Cardiovascular and respiratory responses in Thoroughbred horses during treadmill exercise.

This research measures the cardiovascular and respiratory responses of six Thoroughbred horses during treadmill exercise. The team analyzed the expired gas to determine the oxygen consumption and its relationship to the work rate, heart rate, stroke volume, and other factors. The findings suggest that the high VO2max in horses is dependent on a large arteriovenous oxygen content difference, despite the development of hypoxaemia (low oxygen) and haemoglobin desaturation during strenuous exercise.

Details of the Study

The study was conducted using six Thoroughbred horses who were detrained, meaning they weren’t previously conditioned for prolonged exercise. They performed incremental treadmill tests while the researchers measured several variables. These variables include:

• Maximal oxygen uptake (VO2max)
• Heart rate (HR)
• Cardiac output (Q)
• Stroke volume (SV)
• Arteriovenous oxygen content difference [C(a-v)O2]

Findings of the Study

The research collected some notable findings:

• Average VO2max was found to be 129.7 ml kg-1 min-1, which occurred at a mean speed of 8.0 m/s, with the treadmill set at a slope of 10%.
• The average heart rate at VO2max was 222 beats per minute.
• The average cardiac output at max was 534 ml kg-1 min-1, and the average stroke volume was 2.4 ml kg-1.
• The mean arteriovenous oxygen content difference was 24.5 ml 100 ml-1 blood.
• Linear relationships were found between oxygen consumption (VO2) and work rate, heart rate, cardiac output, and arteriovenous oxygen content difference.
• Stroke volume did not increase significantly during exercise.
• Increasing the metabolic rate during exercise was associated with linear increases in arterial haemoglobin concentration and oxygen content, and decreases in arterial oxygen partial pressures and haemoglobin saturation.

Conclusion of the Study

The study concluded that for detrained Thoroughbred horses, the high maximal oxygen uptake is dependent on the large arteriovenous oxygen content difference. This is the case even as oxygen levels in the blood decrease and haemoglobin becomes less saturated during exercise. Hence, it indicates that the organisms are capable of maintaining a high oxygen consumption rate during strenuous exercise by extracting more oxygen from the blood delivered to the muscles.