Pulmonary vascular resistance of horses decreases with moderate exercise and remains unchanged as workload is increased to maximal exercise.

The research investigates how the resistance in horses’ pulmonary blood vessels reacts during different levels of exercise intensity. It concludes that this resistance decreases moderately during exercise but doesn’t change when the exercise intensity is increased to its maximum.

Objectives and Study Design

• The main aim of this study was to understand why the blood pressure of exercising horses in the pulmonary artery increases progressively as the intensity of work intensifies. Understanding this could inform effective exercise programs for these animals.
• As part of the research, two groups of healthy, sound, exercise-trained horses were observed while they were at rest and during exercise. The exercise intensity was varied for each group.
• Group 1 comprised eight horses that were studied at rest and during exercise performed at 8 and 13 m/s; the latter workload inciting maximal heart rate.
• Group 2 consisted of seven Thoroughbreds. Their reaction to rest and galloping at 14.5 m/s at a 5% uphill, a workload that elicited maximal heart rate, was studied.
• Pulmonary vascular resistance (PVR) was calculated by dividing the pulmonary perfusion pressure gradient with cardiac output.

Findings and Conclusion

• The data collected revealed that the pulmonary arterial and wedge pressures, pulmonary perfusion pressure gradient, and cardiac output increased significantly with exercise in both groups.
• It’s also important to note that there were no notable differences in PVR at rest between the two groups of horses.
• Results showed a significant decrease in PVR with exercise at 8 m/s in the horses of Group 1. However, no additional pulmonary vasodilation manifested as the workload increased to 13 m/s.
• Similarly, in Group 2, PVR decreased significantly during exercise at 14.5 m/s on a 5% grade. This resistance was not different from the reaction to 8 or 13 m/s in Group 1.
• In conclusion, the research found that PVR reaches its lowest during moderate exercise. This is likely because the upper limit of recruitment and distension has been achieved. This means that the horses’ pulmonary blood flow remains the sole determinant for the rise in pulmonary arterial blood pressure when moving to higher workloads, as per Ohm’s law.
• Finally, the research also indicates that pulmonary artery wedge pressure is another important variable in determining the absolute value of pulmonary arterial blood pressure.