Exercise-induced pulmonary haemorrhage in the horse: results of a detailed clinical, post mortem and imaging study. III. Subgross findings in lungs subjected to latex perfusions of the bronchial and pulmonary arteries.

This study looks into the cause and characteristics of exercise-induced pulmonary haemorrhage in horses, a condition where blood vessels in the lungs rupture due to intense physical activity. The results suggest it may be due to issues with small airways and blood vessel changes.

Methodology

• The investigators used latex to visualize blood flow in the lungs of Thoroughbred horses. The latex was injected into different arteries, bronchial and pulmonary, of the inflated lungs, and then transverse sections were taken.
• The purpose of the latex injection was to calculate the extent of the lesions resulting from exercise-induced pulmonary haemorrhage.

Findings

• The study found that extensive areas of dense brown haemosiderin, an iron-storage complex which is often an indicator of bleeding, were present. These areas make up to 45% of total lung volume and are predominantly in the dorsocaudal lungfields, which are the upper rear sections of the lungs.
• Arterial proliferation or the multiplication of blood vessels from the bronchial artery seemed to replace the pulmonary supply in the affected areas of the lung. This suggests that the bronchial arteries had developed more as an adaptation due to exercise-induced pulmonary haemorrhage.
• Accompanying bronchial arterialisation, there was evidence of widespread small airway disease. Airway disease generally implies the narrowing or blockage of the airway, which limits the flow of oxygen.
• The most severely affected bronchioles, or small airways in the lungs, contained thick exudate, mucoid plugs and had significantly thickened walls.

Conclusions

• These findings suggest that the source of haemorrhage in exercise-induced pulmonary haemorrhage comes from alveolar capillaries that are abnormally supplied by the bronchial arterial circulation through the development of pathological shunts. Shunts are abnormal vessels causing blood flow diversion from its normal path.
• Small airway disease seems to play a significant role in the development of this condition, and it may even trigger the initial growth of the bronchial circulation, thus contributing to the haemorrhage.