Cardiorespiratory responses to exercise in horses with different grades of idiopathic laryngeal hemiplegia.

This is a research study examining the link between different levels of laryngeal function and cardiorespiratory responses during exercise in horses. The main finding suggests that horses with partial or complete paralysis of the larynx display similar ventilatory effects and blood gas responses during maximal exercise.

Research Purpose

• This study aims to establish the relationship between varying degrees of laryngeal function and indicators of cardiorespiratory function (gas exchange and exercise capacity) in horses. The horses’ laryngeal function was assessed through an endoscopic examination at rest.

Study Methodology

• A standardised treadmill exercise test was performed on 149 horses.
• The study excluded any horses with abnormalities not related to Idiopathic Laryngeal Hemiplegia (ILH), a condition that affects normal laryngeal function.
• The researchers utilized an established grading system to categorize the laryngeal function of each horse.

Key Findings

• No significant differences were observed in age, weight, maximum oxygen uptake, maximum respiratory exchange ratio, maximum oxygen pulse, and run time between the different laryngeal function grades.
• Horses with a grade 5 laryngeal function (severe symptoms) had higher blood lactate concentration during heavy exercise compared to other grades.
• Horses with grades 4 and 5 laryngeal function (moderate to severe symptoms) had lower minimum oxygen partial pressure and oxygen saturation, and higher maximum carbon dioxide partial pressure.
• Grade 4 horses had a lower minimum oxygen content than horses with other grades.
• Minimum partial pressure in the alveoli decreased and minimum alveolar ventilation was lower in horses with grades 4 and 5 laryngeal function.

Conclusions and Implications

• The study suggests that the resting assessment of laryngeal function, using the simple grading system, can indicate changes in ventilation and effects on blood gases during exercise.
• It was noted that horses that have some movement in the left arytenoid cartilage, but cannot achieve full abduction, have ventilatory effects and blood gas responses during maximal exercise that are similar to those with complete paralysis.
• The data also showed that some horses with grade 3 laryngeal function had blood gas results similar to those of horses with grades 4 and 5 laryngeal function, suggesting that resting assessment and laryngeal function during intense exercise may not always align.