3. Evaluation of Swallowing Movement by Posture Changeusing Magnet-Impedance Sensor
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K.Tanida , M.Akutagawa , Y.Kinouchi , T.Ichikawa , S.Hongama
1Graduate School of Advanced Technology and Science The Univ. of Tokushima
2
Institute of Technology and Science The Univ. of Tokushima
3
Institute of Health Biosciences The Univ. of Tokushima

Introduction
The objective of this study is to develop a screening device for the swallowing difficulty using
Magneto-Impedance sensor. VideoFluorography (VF) is effective to the diagnosis of swallowing
difficulty. This diagnosis method is not effective to every patient. Because it has radiation exposure
hazard, and is costly and takes long time for the diagnosis [1]. Consequently, an easy screening
method has been widely used. The Repetitive Saliva Swallowing Test (RSST) is one of effective
screening methods of the swallowing difficulty.
In this study, we developed the screening device to automate the RSST using a Magnet-Impedance
sensor (MI sensor). And we verified whether the measurement of swallowing movement waspossible by using the screening device. In addition, the influence of posture change on swallowingmovement was evaluated by the change in subjects’ posture when measuring it. Measurement result
was different respectively by subject’s posture change at measurement. We examined the posture that
was appropriate for swallowing by analyzing measurement result.
However, the screening device seems to be hard to obtain enough result, because its body moves
when swallowing. In this time, we did the measurement that used Three-Dimensional MI sensor as
countermeasure of this problem.

Materials and Methods
The Repetitive Saliva Swallowing Test (RSST) is safe and simply screening method of theswallowing difficulty. It is performed by counting the frequency of swallowing over a 30 seconds.
When the count of swallowing is less than 3 times/30 seconds, the subject is suggested to be further
investigated for functional dysphagia by RSST [2].
We developed the screening device to automate the RSST. The screening device consists of a MIsensor and a magnet as shown in figure 1. Figure 2 shows the layout of the screening device on apatient. A magnet was attached on the larynx, and a MI sensor was attached on breastbone. The
movement of magnet, which was the movement of the larynx according to swallowing, was detectedwith MI sensor as a change in the magnetic field. The output signal from MI sensor shows themovement of the larynx with swallowing.
In this time, we measured the swallowing movement by this method for healthy subjects and senioradult subjects. The screening device measured the swallowing movement, when subject was healthypeople (figure 3). However, we were hard to obtain enough result, when subject was senior adults(figure 4). Because a MI sensor moved by body movement of senior adult, when swallowing. A MIsensor detects terrestrial magnetism besides the swallowing movement by this cause [3].
Consequently, we examined the influence of subjects’ posture on swallowing movement bymeasuring it by various postures. We are expected that body movement when swallowing wassuppressed by examining the posture that was appropriate for swallowing as a result of obtaining. In
this time, we measured it by five kinds of posture of standing position, dorsal position, seatedposition, and cervix part bent position (the angle is 30 and 60 degrees).
In addition, we developed the screening device, using Three-Dimensional MI sensor as
countermeasure of terrestrial magnetism by body movement. Figure 5 shows the layout of thescreening device using Three-Dimensional MI sensor. This screening device can detect swallowing
movement in three directions. However, it is necessary to switch the axial direction by control
program when measuring, because only one output pin was mounted on this MI sensor. In this time,
we did two kinds of measurements. One was measurement that changed axis every 5 seconds. And
the other was measurement that changed axis every 1 millisecond.
MI sensor : MI-CB-1DS
High sensitivity AC magnetic filed
detection typeMade by
Aichi Micro Intelligent Corporation
Sensitivity : 40[mV/mG]
Frequency band restriction : 0.3~5.0[Hz]
Magnet : Nd-Fe-B
Maximum energy product : 50.0[MGOe]
31[mm]

10[mm]

4.5[mm]Figure 1 : The MI sensor and a magnet

Analysis on the PC“Judgment of presenceof swallowing”“Count the number ofswallowing”
MagnetMI sensor

16bit A/D card

Figure 2 : The layout of the screening device

4vo ltag e [V ]4vo ltag e [V ]o u tpu t s ig n al

5o u tpu t s ig n al5323211000

2

46tim e [s ]8100

12Figure 3 : Swallowing three times(healthy subject, male, 22 years old)

51015tim e [s ]

20

25

30

Figure 4 : Swallowing eight times(senior adult, male, 77 years old)

G2 Motion sensor : AMI501

X axisZ axisMade by
Aichi Micro Intelligent Corporation

Y axisMagnetThree-Dimensional MI sensor
Figure 5 : The layout of the screening device (using Three-Dimensional MI sensor)

