Dorsal displacement of the soft palate (DDSP) is a common condition in racehorses for which various surgical treatments are often performed. In light of recent findings that suggested the position of the larynx may influence the occurrence of DDSP, we investigated whether a noninvasive mean of affecting the position of the larynx could be effective in the management of DDSP.
An external device (laryngohyoid support; LHS) positioning the larynx in a more rostral and dorsal location and preventing caudal displacement of the basihyoid bone would be effective in preventing DDSP during strenuous exercise.
Ten horses were exercised on a high-speed treadmill under 4 different treatment conditions: control (n = 10); control with external device (n = 10); after bilateral resection of thyrohyoid (TH) muscles (n = 7); and after bilateral resection of TH muscles with external device (n = 7). Two trials were performed randomly for each of the 4 conditions. In Trial 1, videoendoscopic images of the upper airway, pharyngeal and tracheal static pressures, and arterial blood gases were collected. In Trial 2, airflow measurement combined with mask and tracheal static pressure was obtained, and upper airway impedance calculated. The trials allowed calculation of airway impedance and respiratory frequency, and assessment of ventilation using arterial PO2 and PCO2.
Under control conditions, none of the 10 horses developed DDSP. There was no statistically significant effect from the LHS on airway impedance or respiratory frequency, nor on arterial PO2 and PCO2. Seven of the 10 horses developed DDSP during exercise after resection of the TH muscles. None of these 7 horses continued to experience DDSP during exercise with the external device. In the latter group and condition, the LHS significantly improved inspiratory and expiratory flow and impedance.
The LHS helped prevent experimentally induced DDSP at exercise, probably by statically positioning the larynx in a more rostral and dorsal position.
Field studies are required to investigate whether the LHS can successfully prevent DDSP in horses with naturally occurring disease.