Equine pulmonary disease: a case control study of 300 referred cases. Part 3: Ancillary diagnostic findings.

This research study explores the diagnostic findings in 270 adult horses suffering from chronic pulmonary diseases, paying special attention to the level of respiratory secretions, neutrophil ratios in tracheal respiratory secretions, arterial oxygen partial pressures, bronchoalveolar lavage fluid neutrophil ratios, and changes in intrapleural pressures.

Key Findings

• Most of the 270 adult horses that suffered from chronic pulmonary diseases were found to have unusually high volumes of respiratory secretions in their trachea and elevated tracheal respiratory secretion neutrophil ratios. It was also observed that these animals presented with reduced arterial oxygen partial pressures. A neutrophil is a type of white blood cell that’s often involved in inflammation and combating infection, so heightened levels might indicate respiratory inflammation or infection.
• Interestingly, some control horses—that is, horses not suffering from any chronic pulmonary diseases—also displayed elevated trachael respiratory secretion neutrophil ratios, without an identifiable cause.
• However, only horses suffering from chronic obstructive pulmonary disease (COPD) had significantly elevated bronchoalveolar lavage fluid (BALF) neutrophil ratios. A bronchoalveolar lavage is a medical procedure involving the examination of the bronchi and the alveolar regions of the lungs, often used to diagnose lung disease. Elevated BALF neutrophil ratios specifically in these horses could suggest a unique, distinguishing feature of equine COPD.
• Elevated maximal intrapleural pressure changes (max dPpl) were reported in 48% of the COPD cases but were rarely seen with other pulmonary diseases. Intrapleural pressure is the pressure within the pleural cavity, which contains the lungs. Changes in this pressure have implications for lung function and can be indicative of disease states.
• Values for arterial pH or carbon dioxide partial pressures were seldom altered across most pulmonary diseases. This implies that these parameters may not be reliable indicators of chronic pulmonary disease in horses.
• Increased tracheal respiratory secretion and BALF eosinophil ratios were observed in cases of lungworm infection and idiopathic pulmonary eosinophilia. Eosinophils are another type of white blood cell and are often associated with allergic reactions and parasite infections, so elevated levels might suggest these conditions.

Conclusion

The results from this study suggest that various diagnostic processes provide different insights into the nature and severity of diseases of the pulmonary system in horses. Notably, elevated neutrophil ratios in the tracheal respiratory secretions and bronchoalveolar lavage fluid were linked to chronic obstructive pulmonary disease. Future research could further explore these diagnostic tools and their clinical relevance in equine medicine.