Results
Figure 6~9 show the measurement results when 24 years old male did swallowing in state of fivekinds of posture (refer to figure 3 for the result in the state of seated position). A MI sensor could notdetect swallowing movement accurately by the postures of standing position and dorsal position(figure 6, figure 7). On the other hand, a MI sensor detected swallowing movement accurately by theposture of cervix part bent position (figure 8, figure 9). The comparable result was obtained from themeasurement intended for other healthy subject of several people.
Figure 10 shows the measurement result of using Three-Dimensional MI sensor when the axischanged every 5 seconds (figure 11). The larynx did movement different in each axis. Figure 12 andfigure 13 show the measurement result when the axis changed every 1 millisecond (figure 14). The
screening device made the terrestrial magnetism by sensor movement constant by calculating theabsolute value of the output (figure 15).
o u tput s ig n aloutput
signal544
vo ltage [V ]vo ltag e [V ]o u tpu t s ig n al53232110002406246Figure 6 : Result by standing position

4vo ltage [V ]vo ltag e [V ]o u tpu t s ig n al

5432132

10001234567Figure 8 : Result by cervix part bent position(angle of posture is 30 degrees)
X ax is

1 .5

Y ax isZ ax is10 .5

002460123456tim e [s ]tim e [s ]vo ltage [V ]10Figure 7 : Result by dorsal positiono u tpu t s ig n al

58tim e [s ]tim e [s ]8- 0 .5-1
tim e [s ]101214Figure 9 : Result by cervix part bent position(angle of posture is 60 degrees)7Figure 11 : The axis change every 5 seconds

Figure 10 : Result when the axis changed every 5 seconds
o u tpu t s ig n al = | B |32vo ltag e [V ]2vo ltag e [V ]o u tpu t s ig n al = | B |310100510tim e [s ]1520

Figure 12 : Swallowing three times(when body was not moved)

0510tim e [s ]1520

Figure 13 : Swallowing three times(when body was moved by intention)
Value of terrestrial magnetism : B0
Value of magnet movement : Bm
Value of output of sensor :B = B0 + Bm = BX + BY + BZ
Final output : B =Figure 14 : The axis change every 1 millisecond

BX2 + BY2 + BZ2

Figure 15 : Calculation of absolute valueDiscussions
As a result of the analysis, swallowing movement appeared remarkably when subjects’ posture wascervix part bent position (figure 8, 9). One reason of this result was considered that the subject’s
esophagus was expended by gravitation. The other reason was considered that subject’s trachea wasnarrowed by gravitation [4]. For these reason, Cervix part bent position produced the best situation
for swallowing.
In addition, the larynx greatly moved in the direction of Z axis (figure 10). Because, movement ofepiglottis appeared remarkably to the direction of Z axis when swallowing.
The Three-Dimensional MI sensor did not influence body movement when swallowing, because
figure 12 resembles figure 13 closely. Reason of this result was the Three-Dimensional MI sensor
made the terrestrial magnetism by sensor movement constant, by the axis was changed fast (figure14).

Conclusions

In this time, we developed screening device for the swallowing difficulty using Magnet-Impedance
sensor. And we could measure the swallowing movement. In addition, we examined the influence ofsubjects’ posture on swallowing movement. The results presented in this paper indicate that the mostsuitable posture for swallowing was cervix part bent position.
However, the screening device seems to be hard to obtain enough result, when patients’ body
moved when swallowing. To combat this problem, we measured the swallowing movement using theThree-Dimensional MI sensor, and made the terrestrial magnetism by sensor movement constant.
For the future, it is necessary to make the high precision analysis method, and to measure for thesenior adults and patient.

References[1] S.Hongama, T.Ichikawa, K.Nagao, M.Murata,“MI-sensor Navigated Measuring System for Repetitive Saliva Swallowing Test (RSST)”[2] K.Oguchi, E.Saitoh, M.Mizuno, M.Baba, M.Okui, M.Suzuki“The Repetitive Saliva Swallowing Test (RSST) as a Screening Test of Functional Dysphagia (1)Normal Values of RSST”
The Japanese Journal of Rehabilitation Medicine Vol.37, 375-382, 2000
[3] K.Tanida, Y.Ikeda, Y.Sato, M.Akutagawa, Y.Kinouchi, T.Ichikawa, S.Hongama“Measurement Device for Movement of the Larynx using Magneto-Impedance Sensor”
The Journal of the Japanese society for the 7th International Conference on MagneticApplications in Dentistry, JSMAD, March 3-March 21, 2008[4] N.Kitaoka, T.Ichikawa“Influence of Body Position on Swallowing”
The Journal of Japanese Society of Stomatognathic Function Vol.8, 51-52, 2001