J. p. SPANN, JR. AND G. M. LEMOLE 
145 
2 1 
1.9 
Wtlun 1 
1,7 
OF 
RIGHT 
1,5 
\/ENTRICLE 
13 
g/Kg 
II 
09 
0.7 
0.5 
■ A 
i' 
H h 
20 40 
DAYS 
60 
80 
100 
Figure 3. — Relation between right ventricular weight 
and time at which pulmonary artery was banded. Av- 
erage normal right ventricular weight and standard 
error are represented by the sawtooth line. Circles 
and triangles = animals with a 2.8-mm. clip. 
Squares — animals with a 3.5-mm. clip. The abscissa 
represents days after pulmonary artery was con- 
stricted. (Reproduced with permission from the 
American Heart Association, Inc. from Circulation 
Res. 21:341, 1967.) 
surprising. The wet weight to dry weight ratio 
is the same in the normal and hypertrophied 
groups of heart muscles 48 hours after contric- 
tion of the pulmonary artery, thus, excluding 
the possibility that the increase in ventricular 
weight is due to excessive tissue water. My- 
ocardial RNA synthesis, as measured by RNA 
polymerase activity, has also been shown to be 
increased within 24 hours after an excessive 
work load was imposed on the left ventricle.^'' 
Some evidence is available to suggest that ven- 
tricular hypertrophy can occur with similar 
rapidity in man. Thus, the data reinforces the 
concept that when the heart is faced with an ab- 
normal load, there is a rapid increase in the 
contractile element mass. 
monic constriction and right ventricular hyper- 
trophy, but without congestive heart failure; 
(c) cats with pulmonic constriction in which, 
despite the development of right ventricular hy- 
pertrophy, heart failure developed. All muscles 
were studied under the same condition in a my- 
ograph in oxygenated Kreb's solution. This sys- 
tem allowed measurement of the force, muscle 
length and first derivative of these variables." 
Length-tension relations, the isometric contrac- 
tion, force velocity relations and the response to 
inotropic interventions also were determined. 
The length-tension relation is qualitatively 
similar but quantitatively quite different in 
muscles from the three groups of animals (Fig- 
ure 4) . The actively developed tension is less 
than normal at all muscle lengths along the 
length-tension curve in preparations from ani- 
mals with right ventricular hypertrophy and 
congestive heart failure. Maximal active tension 
in the muscles from the cats with hypertrophy 
is reduced, averaging 5.5 ± 0.6 gms./mm. sq. 
compared with the normal value of 6.2 ± 0.7 
gms./mm. sq. whereas, the maximal isometric 
tension of the muscles from cats with conges- 
TENSION 
s- 
Normal 
(11) 
—5 
<- 
RVH 
(10) 
□C 
> — 
CHF 
(II) 
-> 
ACTV£ 
TENSION 
RESTING 
TENSION 
Active 
tension \^ 
-45 -40 
-35 -30 -25 
-15 -10 -5 LMax+3 
LENGTH 
Percent change from Lmax 
Contractility 
Next to be considered is the contractile func- 
tion of the myocardial units within this in- 
creased contractile mass. The following discus- 
sion is based on data from an experimental plan 
which compared, under controlled conditions, 
the function of isolated papillary muscles ob- 
tained from the right ventricles of three groups 
of cats: (a) normal cats; (b) cats with pul- 
FiGURE 4. — Relation between muscle length and ten- 
sion of the papillary muscles from normal (circles), 
hypertrophied (squares) and failing (triangles) right 
ventricles. Open symbols = resting tension; solid 
symbols — actively developed tension. Each value is 
the average of the group; vertical lines with cross 
bars — ± 1 S.E.M. Tension is corrected for cross- 
sectional area (gm./mm."). Numbers in parentheses 
= number of animals. (Reproduced with permission 
from the American Heart Association, Inc. from Cir- 
culation Res. (21:341, 1967.) 
