Distribution of blood flow during moderate and strenuous exercise in ponies (Equus caballus).

This study examines how blood flow to various areas of the body changes in ponies during rest and different levels of exercise. The researchers found that while blood flow to some areas remained constant, others saw marked increases or decreases during moderate and severe exercise.

Key Findings

• The researchers identfied important hemodynamic changes during exercise, manifesting as dramatic increases in several components including cardiac output, mean aortic pressure, left ventricular end-diastolic pressure, and right ventricular systolic and end-diastolic pressures.
• They found that blood flow to the brain stem and cerebral hemispheres remained unchanged during moderate and severe exercise, indicating that the body prioritises maintaining blood flow to these critical brain regions even during high exertion levels.
• In contrast, the cerebellum – another part of the brain – experienced a significant increase in blood flow (32%) during severe exercise. This was despite a large drop in the level of carbon dioxide in the blood (hypocapnia).
• Notably, the myocardium – the heart muscle – also experienced an increase in blood flow across different layers with both levels of exercise. However, the ratio between the perfusion of the inner and outer part of the left ventricle and the interventricular septum decreased during exercise.
• The study reports a drastic drop in renal blood flow (down to only 19% of its resting value) during severe exercise, showing that the body directs less blood flow to the kidneys during high-intensity exercise.
• Interestingly, blood flow to the diaphragm exceeded that to the skeletal muscles during both intensities of exercise. Meanwhile, blood flow to the exercising muscles of the brachium and thigh experienced dramatic increases, especially during severe exercise.

Conclusion

• In conclusion, the researchers found that the cardiovascular response to strenuous exercise in ponies involves selectively increasing blood flow to certain parts of the body (the cerebellum, heart muscle, diaphragm, and exercising skeletal muscles), while reducing it to others (the kidneys).
• These findings suggest that the pony’s cardiovascular response to severe exercise is similar to human responses, re-emphasising the value of the pony as an animal model in exercise physiology studies.