THE USE OF ANIMALS IN MEDICAL RESEARCH 
AND EXPERIMENTATION* 
H. Sandler, T. B. Fryer* and H. L. Stone" 
AH parameters necessary for the description of car- 
diovascular performance in hydraulic or mechanical 
terms can be presently obtained by telemetry from units 
implanted completely inside the body. These include 
the electrocardiogram (ECG), pressure, dimensions 
and flow. Single channel ECG units have been im- 
planted in animals ranging in size from a mouse to a 
Rhesus monkey to a dog. Such units have functioned 
with continuous transmission of data for periods in ex- 
cess of one year. Multichannel units have been chroni- 
cally implanted in dogs and chimpanzees and have 
functioned for periods in excess of one year. Battery 
power for multichannel units has been conserved by the 
use of implantable switches. Multichannel operation is 
provided by a time sharing multiplex scheme for 
switching between various sensor inputs. Data are 
transmitted on a single carrier frequency so that only 
one receiver is required for recording 5-8 channels of 
data. Sampling rate is 0.7 msec per channel. Present 
range of transmission for single channel units (continu- 
ous operation) is 3 to 5 feet; multichannel units trans- 
mit 50 to 100 feet. A system has recently been devel- 
oped to recharge the implanted battery using RF ra- 
diated to a subcutaneously implanted coil. Recently, 
multichannel backpack units have been developed for 
measuring flow using Doppler and electromagnetic flow 
transducers. Backpack units have also been designed to 
contain a transponder which receives the weaker trans- 
mitted signal from an implanted unit and retransmit the 
received signals for far greater distances. Distance and 
duration of transmission with such latter units depend 
solely on the available power supply in the backpack. 
INTRODUCTION 
As a consequence of continued advances in 
bioinstrumentation and microelectronics, single 
and multichannel systems are now available for 
transmitting selected physiologic signals from 
surgically implanted units. Interest in the use 
of such systems has been strongly stimulated by 
recent investigations which require information 
from experimental subjects in a relatively nor- 
* NASA-Ames Research Center Moffett Field, California. 
*♦ Marine Biomedical Institute Galveston, Texas. 
mal physiological and psychological state and 
under conditions which interfere with normal 
patterns of activity as little as possible. Biologic 
use of these systems can now be traced back ap- 
proximately 15 years and have been made possi- 
ble by the development of the transistor. This 
latter device has allowed for construction of te- 
lemetry units which are small in size and low in 
power consumption, leading eventually to units 
which can be swallowed or implanted inside the 
body cavity without significant alteration of 
physiologic function. 
The use of completely implantable systems 
rather than backpack devices for measuring the 
same functions involves added complications to 
any experiment. Chief among these are the 
needs for miniaturization, protection of all com- 
ponents against corrosion by body fluid and 
high reliability of operation for long periods of 
time, since they become inaccessible once im- 
planted inside the body. The need for a totally 
implanted power source, usually batteries, is 
also a serious design problem since they ordi- 
narily have a limited life expectancy. On the 
other hand, the use of backpack units which uti- 
lize equipment placed on the surface of the body 
have other problems. These include the require- 
ment that transducer leads penetrate the skin 
and that the transmitting system be worn in 
some protected fashion on the body surface if 
chronic or long-term measurements are to be 
made. The site at which the leads or wires 
emerge from the skin frequently become in- 
fected or act as a means for body surface bac- 
teria to enter inside the body cavity and are 
often a source for irritation to the animal and 
must also be protected ; they may often be dam- 
aged deliberately or unintentionally by the ani- 
mal or man. Many protection devices have been 
designed for the backpack transmitters such as 
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