128 
CARDIAC MODELS 
concern about excessive blood trauma and the 
possibility of reported deleterious effects upon 
peripheral circulation during prolonged coun- 
terpulsation,'"^'-^- counterpulsation was limited 
to one hour (a period found to be safe and well 
tolerated by dogs in Study I). The animals were 
carefully followed until death or sacrifice after 
twenty-four hours. 
Group III 
Six dogs were treated by intra-aortic balloon 
counterpulsation for four hours (Figure lOA). 
When pumping was discontinued, the animals 
were observed for one hour, then sacrificed. 
A monosegmented balloon with a volume of 
15 cc. was used. The balloon catheter was in- 
serted through a femoral arteriotomy and posi- 
FiGURE 10. — a. Schema for intra-aortic balloon counter- 
pulsation and photograph of the electronic controller 
connected to the pneumatic actuator and intra-aortic 
balloon catheter. 
tioned in the descending thoracic aorta under 
radiologic control. Preliminary experiments in 
normal adult dogs (20-30 Kgm) demonstrated 
that with this caliber balloon (fully inflated and 
just subocclusive), intra-aortic balloon counter- 
pulsation was well tolerated for at least four 
hours without evidence of thrombosis, emboli- 
zation or local aortic injury.^-' Balloon counter- 
pulsation reduced systolic pressure an average 
of 15 percent, augmented diastolic pressure 44 
percent (Figure lOB) and diminished left ven- 
tricular work 17 percent while coronary, carotid 
and renal flow was maintained. The hourly in- 
crement of plasma hemoglobin was 6 mgm. 
percent. 
Group IV 
Six animals were treated by synchronous pul- 
satile venoarterial bypass with oxygenation 
(Figure 11). Venous drainage was achieved by 
cannulating the external jugular veins with a 
No. 28 Fr. catheter and arterial infusion was 
through a single No. 24 Fr. femoral cannula. 
The oxygenator was primed with 1000 cc. of 
Ringer's lactate solution. Bypass was main- 
tained for four hours following which the ani- 
mals were observed for an additional hour, 
then sacrificed. 
A pulse pressure generator was specifically 
developed for this method of assist (Cardio- 
vascular Specialties, Scarborough, Ontario). 
The generator is a compact device measuring 
10 X 10 X 10 cm. consisting of two polycarbonate 
chambers separated by a silastic diaphragm. 
The outer contours are convex. The posterior 
chamber has a central port, which is connected 
to a pneumatic or hydraulic actuator and an 
electronic controller. The forward chamber is 
the pumping chamber in line with the circula- 
tion. It has an eccentric ball-valved inlet port 
which connects with the outflow of an oxygena- 
tor and a central valveless port which connects 
with an arterial catheter. During pump diastole, 
because of diflferential resistances in the inflow 
and outflow lines, withdrawal of the diaphragm 
results in almost complete filling (96 percent) 
from the oxygenator (Figure 11). Conversion 
to arterio-arterial counterpulsation and back to 
venoarterial bypass can be readily achieved if 
