T. AKUTSU, H. TAKAGI AND H. TAKANO 
285 
since deep anesthesia with Fluothane causes ex- 
treme decrease of arterial pressure particularly 
in a very young calf. The arterial pressure itself 
is the most sensitive index to the depth of anes- 
thesia with Fluothane. Usually a 0.5 per cent 
concentration of Fluothane was sufficient for 
anesthesia. Occasionally, especially during total 
bypass, the flow of Fluothane was completely 
shut off, to be restarted only at the sign of wrig- 
gling or spontaneous movement of the dia- 
phragm. 
DISCUSSION 
In the first ten calf experiments, the total ar- 
tificial heart was started immediately after the 
extracorporeal circulation was stopped. It was 
found that blood coming back to the left atrium 
was not oxygenated at all,^ and none of the 
calves survived longer than five hours. In order 
to elucidate this unexpected impairment in pul- 
monary function, we carried out some experi- 
ments in which only the right side of the natu- 
ral heart was replaced by a pump.*' We have 
found that the flow rate at the beginning of 
pumping of the artificial heart is a critical fac- 
tor. The pulmonary insufficiency seemed to be 
due to opening of arterio-venous shunts, be- 
cause of the considerable increase in pulmonary 
resistance after a period of complete cessation 
of pulmonary blood flow during cross clamping 
of the pulmonary artery while inserting the 
prosthetic heart. Oxygenation was improved by 
gradually increasing the cardiac output of the 
prosthetic heart while the major part of the an- 
imal's circulation was maintained by the extra- 
corporeal circulation which was then gradually 
reduced. The time of safe transition from the 
extracorporeal circulation to the artificial heart 
varied from 15 minutes to two hours. Use of 
vasodilator such as isoproterenol was not effec- 
tive. 
Cumbersome procedures in calves made us 
change the experimental animal from the calf 
to the sheep. The sheep has certain advantages 
over the calf as described by Borrie et al.^ (1) 
It is cheap. (2) It is easy to transport. (3) It is 
easy to maintain in long-term survival experi- 
ments. (4) It does not grow to unwieldy sizes. 
(5) Physiologically its size approximates man. 
However, after four years of experience with 
sheep, we found the following drawbacks and 
went back to the calf. (1) The salivary and res- 
piratory tract secretions were troublesome. 
(2) Its red blood cells are fragile.^ (3) Its oxy- 
genation after extracorporeal circulation is 
poor. (4) It has weak resistance to traumatic 
shock. (5) Its chest cavity is small for its body 
weight. (6) It is difficult to obtain large sheep. 
Using calves weighing from 70 to 90 kg, we 
now have no problem with oxygenation immedi- 
ately after the cessation of extracorporeal cir- 
culation. Recently, we have used Surital alone 
throughout experiments with assist devices 
without any trouble in postoperative respira- 
tion. However, with this agent, we have noted 
insufficient oxygenation in some total artificial 
heart experiments. It is obvious that about one 
dozen tubings and wires traversing the left 
chest cavity and penetrating the chest wall defi- 
nitely affects the respiratory function. The left 
lung is compressed, and the thorax movement is 
disturbed physically as well as by pain. Al- 
though these effects alone would not kill the ani- 
mal, they are additive to other adverse factors 
in implantation surgery. 
SUMMARY 
Sheep and calves to be used for implantation 
surgery of various types of artificial hearts 
have been compared from various standpoints. 
Anesthesia with a short-acting barbiturate 
for induction and with Fluothane for mainte- 
nance seems satisfactory in large experimental 
animals. 
Surgical implantation techniques of B- 
LHAD, S-LHAD, and TAH have been discussed 
in detail. 
Control of the movement of postoperative an- 
imals for safe monitoring of necessary parame- 
ters has been described. 
REFERENCES 
1. Larson, R. E., Moffitt, E. A., and McGoON, D. 
C. Experimental cardiac surgery in calves. I. Anes- 
thesia. J. Surg. Res. 3:101, 1963. 
2. Larson, R. E., and McGoon, D. C. Experimental 
cardiac surgery in calves. IL Management for aortic 
valve surgery. J. Surg. Res. 3:104, 1963. 
