Hemodynamic Measurements
and
Dynamics
of
Assisted Circulation
23
1
Thus, if the area under the concentration vs. time curve is found, flow
can be easily obtained.
For measurement of blood flow in a single
vessel, the above formulation works well. When applied to measuring
cardiac output, however, the continuous pumping of the heart introduces
the problem
of
recirculation.
To
overcome this,
an
exponential
extrapolation
of
the concentration-time curve's
descending limb
is
imposed such that an approximation of the integral with the area under
the curve
is
achieved.
Fig.
8.1.12:
Thermodilution method in man. The injection catheter is in the superior vena
cava
(SVC).
The thermistor for measurement
of
indicator temperature
is
inside the
injection catheter
1
to
2
cm from the tip. The thermistor
for
measurement of blood
temperature is in a main branch of the pulmonary artery
(PA).
RA and
RV
are right
atrium and right ventricle, respectively.
Indicators that have commonly been used include Evans blue dye,
Indocyanine green and some radioactive isotopes, such as Albumin
I~dide'~'. The advantage of the non-toxicity and affordability of
repeated determinations within a short time span makes cold solutions
