L. N. COTHRAN, E. W. HAWTHORNE AND H. SANDLER 
557 
LEFT VENTRICULAR 
CIRCUMFERENCE, cm 
LEFT VENTRICULAR 200 
PRESSURE, mmHg 
LEFT VENTRICULAR 
INTERNAL DIAMETER, Cm 
I ATRIAL CONTRACTION 
H ISOVOLUMIC CONTRACTION 
m EJECTION 
m DIASTASIS 
Figure 5. — A recording of transverse dimensions and 
ventricular pressure. 
cordings. A recording obtained from one dog 
instrumented for measurements of left ventricu- 
lar circumference, internal diameter and pres- 
sure is exhibited in Figure 5. Figure 6 is a re- 
cording of the cyclic variations in dimensions 
and pressures in a dog in which the external di- 
ameter and the wall thickness were measured 
by means of variable inductance gages. In each 
of the three animal preparations which were 
used in this study only two direct measurements 
of linear dimensions in the transverse plane 
were made. However, it was possible in each 
case, to derive other linear measurements in 
this plane from only two direct recordings. Fig- 
ure 7 demonstrates four linear dimensions in 
the transverse plane of the left ventricle which 
may be obtained from the direct recording of an 
appropriate pair. In addition, by recording the 
left ventricular pressure it is possible to obtain 
an estimate of the force acting upon the wall. In 
the example shown (Figure 7), the left ventric- 
cular wall force was calculated as the product 
of pressure and internal cross sectional area. 
The individual measurements of left ventric- 
ular transverse dimensions at selected times 
during a cardiac cycle are listed in Table I. The 
average end-diastolic external diameter in the 
group of dogs studied was 6.47 centimeters. A 
3.55 per cent decrease in this dimension oc- 
curred as the left ventricle reached its end-sys- 
tolic size. This change was associated with a 33 
per cent increase in left ventricular wall thick- 
ness and a 21 per cent decrease in the internal 
diameter. From the linear measurements pre- 
viously described several derived dimensions of 
the underlying rim of muscle were obtained at 
similar times during the cardiac cycle (Table 
II). The decline in the external diameter of the 
left ventricle during systole is associated with a 
rapid increase in wall thickness. This resulted 
in a marked increase (61.4%) in the estimated 
ratio of wall thickness to internal radius (thick- 
ness ratio). A 28 per cent increase in the cross 
sectional area of the left ventricular wall was 
found to occur and the internal circumference 
decreased by 22 per cent during systole (Table 
11). 
The cyclic changes in left ventricular length 
were studied in five dogs by biplane cineradiog- 
raphy. Simultaneous recordings of the trans- 
verse dimensions and the intracavitary pressure 
of the left ventricle in these dogs were ob- 
FiGURE 6. — A recording of left ventricular external 
diameter (LVED), wall thickness (LVWT), pres- 
sure and derived variables. 
