EFFECT OF HIGH-INTENSITY EXERCISE ON ARTERIAL BLOOD-GAS TENSIONS AND UPPER AIRWAY AND CARDIAC-FUNCTION IN CLINICALLY NORMAL QUARTER HORSES AND HORSES HETEROZYGOUS AND HOMOZYGOUS FOR HYPERKALEMIC PERIODIC PARALYSIS

Objective-To determine the effect of exercise on arterial blood gas te nsions and upper airway and cardiac function in clinically normal Quar ter Horses and horses heterozygous and homozygous for hyperkalemic per iodic paralysis (HYPP). Animals and Procedure-5 clinically normal Quar ter Horses, and 5 heterozygous and 2 homozygous HYPP-affected horses w ere examined before, during, and after exercise on a high-speed treadm ill. Arterial blood gas tensions, EGG, and echocardiogram were obtaine d prior to exercise. Upper airway endoscopy, collection of arterial bl ood samples, and continuous electrocardiography were performed during a high-intensity stepwise exercise test. An ECG was obtained within 1 minute after completion of the final step. Results-None of the horses homozygous or heterozygous for HYPP had signs of weakness or muscle fa sciculations before, during, or after exercise. Horses homozygous for HYPP had intermittent laryngospasm, dynamic pharyngeal collapse, and a ppreciable hypoxemia, hypercapnia, and ventricular premature contracti ons during exercise. Heterozygous and clinically normal horses did not have any abnormalities. Potassium concentration increased significant ly above the baseline reference range during exercise in all groups of horses. Conclusions-Horses homozygous for HYPP had laryngospasm and d ynamic pharyngeal collapse associated with exercise, most likely secon dary to increase in potassium concentration. Upper airway dysfunction is the most likely cause of hypoxemia and hypercapnia. Cardiac arrhyth mias were most likely caused by a combination of hypoxemia and hyperka lemia.