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.

The research article investigates the impacts of high-intensity exercise on blood gases and the function of the upper airway and heart in normal Quarter Horses and those affected by hyperkalemic periodic paralysis, a condition that causes muscle weakness. The study found that exercise can increase potassium levels and potentially cause breathing and heart function problems in horses with this condition.

Research Methodology

• The study included five healthy Quarter Horses, five horses heterozygous for hyperkalemic periodic paralysis (HYPP), and two horses homozygous for HYPP.
• A high-speed treadmill was employed to simulate high-intensity exercise in horses.
• To determine the exercise’s impact on the horses’ cardiac and upper airway function, as well as blood gases, testing protocols were implemented both before and during the exercise, and immediately after its completion. These included arterial blood sampling, ECG, echocardiogram, and upper airway endoscopy.

Results of the study

• The study observed that none of the HYPP-affected (heterozygous or homozygous) horses showed signs of weakness or muscle tremors before, during, or after the exercise.
• However, during the exercise, the homozygous HYPP horses experienced intermittently restricted airways (laryngospasm), dynamic pharyngeal collapse (improper functioning of the upper part of the throat), observable hypoxemia (low blood oxygen levels), increased levels of carbon dioxide (hypercapnia), and abnormal early heartbeats (ventricular premature contractions).
• Such abnormalities were not observed among heterozygous horses or clinically normal horses.
• Exercise resulted in a significant rise in potassium concentration across all horse groups, surpassing the baseline reference range.

Research Conclusions

• The study concluded that horses homozygous for HYPP had exercise-induced upper airway dysfunctions, particularly laryngospasm and dynamic pharyngeal collapse, likely triggered by a rise in potassium concentration.
• This upper airway dysfunction was identified as the probable cause of hypoxemia (lower oxygen levels) and hypercapnia (higher carbon dioxide levels) in the blood of these horses.
• The cardiac arrhythmias experienced by these horses were most likely triggered by the combination of hypoxemia and elevated potassium levels (hyperkalemia).