Development of Evaluation of Swallowing Using Neck Electrical Impedance

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We have proposed impedance pharyngograpy (IPG) which is a new evaluation method of swallowing disorders, In the measuring method of IPG is used the four-electrode technique, which is hardly influenced by skin impedance, based on sinusiodal constant current (50 kHz, 0.5 mA). The equivalent series resistance of the evaluated part is measured as impedance using synchronous rectified method. Considering the below mentioned frequency characteristics of IPG, the cut-off frequency of low pass filter is decided as 25 Hz. The electrodes are non-polarization Ag-AgCl skin surface type of 10 mm diameter.We decided the locations of electrodes, considering the conditions about the location of the measured part and change value of impedance. The location of current electrodes is a point of meeting the following two straight lines. The one line joins angle of mandible and condyloid process of mandible. The other line is parallel to mandible and this line is required that adhesive collars for electrodes is on the border between neck and chin. The location of potential electrodes is on line parallel to mandible and inside of the location current ones. The distance between electrodes is 25 mm. A subject sits on a chair and keeps 10 cc water in his mouth. The angle of the chair back is 75 deg.The changes of impedance is caused by the changes of the sharp of esophagus with movement of the bolus of food. We found that the period of main impedance decrease was the same period of pharynx. The phase of swallowing in normal subject can be divided by IPG.The power spectrum density in frequency component of more than 10 Hz is less than -60 dB, From this view point one may say that information about swallowing movement almost includes frequency component of less than 10 Hz.This method can be applied for diagnosis of swallowing disorders. Our future study is to investigate diagnosis considering patterns of IPG using normals and patients data.