胃内 pH モニタ用テレメータカプセル Telemetry Capsule for Gastric pH Monitoring
This paper presents a telemetry capsule for measuring gastric pH. The electrode of the new capsule is iridium oxide. Contrary to an antimony electrode, this iridium electrode does not possess toxicity and is more solid than a glass electrode. The electromotive force and the diameter of the iridium electrode is 57mV/pH and 0.25mm. The process of modulation is PFM-FM, because the instability of the frequency of the FM circuit lacks reliability to pH monitoring using telemetry. The PFM circuit is a voltage controlled oscillator (VCO) circuit. The current consumption of VCO is 770μA. The range of the frequency variation is less than ±10Hz when the center frequency of VCO is 6.54kHz. The voltage of the power supply which is two 1.5V silver oxide batteries is held in 2.5V by two voltage regulators. The electronic circuits required for the capsule were customized into 2 hybrid ICs. The capsule diameter and length are 12mm and 28.5mm. The total current consumption of the electronic circuit is 3.51mA. The measurable time is 2.5 hours and the error is 0.2 pH. In order to confirm the usableness of our capsule, the gastric pH of a fasted dog was monitored. After confirming that the capsule was in the stomach with an endoscope, ranitidine which is and inhibitor of acid secretion was injected to the dog's vein in order to measure pH alteration. After intravenous injection, pH value started to increase from pH1.5 to pH4 remarkably. Though the suction pump and the driver of the endoscope were working during this measurement, the demodulated wave form was not influenced by the electromagnetic noise of these devices. We conclude that our capsule is usable to measure gastric pH. Further studies, however, are necessary for improvement of the miniaturization of capsule size for clinical application.
計測自動制御学会論文集 31(6), 699-704, 1995-06
The Society of Instrument and Control Engineers