104
Dynamics
of
the
Vascular
System
and
aapp,
the apparent attenuation coefficient, is obtained from:
(4.3.1 1)
where
Ip,l
and
lp21
are the harmonic moduli ofp, and p2, respectively. It
is clear that
aapp,
describes the degree of damping or the attenuation of
the pressure pulse
as
it propagates between the two arterial sites.
The apparent phase constant
Papp
is obtained from:
where
$1
and
$2
are the harmonic phases ofp, and p2, respectively. The
apparent phase velocity of propagation is calculated from:
w
(4.3.13)
--
caPP
-
PUPP
or more explicitly
(4.3.14)
capp
is also known as the measured velocity. This apparent phase velocity
is significantly affected by the presence of wave reflections, in the
similar manner
as
vascular impedance.
The true and apparent propagation constants can be related to
characteristic and input impedances as:
(4.3.1
5)
