There are many conditions or diseases affecting the patency or openness of the upper airways and the neck region that cause numerous problems for both animals and humans. One well-documented disease that occurs primarily in horses is known as intermittent dorsal displacement of the soft palate (DDSP). DDSP results in an expiratory upper-airway obstruction that is often associated with an expiratory noise in horses during exercise. Horses typically present with a complaint of impaired performance and/or upper respiratory noise. It is thought that DDSP occurs near the end of maximal exercise intensity but it is seen earlier in some horses and also at less than maximal exercise. Because of the immediate marked effect of DDSP on ventilation, decreased performance is seen soon after its occurrence and is more obvious in horses performing at maximal exercise intensity. Respiratory noise associated with DDSP resembles a flutter or snoring coming from the back of the throat. However the sound is not always present or reported by the trainer/owner. Some trainers report that DDSP occurs as a result of a sudden event during the end of competition. It appears that if the concentration of the animal can be maintained, i.e. there is no change in demand placed in the horse, the horse will not experience DDSP and can compete successfully.
As the horse inhales and exhales, air pumps in and out of the lungs through the larynx (voice box) and the airflow is directed to the nasopharynx located above the soft palate and the epiglottis. The airflow can catch and lift the palate on exhalation so that half or more of the airway is blocked. As a result of this observation, it was originally thought that DDSP was caused by an abnormal soft palate that was either weak or elongated. It is also known that inflammation of the airway (pharyngitis) can trigger some DDSP cases by damaging the function of the nerve supply to the soft palate, although most horses with DDSP do not experience such inflammation.
As general management of this condition, a tongue-tie is often placed on the affected animal. The tongue-tie consists of a band of material (generally of cotton material) applied around the tongue in a constricting matter and fixing it to the bottom jaw. This results in reversible interference of the blood supply to the tongue and exterior position of the tongue. This clearly raise question of humane treatment as this blue tongue protrudes from the mouth of the animal during competition. This frequent treatment is thought to improve the patency of the upper airway and prevent swallowing of the tongue (an unproven condition yet still part of popular belief). Other attempts at solving this problem include positioning a coffee can (or similar device) under the horse's throat to prevent it from bending its neck, and other homemade measures. None of these attempts have enjoyed proven success and can also be uncomfortable for the horse.
Additionally, in spite of the often poor knowledge as to what precisely causes DDSP, various surgical procedures are often used in an attempt to correct DDSP. Surgery to remove a small section of the palate, i.e., staphylectomy, seems to help about 60 percent of the time. Another surgery that involves cutting the strap muscles on the lower side of the neck, to prevent the larynx from slipping back and away, i.e., a sternothyroid muscle resection, is also helpful about 60 percent of the time. Some practitioners perform both procedures, but the success rate with the combination surgery remains about 60 percent.
With no surgical treatment of intermittent DDSP being entirely satisfactory, investigators continue to seek alternative therapies. For example, one method involves attempting to stiffen the palate through injection of various materials directly into the palate or by cauterization or lasering of the soft palate. Such procedures also have a success rate of about 60%.
It should also be noted that animals other than horses can experience DDSP. Additionally, these animals can experience other problematic conditions of the upper airway. These include, but are not limited to, snoring, sleep apnea, dynamic nasopharyngeal and velopharyngeal collapse and the like.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a significant need in the art for a practical and effective non-invasive means for diagnosing and treating upper airway dysfunction in animals.