Intra-aural swallowing sound analysis with simultaneous videofluoroscopy and cervical swallowing sound recording

Haji et al. reported that characteristic click-like sounds during the swallowing reflex were recorded with a small lavalier microphone placed in the ear. They also reported that endoscopic and phototubometric observations showed that these sounds were likely related to the opening and closing of the Eustachian tube during swallowing. In the present study, we performed simultaneous videofluoroscopy and intra-aural swallowing sound recording, as well as simultaneous recording of intra-aural and cervical swallowing sounds, to further verify that intra-aural swallowing click sounds reflect the opening and closing of the Eustachian tube. Additionally, we sought to evaluate the characteristics and usefulness of these sounds for evaluating swallowing function and studying swallowing dynamics.

We performed simultaneous videofluoroscopy and intra-aural swallowing sound recordings in 27 patients without ear lesions whose swallowing function was evaluated as normal, and simultaneous intra-aural and cervical swallowing sound recordings in 25 healthy young adults without subjective dysphagia or ear disease. Intra-aural swallowing sounds were recorded with a lavalier microphone placed in the ear. From simultaneous videofluoroscopy and intra-aural swallowing sound recordings, the point of rise of the intra-aural swallowing click sound, the point of nasopharyngeal closure, the point where the contrast medium reached the hypopharynx, and the point of maximum elevation of the larynx were determined, and their temporal relationship was examined. The differences between the simultaneously recorded intra-aural and cervical swallowing sounds were also investigated in dry and water swallowing.

Intra-aural swallowing click sounds occurred immediately before nasopharyngeal closure, followed by contrast medium reaching the hypopharynx and laryngeal elevation. Intra-aural swallowing click sounds were observed to precede cervical swallowing sounds in all cases of both saliva and water swallowing. Conversely, no corresponding click sounds were recorded in cervical swallowing sounds. The interval between the onset of the intra-aural swallowing click sounds and the maximum sound pressure of the cervical swallow sound was found to be significantly different between water and saliva swallowing.

The results of this study suggest that intra-aural swallowing click sounds are produced by the opening and closing of the Eustachian tube during swallowing and serve as a temporal indicator of the constant point at which the swallowing reflex begins its sequence. Therefore, recording and analyzing intra-aural swallowing click sounds could be a useful tool for studying swallowing dynamics and assessing swallowing function without the need for expensive equipment. It is important to note, however, that these click sounds may be influenced by Eustachian tube function.