190
Dynamics
of
the
Vascular System
63%
to
92%
per wavelength. This compares with
0.7
to
1
.O
for the aorta.
Thus, greater attenuation and slower pulse wave propagation velocity are
found in the vena cava.
Fig.
6.3.6:
Attenuation of
short
trains of high frequency small amplitude sinusoidal pulse
waves were imposed on the dog's abdominal vena cava. Attenuation is represented by
the amplitude ratio
(a/%)
as a function of changes
in
propagating distance as a fraction of
wavelength
(dk).
From Anliker et al.
(1969)
The attenuation was attributed to the viscosity
of
blood, the radial
transmission to surrounding tissues and the viscoelastic properties
of
the
walls. This latter is the predominating factor, as have been found for the
systemic arteries by Li et al.
(198
1).
That the attenuation per wavelength
is practically
independent of frequency
suggest that the energy
dissipation is independent
of
strain rate. This study uses frequencies
of
20-100
Hz,
much higher than the highest significant component of
natural pulse pressure and flow waveforms.
Pulse
wave velocity
as
seen from the above experimental
measurements, is significantly lower in veins than in corresponding size
arteries. This can be measured as foot-to-foot velocity or can be readily
estimated from the Moens-Korteweg formula.
But with the changing cross-sectional area and the transmural
pressure, pulse wave velocity is seen to be dependent on both vessel
