Hemodynamic Measurements and
Dynamics
of
Assisted
Circulation
22
1
contains much higher frequency components than the femoral arterial
pressure.
The first derivatives of pressure, such as LV dp/dt, also
requires higher frequency response for accurate recording.
When the blood pressure waveform
is
recorded with a low resonant
frequency
and
low
damping
ratio
fluid-filled blood
pressure
measurement system, erroneous phase shifts and large oscillations can be
observed. Fig.
8.1.4
illustrates this point with the aortic pressure
waveform measured simultaneously by a high fidelity catheter-tip
pressure transducer and a low fidelity fluid-filled catheter-pressure
transducer system. The two waveforms are calibrated and superimposed.
Overestimation of systolic pressure and underestimation of diastolic
pressure can be observed. In addition, end-systolic pressure at aortic
valve
closure,
systolic,
diastolic and ejection
periods
cannot be
accurately determined.
Fig.
8.1.4:
Aortic
blood pressure waveform measured with an underdamped catheter-
manometer system and a high-fidelity catheter-tip pressure transducer.
Overshoot and
oscillations are clearly seen.
Li
and Noordergraaf (1977) have analyzed responses of differential
manometer systems.
For these systems, the individual frequency
response, as well as static and dynamic imbalances are important factors
to be considered. Catheter-tip pressure transducers offer
superior
frequency response, sufficient even for cardiac sound recording. They,
however, suffer from fragility, temperature-sensitivity, and the need to be
calibrated
against known manometric
systems. The efficacy
of
