Regional pulmonary veno-occlusion: a newly identified lesion of equine exercise-induced pulmonary hemorrhage.

The research paper investigates the causes of exercise-induced pulmonary hemorrhage (EIPH) in thoroughbred racehorses. The study reveals a new lesion associated with EIPH, termed as regional veno-occlusive remodeling, and suggests that it could contribute to the development of EIPH, leading to issues like vascular congestion, hemorrhage, fibrosis, and bronchial angiogenesis.

Study Background and Methodology

• Exercise-induced pulmonary hemorrhage (EIPH) is a condition that affects thoroughbred racing horses after intense physical activity. Despite its prevalence, with up to 75% of racing Thoroughbreds and Standardbreds being affected, the pathogenesis of EIPH remains uncertain.
• The study examined seven Thoroughbred horses with EIPH. From each horse’s lungs, six sections were collected, covering both the left and right lung from different regions of the dorsal and ventral lung, totaling 84 sites.
• The lungs had numerous dark brown to blue-black spots, primarily along the caudodorsal visceral pleura. Histologic scores were assigned based on the presence and severity of five observed features: interstitial fibrosis, hemosiderin accumulation, thickness of pleural/interlobular septal, and arterial and venous wall, and evidence of angiogenesis.

Findings and Interpretation

• Out of the 84 sections, almost half (46%) were histologically normal. About 39% were mildly to moderately affected, exhibiting small amounts of hemosiderin and fibrosis. The remaining 14% had severe symptoms, including vascular remodeling, fibrosis, and hemosiderin accumulation, primarily in the dorsocaudal lung region.
• In the most severely affected sections, there was evidence of veno-occlusive remodeling. This remodeling was associated with hemosiderosis, fibrosis, enlargement of vessels within the pleura and interlobular septa, and bronchial neovascularization.
• The findings propose that the regional veno-occlusive remodeling, particularly within the caudodorsal lung fields, contributes to the development of EIPH. It suggests that the venous remodeling leads to regional vascular congestion and hemorrhage, hemosiderin accumulation, fibrosis, and bronchial angiogenesis.

Conclusion

• This research has helped identify a potentially significant factor in the pathogenesis of EIPH in Thoroughbred horses. Understanding this veno-occlusive remodeling process could provide valuable insights into the prevention and treatment of EIPH and help enhance the athletes’ wellness and performance.