JAMES AMEND, HAROLD GARNER, JOHN ROSBOROUGH, AND HEBBEL HOFF 
519 
selected group of normal ponies to the group of 
hypertensive animals by age, sex, body weight, 
and heart rate. Determination of similarities 
and dilTerences was then made by comparing 
paired values for the particular parameters. 
RESULTS 
General Animal Data 
Table I presents physical characteristics of 
the pony population. The group was approxi- 
mately evenly divided between males and fe- 
males, and contained four geldings. The range of 
weights was rather wide (53.6 kg to 161.5 kg) ; 
the average weight, however, was similar to 
weights reported for three-month-old calves.- 
( Comparative data presented in this section has 
been obtained from Weber et al.- and from 
Kuida et al.^ for the calf; from O'Rourke and 
Bishop^ for the dog ; and from the Handbook of 
Circulation'^ for man.) Although the ponies 
ranged in age from 8 months to 9 years, the 
bulk of the population was 2 to 3 years of age 
(mean age 1.9 years). Heart weights of the 
ponies ranged from 4.4 to 7.0 gm per kg of body 
weight. Similar data for man shows heart 
weights of 3.7 to 7.5 gm per kg body weight; 
data for the calf shows 5.7-6.2 gm per kg body 
weight. 
Parameters of hemodynamic function in the 
ponies are shown in Table II. Average heart 
rate (during cardiac output determination) 
was 72.8 beats/min. The rather high rate is no 
doubt reflective of the manipulations necessary 
for executing the dye dilution procedure. The 
range of values for cardiac output was broad 
(5.2-22.3 L/min), and the mean value (11.1 
L/min) was somewhat larger than the largest 
Table I. — General Animal Data for the Experimental 
Pony Population 
Table II. — Hemodynamic Parameters in Normal 
Domestic Ponies 
Parameter 
Range of Values 
Mean Value 
No. of Ponies 
31 
Age 
8 mo. — 9 years 
1.9 years 
Sex 
14 M, 13 F, 4 G 
Body Weight (kg) 
53.6 —161.5 
94.0 
Body Surface Area 
1.44 — 6.85 
2.18 
(sq meters) 
Heart Weight (kg) 
0.298—0.890 
0.580 
Heart Weight/kg Body 
4.4 — 7.0 
6.2 
Weight (gm/kg) 
Parameter 
Range of Values 
Mean Value 
Heart rate (beats/min) 
38.0 
—116.0 
72.8 
Cardiac Output (L/min) 
5.2 
— 22.3 
11.1 
Cardiac Index (L/min/sq 
3.18 
— 7.98 
5.10 
meter) 
Cardiac Output/kg Body 
66 
— 184 
118 
Weight (ml/min/kg) 
Stroke Volume (ml/beat) 
44.5 
—312.5 
151.0 
Stroke Index (ml/beat/ sq 
45.7 
—242.3 
69.9 
meter) 
Stroke Volume/kg Body 
0.78 
— 2.46 
1.64 
Weight (ml/beat/kg) 
Systemic (Aortic) Blood 
120/70 
—158/100 
144/107 
Pressure (mm Hg) 
Systemic Vascular Resistance 
0.43 
— 1.08 
O.70 
(PRU) 
Left Ventricular Work 
1.49 
— 4.94 
2.87 
(joules/stroke) 
Left Ventricular Ejection Rate 
101.3 
—357.4 
209.1 
(ml/sec/M-) 
Pulmonary Artery Blood 
30/10 
—60/35 
45/20 
Pressure (mm Hg) 
Pulmonary Vascular 
0.11 
— 0.36 
0.19 
Resistance (PRU) 
Right Ventricular Work 
0.31 
— 0.95 
0.60 
(joules/stroke) 
output value reported for the calf.^ Cardiac 
index (L/min/sq meter) and cardiac output per 
kg body weight were also greater than values 
reported for the calf, or for man. They were, 
however, very close to figures found in the con- 
scious dog. Similar comparisons were found for 
stroke volume, stroke index, and stroke volume 
per kg body weight. 
Systemic blood pressure averaged 144/107 
mm Hg in the group of ponies, while pulmonary 
artery pressure averaged 45/20 mm Hg. Seven 
of the ponies consistently showed mean aortic 
pressures of 135 mm Hg or more ; they were ar- 
bitrarily grouped as "hypertensives," and their 
data were separately analyzed. The pressures 
obtained for the group of normal animals were 
higher than normal for man, but not signifi- 
cantly different from calf or dog. Calculated 
vascular resistance in the pony was less than 
that of the calf, reflecting the relatively higher 
cardiac output in the ponies, with similar blood 
pressures in the two species.^'' Values for vas- 
cular resistance were quite similar to those re- 
ported for man. Ventricular work was greater 
in the pony than in calf, but less than that 
found in man. 
Table III presents ventricular systolic time 
intervals for the group of ponies. Those meas- 
urements which were found to be constant as 
