46 
CARDIAC MODELS 
Exteriorized 
Silastic Tubing 
45 mm 
1 0mm 
Figure 7. — Above: Schematic representation of bal- 
loon cuffs implanted on the left anterior descending 
and circumflex coronary arteries of a calf. 
Below: Dimensions of balloon cuff and tubing. (By 
permission.") 
infusion of various substrates or induction of 
hypothermia, since a well defined endpoint of 
hemodynamic improvement or deterioration is 
present. Such studies remain to be carried out. 
Studies in Calves 
The method of balloon cuff coronary occlusion 
has been studied in seven intact conscious 
calves. The technique employed is similar to 
that used for canine studies except that a larger 
balloon device is employed to accommodate the 
larger coronary arteries in the calf (Figure 7). 
Hemodynamic changes indicative of mild to 
moderate left ventricular failure were also pro- 
duced by balloon cuff coronary occlusion (Table 
III). It is noteworthy that, despite hemody- 
namic changes comparable to those occurring in 
dogs, calves invariably develop ventricular fi- 
brillation in the first hour after major coronary 
occlusion, and that the rapidity of onset of ven- 
Table III. — heft Anterior Descending Coronary Artery 
Occlusion in Seven Intact Conscious Calves (mean ± 
SEM) 
Left Ventricular 
Aortic Mean 
Heart 
End-Diastolic 
Cardiac 
Pressure 
Rate 
Pressure 
Output 
(mm Hg) 
(beats/min) 
(mm Hg) 
(L/min) 
Control 
129± 8 
103±10 
7.6±1.6 
5.2±0.7 
Occlusion 
131±10 
112± 8 
15.7±4.4* 
4.4±0.6* 
tricular fibrillation appears to be related to the 
severity of failure (Figure 8). 
Studies in Pigs 
Studies have been carried out in seven intact 
conscious pigs. In general these animals are 
more difficult to work with than either dogs or 
calves, and often require heavy sedation. Hemo- 
dynamic studies are incomplete in this species ; 
however, electrocardiographic monitoring has 
been carried out. Electrocardiographic changes 
of ischemia appear to be less marked in pigs 
than in dogs, and the incidence of ventricular 
fibrillation is high (four of seven animals). Be- 
cause of the similarity of the porcine coronary 
circulation to man, further studies in this some- 
what more difficult preparation may be indi- 
cated. 
General Comments 
The desirability of carrying out studies of 
circulatory physiology in unanesthetized as op- 
posed to anesthetized animals is established, 
and this may apply particularly to studies of 
myocardial ischemia.-^ Acute myocardial in- 
farction in unanesthetized animals is character- 
ized by sinus tachycardia and a rise in left ven- 
tricular end-diastolic pressure. On the other 
f 
* P <0.05, paired differences 
30 40 50 
MINUTES 
Figure 8. — Height of left ventricular end-diastolic pres- 
sure plotted in relation to time of onset of ventri- 
cular fibrillation following occlusion of the left anter- 
ior descending coronary artery in calves. (By 
permission.") 
