Changes in arterial, mixed venous and intraerythrocytic ion concentrations during prolonged exercise.

This research study examines the changes in certain ion concentrations in the blood of horses during prolonged physical activity. It suggests that these changes in ion concentrations play a significant role in regulating acid-base balance in the body and that horses become hypokalaemic (low potassium levels in the blood) after long bouts of exercise.

Research Objective and Methodology

• The primary objective of this study was to measure changes in blood gases and major plasma and intraerythrocytic (iRBC—inside of red blood cells) ion concentrations in horses during prolonged exercise of a submaximal nature (around 30% of maximal oxygen uptake, VO2max).
• The horses were made to trot on a treadmill for 105 minutes, and blood samples were taken every 15 mins, as well as before and after exercise.
• Samples were tested for several parameters, including the presence of blood gases and plasma concentrations of sodium, potassium, chloride, and protein.
• The data from these tests were then analyzed to identify any significant changes and reflect the role of ion movement across cell membranes in maintaining acid-base balance and ion concentrations.

Key Findings

• The signs of prolonged equine exercise were visible in the decrease of P(a)CO(2). P(a)CO(2) refers to partial pressure of carbon dioxide in arterial blood, and its reduction indicates effective exhalation of carbon dioxide during exercise.
• There were decreases in arterial and intraerythrocytic chloride concentrations, coinciding with an increase in bicarbonate ion concentration in mixed venous blood. This shift is an instance of hypochloraemic alkalosis, a condition that arises due to loss of chloride ions and results in higher blood pH.
• Both arterial and intraerythrocytic potassium concentrations initially spiked but subsequently dropped, resulting in horses being hypokalaemic post-exercise. This indicates that loss of potassium ions in sweat during exercise leads to hypokalaemia.
• Despite decreases in the concentration of chloride ions in both arterial blood and red blood cells during exercise, there was no change in the arteriovenous difference between them. This suggests a consistent ratio between arterial and venous chloride concentrations regardless of exercise.
• Significant arteriovenous differences in sodium and protein concentration point towards the shift of these substances into or out of red blood cells in response to exercise, helping in regulating the acid-base balance and ion concetrations.

Conclusions

• The research concluded that the notable differences in intraerythrocytic and plasma concentrations of chloride, potassium, and sodium indicate the role ion movement across red blood cell membranes play in regulating acid-base balance and ion concentrations during prolonged exercise in horses.
• Another significant finding pertains to the impact of carbon dioxide exhalation on ion flux. This is described as a major influence on these ion concentration changes during exercise.