Further, it suggests that the aetiopathogenesis of EIPH is not driven by events within the airspace lumen, but rather emanates from within the vasculature and lung interstitium.
authors.affiliation: Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, USA. will1273@msu.edu
authors.forename: K J
authors.initials: KJ
authors.lastname: Williams
authors.forename: F J
authors.initials: FJ
authors.lastname: Derksen
authors.forename: H L
authors.initials: HL
authors.lastname: Defeijter-Rupp
authors.forename: N E
authors.initials: NE
authors.lastname: Robinson
mesh_terms: D000818:Animals; D001989:Bronchiolitis Obliterans / Q000473:pathology / Q000662:veterinary; D006734:Horse Diseases / Q000473:pathology*; D006736:Horses; D011658:Pulmonary Fibrosis / Q000473:pathology / Q000662:veterinary*