Hemodynamic Measurements and
Dynamics
of
Assisted
Circulation
229
have been popular thermal velocity probes mounting on either a catheter
or
a needle.
These sensors have been applied to clinical settings
(Roberts, 1972).
In general, Doppler measured blood flow velocity (Fig. 8.1.10; Yao
and Pearce, 1991) compares well with that obtained by electromagnetic
method.
Fig.
8.1.10:
Doppler ultrasound measured spectral blood flow velocity
8.1.3.3 Indicator Dilution Methods and Thermodilution
Quantification of blood flow, even in the microcirculation by the
introduction of indicators to the circulatory system has been exercised for
quite some time. Dye dilution has been used for many decades.
The
indicator dilution method for measurement of blood flow is well
illustrated in Fig. 8.1.1 1 (Geddes, 1984) in which an indicator of known
mass is injected upstream. With the velocity
of
blood flow, the indicator
is diluted and its concentration
is
detected and sampled downstream.
The amount of flow,
Q,
is calculated from the following relation:
m
Q=-
c,
xt
(8.1.18)
