The displaced equine soft palate as a source of abnormal respiratory noise during expiration.

Summary Reasons for performing study: To develop the technique of respiratory sound analysis for the diagnosis of dorsal displacement of the equine soft palate. Objectives: To show that 1) the displaced soft palate can spontaneously vibrate in the presence of expiratory airflow; 2) the observed frequency of vibration can be detected in respiratory sound recordings; and 3) the frequency of vibrations measured in cadaveric specimens are similar to those obtained from audio spectra in exercising horses with DDSP. Methods: Palatal movements and respiratory sounds were recorded from artificially ventilated cadaveric heads. The fundamental mode of palate vibrations calculated from high-speed videoendoscopic recordings was compared with frequencies detected in the audio spectra and with data collected from exercising horses with DDSP. Results: Palate vibrations occurred when air was blown through the trachea. The fundamental mode of vibrations was present in the audio spectra and was not significantly different from those recorded in vivo. Conclusions: Vibrations of the soft palate are the probable source of expiratory sounds recorded in horses with DDSP. Potential relevance: This study strengthens the case for the application of respiratory sound analysis in the diagnosis of DDSP in exercising horses.