554 
HEMODYNAMICS 
an internal axis ratio greater than unity. The use 
of an ellipse of revolution as a geometric analog 
of the left ventricular chamber introduces the 
requirement for simultaneous measurements 
across tv^o perpendicular axes in order to calcu- 
late volume from linear dimensions. Of the lin- 
ear dimensions required for the derivation of 
the volume of an ellipsoid, the measurement of 
length has proved to be the most difficult to ob- 
tain by analog techniques.^ 
This study deals with, the measurement of 
transverse and longitudinal dimensions of the 
left ventricle using a combination of analog and 
cineradiographic techniques. From the linear 
measurements which v^ere made, the cyclic var- 
iations in several dimensions and wall stresses 
were derived. In addition, an opportunity was 
provided to examine the cyclic changes that 
occur in the internal axis ratio of the left ven- 
tricle and to use this variable in estimates of 
chamber volume. 
METHODS 
Only conditioned, adult, male dogs were se- 
lected for use in these studies. The body weights 
of these animals ranged from 28 to 35 kilo- 
grams. Final preoperative preparation of these 
animals consisted of a 12-hour fast period and 
administration of a broad-spectrum antibiotic. 
Pentobarbital sodium was used to achieve a 
surgical plane of anesthesia. A left, anteriola- 
teral thoracotomy was performed at the level of 
the fifth costal interspace. Respiration was 
maintained with a 40 per cent oxygen, 60 per 
cent air mixture administered through an endo- 
tracheal tube attached to a positive pressure res- 
pirator which was activated by a demand type 
valve. 
Three methods were used for measurement of 
the transverse dimensions. In three of the ten 
dogs studied, the left ventricle was instru- 
mented with a mercury-in-rubber strain gage 
for monitoring the external circumference. The 
gage was positioned around the equator of the 
ventricle. A set of disc-shaped coils were im- 
planted coaxially across the anterior wall to 
monitor the changes in wall thickness (Figure 
l).^** In two dogs, external circumference of 
the left ventricle was measured with a mercu- 
FiGURE 1. — A schematic representation of the left ven- 
trical showing transducer placement (type I). (LVC) 
left ventricular circumference gage (Ci — C:) left ven- 
tricular wall thickness coils, (LVP) left ventricular 
pressure, (AP) aortic pressure. 
ry-in-rubber gage and internal diameter was 
measured by means of a sonomicrometer system 
(Figure 2)." In the five remaining animals, 
external diameter and wall thickness were 
measured by means of set of three coils im- 
planted in a straight line across the left ventri- 
cle (Figure 3). In this group radiopaque mark- 
ers were implanted on the left ventricle at the 
bifurcation of the left main coronary and at the 
apical dimple. These markers were used to mon- 
itor the changes in length of the left ventricle 
utilizing the biplane cineradiographic technique 
previously described by Mitchell et al.^^ jn six 
of the dogs used in this study pressure cells 
were implanted in the left ventricle through the 
apical dimple and in the thorocic aorta two to 
three centimeters distal to the arch. Left ventric- 
