Effect of head position on upper airway function in exercising horses
How Head and Neck Position Affects Airflow in Exercising Horses
I came across this study while researching the literature for my masters. I feel this is something to think about when exercising and riding our horses.
When horses exercise, their breathing and airflow are essential to their performance. This study aimed to understand how different head and neck positions during exercise affect the way air flows through their upper airways. The results help highlight on how head and neck positions can influence a horse's ability to breathe, particularly during intense exercise.
The Study Setup
Five Standardbred horses were used in this study. Each horse had an average weight of 452 kg and was between 4 and 5 years old. The horses were exercised at two different intensity levels:
- Period A: When the horses worked at 75% of their maximum heart rate.
- Period B: When the horses pushed to 100% of their maximum heart rate.
During these periods, the horses' head and neck positions were altered in three ways:
- Unrestrained (neutral position)
- Flexed (head on or slightly behind the vertical)
- Extended (head and neck stretched out)
To measure airflow and breathing mechanics, the researchers used various tools like a facemask with a pneumotachograph to measure airflow and a nasotracheal catheter to measure pressure during inhalation and exhalation.
Results
Here’s what the study discovered:
Unrestrained Head and Neck Position: When the horses had their heads and necks in a unrestrained head position, their breathing mechanics were typical of what’s been observed in similar studies. There were no statistical significant results for changes in how the air flowed during this position, whether they were working at 75% or 100% of their heart rate.
Head and Neck Extended: Stretching the horse's head and neck did not seem to have much of an effect on their airflow during exercise. However, two small changes were noticed:
- Expiratory Time (Te): The time it took for the horses to exhale was slightly longer in period A.
- Peak Expiratory Flow to Peak Inspiratory Flow Ratio (PEF/PIF): This ratio was significantly increased when the horses were at 100% of their maximal heart rate (period B), indicating a slight change in the efficiency of airflow during exhalation.
Head and Neck Flexed: When the horses’ heads were in the flexed position, the results were quite different:
- Increased Impedance (Z): There was more resistance to airflow, especially at the higher heart rate (Period B).
- Decreased Inspiratory Flow at 50% of Tidal Volume (IF50): The ability to inhale air was reduced.
- Increased Expiratory Flow Rates: Both the ratio of peak flow during exhalation and the total expiratory flow were higher, showing changes in how the air was moving.
- Increased Inspiratory Pressure (PuI): The horses had to work harder to breathe in when their heads were flexed, especially at the higher exercise intensity.
What Does This Show Us?
The results show that during intense exercise, unrestrained head and neck position doesn't alter the airflow in horses.
However, head and neck flexion (on or behind the vertical) can cause problems. It creates more resistance in the airways, reduces the ease of inhalation, and increases the effort needed for breathing.
The researchers noted that when the horses' heads were flexed, the biggest changes happened in airflow resistance and the amount of air they could inhale. This suggests the horses were experiencing a dynamic airway obstruction, meaning the airway was getting blocked during breathing, but the blockage was not permanent.
Unlike a fixed obstruction, which would block airflow both when inhaling and exhaling, the dynamic obstruction only affected inhalation in this case. The moving of head and neck may cause the airway to become more flexible, allowing tissues to collapse into the airway and partially block it.
Overall, this is an interesting insight into the breathing mechanics of the horse during exercise. It is important to take note of this when we are asking our horses to flex their head during performances in the dressage arena or show jumping ring, as it can be affecting their breathing.
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Reference
PETSCHE, V. M., DERKSEN, F. J., BERNEY, C. E. and ROBINSON, N. E. (1995) 'Effect of head position on upper airway function in exercising horses.', Equine Veterinary Journal, 27(18), pp. 18-22.