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Anti-inflammatory agent, dexamethasone, does not affect exercise-induced arterial hypoxemia in Thoroughbreds
Murli Manohar1, Thomas E Goetz, Aslam S Hassan
1Department of Veterinary Biosciences, College of Veterinary Medicine, University of Illinois at Urbana-Champaign, 61801, USA. mmanohar@uiuc.edu
Journal of Applied Physiology (Bethesda, Md. : 1985)
|June 19, 2002
Summary
Dexamethasone did not prevent exercise-induced arterial hypoxemia (EIAH) in horses, suggesting airway inflammation is not a primary cause. EIAH appears to have a functional basis due to rapid blood transit time in pulmonary capillaries during intense exercise.
Area of Science:
- Equine exercise physiology
- Respiratory medicine
- Pharmacology
Background:
- Exercise-induced arterial hypoxemia (EIAH) in athletes is potentially linked to histamine release from airway inflammatory and mast cells.
- Understanding the role of inflammation in EIAH is crucial for optimizing equine athletic performance and health.
Purpose of the Study:
- To investigate the effect of dexamethasone, a potent anti-inflammatory agent, on EIAH and hemoglobin desaturation in horses.
- To determine if airway inflammation contributes significantly to EIAH in Thoroughbred racehorses.
Main Methods:
- Seven healthy, exercise-trained Thoroughbred horses underwent two experimental conditions: control (no medication) and intravenous dexamethasone treatment.
- Horses performed incremental exercise to maximal exertion on an uphill treadmill, with blood-gas measurements taken at rest and during exercise.
- Pulmonary hemorrhage was induced in all horses, confirming stress failure of pulmonary capillaries.
Main Results:
- Both control and dexamethasone treatments resulted in significant EIAH, hemoglobin desaturation, hypercapnia, acidosis, and hyperthermia during maximal exercise.
- No significant differences in EIAH or related parameters were observed between the dexamethasone and control groups.
- EIAH developed rapidly within 30 seconds of exertion and was not affected by exercise duration up to 120 seconds.
Conclusions:
- Pretreatment with dexamethasone did not alter EIAH, suggesting that pulmonary injury-evoked airway inflammation plays a minor role in EIAH in racehorses.
- The rapid onset and exercise duration-independent severity of EIAH indicate a functional basis, likely related to reduced pulmonary capillary transit time during high cardiac output.