Hemodynamics
of
Large
Arteries
101
simultaneous measurements of two pressures separated by a finite
distance,
Az,
normally 4-6 cm apart.
A
double-lumen catheter with
two
pressure ports connected to
two
pressure transducers or a Millar catheter
with dual pressure sensors suffice for such measurement. Thus, the foot-
to-foot velocity, cf is calculated from:
Cf
=
-
At
(4.3.4)
Fig.
4.3.1
:
Diagram illustrating how foot-to-foot velocity
is
calculated given pressure
measurements
at
different sites separated
by
a
known
distance Az
.
Here the foot-to-foot
velocity
is
given by
cf
=
AdAt.
At
is
pulse transit time delay. Notice the peak-to-peak
transit time is different from that of the foot-to-foot.
This method assumes that reflected waves
do
not interfere with the
onset of the propagating pulse.
As
an example, referring to Fig. 4.3.1, the
distance between the
two
pressure measurement sites is
5
cm and the
calculated time delay, At,
is
60
msec, or 0.06 sec, then the foot-to-foot
velocity is
C
3
-
833cds
Cf
=--
0.06
or 8.33
ds.
(4.3.5)
Fig. 4.3.2 shows the foot-to-foot velocity measured in different
arteries (Nichols and McDonald,
1
972).
Wave velocity increased from
