BOWIE, PUROHIT, ADAMS, SOMAIAH, HAWTHORNE AND HINDS 
543 
Figure 1. — Plastic casts of the horse's ventricle in diastole and systole. 
tained by use of equations 1 and 2 assuming 
a constant axis ratio of 3.86. 
This report will be confined to the effects of 
catecholamines, (epinephrine, norepinephrine 
and isoproterenol) glucagon and tyrode's infu- 
sion on cardiac dynamics in the equine heart. 
Thirteen horses were used for epinephrine stud- 
ies, sixteen for norepinephrine and fifteen for 
isoproterenol. Equimolar concentrations (1 
mg/ml) of the drugs, epinephrine, norepineph- 
rine, and isoproterenol were infused via the 
jugular vein. The rate of infusion for epineph- 
rine and norepinephrine was 0.764 ml per 
minute, whereas it was 0.191 ml per minute for 
isoproterenol. Cardiac cycles being analysed 
and compared were taken at peak response 
time. In three conscious, standing horses, 10 mg 
of glucagon having a concentration of 1 mg/1 
ml was administered into the jugular vein. To 
study the effect of volume overload on the car- 
diac function, a rapid infusion of Tyrode's solu- 
tion was given into the jugular vein. 
Figure 8 illustrates the variables normally re- 
corded in the conscious standing horse (EKG, 
left ventricular internal diameter, left ventricu- 
lar pressure, aortic pressure and dp/dt). All 
variables were recorded simultaneously on an 
eight channel strip chart recorder and on elec- 
tromagnetic tape. 
RESULTS AND DISCUSSION 
In acute studies, twelve horses were used for 
the control measurements of the cardiovascular 
dynamics (Table I). The data for these horses 
were derived from the linear dimensional meas- 
urements previously described. These horses 
were under the influence of an anesthetic agent 
for the entire period of the experiment. The 
mean cardiac output in the absence of the effects 
of the catecholamines was 22.1 ± 2.0 liters per 
minute which is similar to our previously re- 
ported values^ and those of Eberly and his 
collaborators. ^^'^^ Horses anesthetized with 
barbiturates alone had an average cardiac out- 
put of 21.47 liters/min, while those anesthetized 
