98
Dynamics
of the
Vascular System
where c is pulse wave velocity, r is radius and
p
is blood density,
1.06
g/cm'.
This method can be applied clinically where the cross-section
area can be obtained with ultrasound echocardiograph and the foot-to-
foot pulse wave velocity with a dual-sensor catheter.
c*
Ascending aorta
w
Descending thoracic
aorta
-
Brachiocephalic artery
-
Left
subclavian artery
- -
-.
Carotid artery
R
10
20
Frequency
(Hz)
Fig.
4.2.5:
Vascular impedances measured in several systemic arteries at aortic arch.
Notice that impedance modulus increases dramatically in smaller arteries. From
Cox
and Pace
(1975).
Both the input impedance and characteristic impedance moduli
increase as the measurement site becomes further away from the heart.
In
addition, zero crossing
of
the phase occurs at a much higher
frequency. Since only harmonic components can appear in the spectrum,
extended information can often be obtained by imposing cardiac pacing
at
different frequencies. The Vascular impedances obtained by
Cox
and
