Validation
of a physical model - Calculation of Impedance
In order
to characterize the quality of signal recorded on an in vitro
test bench, it is essential to realize a comparison with physiologic
data. The in vitro signal often show high frequency oscillations
due to the intrinsic rigidity of the mechanical model. To clear
these perturbations from the analysis and make sure that they
actually are secondary perturbations of no regrettable influence
on the flow, a frequency analysis of the recorded signal is
done. The analysis leads to, for instance, the specter of intake
impedance of the aorta, where the couple pressure/debt measured
in a precise point of the arterial system is studied.
The intake impedance gives an idea of the dynamic properties
of the arterial tree. This parameter does not only just take
into account the relationship between the average pressure and
the average debt of the aorta (the intake resistance) but also
the mechanical properties of the aorta, the hemodynamics properties
of blood, and the wave reflections effects in the arterial system.
In order to determine the intake impedance, the continuous and
periodical character of the signals of pressure and aortic debt
allows to decompose the recorded signal using the Fourier Series.
Impedance
Angle
Comparison between the intake impedance
and phase for in vivo and simulated signals.
The graphs above represent the intake impedance (normalized
modulus and phase). The good coincidence between in vivo and
in vitro studies for low frequencies should be noticed. The
slightly superior aspect of our values traduces a light over-tenderness
of our simulator in comparison with literature data. These results
show anyway the good accuracy of the simulation of physiological
flows.
