Veterinary session

Upper airway functional disorders (UAFD) are one of most common causes of poor performance or exercise intolerance in the equine athlete. The two most frequently diagnosed UAFDs at the Large Animal Clinic (Szent István University, Faculty of Veterinary Science) are the left laryngeal hemiplegia (LLHP) and the dorsal displacement of the soft palate (DDSP).

We suppose that the DDSP and the LLHP, in addition to causing ventilation and flow dynamics disturbances or maybe through these effects, can cause or predispose the patient for lower airway inflammation. A possible explanation for this in case of LLHP might be the decreased activity of laryngeal adductor muscles and associated dysphagia, and secondary inflammation. This may also be a trigger factor in case of DDSP patients, secondary to the soft palatal and epiglottal dysfunction. Partial upper airway obstruction will lead to decreased lower airway pressure and pulmonary hemorrhage during exercise (EIPH), and recurrent bleeding will result in airway inflammation. Furthermore, it can be true vice versa as well, where abnormal upper airway function is a consequence of lower airway obstruction (eg.: Inflammatory Airway Disease, IAD or Recurrent Airway Obstruction, RAO).

In our study we examined 17 horses with UAFD and as controls we used 15 horses admitted to our clinic with non-respiratory signs. We hypothesized that the prevalence of lower airway inflammation will be higher in the group of horses with UAFD than the control group. First we performed a general clinical examination, then an endoscopic examination, where UAFD cases were diagnosed and classified. We examined the lower respiratory tract for any sign of inflammation. Cytology samples were taken with bronchoalveolar lavage (BAL). We evaluated and compared the percentage of inflammatory cells, epithelial cells and red blood cells between the two groups, and also noted the occurrence of plant particles.

There were significantly more haemosiderophages present in the BAL fluid of the UAFD group patients, and rounded carina was also associated with UAFD diagnosis. We observed pathologic cellular percentages in 12/15 horses of the control group.

Increased presence of haemosiderophages in the BAL fluid reflects that lower airway transcapillary pressure increased due to partial upper airway obstruction and led to consequent bleeding in the lower airways. Recurrent bleeding can lead to inflammation but this was not reflected in the results of our study. We concluded, that upper and lower respiratory tract can not be examined and evaluated separately -which is often the case in general practice-, but should be considered as a single unit when looking for the cause of any type of respiratory sign. It was a surprising result that we recorded abnormal BAL cytology in such a percentage of horses of the control group. The reason for the frequent lower airway abnormal cytology results may be the general dusty stabling environment and the common practice of dry hay feeding in Hungary.