J. F. SPANN, JR. AND G. M. LEMOLE 
143 
that the ratio to collagen to muscle protein in 
human left ventricles was unaltered in var- 
j ious types of heart disease accompanied by 
myocardial hypertrophy while Oakin and 
Bouecek^'' found an increase in the left ventric- 
ular collagen content in nearly all of twenty- 
two hearts with significant hypertrophy. Since 
connective tissue contributes to ventricular 
compliance and since increases in its concentra- 
tion might interfere with contractile activity, it 
is of significance to determine the changes in 
connective tissue which accompany hypertro- 
phy in an experimentally controlled setting, in 
the absence of such potentially modifying fac- 
tors as coronary disease and ischemia. Since hy- 
droxyproline is found only in collagen and 
forms a constant portion of collagen, the con- 
centration of collagen and thus, the connecting 
tissue components in the myocardium can be de- 
termined by measuring hydroxyproline. 
TECHNIQUE 
The pulmonary artery of the cat is con- 
stricted by a circular clip which is applied in 
the following manner. Animals are anesthetized 
with intravenous sodium methahexatol 15 
mgm./kg. To permit endotracheal intubation 
and control of respiration, intravenous succi- 
nylcholine Img/kg. is then given and intermit- 
tent positive pressure ventilation is rpplied by a 
Harvard respirator using air. Under sterile 
conditions, the chest is opened through the an- 
terior one third of that left intercostal space 
which lies 2 cm. cephalad from the apical im- 
pulse ; the pericardium is widely excised and a 5 
mm. segment of main pulmonary artery just 
distal to the pulmonic valve is dissected free of 
the ascending aorta. This segment of the pul- 
monary artery is cleaned of adipose and connec- 
tive tissue and a curved hemostat passed from 
left to right behind the pulmonary artery so 
that its tip is exposed between this vessel and 
the aorta. One free end of the suture threaded 
thru the tubing of the clip (Figure 1) is then 
picked up and pulled around the pulmonary ar- 
tery as the hemostat is removed. The clip is 
then positioned posterior to the pulmonary ar- 
tery and this vessel is insinuated thru the open- 
ing in the circle into the clip. The ends of the 
clip are approximated by slight tension on the 
two ends of the suture which are then tied to- 
gether. After the clip is in place, the respiratory 
gas mixture is changed to 95% oxygen and 5% 
carbon dioxide, the incision closed, the endotra- 
cheal tube removed, and the animal allowed to 
recover for 30 minutes in a chamber containing 
95% and 5% carbon dioxide. 
The clips are made in the following manner. 
PE-50 polyethylene tubing is wound in a spiral 
around a rod with a diameter equal to that de- 
sired as the internal diameter of the clip. A sin- 
gle cut is then made through the spiral tubing 
in the long axis of the rod so as to result in sev- 
eral pieces of tubing of appropriate length. Cop- 
per wire of 0.016 inch diameter and a 40 cm. 
length of 00 silk suture are inserted into each 
segment of tubing and the wire is cut to corre- 
spond to the length of the polyethylene. The 
tubing, wire and suture are bent around the rod 
until the cut ends of the tubing are brought to- 
gether, thus, forming a circle with the shape 
maintained by the stiffness of the wire. Clips 
with an internal diameter of either 2.8 or 8.5 
mm. are used in the adult cat weighing between 
1.8 and 2.4 kilograms. 
Up to 90 days after the pulmonary banding 
procedure, right heart catheterization is carried 
out under light intravenous Nembutal anes- 
thesia, 20 mg./kgm. A cannula is placed in the 
Figure 1. — Clip used to constrict the pulmonary ar- 
tery. It consists of malleable wire and silk suture 
within polyethylene tubing. The slot which interrupts 
the circumference of the clip is 0.5 mm. wide. (Re- 
produced with permission from Proceedings of the 
Society for Experimental Biology and Medicine 
125:523,1967.) 
