On the Measurement of the Mechanical Impedance of Human Chest Wall with a Vibrometer of Dynamically Driven and Electrostatically Measuring Type

Abstract

Detailed information on the mechanical impedance of human chest wall is mandatory in estimating the heart sound and designing the phonocardiographic microphone. In order to meet the purpose of obtaining the infomation, an electrostatic transducer has been constructed on a phonocardiographic microphone of contact type as a mechanical impedance-measuring device (vibrometer) which is driven electrodynamically and picks up the signals electrostatically. With the aid of this device, the mechanical impedance of human chest wall has been measured under various contact forces. According to this method the contact force is controlled very easily and accurately during measurement.
The experimental results indicate that the magnitude of the mechanical impedance of human chest wall, having its minimum value at 100 to 200 cps, increases along with the contact force below the frequency giving the minimum inpedance but is not sensitive to the change of the force above this frequency.