PHILOSOPHY OF MICROWATT CHEST TO POCKET TELEMETRY AND UNDERWATER ELECTROMAGNETIC WAVE TRANSMISSION

Yasuhito Takeuchi
GE-Yokogawa Medical Systems, Ltd.
Hino 191 Japan
takeuchi@us.geyms.med.ge.com

INTRODUCTION A truely wireless signal acquisition and transmission system using microwatt coin-size transmitter taped on to the patient skin, is studied. It has no wire from patient body surface to recording or transpoding device loated in his/her inner pocket of clothing. Design examples and experiences in real world usage, are presented.

METHODS A 5SFr coin size plastic container carries all necessay electronics for 1ch. ECG acquisition and transmission. Lithium coin battery and 433MHz "NBFM FM" single transistor SAW controlled oscillator and LiMnO2 coin battery are also included. It basically aims sealed-off, water-tight, one-time use design for patient own management. Its battery retention time clears 24 hours continuous operation, aerial power is 50 to 100 microwatt level, the electrode leads are used also for antenna. Aerial signal reachs to about 3 to 5 meter distance in office and home environments, to a professional communication receiver. This coverage is quite sufficient to reach to recording or memory device stored in patient clothing pocket, or handbag, or portmanteau. Application includes 24h holter monitoring with patient own management under completely unrestricted, clothing closed as usual, data acquisitions.

RESULTS One of most danger-full spot for heart, in Japanese lifestyle, other than daily work, travel and sports, etc., is the dipping into Japanese style bath, and out. The device, on patient chest, nearly 50cm underneath the water surface, survived and has kept signal continuity for almost all cases. In-water transmission of 433MHz aerial signal was also very clearly seen, and utilized by underwater antenna to form in-water/in-air diversity reception. This style of diversity is crucial for signal continuity in this case. This is reasonable since because flesh (tapped) water for bathing is just a dielectric material, even in this fequency, than sea water being always so lossy media unapplicable for electromagnetic wave propagation. Using another version of this device where aerial frequency and power (in-water) being 100MHz and 1mW, more than 10 meter distance subsurface transmission was obtained with diagnostic quality of output signal, in a swimming pool.

CONCLUSION Chest to pocket telemetry is applicable philosophy for truely wire-less, unconstrained, live study of biological signal. In-water/in-air diversity reception is also crucial, if taking account of bathing and swimming.