G. SANDBERG, JR., F. MOLOKHIA, P. PONN, F. HUFFMAN AND J. NORMAN 
935 
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Figure 3. — Photomicrograph (500X) of tissue within 1 cm of Radiation Equivalent Source capsule after 14 
months, showing probable radiation effects. Note abnormal fibrocyte (arrow at left) and abnormal endothe- 
lium (arrow at right). 
power source capsule, the largest likely to find 
clinical application. Two ^'^^Am/Be neutron 
sources, each similar to that in the canine RES 
are used in the RES-50, together with a ^''Sr 
Bremsstrahlung source of appropriately greater 
size. RES-50 capsules were implanted in the 
iliac fossae of two baboons and one chimpanzee. 
(Figure 4) Monitoring in the 10 months since 
implantation has failed to reveal systemic evi- 
dence of radiation effect. Extensive gross and 
histopathological studies to characterize tissue 
response to the elevated radiation dose rates 
are planned after the period of chronic observa- 
tion. 
SUMMARY 
Continuing animal model studies of the bio- 
logical effects of chronic intracorporeal heat and 
radiation of the magnitude to be obtained from 
totally implantable nuclear power sources for 
circulatory support devices have been described. 
The acute and chronic responses of dogs to im- 
planted 238pu_f ueled aortic heat exchangers have 
been studied; canines and primates have been 
studied after implantation of heatless "Radia- 
tion Equivalent Sources" of neutrons and pho- 
tons. Major observations from these studies 
can be summarized : 
(1) Animals appear to be able to tolerate ad- 
ditional endogenous heat loads of up to 0.4 
watts/kg both in the acute adjustment and 
chronic exposure periods. Local intra-aortic 
blood temperatures of 45° to 46°C are not in- 
compatible with long-term survival. 
(2) Dogs appear to be able to tolerate for 
more than 3 years continuous intracorporeal 
