L. N. COTHRAN, E. W. HAWTHORNE AND H. SANDLER 
Table II. — Derived Dimensions During the Cardiac Cycle 
559 
Wall Area Internal Circumference 
DoK 
Thickness Ratio 
(cm^) 
(cm) 
(ED) 
(EIVC) 
(ES) 
(ED) 
(EIVC) 
(ES) 
(ED) 
(EIVC) 
(ES) 
1 
.370 
.410 
.610 
15.64 
16.42 
19.10 
15.00 
14.50 
12.30 
2 
.390 
.420 
.570 
16.42 
16.50 
18.79 
14.95 
14.60 
12.60 
3 
.410 
.420 
.820 
17.46 
17.58 
22.15 
14.95 
14.60 
11.00 
4 
.310 
.370 
.690 
14.17 
15.53 
20.03 
15.70 
14.90 
11.60 
5 
.270 
.310 
.550 
10.89 
12.93 
16.44 
15.35 
14.90 
12.20 
6 
.390 
.410 
.620 
16.11 
16.33 
18.11 
14.66 
14.30 
12.00 
7 
.440 
.480 
.680 
16.80 
17.57 
19.55 
14.07 
13.60 
11.60 
8 
.460 
.590 
.870 
15.83 
18.24 
24.46 
13.28 
12.20 
10.00 
9 
.490 
.560 
.950 
16.64 
18.17 
21.47 
13.12 
12.60 
9.80 
10 
.370 
.420 
.750 
16.83 
18.09 
21.20 
15.42 
15.00 
12.40 
Av. 
.390 
.440 
.710 
15.68 
17.64 
20.13 
14.60 
14.10 
11.50 
Key: (ED) end-diastole, (EIVC) end-isovolumic contraction, (ES) end-systole. 
I AC I IVC I Ejection I 
Figure 8. — Phasic variations of the left ventricular di- 
mensions and pressure during the cardiac cycle. 
(LVL) left ventricular length, (LVED) left ven- 
tricular external diameter, (LVWT) left ventricular 
wall thickness. 
In the animals in which the temporal change 
in axis ratio was measurecJ, calculation of the 
left ventricular volume was possible. The actual 
numerical values for internal radius and axis 
ratio of the left ventricle were substituted in 
the equation for the volume of an ellipse of rev- 
olution (eq. 4), and approximations of left ven- 
tricular chamber volume vi^ere made at end- 
diastole and end-systole on five dogs (Figure 
12). 
The changes which we observed in left ven- 
tricular geometry indicated that ejection was 
the result of a decrease in the internal dimen- 
sions of the left ventricle in both the longitudi- 
nal and transverse planes. It should be empha- 
sized that although the changes that occurred in 
length were significant (6%) (Table III), the 
decrease in the transverse plane was the most 
important dimensional change (21%) (Table 
I). Therefore, we examined the relationship be- 
tween the changes in stroke volume and the in- 
ternal radius of the left ventricle throughout 
the ejection period in a dog instrumented with 
an internal diameter gage and an aortic fiow 
probe. We found, as did Bishop and 
Horovi^itz,^^ a linear relationship between these 
variables. 
An example of the typical relationship be- 
tvi^een stroke volume and internal radius is il- 
lustrated in Figure 13. This experimental prep- 
aration also provided a convenient method to 
test the closeness of fit of our estimations of the 
changes in internal volume during ejection to 
actual values. To do this, we substituted the ac- 
tual numerical value for the internal radius into 
the equation for the volume of a prolate ellips- 
