558 
HEMODYNAMICS 
Table I. — Left Ventricular Dimensions During the Cardiac Cycle 
Dog 
External Diameter 
Wall Thickness 
Internal Diameter 
(cm) 
(cm) 
(cm) 
(ED) 
(EIVC) 
(ES) 
(ED) 
(EIVC) 
(ES) 
(ED) 
(EIVC) 
(ES) 
1 
6.54 
6.50 
6.30 
.879 
.941 
1.19 
4.78 
4.62 
3.92 
2 
6.60 
6.52 
6.32 
.921 
.950 
1.21 
4.76 
4.62 
3.82 
3 
6.70 
6.61 
6.35 
.970 
1.00 
1.43 
4.76 
4.61 
3.49 
4 
6.57 
6.50 
6.25 
.780 
.880 
1.28 
5.00 
4.74 
3.69 
6 
6.23 
6.24 
6.00 
.670 
.750 
1.06 
4.89 
4.74 
3.88 
D 
6.60 
6.45 
6.20 
.910 
.940 
1.19 
4.67 
4.56 
3.82 
7 
6.44 
6.42 
6.20 
.you 
1 (\A 
1 Oct 
4.o4 
O.DO 
8 
6.17 
6.20 
6.00 
.970 
1.15 
1.40 
4.23 
3.90 
3.20 
9 
6.22 
6.27 
6.09 
1.02 
1.12 
1.48 
4.18 
4.03 
3.13 
10 
6.75 
6.77 
6.55 
.920 
1.00 
1.48 
4.91 
4.77 
3.96 
Av. 
6.47 
6.45 
6.22 
.900 
.980 
1.25 
4.67 
4.49 
3.68 
Key: 
(ED) end-diastole, (EIVC) 
end-isovolumic 
contraction, 
(ES) end-systole. 
tained from implanted transducers. Figure 8 
shows the temporal relationship of left ventric- 
ular pressure, length, external diameter and 
v^^all thickness from an animal of this group. 
The average length of the left ventricle at the 
beginning of systole in the group of dogs stud- 
ied v^^as 7.58 centimeters and the average end- 
systolic length vi^as 7.12 centimeters (Table 
III). This decrease of 6.06 per cent in the 
length of the ventricle was considerably smaller 
I EFT VENTRICULAR EXTERNAL CIRCUMFERENCE 
isoimn: 
conuniM 
»THI*l ■ - 
niucTiai EiEcm oususis 
LEFT VENTRICULAR WALL THICKNESS 
ISOVOUJIIC 
umnMiiO) 
ATRIAL — 
CMTHICTin EJiCtlOl DIISTISIS 
35 85 135 185 235 285 335 385 435485 
U car* 
35 85 135 185 235 285 335 385 435 48 
M. sec 
Figure 7. — A replot of left ventricular transverse di- 
mensions, pressure and wall force. 
than the associated reduction in the internal di- 
ameter (21%). 
By obtaining simultaneous measurements of 
the internal dimensions, wall thicknesses and 
pressures of the left ventricle we were able to 
calculate the average stresses generated by the 
myocardium throughout systole (Table IV). 
Plots of the average meridional stress and hoop 
stress and the corresponding left ventricular 
pressure are shown in Figure 9. The vertical ar- 
rows indicate the points of peak stress (Ps) 
and pressure (Pp). These forces are those oc- 
curring in an element of myocardium underly- 
ing the dimension gages at the equator of the 
left ventricle. 
In addition to the foregoing possibility, si- 
multaneous measurements of the internal di- 
mensions of the left ventricle in two planes 
provided the required quantities necessary for 
examining the relationship between the major 
and minor axes of the chamber and for estimat- 
ing the volume. Figure 10, panel 1 shows the 
curvilinear temporal relationship of the internal 
axis ratio during ventricular systole. Of the 
22 % average increase in the axis ratio occurring 
during systole (Table III), 14% of this amount 
occurred during ejection, and when the axis 
ratio was plotted against the internal trans- 
verse radius over this period, a linear relation- 
ship was obtained (Figure 10, panel 2). The 
data from the group of dogs, in which this rela- 
tion was examined, were subjected to a linear 
regression routine and the line of best fit was 
found to be: AR = -0.6Ri + 3 (eq. 5) (Fig- 
ure 11). The correlation coefficient for this line 
was 0.934 and the standard deviations of X and 
Y were ± 0.130 and ± 0.079, respectively. 
