  Arterial wall shear stress (WSS) parameters are widely used for prediction of
the initiation and development of atherosclerosis and arterial pathologies.
Traditional clinical evaluation of arterial condition relies on correlations of
WSS parameters with average flow rate (Q) and heart rate (HR) measurements. We
show that for pulsating flow waveforms in a straight tube with flow reversals
that lead to significant reciprocating WSS, the measurements of HR and Q are
not sufficient for prediction of WSS parameters. Therefore, we suggest adding a
third quantity - known as the pulsatility index (PI) - which is defined as the
peak-to-peak flow rate amplitude normalized by Q. We examine several pulsating
flow waveforms with and without flow reversals using a simulation of a
Womersley model in a straight rigid tube and validate the simulations through
experimental study using particle image velocimetry (PIV). The results indicate
that clinically relevant WSS parameters such as the percentage of negative WSS
(P[%]), oscillating shear index (OSI) and the ratio of minimum to maximum shear
stress rates (min/max), are better predicted when the PI is used in conjunction
with HR and Q. Therefore, we propose to use PI as an additional and essential
diagnostic quantity for improved predictability of the reciprocating WSS.
