Often horses that suffer from upper airway obstruction make a noise when exercising. This noise is quite variable as it results from oscillation/vibration of various soft tissue structures within the airway. In some cases it may be barely audible. In other cases it can be heard from great distances.

Technology developed by Dr. Fred Derksen at Michigan State University has enabled New Jersey Equine Clinic veterinarians to make recordings of these abnormal airway sounds while your horse is exercising. A directional microphone is positioned in front of the horse’s nostrils, using a head stall that fits beneath the regular bridle. This microphone is connected to a small MP3 digital recorder that records the audio signals throughout the workout. This digital file is downloaded into a laptop computer and analyzed, using biological “voiceprint” software.

Normal horses make very little noise during inspiration. This is a reflection of the ability of normal horses to stabilize the soft tissues of the upper airway to create a relatively turbulence-free path for airflow. The audio spectrogram to the right was recorded from a normal Thoroughbred galloping on the racetrack.  Notice the bands of bright colors separated by bands of black.  The black areas represent no noise signals, as seen here during inspiration in a normal horse.  The colored bands indicate an acustical signal.  The brighter the color, the more intense the noise.  In the normal image to the right the bright blue, green and yellow bands are caused by vibration of upper airway soft tissues during expiration.  Horses affected by left side laryngeal hemiplegia have a very characteristic acoustical signal that is found during inspiration that correlates well with vibration of the relaxed vocal fold.  Horses with dorsal displacement of the soft palate make a unique frequency noise that is heard primarily during expiration. Intermittent dorsal displacement of the soft palate is difficult to detect during an endoscopic examination performed at rest. Audio spectral analysis provides a convenient and accurate means to see if your horse is displacing its palate during exercise.

The second audio spectrogram on the right was recorded from a Thoroughbred racehorse with exercise intolerance and a loud inspiratory noise.  Notice the difference between this recording and the normal horse.  In this horse there are bright colored bands seen during inspiration.  These bands are located in a frequency range and intensity that is consistent with grade 4 left side laryngeal hemiplegia. 

Using audio spectral analysis, our veterinarians have discovered some interesting findings at the racetrack. For instance, many horses thought to be normal have a mild degree of left side laryngeal paresis. Although the noise related to this condition may not be audible to the jockey, the sensitive microphone detects the unique audio signature. Although horses with this degree of paresis are not good candidates for tieback surgery, ventriculocordectomy in conjunction with management changes can improve performance in many cases. This diagnostic test is simple to perform, convenient and economical. Further, it can be used as a screening test to see if Dynamic Respiratory Endoscopy is indicated to make a more definitive diagnosis. If you would like to learn more about this exciting new ambulatory service offered by the New Jersey Equine Clinic, please give us a call.