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Home / Equine Research Bank / Equine Vet J / Complete upper airway collapse and apnoea during tethered sw...
Equine veterinary journal2019; 52(3); 352-358; doi: 10.1111/evj.13177

Complete upper airway collapse and apnoea during tethered swimming in horses.

Abstract: There is limited knowledge of the breathing strategy and impact on the patency of the upper respiratory tract (URT) in swimming horses. Objective: To describe the respiratory responses and endoscopic appearance of the URT during tethered swimming in horses. Methods: Prospective descriptive study. Methods: Ten race-fit horses, with no history of URT obstruction, were examined during tethered swimming. Endoscopic examination, heart rate, sound recordings and above and below water video recordings were obtained. Plasma lactate concentration was measured before and 5 min after swimming and tracheal endoscopy was performed 30 min after exercise to assess for presence of blood or mucus. Four horses also underwent endoscopy during exercise on the track. Results: Mean (±s.d.) breathing frequency was 28 ± 5 breaths/min during swimming, with a brief inspiration (mean ± s.d. T  = 0.51 ± 0.08 s), followed by a period of apnoea (1.59 ± 0.53 s) and then a short, forced expiration (T  = 0.42 ± 0.5 s). During apnoea all horses exhibited complete collapse of the URT including closure of the external nares, nasopharynx and rima glottidis (with bilateral adduction of the arytenoid cartilages and vocal folds) and, in two horses, epiglottic retroversion. No horses had URT collapse during overground exercise. Locomotor-respiratory coupling was not observed during swimming. Median (IQR) plasma lactate post swim was 4.71 mmol/L (2.08-8.09 mmol/L) vs 0.68 mmol/L (0.65-0.71 mmol/L) preswim. Post swim endoscopy revealed grade 1 exercise-induced pulmonary haemorrhage (EIPH) in 2 horses. Median mucus grade was 1 (range 0-3). Conclusions: Overground endoscopy was not performed in all horses. Conclusions: Horses experienced complete URT collapse associated with post inspiratory apnoea when swimming. The reason for this is unknown but may be to aid buoyancy or associated with the mammalian dive response - a survival reflex to preserve oxygen stores and prevent water entering the lungs.
© 2019 EVJ Ltd.
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Publication Date: 2019-10-08 PubMed ID: 31495963DOI: 10.1111/evj.13177Google Scholar: Lookup
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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 article focuses on understanding the impact of swimming on the breathing strategy and the patency of the upper respiratory tract (URT) in horses. The study reveals that horses experienced a complete collapse of the URT following every inspirational cycle while swimming, for reasons that are yet to be fully understood.

Methods

  • The research was conducted as a prospective descriptive study, which involved ten race-fit horses. These horses did not have any history of obstruction in the URT.
  • The horses were examined during tethered swimming using endoscopic examination, heart rate measurements, sound recordings, and above and below water video recordings.
  • The presence of blood or mucus was monitored by performing tracheal endoscopy 30 minutes after the exercise.
  • Plasma lactate concentration was measured before and 5 minutes after the swimming exercise to monitor the lactate difference which indicates the level of exercise intensity and fitness.
  • Four of these horses additionally underwent endoscopy during exercise on the track, done to compare the horses’ respiratory functions during swimming and running.

Results

  • Observations show that the mean breathing frequency of the horses was 28 ± 5 breaths/min while swimming. Inspiration period was brief, followed by a period of apnoea, and then a short, forced expiration.
  • All horses exhibited complete collapse of the URT during apnoea (breath holding), including the closure of the external nares, nasopharynx, and rima glottidis. In two horses, backwards flipping of the epiglottis (epiglottic retroversion) was observed.
  • There was no evidence of URT collapse during terrestrial exercise, revealing that this issue was unique to swimming.
  • Respiratory movements weren’t synchronized with their stroke cycle in the water, unlike in terrestrial locomotion where such a synchronisation (locomotor-respiratory coupling) is typically observed.
  • Lactate levels post-swim increased considerably, indicating a high-intensity effort during swimming.
  • Two of the examined horses were found with exercise-induced pulmonary haemorrhage (EIPH).

Conclusion

  • Not all horses underwent endoscopy on the track, which limits the comparisons that can be made between running and swimming for horses.
  • The study concludes by stating that horses experience a complete URT collapse after every inspiration while swimming.
  • The reason for this abnormal response is not clear, but the authors suggest it may help with buoyancy or it might be a reflex action – mammalian dive response – that helps to preserve oxygen stores and prevent water entry into the lungs during submersion.

Cite This Article

APA
Jones S, Franklin S, Martin C, Steel C. (2019). Complete upper airway collapse and apnoea during tethered swimming in horses. Equine Vet J, 52(3), 352-358. https://doi.org/10.1111/evj.13177

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 52
Issue: 3
Pages: 352-358

Researcher Affiliations

Jones, S
  • University of Melbourne Equine Centre, Melbourne, Victoria, Australia.
Franklin, S
  • University of Adelaide Equine Health and Performance Centre, Roseworthy, South Australia, Australia.
Martin, C
  • Sperero Pty Ltd, Melbourne, Victoria, Australia.
Steel, C
  • University of Melbourne Equine Centre, Melbourne, Victoria, Australia.

MeSH Terms

  • Animals
  • Apnea / veterinary
  • Horse Diseases
  • Horses
  • Physical Conditioning, Animal
  • Prospective Studies
  • Respiratory System Abnormalities / veterinary
  • Swimming

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Citations

This article has been cited 1 times.
  1. Moreno-Martinez F, Byrne D, Raisis A, Waldmann AD, Hosgood G, Mosing M. Comparison of Effects of an Endotracheal Tube or Facemask on Breathing Pattern and Distribution of Ventilation in Anesthetized Horses.. Front Vet Sci 2022;9:895268.
    doi: 10.3389/fvets.2022.895268pubmed: 35836499google scholar: lookup
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