Biomedical telemetry techniques.

The landmarks and important state-of-the-art work in biomedical telemetry are reviewed. The advantages provided by transmission of physiologic data from minimally restrained to completely unencumbered subjects with biomedical telemetry systems is discussed both from the standpoint of the wide variety of physiologic parameters and subjects that can be monitored and in terms of the various proven electronic techniques for implementing this mode of physiologic data transmission and recovery. Monitored parameter capabilities now include biopotentials (ECG, EMG, EEG), temperature, mechanical events (muscle force, limb motion), pH, pressure (ICP, blood pressure), and others. The system developments in biomedical telemetry have had the aims of minimizing size, weight, and volume while extending the operating capabilities of the systems in terms of minimum required power, multiplicity of data channels, and reliable operation in the intended operating environment. These developments have progressed from discrete transistor to integrated microcircuit implementations in systems which can encode the physiologic data as FM, PAM, PWM, or PCM. Biotelemeters can be utilized as external (backpack) or completely implantable devices and today may be found in the research laboratory, the intensive care unit, portable patient care units, and in the freely ranging animal in the field usually employing a radio link. Also discussed are considerations for power sources and power source recharging through the tissues of implanted subjects. There are advantages and disadvantages to using biomedical telemetry, to using implanted or external biotelemeters, and to each of the various encoding techniques. These are considered, and the future of biomedical telemetry is projected.