A FOUR-YEAR STUDY OF LONG-TERM EFFECTS OF 
IMPLANTED DISCRETE HEAT AND RADIATION SOURCES 
IN DOGS AND PRIMATES: PRELIMINARY STUDIES LEADING 
TO IMPLANTABLE NUCLEAR-FUELED 
CIRCULATORY SUPPORT SYSTEMS 
G. W. Sandberg, Jr., F. A. Molokhia, 
P. R. Ponn, F. N. Huffman and J. C. Norman" 
Recipients of totally implanted nuclear powered cir- 
culatory support systems will be exposed continually to 
intracorporeal heat and radiation. Physiologic effects 
of thermal and nuclear radiation doses expected from 
clinical systems are being investigated using canine and 
primate models. Plutonium 238-fueled heat exchangers 
were implanted in series with the aortas of large dogs; 
chronic preparations have been obtained and effects of 
the thermal, gamma, and neutron radiation studied. 
Radiation equivalent sources (RES) composed of 
Americium 241-Beryllium /"Strontium with equivalent 
photon and neutron dose rates but without thermal out- 
puts were implanted in dogs and primates; chronic 
effects have been studied. A dog with a 16 watt ^^Pu 
heat exchanger in the abdominal aorta survived 25 
months before dying from unrelated causes ; and another 
mongrel lived for 26 months with a 24 watt thoracic 
aortic implant. Serial blood studies showed no significant 
abnormality, and at post-mortem, microscopic changes 
were only seen within 1 cm of the radiation source. 
These and similar results from chronic RES implants 
suggest that there are no compelling biologic reasons to 
prevent eventual application of totally implanted nu- 
clear power sources for artificial circulatory support 
systems. 
INTRODUCTION 
Research leading to the development of nu- 
clear-fueled thermal power sources ^ for totally 
implantable cardiac support and replacement 
devices has been in progress in our laboratories 
for the last six years. An integrated system v^^ill 
contain a radioisotope heat source, a thermal 
engine capable of supplying power for blood 
pumping* to a circulatory assist^ or cardiac 
replacement pump, as well as the necessary 
control logic package. 
* Present address: Medical Devices Applications Program, National 
Heart and Lung Institute, National Institutes of Health, Bethesda, 
Maryland. 
** Sears Surgical Research Laboratory, Harvard Medical School, 
Boston City Hospital, Boston, Massachusetts; and Thermo Electron 
Corporation, Waltham, Massachusetts. 
The recipient of such a nuclear-powered de- 
vice will be exposed to continuous intracorporeal 
thermal and nuclear radiation. Preliminary in- 
vestigation suggested that intracorporeal ther- 
mal loads up to 0.64 watts/kg are well tolerated 
in the acute experimental situation.^ In order 
to determine if an animal can tolerate chronic 
thermal and nuclear radiation levels of the mag- 
nitude expected from clinically implanted nu- 
clear power sources for artificial circulatory 
support systems, animal model studies using im- 
planted radioisotope capsules have been carried 
out. 
Animals were studied after the implantation 
of one of three kinds of radioisotope capsules: 
(1) Canine aortic heat exchangers fueled with 
Plutonium-238 (^^spu) capsules with thermal 
outputs of 16 to 24 watts; (1) Canine thoracic 
or iliac fossa implants of "Radiation Equivalent 
Source" capsules (RES) which have radiation 
outputs similar to 24 watt 238p^ capsules, with- 
out significant thermal output; and (3) Primate 
iliac fossa implants of "RES-50" capsules with 
radiation characteristics similar to 50 watt 
2^^Pu sources. The sections which follow de- 
scribe each model and summarize the results 
obtained from the studies. 
=^Pu-FUELED AORTIC HEAT 
EXCHANGER MODEL 
Plutonium-238 is the nuclear fuel most likely 
to be utilized as a heat source in implantable 
thermal engines which can power artificial cir- 
culatory support devices.^ Already, the isotope 
is used in the nuclear powered pacemakers be- 
ing studied in the U.S., England, and France.^ 
Plutonium 238 is an artificial radioisotope pro- 
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