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ANATOMY AND PATHOLOGY 
deposited fibrin, but we have not yet been able 
to discern differences as a function of type of 
material. With regard to your second question, 
all of these procedures are done under aseptic 
or sterile conditions, so we do not believe that 
sepsis is a problem. 
Dr. Peters : Have you developed a model for 
the venous system as yet? There are those that 
might argue that the severity of the test is 
perhaps not as sensitive or as severe as it 
should be considering the velocity and the char- 
acteristics of arterial blood. 
Dr. Kusserow: There undoubtedly is a 
difference in the propensity of arterial and ve- 
nous blood to form thrombi. We would strongly 
recommend Dr. Gott's system for testing ve- 
nous thrombosis on surfaces. The problem here 
is that it is difficult to assess the embolic 
propensity of implants which are positioned in 
the venous circulation. This is because one can- 
not detect them easily in the lungs. Small pul- 
monary emboli are very difficult to identify. 
Questioner (Unidentified) : What would you 
say about the role of the downspeed flow? The 
second question is what type of sterilization do 
you use? 
Dr. Kusserow: If I understand your first 
question correctly, you would like to know 
whether altered rheology at the implant 
site might account for some of the embolic 
phenomena and the infarcts. I think that we 
have ruled this out by our control studies. 
Thus, in a series of dogs with constric- 
tions alone there were no infarcts. Secondly, 
in another series of controls we inserted rings, 
kept them there momentarily, and then removed 
them. Again, no infarcts were observed. These 
two series of control experiments lead us to 
believe that rheology probably doesn't cause 
infarcts. I hasten to add that those experiments 
in which we ligated or constricted the aorta 
without rings were conducted for a long period 
of time. Accordingly, if altered rheology did 
play a part, it had ample opportunity to do so. 
These preparations were maintained for as long 
as a week or so and we did not see infarcts. 
With regard to your second question: the 
sterilization varied acording to the nature of 
the material. Most materials may be auto- 
claved, and whenever we can we autoclave our ] 
rings. Those which cannot be auotclaved are 
usually sterilized by ethylene oxide. When 
we sterilize with ethylene oxide, we carefully j 
consult with a manufacturer to make sure that 
this procedure in itself will not alter the sur- 
face. 
Charles Meals, V.A. Hospital, Dallas, 
Texas : I was interested when you said the lin- 
ing of your implant was benzalkonium. We're 
putting heparin lining in our tubing at Dallas 
now. We've been cross-linking it with heparin 
and glutar-aldehyde, and it seems to work very 
well being nonthrombogenic. Did you put that on 
these implants? 
Dr. Kusserow : The particular implants that 
I exhibited during the presentation were pre- 
pared according to the initial Gott technique. 
There is an absorbed lining of heparin 
upon the implant. It is apparently not as perma- 
nent as the heparin binding which one obtains 
with cross-linking or with covalent bonding. 
Accordingly, there is a very good possibility that 
the surfaces of which you speak would fare 
better in our test system. 
Dr. Meals : Did you do any of the blood stud- 
ies, for instance, like fibrinogen or any of the 
normal blood studies in comparison with this 
work? 
Dr. Kusserow: No, these are basically 
screening tests, and we have not done detailed 
studies of clotting factors, fibrinogen, and so 
forth. This should ultimately be done and prob- 
ably would be done for any very promising test 
material. 
Questioner (Unidentified) : Considering that 
the kidney is actively functioning during your 
studies, in any of your series had you assayed 
renal function for chemical substances or in- 
ternal pressure fiow changes as they may be 
associated with the infarct itself? Or did you 
do assays as an additional sensitive measure of 
the presence of your test samples? Did you do 
any renal function assays ? 
Dr. Kusserow: No, we have not. This is a 
very interesting suggestion, and my answer 
is that we haven't. 
Tetsuzo Akutsu, Univ. of Mississippi Medi- 
cal Center, Jackson, Mississippi: How many 
