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Is ventilation during maximal exercise limited by dynamic airway closure?
1Equine Research Institute, Japan Racing Association, Tochigi Prefecture, Japan.
Equine Veterinary Journal. Supplement
|February 5, 2000
Summary
Horses do not appear to hypoventilate during exercise due to expiratory flow limitation. Their airways show no mechanical limitation at typical running lung volumes, suggesting potential for increased expiratory flow.
Area of Science:
- Equine respiratory physiology
- Exercise-induced hypoventilation
Background:
- Horses often exhibit hypoventilation during strenuous exercise.
- Dynamic airway closure and expiratory flow limitation are hypothesized causes.
Purpose of the Study:
- To investigate if expiratory flow limitation causes hypoventilation in exercising horses.
- To compare peak expiratory flows during galloping with maximal dynamic expiratory flows.
Main Methods:
- Measurements of peak expiratory flows in a Thoroughbred horse during treadmill galloping.
- Comparison with peak dynamically-limited flow during a forced expiratory flow-volume maneuver.
Main Results:
- The horse's expiratory flows during galloping were not mechanically limited.
- At running lung volumes, the horse appeared to have available reserve capacity for increased expiratory flow.
Conclusions:
- Expiratory flow limitation due to dynamic airway closure is unlikely to be the primary cause of hypoventilation in exercising horses.
- Horses may possess untapped potential for greater expiratory airflow during strenuous exercise.