WEN H. KO 
1137 
(8) Compliance with Federal Communica- 
tions Commission regulations for radio 
transmission. 
Major considerations in selecting a telemetry 
system are : 
(1) Characteristic of signal and perform- 
ance required ; 
(2) Size, weight, and package as deter- 
mined by the required life-span of 
the implant device ; 
(3) Implant location and techniques ; 
(4) Environmental interference and sys- 
tem requirements; 
(5) Reliability and cost. 
The earliest medical telemetry recorded was 
an FM link used to transmit pneumograms in 
1948.'' After the transistor became available 
about 1954, the telemetry development flour- 
ished. A good historical review of biomedical 
telemetry has been given by Caceres and Mac- 
kay.* Surveys and bibliographies on biotelem- 
etry are also available.^-^ Journals on bio- 
medical engineering, medical instrumentation 
and telemetry usually carry recent developments 
in biotelemetry. Many physiological signals 
have been telemetered. The characteristics of 
these signals are summarized in Table I. 
According to special considerations in each 
application, the engineering decision in design- 
ing an implant telemeter will include : 
(1) Power Supply: Active (powered by 
battery or other active sources) or 
Passive (externally powered) ; 
(2) Number of signal channels: single 
channel or multiplex ; 
(3) Range; 
(4) Function: Tracking or signal trans- 
mission ; 
(5) Modulation scheme: (a) direct mod- 
ulation or with subcarrier; (b) AM, 
FM, or PM. 
Advantages and disadvantages of these choices 
are the same as for space and industrial telem- 
etry and can be found in regular textbooks. 
Active power supply may be chemical pri- 
mary, secondary, nuclear batteries or energy 
converters which convert body energy into elec- 
trical energy. The passive implant telemeter 
may contain a resonant circuit in which the 
resonant frequency, made to vary with body 
signal, can be detected by a grid dip meter ^ or 
may contain transmitters powered by pulses of 
radio energy stored on a capacitor, or the trans- 
mitter may be powered by continuous radio en- 
ergy supplied at other frequencies.® 
Many single channel telemetry units have 
been used. Compelled by the limitations on size 
and weight, most of the present transmitting 
units use one or two transistors to obtain trans- 
ducer, conditioner, and transmitter functions. 
With the new micropower techniques, these 
Table I. — Signal Characteristics of Telemetered Parameters 
Physiological Parameters 
Transducer 
Amplitude Range 
Frequency Range 
Electrocardiogram (EKG) Electrodes 
Electroencephalogram (EEG) Electrodes 
Electrogastrograph Surface electrodes.. 
Electromyogram (EMG) Electrodes 
Eye Potential; EOG or ERG.. 
Nerve Potentials 
Electrodes- 
Electrodes- 
0.05—4 mV pulse 0.1—100 Hz 
10—75 iiV 0.5—200 Hz 
10—350 fiV 0.05—0.2 Hz 
0.1 — 4 mV pulse.. 
500 /iV 
3 mV peak.. 
2—105 Hz 
(10—500 Hz clinical) 
0—250 Hz 
up to 1000 pulses/second 
rise time 0.3 /isec 
Bladder Pressure- 
Blood Flow 
Blood Pressure.. 
Gastrointestinal Pressure 
Intestinal Forces 
Respiration Rate 
Stomach pH 
Temperature. 
Tidal Volume- 
Strain gauges 
Electromagnetic flowmeter; 
ultrasonic flowmeter— 
Strain gauge on artery; hydraulic 
coupling to transducer; cuff gauges.. 
Variable inductance 
Strain gauges 
Electrode impedance; piezoelectric 
devices; pneumograph 
0 to 100 cm H2O 0—10 Hz 
1—300 cm/sec... 1—20 Hz 
0 — 400 mm Hg...^ 
20 — 100 cm haC. 
1— 40 gm 
0.5—100 Hz 
0—10 Hz 
0—1 Hz 
0.15—6 Hz 
Glass electrode; antimony electrode 3 — 13 
Thermistor; thermal expansion 90° — 100 
Impedance; pneumograph 
0 — 1 cp-min 
F 0—0.1 Hz 
50—100 ml per breath—..^... 0.15—6 Hz 
