Development of the Screening Device for Dysphagia using Magneto-Impedance Sensor

K. Tanida, Y.Ikeda¹, Y. Sato¹, M. Akutagawa¹, Y. Kinouchi¹, T. Ichikawa², T. Yamamoto², Y. Ishida²

Dept. of Electrical and Electronic Engineering, The University of Tokushima

¹ Institute of Technology and Science, The University of Tokushima

² Institute of Health Biosciences, The University of Tokushima

Introduction

The objective of this study is to develop a screening device for the dysphagia using the Magneto-Impedance (MI) sensor. The Repetitive Saliva Swallowing Test (RSST) [1] is used for screening of the dysphagia. The Repetitive Saliva Swallowing Test (RSST) is a safe and simply screening method for functional dysphagia. In the RSST, when the count of swallowing is less than 3 times / 30 seconds, the subject is suggested to be further investigated for functional dysphagia. After the screening by the RSST, the X-ray videofluorography will be used as accurate diagnosis. Currently, particular training for doctors is required for the RSST.

We developed a screening device to automate the RSST for operating the test without training. The screening device is simply consisted of a MI sensor and a neodymium magnet. The MI sensor can sense the movement of the magnet as the change of magnetic field. The magnet will be attached on larynx of a patient and the waveform from the MI sensor represents the movement of larynx by swallowing. Experimentations are performed to evaluate the availability of the device for two healthy subject. The device can measure the movement of larynx and count the number of swallowing.

Methods

We developed a screening device to automate the RSST. The screening device is simply consisted of a MI sensor and a neodymium magnet as shown in Figure 1. Figure 2 shows the layout of the screening device on a patient. The MI sensor is placed on the manubrium of the patient for that the MI sensor will not to be moved by swallowing, because the MI sensor will sense the geomagnetic field and the movement of the sensor will cause large noises. The magnet is placed on the larynx of the patient to sense the movement of the larynx with swallowing as the change of the magnetic field. Hence, the output signal from the MI sensor represents the movement of larynx with swallowing.

The output signal will be analyzed to count the number of swallowing using a threshold-based algorithm. Figure 3 shows the threshold-based swallowing count algorithm. Vmax is the maximum voltage in the output signal, Vmin is the minimum voltage and Vmean is the mean voltage. Vth1 is first threshold voltage and Vth2 is second threshold voltage defined as (1) and (2).

... (1)

... (2)

When the output signal level is over the Vth2 after the signal was under the Vth1, the count of swallowing will be increased. When there are any other signal pattern, the count will not to be increased.

Results

Figure 4 and Figure 5 show the output signal from the MI sensor when healthy subjects (authors) dry swallow for three times. The count of swallowing were obtained from the output signal using the threshold-based algorithm. In the figures, the circled number 1, 2 and 3 are the count of swallowing. In Figure 4, on the count 3, the output signal level overs Vth1 for two times. The second time of the level overs Vth1 was ignored, because there was no under Vth2 signal after the previous over Vth1 signal. In Figure 5, the over Vth1 signal between the count 1 and 2 was also ignored by the same reason. The threshold-base algorithm could count the number of swallowing when there were noise and distortion in the output signal waveform.

The threshold-based algorithm could response to the difference among individuals. The waveform of the signal in Figure 5 is smaller than Figure 4. The signal was affected from differences of the layout of the MI sensor and the magnet, and differences of the swallowing movement between individuals.

Conclusion

We developed the screening device to automate the RSST. The device is simply consisted of the MI sensor and a neodymium magnet. The device senses the movement of larynx as the change of magnetic field. The threshold-based algorithm could count the number of swallowing regardless of individual difference.

The experimentations were succeeded for young healthy subjects. However, the proof of concept for senior adults and patients of the dysphagia have not to be enough. For the future, we will try the experiments for seniors and patients, and we will improve the device to be practical one.

References

1. Oguchi K, Saitoh E, Mizuno M, et al. The Repetitive Saliva Swallowing Test (RSST) as a Screening Test of Functional Dysphagia (1) Normal Values of RSST. (In Japanese, English abstract). Jpn J Rehabil Med 2000; 37:375-82.

Discussion Board