Cardiac output but not high pulmonary artery pressure varies with FIO2 in exercising horses.
Abstract: Horses have high mean pulmonary artery pressure (Ppa) both at rest and during exercise (approximately 30 and > or = 80 mmHg, respectively). The mechanisms are unknown. To see if hypoxic pulmonary vasoconstriction (HPV) plays a role, we compared pulmonary artery pressure-flow (Ppa-Q) curves when inspired O2 fraction (FIO2) was 0.16, 0.21, and 0.30, in 5 normal Thoroughbred horses standing quietly and while galloping at 10 and 14 m/sec on a level treadmill. We calculated O2 consumption (VO2) from measurements of respired gas composition and flow, and calculated Q from VO2 and measurements of oxygen content in arterial and mixed venous blood (CaO2 and CVO2). VO2 was 3.8, 74 and 128 ml.min-1.kg-1, at rest and at 10 and 14 m/sec, and did not vary with FIO2 at any speed. At 14 m/sec only, when FIO2 was lowered to 0.16, CaO2 fell (to 14.7 from 20 ml/dl on air), Q increased (to 0.86 from 0.66 L.min-1.kg-1 on air), and stroke volume increased (to 4.1 from 3.2 ml.kg-1 on air). Slopes and intercepts of Ppa-Q curves did not vary with FIO2. We conclude that HPV does not contribute to the high Ppa of exercising horses breathing air near sea level.
Publication Date: 1993-01-01 PubMed ID: 8441873DOI: 10.1016/0034-5687(93)90091-nGoogle Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research article is an investigation into why horses have a high mean pulmonary artery pressure (Ppa) and whether hypoxic pulmonary vasoconstriction (HPV) could be a factor. It concludes that HPV does not contribute to high Ppa in exercising horses.
Research Purpose and Methods
- The main objective of this research was to investigate why horses have high mean pulmonary artery pressure (Ppa) at rest and during physical activity. Particularly, the study aimed at elucidating the role of hypoxic pulmonary vasoconstriction (HPV) in this phenomenon.
- The research involved five thoroughbred horses, which were subjected to different levels of inspired O2 fraction (FIO2) both at rest and during exercise. The levels of inspired oxygen (FIO2) tested were 0.16, 0.21 and 0.30.
- The exercise conditions were standing quietly, and galloping at 10 and 14 m/sec on a level treadmill.
- Two key measurements performed were O2 consumption (VO2), and the quantity of blood [(CaO2 and CVO2)] pumped out of the heart (Q). These measurements helped determine the relationship (Ppa-Q) between pulmonary artery pressure-flow and the associated oxygen content.
Findings
- VO2, the oxygen consumption, remained consistent at 3.8, 74, and 128 ml.min-1.kg-1 at rest and respectively at 10 and 14 m/sec, regardless of FIO2.
- However, when the horses exercised at 14 m/sec and FIO2 was reduced to 0.16, the oxygen content in the arterial and mixed venous blood (CaO2) fell, while Q and stroke volume increased.
- Despite these changes, the research indicated that the slopes and intercepts of the Ppa-Q curves, hence the relationship between Ppa and Q, remained unaffected by FIO2.
Conclusions
- The study concluded that hypoxic pulmonary vasoconstriction doesn’t contribute to the high Ppa of horses when they are exercising and breathing air near sea level.
- Thus, even if the FIO2 varies, the arterial pressure remains high in horses both at rest and during physical activities.
Cite This Article
APA
Pelletier N, Leith DE.
(1993).
Cardiac output but not high pulmonary artery pressure varies with FIO2 in exercising horses.
Respir Physiol, 91(1), 83-97.
https://doi.org/10.1016/0034-5687(93)90091-n Publication
Researcher Affiliations
- Department of Clinical Sciences, College of Veterinary Medicine, Kansas State University, Manhattan 66506.
MeSH Terms
- Animals
- Blood Pressure
- Carbon Dioxide / physiology
- Cardiac Output
- Heart Rate
- Horses / physiology
- Male
- Oxygen / physiology
- Oxygen Consumption
- Physical Conditioning, Animal
- Stroke Volume
- Vasoconstriction
Citations
This article has been cited 1 times.- Birks EK, Ohmura H, Jones JH. Measuring V̇O(2) in hypoxic and hyperoxic conditions using dynamic gas mixing with a flow-through indirect calorimeter. J Equine Sci 2019;30(4):87-92.
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