Repeated blood instillation into the airway of the horse does not cause pulmonary fibrosis.

The research investigates whether repeated blood exposure in a horse’s airways causes lung fibrosis, a particular concern for exercise-induced pulmonary haemorrhage (EIPH), a condition found in almost all strenuously exercising horses. The researchers found that contrary to some theories, blood exposure doesn’t cause collagen buildup, a marker of fibrosis, within an 8-10 week timeframe.

Introduction and Objective

• The paper focuses on Exercise-induced pulmonary haemorrhage (EIPH), a common occurrence in horses that undergo strenuous exercise.
• The hypothesis put forward was that repeated exposure of the equine lung to autologous blood may cause lung fibrosis that resembles the fibrosis observed in spontaneous EIPH.

Methods

• Forty milliliters of autologous blood, blood coming from the same individual, was instilled in specific lung regions of six horses either 1, 2, 3, 4, or 5 times, with a gap of two weeks between each procedure.
• This method allowed researchers to simulate the process of EIPH in a controlled manner.
• A control group had saline solution instilled in the counterpart lung regions.
• The first procedure to euthanasia ranged from 2-10 weeks.
• Post-euthanasia, the area around each instillation site was harvested. Histopathology then scored the regions based on the presence and degree of blood, haemosiderin (a byproduct of blood degradation), and interstitial collagen (a marker of fibrosis).

Results

• Except for blood retention and haemosiderin accumulation, the researchers found no notable increase in perivascular and interstitial collagen within the blood-instilled lung sites.
• Certain regions showed occurrences of bronchiolitis obliterans organising pneumonia along with some amount of collagen accumulation within these focal points.
• However, the article notes that they didn’t find any significant collagen accumulation characteristically associated with EIPH.

Conclusions

• The authors concluded that free blood within the horse’s airways does not result in a qualitative increase in the interstitial collagen amount within 8-10 weeks. Therefore, it is unlikely to be a causal factor in lung collagen accumulation often observed in EIPH.
• The research emphasizes the equine lung’s efficiency in clearing blood from the airspaces.
• Moreover, it suggests that the underlying causes behind EIPH are not driven by happenings within the airspace’s lumen but from within the vasculature and the lung interstitium itself.