Exercise-induced hypercapnia in the horse.
Abstract: The effects of exercise intensity and duration on blood gases in thoroughbred horses were studied to characterize the apparent exercise-induced failure in pulmonary gas exchange that occurs in these animals. In response to 2 min of exercise, arterial CO2 tension (PaCO2) decreased in mild and moderate exercise, returned to normocapnic levels in moderate to heavy exercise, and rose 5-10 Torr above resting values during very heavy exercise when CO2 production (VCO2) exceeded 20 times the resting value, and mixed venous CO2 tension approximated 140 Torr. Exercise-induced hypoxemia occurred at the onset of heavy exercise and was associated with the absence of a hyperventilatory response and an alveolar-arterial PO2 difference that increased four to six times above rest with very heavy exercise. PaCO2 was related to VCO2 but not fb, as changes in breathing frequency (fb) of 8-20 breaths/min at comparable VCO2 did not affect PaCO2. Prolonging very heavy exercise from 2 to 4 min caused a severe metabolic acidosis (arterial pH less than 7.15) and hypoxemia was maintained; however, CO2 was no longer retained, as PaCO2 gradually fell to below resting levels, due to an increased tidal volume at constant fb. We conclude that a truly compensatory hyperventilation to very heavy exercise in the horse is not achieved because of the excessive volumes and flow rates required by their extraordinarily high VCO2 and VO2. On the other hand, the frank CO2 retention during short-term high-intensity exercise occurs even though the horse is not apparently mechanically obligated to tolerate it.
Publication Date: 1989-11-01 PubMed ID: 2513313DOI: 10.1152/jappl.1989.67.5.1958Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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This research explores how exercise intensity and duration affect blood gases and pulmonary gas exchange in horses, revealing that very heavy exercise can lead to increased arterial CO2 tension and hypoxemia. Prolonged intense exercise can induce severe metabolic acidosis, however, CO2 is not retained due to increased tidal volume at a constant breathing frequency.
Exercise Intensity, Duration, and Blood Gases
- The research focused primarily on thoroughbred horses, looking into how their blood gases are affected by different intensities and durations of exercise.
- It appears that for very heavy exercise, where CO2 production exceeded 20 times the resting value, arterial CO2 tension (PaCO2) started increasing, going beyond the resting values.
Failure in Pulmonary Gas Exchange
- Onset of heavy exercise induced hypoxemia, which is essentially low blood oxygen.
- This was associated with the suspension of a hyperventilatory response. Instead of compensating through increased breathing, the body seems to allow a decrease in oxygen while also tolerating an increase in CO2 levels.
- Interestingly, breathing rate adjustments didn’t affect the arterial CO2 tension. The research found that variations in breathing frequency between 8-20 breaths/min at comparable CO2 production did not influence the amount of CO2 in the blood.
Prolonged Very Heavy Exercise Effects
- Extending very heavy exercise from 2 to 4 minutes caused a severe metabolic acidosis, bringing down the arterial pH to less than 7.15. This means the blood becomes more acidic than normal.
- However, during prolonged exercise, CO2 was not retained in the body as before. The arterial CO2 tension gradually fell to below resting levels due to increased tidal volume at constant breathing frequency.
Conclusion
- The research concluded that horses don’t achieve a compensatory hyperventilation, despite undertaking very intense exercise. This is due to the massive volumes and flow rates required by their extremely high CO2 production and oxygen consumption.
- However, the clear CO2 retention during short-term high-intensity exercises happens even though the horse is not apparently mechanically obligated to handle it.
Cite This Article
APA
Bayly WM, Hodgson DR, Schulz DA, Dempsey JA, Gollnick PD.
(1989).
Exercise-induced hypercapnia in the horse.
J Appl Physiol (1985), 67(5), 1958-1966.
https://doi.org/10.1152/jappl.1989.67.5.1958 Publication
Researcher Affiliations
- Department of Veterinary Clinical Medicine and Surgery, College of Veterinary Medicine, Washington State University, Pullman 99164-6610.
MeSH Terms
- Analysis of Variance
- Animals
- Carbon Dioxide / blood
- Exercise Test / veterinary
- Hemodynamics
- Horses
- Hypercapnia / blood
- Hypercapnia / etiology
- Hypercapnia / veterinary
- Male
- Physical Conditioning, Animal / adverse effects
- Pulmonary Gas Exchange
- Respiration
Citations
This article has been cited 19 times.- Mazan M. Equine exercise physiology-challenges to the respiratory system. Anim Front 2022 Jun;12(3):15-24.
- Stefanik E, Drewnowska O, Lisowska B, Turek B. Causes, Effects and Methods of Monitoring Gas Exchange Disturbances during Equine General Anaesthesia. Animals (Basel) 2021 Jul 9;11(7).
- Dempsey JA, La Gerche A, Hull JH. Is the healthy respiratory system built just right, overbuilt, or underbuilt to meet the demands imposed by exercise?. J Appl Physiol (1985) 2020 Dec 1;129(6):1235-1256.
- Katz LM, Stallard J, Holtby A, Hill EW, Allen K, Sweeney J. Inspiratory muscle training in young, race-fit Thoroughbred racehorses during a period of detraining. PLoS One 2020;15(4):e0225559.
- Meir JU, York JM, Chua BA, Jardine W, Hawkes LA, Milsom WK. Reduced metabolism supports hypoxic flight in the high-flying bar-headed goose (Anser indicus). Elife 2019 Sep 3;8.
- Dempsey JA. Respiratory Determinants of Exercise Limitation: Focus on Phrenic Afferents and the Lung Vasculature. Clin Chest Med 2019 Jun;40(2):331-342.
- 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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- Hillman SS, Hancock TV, Hedrick MS. A comparative meta-analysis of maximal aerobic metabolism of vertebrates: implications for respiratory and cardiovascular limits to gas exchange. J Comp Physiol B 2013 Feb;183(2):167-79.
- Perez-Moreno CI, Couëtil LL, Pratt SM, Ochoa-Acuña HG, Raskin RE, Russell MA. Effect of furosemide and furosemide-carbazochrome combination on exercise-induced pulmonary hemorrhage in Standardbred racehorses. Can Vet J 2009 Aug;50(8):821-7.
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- Harms CA, McClaran SR, Nickele GA, Pegelow DF, Nelson WB, Dempsey JA. Exercise-induced arterial hypoxaemia in healthy young women. J Physiol 1998 Mar 1;507 ( Pt 2)(Pt 2):619-28.
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- Hodgson DR, Rose RJ, Kelso TB, McCutcheon LJ, Bayly WM, Gollnick PD. Respiratory and metabolic responses in the horse during moderate and heavy exercise. Pflugers Arch 1990 Sep;417(1):73-8.
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- Peters CM, Dempsey JA, Hopkins SR, Sheel AW. Is the Lung Built for Exercise? Advances and Unresolved Questions. Med Sci Sports Exerc 2023 Dec 1;55(12):2143-2159.
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