1136 
MONITORING 
to provide simple body functions or control of 
paralyzed limbs. For example, it is proposed 
to use processed control signals from ear or 
shoulder muscles, not used in normal activity, 
to stimulate and control the paralyzed limb 
muscle to recover some simple limb function. 
Implant Manipulators 
Implant manipulators can be used to release 
drugs or provide mechanical or electrical stimuli 
to perform therapeutic functions. For a certain 
type of cancer a nearly continuous release of a 
small amount of drugs into the blood stream 
over a period of months is desirable. The im- 
plant instrument vi^ill be a preferred method. 
Some of the spinal cord deformities or any other 
body malfunctions that require slow adjustment 
can also be performed by implant instruments 
when developed. 
One can visualize many other implant instru- 
ments that can be used in artificial organs, 
prosthetic/orthotic devices, new therapeutic 
procedures, and medical research. 
A literature survey indicates that various 
telemetering devices have been developed and 
tested. These are implanted or surface mounted 
to transmit from 1 to 8 channels of signals from 
a living subject to a remote receiver a few 
inches to several hundred feet away. The sub- 
jects include humans, birds, fish, and other ani- 
mals. The heart, bladder, muscle, peripheral 
and sensory nerves, brain, and spinal cord have 
been stimulated with electrodes from a single 
pair to about 100 units in parallel. Small motors 
and other electromechanical devices have been 
implanted to generate motion or displacement 
in the body and, in the laboratory, the one- 
dimensional motion of a limb has been con- 
trolled by EMG from the shoulder. However, 
the field of implant instrumentation is an "un- 
derdeveloped" area, with the exception of tele- 
metering and, quite recently, the stimulation 
areas. They are technologically feasible, but be- 
fore they can be realized many problems in ma- 
terials, technology, physiology and psychology 
must be solved. This article discusses the state- 
of-the-art and problems of implant telemetry 
and stimulation. However, most of the discus- 
sion is applicable to the general field of implant 
instruments. 
IMPLANT TELEMETRY 
Implant telemetry is used to obtain informa- 
tion from within the body of an unrestrained 
living organism at a remote location through 
electronic transmission linkage. The block dia- 
gram of a typical telemetry system is shown in 
Figure 1. The implant transmitter unit is lo- 
cated totally within the body of the organism. 
The location may be intracavitary such as 
within the intestines, mouth, bladder, etc., or 
may be inside the body between the internal 
as well as external surfaces, such as subder- 
mally or deep in the tissues. Surely, the same 
transmitter can also be mounted on the surface 
of the body when desired. The radio receiver 
and signal processor are remotely located to 
receive, record and display the information. 
Design criteria of implant transmitters are : 
(1) Small size and weight; less than a few 
percent of the size and weight of the 
subject; 
(2) Minimum body reaction: packaged 
with nontoxic materials and with 
proper shape to reduce tissue reaction 
to the implant ; 
(3) High sensitivity (microvolts) and wide 
dynamic range, to handle signals rang- 
ing from microvolts to millivolts ; 
(4) Good fidelity; 
(5) Low power consumption and long life- 
time ; 
(6) Reliable, rigid, and easily handled; 
(7) Suitable transmission range to permit 
the free movement of the subject and 
the use of units with the same fre- 
quency at nearby locations without in- 
terference ; 
IMPLANTED CIRCUITRY 
SENSOR 
CONDITIONER 
TRANSMITTER 
J 1 L 
RECEIVER 
SIGNAL 
PROCESSOR 
READOUT 
1 
1 1 
POWER 
SUPPLY 
RECEIVER CIRCUITRY 
Figure 1. — Block diagram of a telemetry system. 
