CARDIORESPIRATORY RESPONSES TO EXERCISE IN HORSES WITH DIFFERENT GRADES OF IDIOPATHIC LARYNGEAL HEMIPLEGIA

The relationship between different grades of laryngeal function, as as sessed by endoscopy at rest, and the measurements of indices of gas ex change and exercise capacity was assessed during a standardised treadm ill exercise test in 149 horses. Horses with abnormalities other than idiopathic laryngeal hemiplegia (ILH) were excluded from the study and laryngeal function was graded according to an established system. The re were no significant differences in age, weight, maximum oxygen upta ke, maximum carbon dioxide production, maximum respiratory exchange ra tio, maximum oxygen pulse and run time between the grades. Blood lacta te concentration at 10 m/s was greater (P<0.01) in horses with grade 5 laryngeal function than other grades. Minimum PaO2 (P<0.001) and SaO( 2) (P<0.01) were lower and maximum PaCO2 (P<0.001), higher in horses w ith grades 4 and 5 laryngeal function than other grades. Horses with g rade 4 function had a lower minimum CaO2 (P<0.01) than horses with oth er grades. Minimum PAO(2) decreased from grades I and 2 to grades 4 an d 5 (P<0.05). The minimum alveolar ventilation was lower (P<0.05) in h orses with grades 4 and 5 laryngeal function compared to other grades. The results of this study indicate that endoscopic assessment of lary ngeal function at rest, using a simple grading system, provides an ind ication of dynamic changes in ventilation and the effects on blood gas es during exercise. From the data, we suggest that horses that have so me movement of the left arytenoid cartilage but are unable to achieve full abduction have similar ventilatory effects and blood gas response s during maximal exercise to those with complete paralysis, Some horse s with grade 3 laryngeal function had blood gas results similar to tho se of horses with grades 4 and 5 laryngeal function, indicating that d iscrepancies may occur between the resting assessment and laryngeal fu nction during strenuous exercise.