682 
PHYSIOLOGY 
internal transverse diameter. Ventricular pres- 
sure was measured with a miniature solid-state 
pressure transducer* (7 mm diameter) precali- 
brated in-vitro at 38°C. This was inserted into 
the left ventricular cavity through the apical 
dimple after excision of the donor heart. The 
gauge was positioned approximately 5-8 mm in- 
side the endocardial surface to avoid distortion 
of the pressure waveform by muscular entrap- 
ment during systole, and was fixed in place at 
the epicardium by a pursestring suture. Static 
calibration of the gauges against a mercury col- 
umn was linear from zero to 300 mm Hg 
(within one percent) without hysteresis. Fre- 
quency response was limited by the recorder 
and was linear to 80 cps (± 5%). Zero stabil- 
ity in pre- and postimplantation calibrations 
was not found to be reliable, and thus measure- 
ment of absolute pressures was not attempted. 
The rate of left ventricular pressure change 
was obtained with an active differentiator hav- 
ing a frequency response linear to 80 cps. 
Instantaneous, continuous measurements of 
internal transverse left ventricular diameter 
were obtained by ultrasound techniques de- 
scribed elsewhere.* Briefly, two 5 mm diameter 
discs of lead titante-zirconate crystal, mounted 
in lucite housings and fitted with convex Incite 
lenses, were implanted on opposite endocardial 
surfaces of the left ventricle across the maxi- 
mum transverse diameter, in an approximately 
anteroposterior orientation. Lead wires exited 
through the ventricular wall of the site of im- 
plantation, and were exteriorized, along with 
other leads, at the back of the animal's neck. 
The transmitting crystal was pulsed for one mi- 
crosecond at a 5.6 khz repetition rate. The re- 
ceived signal from the opposite crystal, after 
rectification and amplification, was detected by 
a tracking gate similar to that used in radar 
systems.^ The analog output of the tracking 
gate was proportional to distance between the 
crystals (transmitting time) and was precali- 
brated in vitro. The rate of change of the ven- 
tricular diameter thus measured was obtained 
by passive differentiation of the tracking gate 
output after low pass filtering. The phase lag 
through tracker and filter combined was linear 
to 20 cps. 
* Model P-22, Eonigsberg Instruments, Pasadena, California. 
All animals were studied in the intact, awake 
state at rest, lying on the right side, within six 
hours postoperatively, and thereafter at least 
once daily until death due to acute graft rejec- 
tion. Arterial blood gas analyses performed in 
the majority of dogs during the initial postoper- 
ative study, while they were spontaneously 
breathing air, showed average pH 7.41 (± .02 
S. E.), average pOa 83.6 mm Hg (± 2.6 S.E.), 
average oxygen saturation 95.9% (± .4 S.E,), 
average PCO2 29.8 mm Hg (± 1.9 S.E.), 
and average bicarbonate concentration 18.1 
mEq. per liter (dr 1.3 S.E.). 
During each study a 3-lead, standardized 
electrocardiogram (limb leads I, II, III), the 
flow signal,* aortic blood pressure** (refer- 
enced to midchest level), left ventricular pres- 
sure and dp/dt, and the left ventricular diame- 
ter signal as well as its first derivative, were re- 
corded on either a Beckman type R Dynograph 
or Brush 480 recorder and on magnetic tape.*** 
Heart rate, stroke volume, cardiac output, mean 
aortic blood pressure, and peripheral vascular 
resistance were calculated off-line with the aid 
of a digital computer. Peak-to-peak QRS volt- 
age in lead II (normally conducted complexes) 
and cardiac rhythm were ascertained by inspec- 
tion. 
End-diastolic diameter (Dd) was determined 
at the onset of isovolumic contraction, and end- 
systolic diameter (Ds) was taken as the mini- 
mum systolic diameter. These measurements 
were averaged over several cardiac cycles se- 
lected during expiratory pauses. The difference 
between end-diastolic and end-systolic diame- 
ters, divided by end-diastolic diameter, repre- 
sented the percent systolic shortening (Dd- 
Ds) /Dd. The diameter at the end of early, rapid 
diastolic filling was designated Dr, and the ratio 
Dr-Ds/Dd-Ds defined as the percent of rapid 
filling. 
The instantaneous rate of left ventricular di- 
ameter shortening (dD/dt) was determined di- 
rectly from the differentiated diameter signal. 
Maximum systolic — dD/dt was divided by the 
corresponding instantaneous diameter to obtain 
* Biotronex 610 Pulsed-logic Flowmeter, Biotronex Lab, Silver 
Spring, Md. 
** Statham P23db, Statham Instruments, Hato Key, Puerto Rico. 
*♦* Ampex FE 1300, Ampex Corp., Redwood City, California. 
