108 
CARDIAC MODELS 
predictions were compared with the observed 
events. 
Complete postmortem examination was per- 
formed on all animals that had died during the 
observation and on those killed 24 to 96 hours 
after the tightening of the snare. 
Series II 
In 17 animals, 9 male and 8 female adult 
M. miilatta, weighing between 5.1 and 8.3 
kg, nuclide-labeled microspheres (Scandium-46, 
Strontium-85 or Iodine-125) about 50 in di- 
ameter (Minnesota Mining and Manufacturing 
Company) were injected into the left atrium 
during the control period and repeated 15 and 
45 minutes after the induction of myocardial in- 
farction. About 100 /u,Ci, corresponding to 
300,000 microspheres of each isotope, were in- 
jected per animal. Cardiac output was meas- 
ured by indocyanine green dye dilution curves 
(mean of 2 or 3 curves) before each nuclide 
injection. The dye was injected via the left 
atrial catheter, and blood was withdrawn from 
the aortic catheter by a pump (Model 600-900, 
Harvard Apparatus Co., Inc.) at 9.89 cc/min 
through a cuvette densitometer (Model 1031R, 
Gilford Instrument Co.) and recorded on a poly- 
graph (Model M5P, Gilson Medical Electron- 
ics). Arterial blood samples were taken for 
measuring pH and oxygen and carbon dioxide 
tension with a pH meter and gas monitor (Ra- 
diometer, Copenhagen) before and after the 
induction of myocardial infarction. After the 
animal's death, the body was dissected into its 
various organs. The heart was examined grossly 
and the location of the snare was checked; a 
complete autopsy was not done since it would 
interfere with the radioisotope analysis. Larger 
parts, e.g., carcass and skin, were incinerated, 
and an aliquot of about 10 percent of the ash 
was taken for radioactivity measurement. The 
validity of this method had been previously con- 
firmed by total analysis of the ash from other 
animals. Large organs (e.g., kidneys and liver) 
were incinerated and totally analyzed for ra- 
dioactivity. Small organs (e.g., adrenal glands 
and pituitary glands) were placed directly into 
weighed sample tubes for analysis of radioac- 
tivity. Thus, the total radioactivity of each ra- 
dionuclide in the monkey was measured. The 
proportion of radioactivity in an organ multi- 
plied by the cardiac output was then a measure 
of the organ blood flow : 
Organ blood flow (ml/min) = 
Cardiac output (ml/min) X 
organ radioactivity (CPM) 
total CPM in animal 
The radioactivity from each separate nuclide in 
individual sample tubes was determined in a 
three-channel Packard gamma spectrometer, 
Series 5000. Organ blood flow data were ex- 
pressed as percentages of systemic flow perfus- 
ing each organ and flow per 100 gm. of tissue. 
RESULTS 
Series I 
Five animals died postoperatively before liga- 
tion. In the 29 survivors the snare was ligated ; 
in 3 of these the ligation was unsuccessful be- 
cause misplacement of the snare excluded the 
coronary artery or included part of the pulmon- 
ary valve, or the snare broke. The remaining 26 
were divided into two groups: (1) Group I 
("Dead") included the 11 monkeys that died 
within 6V2 hours from myocardial infarction 
with a syndrome resembling cardiogenic shock ; 
(2) Group II ("Alive"), the 15 monkeys that 
survived myocardial infarction more than 12 
hours and in many cases were terminated 24 to 
96 hours after infarction. No deaths occurred 
between 6V2 and 12 hours after infarction. Five 
animals that died during the first night but 
more than 12 hours after infarction may have 
had cardiogenic shock ; however, the possibility 
of a fatal arrhythmia cannot be ruled out. 
Since their aortic blood flow was never under 
55% (percentages refer to control values taken 
as 100 % ) and mean aortic pressure was never 
less than 70 % during the observed period, they 
were placed in Group II ("Alive") . 
Immediately after the snare was pulled, the 
animals became agitated for 1 to 2 minutes. In 
general, animals with initial decreases of more 
than 50 % in aortic blood flow and 30 % in mean 
aortic pressure appeared dazed, did not respond 
