The
Venous
System
I89
dominate at low frequencies (Chapter
4)
and that the wave velocity is
essentially constant, as is dynamic elastic modulus at high frequencies.
They generated high frequency small amplitude sinusoidal pressure
waveforms which were introduced into the abdominal vena cava of
anesthetized dog or by means of an electromagnetic impactor attached to
the veins outer wall.
A
dual-sensor catheter-tip transducers were inserted
into the vein to measure pulse wave velocity from transit time delays, i.e.
foot-to-foot velocity. Their results are shown in Fig.
6.3.5.
It is clear
from our earlier analysis that the pressure-dependence of compliance and
pulse wave velocity are clearly seen with increasing transmural pressure.
Fig. 6.3.5: Propagation velocity
as
a function of transmural pressure. Short trains
of
high
frequency small amplitude sinusoidal pulse waves were imposed
on
the dog's abdominal
vena cava. (Anliker et al.,
1
969).
Their results on attenuation showed that attenuation per wavelength is
independent of frequency. Figure
6.3.6
shows that pulse wave amplitude
declines with distance, described by:
(6.3.15)
-kt
a
a
=
a,e
where
x
is distance along the vessel,
h
is wavelength of propagation, a is
the amplitude and
a,,
is the amplitude at
x=O.
The value of
k
for the vena
cava of the dog
is
between
1.0
to 2.5, corresponding to attenuations
of
