Hemodynamics
of
Large Arteries
119
pressure waveforms were defined in terms of their morphological
differences and separated into different types. Peak systolic pressure
(Ps
or
Pp&
diastolic pressure
(Pd),
pulse pressure (PP), pressure at inflection
point
(Pi)
and the augmented pressure,
AP
are defined. Systolic pressure
augmentation
is
given by
AP
=
P,
-
Pi
(4.4.12)
and the corresponding augmentation index is given by
(4.4.13)
Although the augmentation index has been used to represent the
reflection
ratio,
it is not equivalent to the reflection
coefficient.
Augmentation index
is
merely a single number and does not represent
the frequency content of the reflected wave.
4.4.4
Wave Reflection Sites
Wave reflection sites exist all over the systemic arterial tree, due to
geometric and
elastic nonuniformities,
branching, and impedance
mismatching at arterial terminations.
Therefore, reflections cannot
originate from one site only.
Indeed, there is no agreement on the
location of reflecting sites. Some suggest that the major reflection site as
seen from the proximal aorta, appears to be in the region of the pelvis or
the aorto-iliac branching junction. Others, however, suggest that the first
major potential reflecting site
is
at the aortic arch. Although there is no
major agreement on the reflecting sites, the arterioles are recognized
as
being the principal sites for wave reflection, and the reflection coefficient
as being high.
There are multiple reflection sites and the effects of
repeated
reflections on pressure
and flow waveforms
have been
investigated (Berger et al.,
1993).
The model-based analysis showed
how the forward and reflected waves are actually the summations
of
repeated antegrade and retrograde waves.
The dispersion of such
multiple reflections make direct measurement and quantification of their
