26 
CARDIAC MODELS 
End Bleed | I Bi 
Retronsf usion 
Figure 7. — Aortic blood pressure of dogs subjected to 
hemorrhagic shock at 40 mniHg arterial pressure for 
four hours and treated with a ganglionic blocking 
agent. Upper panel shows results of initial and second 
bleed. Abrupt elevation between the first and second 
bleed is result of change in scale. Each small arrow 
represents the administration of 40 ml of blood. Note 
that administration of first dose of hexamethonium 
(Bistrium) resulted in a dramatic fall in pressure 
which was restored to 40 mmHg by the administra- 
tion of 160 ml of blood. Without this transfusion the 
animals would have died immediately. A pressure of 
40 mmHg was maintained throughout the four-hour 
shock period with only 80 ml of additional blood. Note 
that the second dose of the drug resulted in no es- 
sential change in blood pressure. These dogs re- 
covered. 
high levels of catecholamines in shock, that 
the flow would be much improved in the capil- 
laries. Consequently a series of experiments in 
dogs was set up to test this hypothesis. It was 
found that a vasodilating agent, if supported by 
even a minimal amount of blood volume (much 
less than given under controls), would not only 
prevent DIG, but would indeed prevent mor- 
tality (Figures 6, 7 and 8).^- Not only did vaso- 
dilators prevent mortality, but they prevented 
the development of the coagulation defect which 
normally accompanies DIG (Figure 9). This 
was accomplished even though the vasodilator 
treated animals were actually given less blood 
and had less blood volume than did the control 
animals (Figure 10). 
All of the above determinations have now 
been repeated and documented in human beings. 
The primary diff'erence found between humans 
and dogs is the relative coagulability of the two 
species. For instance, the prothrombin time in 
dogs is roughly 6-7 seconds, whereas in humans 
it is approximately 13 seconds. Therefore, the 
same phenomena that takes place in dogs oc- 
curs in humans, but requires either more severe 
shock or more thromboplastic agent or both. 
SUMMARY 
Animals have been utilized as the primary 
source of scientific observations on shock until 
1964. Valuable information was obtained, lim- 
ited only by the known and unknown differences 
between animals and humans. In 1964, human 
studies in shock became practical for the first 
time, placing animal studies in a position of 
secondary importance. However, continued 
studies in animals will always be required to 
test new ideas, with primates probably playing 
an increasingly important role. 
MORTALITY 
lOO-i 
90 
80 
70 
60 
o 50 
u 
Q. 
40 
30- 
20 
10- 
15/16 
93.8% 
< 
7/28 
25% 
OH 
^- 
0: v::-: 
Figure 8. — Mortality rates of three groups of dogs sub- 
jected to hemorrhagic shock. All were maintained at 
40 mmHg arterial pressure for four hours. Group B 
was treated with a ganglionic blocking agent and 
Group C with a peripheral vasoconstrictor. 
