Ventilatory dynamics and control of blood gases after maximal exercise in the Thoroughbred horse.

The research studies the way horses control their breathing and balance of blood gases after an intense exercise regime, and concludes that the previously proposed locomotory-respiratory coupling (LRC) isn’t the essential driving factor in achieving the desired ventilation rate.

Objective of the Research

• The study aims to understand the dynamics of breath-by-breath, minute ventilation (Ve – the total volume of gas inhaled or exhaled by a person per minute), and the control of blood gases after exertive exercise in a Thoroughbred horse.

Previous Findings and Hypothesis

• Despite high rates of Ve during galloping, the energetic requirements of this exercise raise the blood’s carbon dioxide levels, inducing a condition known as hypercapnia.
• There’s a posited theory called locomotory-respiratory coupling (LRC) which suggests that during high Ve like during galloping, Ve would drop significantly as soon as LRC stops, worsening hypercapnia.
• If this theory was correct, then there should be a drastic decrease in Ve at the transition from gallop to trot.

Research Procedures

• Five Thoroughbred horses were subjected to fatigue on a treadmill to study the breath-by-breath Ve, oxygen uptake, and carbon dioxide output from the peak of exercise to recovery.

Observations and Findings

• Contrary to the LRC theory, the research found that the Ve did not drop immediately after the transition from gallop to a slower trot but remained at peak levels for about 13 seconds. This was achieved through a combination of an increased volume of breath (tidal volume) and a reduced breathing frequency.
• Following this, Ve decreased in a two-phase manner, slower than the decline of carbon dioxide output, which saw a rapid transposition, reversing the post-exercise hypercapnia.

Conclusion

• The research concluded that LRC isn’t a necessary condition for achieving Ve commensurate with maximum exercise or the significant hyperventilation observed during recovery from it. The horse’s body seems to have an independent mechanism to control its blood gas levels and Ve.