Very high pressures are required to cause stress failure of pulmonary capillaries in thoroughbred racehorses.

This study highlights that the pressure required to cause stress failure of pulmonary capillaries in thoroughbred racehorses is between 75 and 100 mmHg, significantly higher when compared to rabbits and dogs.

Research Purpose and Design

• The overarching intent of the research was to ascertain the threshold value for capillary transmural pressure (Ptm) that brings about stress failure in the pulmonary capillaries of thoroughbred horses. This was motivated by a known occurrence of pulmonary hemorrhage in all racing horses and the fact that the necessary pressure for capillary stress failure varies among species.
• The study’s design was based around perfusing the lungs of 15 thoroughbred horses with their own blood at different Ptm values, ranging from 25 to 150mmHg. After perfusion, the lungs were fixated and samples from the dorsal and ventral sections were examined through electron microscopy.

Findings and Analysis

• The results of the microscopic examination revealed few to no disruptions in the capillary endothelium at Ptm less than or equal to 75 mmHg. However, at higher Ptm levels (100 and 150 mmHg), the number of breaks per mm of endothelium increased, indicating stress failure in the capillaries.
• The thickness of blood-gas barrier remained unchanged irrespective of Ptm variation. However, when Ptm was low, the thickness of the interstitial was notably greater than seen in rabbits but similar to dogs.”

Conclusion

• The research concluded that the pressure required to induce stress failure in the pulmonary capillaries of Thoroughbreds ranges between 75 and 100 mmHg, establishing it as appreciably higher compared to both rabbits and dogs.
• This higher tolerance to capillary pressure could potentially be correlated to their athletic performance or might hint towards a unique adaptation mechanism in this animal’s species. However, further research would be required for conclusive evidence.