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Journal of applied physiology (Bethesda, Md. : 1985)1989; 66(3); 1227-1233; doi: 10.1152/jappl.1989.66.3.1227

Mechanism of exercise-induced hypoxemia in horses.

Abstract: Arterial hypoxemia has been reported in horses during heavy exercise, but its mechanism has not been determined. With the use of the multiple inert gas elimination technique, we studied five horses, each on two separate occasions, to determine the physiological basis of the hypoxemia that developed during horizontal treadmill exercise at speeds of 4, 10, 12, and 13-14 m/s. Mean, blood temperature-corrected, arterial PO2 fell from 89.4 Torr at rest to 80.7 and 72.1 Torr at 12 and 13-14 m/s, respectively, whereas corresponding PaCO2 values were 40.3, 40.3, and 39.2 Torr. Alveolar-arterial PO2 differences (AaDO2) thus increased from 11.4 Torr at rest to 24.9 and 30.7 Torr at 12 and 13-14 m/s. In 8 of the 10 studies there was no change in ventilation-perfusion (VA/Q) relationships with exercise (despite bronchoscopic evidence of airway bleeding in 3) and total shunt was always less than 1% of the cardiac output. Below 10 m/s, the AaDO2 was due only to VA/Q mismatch, but at higher speeds, diffusion limitation of O2 uptake was increasingly evident, accounting for 76% of the AaDO2 at 13-14 m/s. Most of the exercise-induced hypoxemia is thus the result of diffusion limitation with a smaller contribution from VA/Q inequality and essentially none from shunting.
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Publication Date: 1989-03-01 PubMed ID: 2496088DOI: 10.1152/jappl.1989.66.3.1227Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't
  • Research Support
  • U.S. Gov't
  • Non-P.H.S.
  • Research Support
  • U.S. Gov't
  • P.H.S.

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research investigates the cause of low oxygen levels in the blood of horses during heavy exercise, attributing it mainly to inadequate transport of oxygen across lung tissues, with factors like ventilation and blood perfusion playing a smaller role.

Study Setup

  • The researchers used an analytical method known as the multiple inert gas elimination technique to study five horses. They conducted the study two times on each horse.
  • The horses were made to run on a horizontal treadmill at varying speeds of 4, 10, 12, and 13-14 meters per second. These speeds are considered as heavy exercise for horses and allowed the researchers to study oxygen levels at different activity levels.

Observations

  • The findings indicated a drop in arterial oxygen pressure (from 89.4 Torr at rest to 80.7 and 72.1 Torr at speeds of 12 and 13-14 m/s) while the levels of carbon dioxide remained fairly constant.
  • The discrepancy between the oxygen levels in the alveoli of the lungs and the arteries (AaDO2) increased significantly during exercise, escalating from 11.4 Torr at rest to 24.9 and 30.7 Torr at speeds of 12 and 13-14 m/s.
  • Despite some horses showing signs of airway bleeding, ventilation-perfusion (VA/Q) relationships—i.e. the efficiency of gas exchange in the lungs—didn’t change notably in 8 out of the 10 studies. The total blood flow bypassing the lungs (shunt) remained less than 1%.

Conclusions

  • At slower speeds (below 10 m/s), the increased AaDO2 was solely attributed to the VA/Q mismatch, signalling inefficient gas exchange in the lungs. However, at higher speeds, the decreased oxygen uptake was predominantly caused by a diffusion limitation. This means that the oxygen was not being transported across the lung tissues effectively, which resulted in the observed hypoxemia (low oxygen levels in the blood).
  • Altogether, the research concluded that exercise-induced hypoxemia in horses is primarily due to limitations in oxygen diffusion, with a smaller contribution from VA/Q inequality, and virtually no effect from shunting.

Cite This Article

APA
Wagner PD, Gillespie JR, Landgren GL, Fedde MR, Jones BW, DeBowes RM, Pieschl RL, Erickson HH. (1989). Mechanism of exercise-induced hypoxemia in horses. J Appl Physiol (1985), 66(3), 1227-1233. https://doi.org/10.1152/jappl.1989.66.3.1227

Publication

Journal of applied physiology (Bethesda, Md. : 1985)
ISSN: 8750-7587
NlmUniqueID: 8502536
Country: United States
Language: English
Volume: 66
Issue: 3
Pages: 1227-1233

Researcher Affiliations

Wagner, P D
  • Department of Medicine, University of California, San Diego, La Jolla 92093.
Gillespie, J R
    Landgren, G L
      Fedde, M R
        Jones, B W
          DeBowes, R M
            Pieschl, R L
              Erickson, H H

                MeSH Terms

                • Animals
                • Carbon Dioxide / blood
                • Cardiac Output
                • Horses / physiology
                • Hypoxia / etiology
                • Hypoxia / physiopathology
                • Male
                • Orchiectomy
                • Oxygen / blood
                • Oxygen Consumption
                • Partial Pressure
                • Physical Exertion
                • Pulmonary Alveoli / physiology
                • Respiration

                Grant Funding

                • HL-17731 / NHLBI NIH HHS

                Citations

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