350 
SURGERY AND TRANSPLANTATION 
Figure 3. — Schematic representation of model 
Ao — Aorta 
LAD — Left Anterior Descending Coronary Artery 
CCA — Circumflex Coronary Artery 
EMF — Electromagnetic Flow Probe 
Note: Pressure monitoring system and adjustable 
occluders. 
ment, each heart was excised and examined 
grossly for visible collateral vessels. Post- 
mortem arteriograms were performed on se- 
lected hearts from each group to demonstrate 
the presence or absence of collateral vessels. 
Results 
No visible evidence of collateral circulation 
was present in Group 1, and arteriograms with 
injection through the graft failed to demon- 
strate collateral channels between the CCA and 
LAD or right coronary artery. Average graft 
flow in these animals was 65 ± 17 cc/min (mean 
± standard deviation), while LAD flow was 20 
± 3 cc/min. After temporary graft occlusion, 
mean peripheral CCA pressure measured 12 ± 
4 mm Hg, and release was followed by the ap- 
pearance of reactive hyperemia in each animal 
in the CCA bed. Occlusion of the LAD caused 
no demonstrable change in graft flow or in 
peripheral CCA pressure. 
Collateral communications between the LAD 
and CCA were angiographically demonstrated 
in Group 2 by injection of the graft with opaci- 
fication of both CCA and LAD. Varying degrees 
of right coronary artery filling were also seen 
in these animals. The proximal CCA was com- 
pletely occluded by the ameroid constrictor in 
each animal. Control graft flow measured only 
16 ± 8 cc/min, compared to 64 cc/min in 
Group 1. This value did not change during an 
average observation period of two and one-half 
hours. Occlusion of the LAD was accompanied 
by an increase in graft flow to 27 ± 13 cc/min 
(p < 0.05). Control peripheral CCA pressure 
was 62 zt 11 mm Hg contrasted to 12 mm Hg 
in Group 1. LAD occlusion was followed by a 
decrease of peripheral CCA pressure to 41 ± 
17 mm Hg (p < 0.05). After release of LAD 
occlusion, flow in this vessel increased by more 
than two times in each animal indicating re- 
active hyperemia. These measurements demon- 
strated a marked decrease in graft flow with 
elevation of CCA peripheral pressure in the 
presence of collateral vessels. Occlusion of the 
LAD partially eliminated this collateral inflow 
to the CCA and was followed by a significant 
increase in graft flow and concomitant reduc- 
tion in peripheral CCA pressure. 
LAD flow in Group 2 during graft occlusion 
was 33 ± 7 cc/^min compared to 20 cc in Group 
1 indicating that flow from the central LAD 
was supplying both peripheral LAD and CCA 
vascular beds. Opening the graft reduced LAD 
flow to 27 ± 7 cc, but this decrease was not 
statistically signiflcant (p > 0.05). Peripheral 
LAD pressure with the graft occluded measured 
23 ± 14 mm Hg, or slightly greater than the 
value obtained for Group 1. Opening the graft 
elevated LAD peripheral pressure to 34 ± 17 
mm Hg, an insignificant change (p > 0.05). 
After release of graft occlusion, nine of ten ani- 
mals in Group 2 did not demonstrate CCA re- 
active hyperemia. 
