負荷による胸壁の機械インピーダンスの変化
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概要
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The mechanical impedance of the chest wall should be observed carefully in measuring the beating of the heart by means of a P. C. G. microphone (Phono cardiograph microphone. ) because various characteristics of the microphone are influenced greatly by the mechanical impedance of the chest wall itself. The author used a vibrating rod to the tip of which a small load with known mass was attached for the measurement of the mechanical impedance of the chest wall (Fig. 1). The rod was driven freely in space in one case and as it was brought in to contact with the chest wall in another case. The ratio of the driving force to the velocity of the rod and the phase difference between the two cases were derived from the result of measurement to calculate the mechanical impedance of the chest wall (Eqs. 14 and 15). The measuring apparatus is shown in Fig. 1, 2 and 5. The mechanical impedance of the chest wall was measured on the left side of the third intercostal sternum with the weight of load varied from 10 to 500 grams, the frequency range varied from 40 to 2000c/s and the contact point of the rod kept at a fixed diameter of 2 centimeters. The principal results of mesurement are shown in Fig. 9, 10 and 11. The author found that the mechanical impedance of the chest wall varied greatly with the weight of load and the stiffness compornent showed a remarkable increase under heavy load weighing 50 grams and above. The average values of the mechanical impedance of the chest wall under various weights of load are shown in Table 2. These results have led the author to the following conclusions: 1) A P. C. G. microphone should be made as light as possible for the measurement of the beating of the heart in hight frequency range. 2) The frequency characteristic of a P. C. G. microphone should rather be decided by its own weight.
- 社団法人日本音響学会の論文
- 1967-01-30