Ventilatory dynamics and control of blood gases after maximal exercise in the Thoroughbred horse.
Abstract: Despite enormous rates of minute ventilation (Ve) in the galloping Thoroughbred (TB) horse, the energetic demands of exercise conspire to raise arterial Pco(2) (i.e., induce hypercapnia). If locomotory-respiratory coupling (LRC) is an obligatory facilitator of high Ve in the horse such as those found during galloping (Bramble and Carrier. Science 219: 251-256, 1983), Ve should drop precipitously when LRC ceases at the galloptrot transition, thus exacerbating the hypercapnia. TB horses (n = 5) were run to volitional fatigue on a motor-driven treadmill (1 m/s increments; 14-15 m/s) to study the dynamic control of breath-by-breath Ve, O(2) uptake, and CO(2) output at the transition from maximal exercise to active recovery (i.e., trotting at 3 m/s for 800 m). At the transition from the gallop to the trot, Ve did not drop instantaneously. Rather, Ve remained at the peak exercising levels (1,391 +/- 88 l/min) for approximately 13 s via the combination of an increased tidal volume (12.6 +/- 1.2 liters at gallop; 13.9 +/- 1.6 liters over 13 s of trotting recovery; P < 0.05) and a reduced breathing frequency [113.8 +/- 5.2 breaths/min (at gallop); 97.7 +/- 5.9 breaths/min over 13 s of trotting recovery (P < 0.05)]. Subsequently, Ve declined in a biphasic fashion with a slower mean response time (85.4 +/- 9.0 s) than that of the monoexponential decline of CO(2) output (39.9 +/- 4.7 s; P < 0.05), which rapidly reversed the postexercise arterial hypercapnia (arterial Pco(2) at gallop: 52.8 +/- 3.2 Torr; at 2 min of recovery: 25.0 +/- 1.4 Torr; P < 0.05). We conclude that LRC is not a prerequisite for achievement of Ve commensurate with maximal exercise or the pronounced hyperventilation during recovery.
Publication Date: 2004-02-06 PubMed ID: 14766783DOI: 10.1152/japplphysiol.00998.2003Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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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.
Cite This Article
APA
Padilla DJ, McDonough P, Kindig CA, Erickson HH, Poole DC.
(2004).
Ventilatory dynamics and control of blood gases after maximal exercise in the Thoroughbred horse.
J Appl Physiol (1985), 96(6), 2187-2193.
https://doi.org/10.1152/japplphysiol.00998.2003 Publication
Researcher Affiliations
- Department of Anatomy and Physiology, 228 Coles Hall, Kansas State University, Manhattan, KS 66506, USA.
MeSH Terms
- Animals
- Blood Gas Analysis / veterinary
- Exercise Test / veterinary
- Horses / blood
- Horses / physiology
- Motor Activity
- Oxygen / blood
- Oxygen Consumption
- Physical Conditioning, Animal
- Respiratory Mechanics
- Rest
Grant Funding
- HL-50306 / NHLBI NIH HHS
- HL-69739 / NHLBI NIH HHS
Citations
This article has been cited 4 times.- Brownlow M, Mizzi JX. An Overview of Exertional Heat Illness in Thoroughbred Racehorses: Pathophysiology, Diagnosis, and Treatment Rationale.. Animals (Basel) 2023 Feb 9;13(4).
- Poole DC, Copp SW, Colburn TD, Craig JC, Allen DL, Sturek M, O'Leary DS, Zucker IH, Musch TI. Guidelines for animal exercise and training protocols for cardiovascular studies.. Am J Physiol Heart Circ Physiol 2020 May 1;318(5):H1100-H1138.
- Frick L, Schwarzwald CC, Mitchell KJ. The use of heart rate variability analysis to detect arrhythmias in horses undergoing a standard treadmill exercise test.. J Vet Intern Med 2019 Jan;33(1):212-224.
- Mellor DJ, Beausoleil NJ. Equine Welfare during Exercise: An Evaluation of Breathing, Breathlessness and Bridles.. Animals (Basel) 2017 May 26;7(6).
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