An experimental evaluation of the use of an ensemble average for the calculation of turbulence in pulsatile flow

Abstract

A comparison was made between turbulence calculated by subtracting an ensemble average from the instantaneous velocity and calculations made with a high pass digital filter. Velocity was measured with a laser Doppler anemometer in vitro in the region of a normal porcine aortic valve and in patients with a hot film anemometer in the region of normal aortic valves. From the velocity obtained in patients, the absolute turbulence intensity calculated using an ensemble average of 50 beats was nearly twice the turbulence intensity calculated using a digital filter. Individual beats sometimes showed differences of 150% compared to calculations based upon the use of a digital filter. Inspection showed that the ensemble average varied widely from the actual nonfluctuating velocity. Studies in vitro showed less beat to beat variation than occurred in patients. The absolute turbulence intensity measured in vitro, when calculated using an ensemble average, was only 20% greater than calculations using a digital filter. The differences were due primarily to beat-to-beat variations of the nonfluctuating velocity, but these beat-to-beat variations were less prominent than occurred in patients. These observations suggest that ensemble averaging may not be appropriate for the calculation of turbulence, particularly in patients.

Flow Patterns in Carotid Bifurcation Models Using Pulsed Doppler Ultrasound: Effect of Concentric vs. Eccentric Stenosis on Turbulence and Recirculation

“…Peak and mean velocities were traced over 10 cardiac cycles. Acquisitions were prospectively gated so that each spectral parameter calculated for each interrogation site can be averaged over 10 cardiac cycles to give an ensemble average (Walburn et al 1983). The ensemble average from 10 complete cycles was calculated for v mean , v peak and SBI, as well as the root-mean-square (RMS) deviation in the 10 contributing values for each of these parameters at each time point in the ensemble average.…”

Cycle-to-cycle variation effects on turbulent shear stress measurements in pulsatile flows

“…Several methods which account for cycle-to-cycle variation have been used to calculate the mean periodic velocity (Rask 1981, Walburn et al 1983, Liou & Santavicca 1985. In each case, some technique is used to identify the mean pulse.…”

“…In the latter, a digital low-pass filter was used to separate the mean periodic signal of each cycle from the turbulent fluctuations. This filter technique is similar to that of Walburn et al (1983) for determining the mean periodic signal. However, Walburn et al reported turbulent…”

Quantification of turbulence intensity in patients with symptomatic carotid atherosclerosis: a pilot study

“…Turbulence is one such hemodynamic phenomenon that is of particular interest, as it has been shown that turbulence near vessel stenoses have been implicated as a risk for thromboembolic stroke [4] and as a potential indicator of significant stenoses [8,9]. The most popular method for quantifying turbulence by Doppler ultrasound is turbulence intensity (TI), which directly measures incoherent fluctuating velocity components [10][11][12][13]. It is possible to quantify TI through ensemble averaging or through frequency filtering methods, where both of these analytical methods are used to decompose the Doppler signal into coherent pulsatile fluctuations and incoherent turbulent fluctuations.…”