AN IMPLANTABLE MULTICHANNEL TELEMETRY SYSTEM

D. Rafolt, M. Bijak, E.Gallasch, H. Lanmüller, W. Mayr,
S. Sauermann, Ch. Schmutterer, G. Schnetz, E. Unger,
Department of Biomedical Engineering and Physics, Univ. Vienna Gen.Hospital
Währinger G. 18-20, Vienna, Austria, A-1090

The realization of an implantable m P-controlled 8-channel telemetry system for the measurement of active biosignals like ECG or EMG and passive signals such as impedance, temperature or pressure is described. Additionally mechanical parameters such as force, acceleration and displacement by means of a magnetic field sensor or a differential transformer can be measured. In general all types of sensors which can be configured as a Wheatstone-bridge are suitable for adaptation. The use of a micro-controller (MC68HC705C8), a fast RF-data-telemetry and a slow bi-directional communication link for parameter setting via a magnetic coupling makes the device suitable for a wide field of applications. The scheme of channel selection and signal priority can be configured and re-configured after implantation as well as gain, offset and current source for the Wheatstone bridges for each channel. Maximum sampling-rate is 8kHz (10kHz EMG only) at 8 Bit. Data transmission is realized by digital FM-modulation of a 433MHz carrier. The fully implantable device is battery powered by a lithium thionyl chloride-battery and has a consumption between 300 m A and 4.4 mA depending on the sampling rate. By reducing the m P´s clock frequency for slow-signal-recordings below a sample rate of 100 Hz, the consumption can be droped below 100 m A. In this case the telemeter prospectively will work for more then 4 years. Full-speed-EMG can be recorded for 27 days - 24 hours per day. The implant is enclosed in a titanium package and has no galvanic path to the environment. As sensors and electrodes are exposed to aging or can break they can be exchanged individually.