A Method of Evaluating Swallowing Function using Swallowing Sounds

Objectives: The purpose of this study was to establish a noninvasive method of evaluating swallowing function using swallowing sounds.

Methods: Five healthy, fully dentate males and four handicapped patients with congenital or postnatal dysphagia were selected as subjects. A jelly on the market for the elderly in need of nursing care was used as the test food. The subjects were requested to swallow a jelly. To record the swallowing sounds, a heart-sound microphone was connected to the ultra-sound diagnostic equipment through a physiologic signal unit. An endoscope was used to observe the bolus and larynx. Furthermore, close-up images of the neck were recorded to observe the rise of the larynx at the surface of the skin using a digital video camera. The swallowing sounds, endoscopic images and video images of the neck were simultaneously recorded on a DVD recorder.

Results: In all the healthy subjects, the first swallowing sound before endoscopic whiteout and the second swallowing sound after endoscopic whiteout were detected in the swallowing test. The larynx started to rise at the same time as the first swallowing sounds. On the other hand, in all the subjects with dysphagia, the first swallowing sound and endoscopic whiteout were detected. However the second swallowing sound was not detected clearly in the 3 subjects with congenital dysphagia. Waveforms of an unclear first swallowing sound or second swallowing sound were observed repeatedly in the subject with postnatal dysphagia. A part of the bolus aspirated into the trachea upon inspiration made some patients choke and cough.

Conclusion: Our findings suggest that the bolus remaining around the epiglottis contributes to an increased risk of aspiration and that observation of the second swallowing sound may be effective in the evaluation of swallowing function.