B. K. KUSSEROW 
819 
RING IMPLANT 
RENAL 
EMBOL US 
TEST SYSTEM 
CELIAC A. 
CRANIAL 
MESENTERIC A, 
SUBTOTAL CONSTRICTION 
SITE OF 
INSERTION 
Figure 1. — The renal vascular bed and tissues serve as a biologic indicator system to document embolic episodes 
at the ring implant site. Subtotal infrarenal aortic constriction diverts the large majority of emboli to the 
kidneys. — Prom Kusserow, Larrov/ and Nichols.^' 
most of the aortic flow at this level into the 
renal vascular bed (Figure 1). The aorta is also 
carefully wrapped with fabric at the implant 
site to eliminate any potential dead space be- 
tween the outer surface of the ring implant and 
the inner surface of the pulsating aorta which 
might serve as a site for adventitious thrombo- 
sis. More complete details of the implantation 
procedure have been described in a previous 
communication.^^ Evaluation of the test ring 
follows implantation periods of 3-5 days, at 
which time the animal is systemically anticoag- 
ulated with intravenous heparin (5 mg/kg) and 
promptly sacrificed. Both kidneys, renal arter- 
ies and the attached segment of aorta (from 
above the level of the implant to a level well 
below the constriction and insertion sites) are 
removed en bloc. The ring implant and tissues 
of the test system are then examined both 
grossly and microscopically for evidence of 
thrombosis or embolization (renal infarcts). 
Hemodynamic Conditions at the Implant Site 
Selected pressure and flow measurements 
were carried out at the implant site to deter- 
mine the nature of the hemodynamic environ- 
ment encountered by the surface under evalua- 
tion. The influence of subtotal infrarenal aortic 
constriction (as described above) upon aortic 
pressure pattern at the implant site is demon- 
strated in Figure 2. Aortic pressure levels show 
relatively little change, although moderate 
blunting of the systolic peaks is apparent 
following constriction. Flow patterns at the im- 
plant site on the other hand appear to be sig- 
nificantly modified following constriction (Fig- 
ure 3). Peak velocities are significantly reduced, 
and there is virtual elimination of the back flow 
component. Measured total renal blood flow 
appears to be well maintained, however. Flow 
measurements further show that approximately 
90% of blood which passes through the aortic 
implant is diverted to the kidneys following the 
aortic constriction maneuver. 
