The Influence of Experimental Condition on the Derivation of Propagation Coefficient in Arterials Systems: Numerical Investigation

Abstract

Over the last few decades several methods have been used to compute the propagation coefficient, which is a complex number that provides information about the viscoelastic properties of blood vessels. Results from these methods show a considerable disparity between them and when they are compared to theoretical values. Moreover, the attenuation and phase velocity obtained by the three-point method shows more significant discrepancies than those obtained by the other methods. In order to clarify the source of the disparity of results carried out by various methods concerning the estimation of phase velocity and attenuation in the arterial network, we made investigations using numerical tool several methods. We studied, for each method, the effects of distance between measurement sites, the sampling interval and measurement errors on the determination of the propagation coefficient by each of these methods. The values of wave speed and attenuation computed by these methods were compared to the known input values. Our simulation demonstrates that the distance between measurement sites and the sampling interval may introduce significant errors when the noise becomes high. Moreover the error on the values of attenuation and phase velocity obtained by occlusion and three-point methods is significantly higher than the error on the values obtained by RV-I and RV-II methods for all experimental conditions studied within the examined frequency range. This result supports the idea that the discrepancy between studies reported in literature seems to be due to the inaccuracy of experimental measurement techniques and not associated with the methods themselves as concluded by some authors.

Comparison of Linear Methods for the Determination of Propagation Coefficient in Arterials Systems: Numerical Investigation

“…The same conclusion can be pronounced for change in wall stiffness and blood viscosity (Figures 4-5). A second fundamental conclusion arising from this study, and confirming our previous conclusions, is that using inexact flow velocity and radius data leads to high errors in the calculation of the propagation coefficient (23), (27) . A small time lag between radius and flow velocity data induces a large scatter on the computed propagation coefficient ( figure 8).…”

“…In other hand, the computed attenuation by all methods becomes highly erroneous when the computer programme was applied to noisy signal as shown in figure 9. The scatter is more apparent when distance between measurement sites becomes small (23), (22) . Moreover, the three-point method exhibits more scatter than two-point methods for small distance between measurement sites.…”

“…Details of these techniques and of the computer model, which are based on the assumption that the system is analogous to a linear transmission line, have been discussed in earlier papers (15,23) .…”

“…Inaccuracies in the measurement data have a number of sources. They can be associated to an internal or external noise from the measurement system (23) . They can also be associated to error in positioning measurement probe or/and to difficulty of synchronizing apparatus (27) .…”

“…K 0 =1) (23) . Figure 9 summarizes results for attenuation coefficient calculated using noisy signal (4%) when reflection coefficient is different of the unit.…”