Noninvasive Swallowing Function Assessment Using an Earphone-type Sensor: A Pilot Study on Validation through Simultaneous Measurement with Swallowing Sounds

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Standard methods for evaluating swallowing function, such as videofluoroscopic swallowing studies and fiberoptic endoscopic evaluation, are invasive and environment-dependent. In our previous study, we confirmed through simultaneous VF measurement that specific waveforms detected by an earphone-type sensor correspond to the timing of soft palate movement during swallowing. The aim of this pilot study was to assess the feasibility and potential applicability of this sensor by examining the temporal relationship between swallowing sounds and sensor waveforms. The earphone-type sensor uses an LED and a phototransistor to detect ear canal movements via reflected infrared light. Six healthy adults swallowed 3 mL of water five times while wearing the sensor in the left ear and a throat microphone on the neck. Swallowing sounds (S I, S II, S III) and waveform points (SA, SB) were analyzed for timing. The mean SA-SB interval was 0.37 ± 0.14 s. SA preceded S I in 52.2% and S II in 100% of cases. No significant difference was observed between SA and S I, whereas SB and S II showed a significant difference (p < 0.001). These findings suggest that the earphone-type sensor waveform reflects the timing of soft palate movement prior to passage of the food bolus into the hypopharynx and esophagus. Although limited by a small sample size, this pilot study provides fundamental evidence supporting the feasibility of noninvasive swallowing assessment using an earphone-type sensor.