132 
CARDIAC MODELS 
mm.Hg 
20 
16. 
12. 
8. 
4. 
O. 
100 
90. 
80. 
70. 
60. 
_ 
LEFT ATRIAL PRESSURE 
CARDIAC OUTPUT 
ngm.°A> 
65 
55. 
45. 
35. 
25. 
15. 
2 
I hou rs ' 
CORONARY FLOW 
1 2 
<hou rs I 
[lactate] 
160. 
130, 
100. 
70. 
40. 
AORTIC PRESSURE 
, , , PERIPHERAL VASCULAR RESISTANCE 
D).nes/(m./se<.-5 Kg.M./min. 
7000_ 2.6. 
2.2. 
6OO0J 
5000. 
12 3 4 
(hours) 
LEFT VENTRICULAR WORK 
4000. 
1 2 
(hours) 
mm.Hg 
200_ 
100. 
0 12 3 
ARTERIAL OXYGEN TENSION 
prior to 
dooth 
Figure 13. — Graphs illustrating mean findings in ten control animals after ligation of left 
coronary artery branches. 
lateral coronary circulation becomes manifest, 
it appears that counterpulsation also provides 
the circulatory support required until improved 
cardiac function becomes apparent and the 
heart can again maintain normal circulation. 
The results also suggest that counterpulsation 
by increasing circulation to ischemic myocar- 
dium may have prevented or restricted the ex- 
tent of myocardial infarction. 
Benefits of counterpulsation obviously stem 
from its three primary hemodynamic effects — 
reduced aortic systolic pressure, lov^^ered peri- 
pheral vascular resistance and enhanced dia- 
stolic pressure. The probable mechanism of 
action in acute cardiogenic shock are schemati- 
cally indicated in Figures 17 A and B. Obvious 
limitation of ai*terio-arterial counterpulsation 
is related to extracorporeal circulation and 
blood trauma. Other studies show that arterio- 
arterial counterpulsation can be tolerated for 
at least four hours with levels of plasma hemo- 
globin not exceeding 50 mg. percent.^^ In addi- 
tion, despite original concern about possible 
peripheral vascular collapse with prolonged 
periods of counterpulsation, recent experiments 
have revealed that, provided accurate synchro- 
nization is achieved and stroke volume of the 
pump does not exceed 40-50% of left ventric- 
ular stroke volume, no adverse effects develop. 
Maximal hemodynamic effects were achieved 
within one hour of initiating circulatory sup- 
port and coronary as well as peripheral blood 
flow was always greater during pumping than 
when the pump was stopped. 
In contrast to arterio-arterial counterpulsa- 
tion, the technical simplicity, stability of re- 
sponse and minimal blood and tissue trauma, 
make intra-aortic balloon counterpulsation a 
more attractive modality for circulatory assist- 
ance. Although balloon counterpulsation aug- 
ments dialstolic pressure, it does not lower 
systolic pressure as strikingly as does arterio- 
arterial counterpulsation. The need to drasti- 
cally reduce systolic pressure is questionable, 
provided coronary and peripheral circulation 
are adequately maintained. Balloon counterpul- 
