Fibrillation detection method using blood pressure sensor and evaluation of output circuit in implantable defibrillator.

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  • 植込み型除細動器における血圧センサを用いた細動検出方法および出力回路の検討
  • ウエコミガタ ジョサイドウキ ニ オケル ケツアツ センサ オ モチイタ サイ

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Abstract

To obtain a high reliability of fibrillation detection in an implantable automatic defibrillator, a new fibrillation sensor has been developed, and also the defibrillator circuit has been improved.<br>For reliable fibrillation sensing, dual criteria before delivering a shock has been required. Therefore, for the first purpose, a new fibrillation sensing method feasible to simultaneous use with existing ECG sensing, was considered. In our research, blood pressure variation was used as another fibrillation detection factor, and a loss of rhythmic output of the sensor was used to detect fibrillation condition. To be more specific, to detect blood pressure variations intravenously, a catheter type variable capacitance pressure sensor of low power consumption was developed. As the sensing unit, an electret condenser microphone (Matsushita Electric Co. Ltd.: WM 063) was used. The outside was covered with an adhesive (Ciba Geigy Co. Ltd.: Araldite) and polyurethane (Nippon polyurethane Co. Ltd.: P-22 S) for waterproofing and providing antithrombogenesity.<br>For the second purpose, the output circuit of the defibrillator was improved. A gate turn-off thyristor (Hitachi Co. Ltd.: GFT 20 B) was used as an output switching device for consuming energy effectively.<br>The developed sensor and defibrillator were tested in animal experiments. The blood pressure sensor was able to detect the right ventricular pressure variations for 6 weeks at maximum in chronic experiments using 4 mongrel dogs. In acute experiments, the sensor detected electrically induced fibrillation, and defibrillating shock was delivered automatically. Moreover, recharge time after the first stimulation was about 25% shorter because of the residual energy remaining in the capacitor by the improved output circuit.<br>From the results, it has become possible to detect fibrillation reliably using blood pressure sensor as well as ECG. Therefore, by combining the blood pressure sensor and ECG sensing for accurate fibrillation sensing, and by improving the output circuit, development of a high-performance defibrillator has become possible.

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