DDSP Diagnosis: Study Boosts Confidence in Sound Analysis

Vibrations of the soft palate are the probable source of expiratory sounds recorded in horses with dorsal displacement of the soft palate (DDSP), says Jeremy Burn, BEng, PhD, lecturer in equine science in the department of anatomy at the University of Bristol in the United Kingdom. He says that this new DDSP research strengthens the case for the application of respiratory sound analysis in the diagnosis of DDSP in exercising horses.

DDSP is one of the most common causes of upper respiratory problems that results in poor performance in racehorses. The condition can create a gurgling noise when the horse is exercised and is sometimes referred to as "choking down" or "swallowing the tongue." In extreme cases of DDSP, the horse’s airway can become completely blocked by the soft palate.

"The cause of DDSP is not known. I think most researchers would agree that it has something to do with neuromuscular dysfunction in the palatal musculature," notes Burns.

So, Burns and his fellow researchers used 11 cadaveric Thoroughbred heads to develop a technique of respiratory sound analysis for the diagnosis of DDSP. They passed an industrial vacuum cleaner nozzle through the trachea and larynx to create unimpeded airflow through the nasopharynx. A microphone was positioned to the right side of the horse’s head, as close as possible to the nostril, but out of direct line of the airflow blast, to record the respiratory sounds made. "The direction of the airflow at the point it was introduced via the larynx was maintained as close as possible to that in exercising horses, based on estimates of trachea angle obtained from horses exercising on a treadmill," says Burns.

Measurements of palatal movements were recorded using high-speed videoendoscopic recordings, and they were compared to the audio frequencies recorded from the cadaveric heads and from data collected previously from exercising horses with DDSP. It was found that palatal movements occurred when air was blown through the trachea, and the fundamental movement was not significantly different from the cadaveric heads versus the exercising horses.

While DDSP is currently managed with a tongue tie or the use of a figure-eight noseband, in severe cases surgery is warranted to remove the muscles in the larynx and keep the soft palate from moving.

This study was published in the Equine Veterinary Journal.

About the Author

Marcella M. Reca Zipp, MS

Marcella Reca Zipp, M.S., is a former staff writer for The Horse. She is completing her doctorate in Environmental Education and researching adolescent relationships with horses and nature. She lives with her family, senior horse, and flock of chickens on an island in the Chain O'Lakes.

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