Pilot Study on an Acoustic Measurements System of the Swallowing Function Using an Acoustic-Emissions Microphone

The goal of this study is to evaluate the swallowing functions of people with dysphagia using an acoustic microphone sensor. As a basic investigation towards this end, we measured the swallowing sounds using an acoustic emissions microphone sensor (AE sensor), then analyzed the frequency range of the measured signals, and we examined the method for obtaining the necessary information to evaluate the swallowing functions. For the measurement, two types of sensors, i.e., a condenser throat microphone and an AE sensor, were employed to measure the swallowing sounds. The acoustic signals obtained were subjected to spectral analysis using the wavelet transformation, and a comparison was performed between the measurable ranges of the acoustic signals obtained by the AE and the acoustic sensors. The results from the wavelet transformation of the acoustic signals obtained by the AE sensor indicated that acoustic signals generated during swallowing contained frequency information of 3 kHz and higher, which were not measurable with the acoustic sensor used in the experiment. In addition, we proposed a method of evaluating swallowing sounds using a novel approach based on the probability distribution. From the analysis results, it was found that the distance between the theoretical values and the measured values has a high correlation with the sample viscosity. Furthermore, it was found that the data measured with the AE sensor more sensitively reflected the difference in the sample viscosity. We were thus able to demonstrate the possibility of evaluating the swallowing function via the proposed method.