Hemodynamics
of
Large
Arteries
107
500;
i
i
s
i
ti
ti
Harmonic
Fig.
4.3.5:
Apparent phase velocities obtained by noninvasive pressure measurements
with tonometers at the carotid and radial arterial sites in normal and hypertensive adults.
(From Li et al.
(1996).
Larger
low
frequency amplitudes and greater oscillations at higher
frequencies can be seen.
4.3.4
Determination
of
the Propagation Constant
Experimental determination of the apparent propagation constant is
simpler than that of the true propagation constant. The former can be
determined by simultaneously measuring either
two
pressures for the
pressure pulse, or
two
flows for the flow pulse. Determination of the
true propagation constant which is independent
of
wave reflections, in
the presence of reflections, however, requires simultaneous measurement
of three variables.
Several methods are available to determine the true propagation
constant, all
of
which are based on linear transmission theory. From the
definition of the propagation constant as
it
relates to longitudinal
(Z,)
and
transverse
(Z,)
impedances:
y=Jz,iz,
(4.3.16)
where
-+I&
Q
2,
=
(4.3.17)
