1088 
MONITORING 
ANIMAL STUDIES 
Animal studies were performed with adult, 
15-20 kg mongrel dogs. Anesthesia was in- 
stituted with the intravenous administration of 
sodium pentobarbital. Following artificial venti- 
lation and hemodynamic stabilization serial re- 
cordings of contrast dilution curves were ob- 
tained in a standard fashion. 
Contrast dilution curve recording was ob- 
tained by positioning the six-channel solid state 
detector array across the central circulation. 
Gain and position circuits were adjusted and 
apnea then induced for the duration of curve 
inscription. Three to five ml. meglumine diat- 
rizoate were then injected into the central ve- 
nous circulation, and contrast dilution curves 
were recorded as shown in Figure 3. Immedi- 
ately following curve transcription, step den- 
sity wedges were placed within the roentgen 
beam path to allow calibration of the indicator 
dilution curve signal. Figure 3 illustrates an 
example of a contrast dilution curve recorded 
over the aorta and reflects stepwise washout of 
indicator from the left ventricle. Replotting the 
_3ml 
Hypaque I 
m £V>.C. 
-A W-ISEC. 
Stepwise washout 
cf Indicator 
Call brat i< 
7 
2 * 
O 10 
\- 
u 
111 IS 
_l 
ltj20 
LOG WASHOUT FROtsA 
LEFT VENTRICLE OF 
DOG, 0.2 CM DETECTOR 
AREA 
40 
Figure 3. — Stepwise indicator washout from the left 
ventricle is illustrated in the recording of a contrast 
dilution curve obtained over the aorta. The calibration 
signal is shown on the right. Replotting of the step- 
wise washout on the logarithm scale demonstrates an 
exponential decrement in indicator from the left ven- 
tricle related to each ventricular ejection. 
step decays on a logarithm scale demonstrates 
an exponential washout pattern related to each 
ventricular ejection. Calibration is nearly linear 
and is employed in replotting the observed 
logarithm scale. 
Pulmonary circulation time is a physiologic 
variable useful in the assessment of respiratory 
and hemodynamic function and can be estimated 
as the difference in indicator transit times com- 
puted from the right and left sides of the cen- 
tral circulation. For estimating pulmonary cir- 
culation time, contrast dilution curves were 
recorded from the central circulation according 
to the method described above. Recorded curves 
reflecting indicator dispersion from the right 
and left sides of the circulation, as shown in 
the insert in Figure 4, were utilized in the com- 
putation of transit time across the pulmonary 
vascular bed. The recorded contrast dilution 
curves were smoothed and then replotted onto a 
logarithm scale. Washout of indicator from both 
sides of the circulation was assumed to be ex- 
ponential and all curves were reconstructed to 
allow computation of mean transit time related 
to the right and left sided contrast dilution 
curves as shown in Figure 4. 
Data obtained from six normal, anesthetized 
mongrel dogs relating to the calculation of pul- 
monary circulation time is shown in Table I. 
The mean transit time to the right side of the 
circulation is represented by MTT^. Point A 
represents the recomputed appearance time for 
the left sided curve and the mean transit time 
to a point in the left circulation is represented 
by MTTo. Pulmonary circulation time, MTTp, 
is then given by the equation. 
MTTp = A + MTT2 — MTTi 
(2) 
Pulmonary circulation times were obtained in 
six normal dogs through the analysis of roent- 
Table I. — Calculation of Pulmonary Circulation Time 
MTTi 
A 
MTT2 
MTTp 
Expt. 
(sec) 
(sec) 
(sec) 
(sec) 
1 
1.35 
2.00 
2.80 
3.45 
2 
1.55 
2.20 
2.10 
2.75 
3 
1.15 
1.40 
2.90 
3.15 
4 
1.50 
2.00 
2.10 
2.60 
5 
1.50 
2.30 
3.30 
4.10 
6 
1.52 
1.60 
2.67 
2.75 
mean 
= 3.13 
S.D. = 
±0.57 
