116
Dynamics
of
the
Vascular
System
0.5-
a,
0
.-
?$
0.4-
0.3-
8
c
a,
=
0.2-
4.4.2
The Reflection
Coeffuients
The reflection coefficient is defined as the harmonic ratio
of
reflected
wave to the forward wave in the frequency domain:
(4.4.9)
It has both
a
modulus and a phase, and vanes with frequency:
r
=
Irl~q+
(4.4.10)
Reflection coefficients calculated for the normal, vasoconstricted and
vasodilated conditions obtained from canine experiments are shown in
Fig.
4.4.5.
For the fundamental harmonic, the mean value of the
reflection coefficient at control is about
0.45.
This is increased
to
0.65
during vasoconstriction and decreased to about
0.15
during vasodilation.
The reflection coefficient remains low for higher frequencies during
vasodilation.
0.7
0.6]
+
control
-#-
NTP
--t
MTX
0.0
I
I
I
I
I
I
I
0
1
2
3
4
5
6
harmonics
Fig.
4.4.5:
Global reflection coefficients obtained during control (circle), vasoconstriction
(triangle) and vasodilation (square) conditions.
