568 
HEMODYNAMICS 
the experimental situation, the extruding part of 
the catheters and the connectors of the flow 
transducers are fixed to the dog's back by mask- 
ing tape and covered with an elastic bandage 
around the trunk of the animal. A washable 
jacket protects the bandage. After the opera- 
tion, the dog is prophylacticly treated with 
antibiotics for about one week. After one week, 
the stitches are removed. 
From the third day after the operation, the 
training of the animal is resumed with the ca- 
bles attached to the externalized connectors and 
with the pressure transducers fixed to the chest 
wall (Figure 2) . The data used for research are 
recorded beginning two weeks after the sur- 
gery, when the flow transducers are well fixed 
by tissue reaction, the body temperature and 
weight as well as the hematocrit are at the 
preoperative level. From this time on we study 
the animal until one of the sensors stops func- 
tioning. This is usually due to a leak in the coat- 
ing of one of the flow transducers. 
THE RECORDINGS 
During the experiments, the animal is in a 
sound-attenuated chamber. Outside of the 
chamber are a flowmeter (Biotronex 610), 
Figure 2. — Experimental animal. 
a recorder (Beckman R-dynograph) , a speak- 
er, a television set for the audiovisual mon- 
itoring of the animal, controls of the tread- 
mill, a feeder, a fluid dispenser, an external 
pacemaker, (Medtronic 5.800), etc. The stabili- 
zation of the environment enhances the repro- 
ducibility of the results. 
The flow transducers (in Vivo metric) are 
calibrated prior to their implantation. The ex- 
cursion levels of the integrators (Beckman cou- 
plers 9873B) are set to produce absolute values 
of flow in the monitored vessels. The zero flow 
level in the circumflex branch is obtained by oc- 
clusion of this vessel. The pressure channels 
and the cardiotachometer are calibrated before 
and after each experimental session. The 30 cm 
long pressure catheters attached to a Statham 
P37 pressure transducer have a natural fre- 
quency response in excess of 67 Hz with a 
damping ratio of 22% critical or better. The re- 
cording of the right atrial pressure and of the 
pleural pressure is filtered to exclude high fre- 
quency artefacts. 
Figure 3 shows a paper strip recording of the 
monitored circulatory functions. The paper 
moves 25 mm. sec~\ The instantaneous flow in 
the aorta is recorded on the first channel. The 
area limited by the curve of each beat and the 
base line indicates the amount of blood ejected 
into the aorta during that beat; that is, the 
stroke volume (less the coronary flow). The 
height of the deflection of the integrator on the 
second channel corresponds to the stroke volume. 
The height of the deflection of the integrator in 
the third channel corresponds to aortic flow in 
two seconds, or to Qao.30-^ min. The instantan- 
eous flow in the circumflex branch of the left 
coronary artery is recorded on the fourth chan- 
nel. The area limited by the flow curve during 
one heart cycle and by the zero line is the amount 
of blood flowing in that coronary vessel during 
one heart cycle. The height of the deflection of 
the integrator in the fifth channel corresponds to 
the flow in that coronary vessel during one cycle. 
The height of the deflection of the integrator in 
the sixth channel corresponds to the amount of 
flow in that coronary vessel in two seconds. 
Qcor.30~^ min. is believed to be indicative of 
flow changes in all coronary vessels ; it is, how- 
ever, actually measured in the circumflex 
