THE EFFECT OF DIFFERENT GRADES OF LARYNGEAL FUNCTION ON ARTERIAL BLOOD-GASES DURING EXERCISE

The effect of grade of idiopathic laryngeal hemiplegia (ILH) in 149 ho rses (Thoroughbred and Standardbred) was assessed using treadmill exer cise tests. Horses with abnormalities other than ILH observed at rest were excluded from the study and laryngeal function was graded accordi ng to an established system, with grade 1 being normal and grade 5 ind icating complete paralysis. Minimum PaO2 (p<0.001) was lower, and maxi mum PaCO2 (p<0.001) higher in horses with grade 4 and 5 laryngeal func tion than in other grades. The results of this study indicate that end oscopic assessment at rest using a simple grading system can provide a n indication of the effects on blood gases during exercise for some gr ades of laryngeal function. From the data we suggest that horses that have some movement of the left arytenoid cartilage but are unable to a chieve full abduction (grade 4) tend to have similar blood gas respons es during maximal exercise to those with complete paralysis (grade 5). However, some horses with grade 1-3 laryngeal function had blood gas results similar to those of horses with grade 4 and 5 laryngeal functi on indicating that discrepancies may occur between the resting assessm ent and laryngeal function during strenuous exercise in some cases.