Hemodynamic Measurements
and
Dynamics
of
Assisted Circulation
2
19
(8.1.7))
within
_+5%
of unity, or
1.
In other words, the measured pressure
is within
+5%
of
the actual pressure. Thus, higher resonant frequencies
and greater damping factors (up to critical damping) offer better dynamic
frequency response.
The step response or pop-test has its advantages
of
simplicity and
rapid tracking
of
system response. This “pop test” or step response
method is shown in Fig.
8.1.2.
One can apply either a positive step (step
increment in pressure) or a negative step (step decrement in pressure).
An ideal blood pressure measurement system follows the step exactly,
with no overshoot or undershoot, and no time delay.
In practice,
however, overshoot and oscillations are common. Fig.
8.
I
.2
also
illustrates the underdamped response
of
a fluid-filled catheter-manometer
system. The dynamic frequency response in terms of relative amplitude
ratio
vs.
frequency for the step response
of
Fig.
8.1.2
is shown in Fig.
8.1.3.
The single resonance peak occurs as the underdamped catheter-
manometer system was approximated by the second order system.
Fig.
8.1.2:
The pop-test (step response) for the dynamic testing of transducer system
performance, f
=
1/T
=
resonant frequency. The catheter transducer system is seen to be
an
underdamped
system.
In general, linearity, hysteresis, and dynamic system response are
necessary considerations in fluid-filled blood pressure measurement
systems.
Linearity refers to the output response vs. input applied
