GERAED S. KAKOS AND H. NEWLAND OLDHAM, JR. 
349 
graded occluder) caused no coronary pressure 
gradient or appreciable change in distal circum- 
flex coronary flow. Data obtained at these times 
mimicked results gathered with the previous ma- 
nipulations and were the same as control values. 
Increasing the proximal circumflex stenosis, 
however, decreased distal circumflex flow by 
35 % to 83 % , depending on the degree of steno- 
sis, and produced pressure gradients across the 
obstruction of 10 mm Hg to 70 mm Hg. While 
maintaining the stenosis, the graft was opened 
and distal circumflex artery flow returned to 
the control value. Flow through the subtotally 
occluded proximal circumflex coronary artery 
was noted to decrease an additional 17% to 
39%, and the bypass graft now supplied 74% 
to 100 % of the total, distal circumflex coronary 
flow (Figure 2). Again, no quantitative or quali- 
tative alterations in distal circumflex of LAD 
Figure 2. — Note marked decrease in proximal coronary 
artery flow through stenotic segment once the bypass 
graft is opened. 
flow or in the cardiac output or aortic and cor- 
onary pressures were noted. 
II. EFFECTS OF COLLATERAL CIRCULATION 
Methods 
Two additional groups, each containing 10 
dogs weighing between 20 and 26 kilograms, 
were studied during identical pentobarital anes- 
thesia and mechanical ventilation. Group 1 con- 
sisted of 10 animals with a jugular vein auto- 
graft acutely inserted between the aortic arch 
and the circumflex coronary artery (CCA), and 
ligation of the CCA proximal to the anasto- 
mosis. Again, the coronary artery anastomosis 
was performed during temporary circumflex oc- 
clusion without the use of cardiopulmonary by- 
pass or a local shunt, using the identical surgi- 
cal technique described in Part I. Group 2 was 
composed of an additional 10 dogs with an 
ameroid constrictor placed on the proximal 
CCA in standard fashion. Six weeks later a by- 
pass graft was inserted between the aorta and 
the CCA distal to the site of the constrictor, and 
these animals were then studied. In both groups 
electromagnetic flow probes (identical to Part 
I) were placed on the ascending aorta, proximal 
left anterior descending coronary artery (LAD) 
and vein graft (Figure 3) . Pressures were moni- 
tored in the ascending aorta, LAD and CCA us- 
ing matched Statham P23Db transducers. Ad- 
justable snares were placed around the graft 
and LAD for temporary occlusion. After 90 
minutes of stabilization, simultaneous control 
pressures and flows were recorded on a multi- 
channel direct writing oscillograph. 
Mean peripheral LAD and CCA pressures 
were used to indicate collateral flow between 
these two vascular beds. Measurements were 
obtained after proximal occlusion of each ves- 
sel for one minute while recording the mean 
pressure in the respective peripheral arterial 
bed. Following release of this occlusion, meas- 
urements of reactive hyperemia were recorded. 
In both groups, graft flow and peripheral CCA 
pressure were recorded with the LAD first open 
and then totally occluded. Group 2 animals also 
had measurement of LAD flow and peripheral 
pressure with the graft both open and com- 
pletely occluded. At completion of the experi- 
