Computation in the rabbit aorta of a new metric – the transverse wall shear stress – to quantify the multidirectional character of disturbed blood flow

Abstract

Spatial variation of the haemodynamic stresses acting on the arterial wall is commonly assumed to explain the focal development of atherosclerosis. Disturbed flow in particular is thought to play a key role. However, widely-used metrics developed to quantify its extent are unable to distinguish between uniaxial and multidirectional flows. We analysed pulsatile flow fields obtained in idealised and anatomically-realistic arterial geometries using computational fluid dynamics techniques, and in particular investigated the multidirectionality of the flow fields, capturing this aspect of near-wall blood flow with a new metric – the transverse wall shear stress (transWSS) – calculated as the time-average of wall shear stress components perpendicular to the mean flow direction. In the idealised branching geometry, multidirectional flow was observed downstream of the branch ostium, a region of flow stagnation, and to the sides of the ostium. The distribution of the transWSS was different from the pattern of traditional haemodynamic metrics and more dependent on the velocity waveform imposed at the branch outlet. In rabbit aortas, transWSS patterns were again different from patterns of traditional metrics. The near-branch pattern varied between intercostal ostia, as is the case for lesion distribution; for some branches there were striking resemblances to the age-dependent patterns of disease seen in rabbit and human aortas. The new metric may lead to improved understanding of atherogenesis.

Impact of 2‐Weeks Continuous Increase in Retrograde Shear Stress on Brachial Artery Vasomotor Function in Young and Older Men

“…Exposure to (unidirectional) retrograde SR relates to upregulation of pro‐atherogenic factors 9, 10. Interestingly, recent observations from Peiffer et al, using a computational technique to describe that multidirectional wall shear stress, suggested that multidirectional shear may be relevant to the development of atherosclerosis 46. Future studies should therefore aim to assess the importance of (in vivo) multidirectional wall shear in the development of atherosclerosis.…”

Influence of shear stress magnitude and direction on atherosclerotic plaque composition

“…These metrics were chosen because they have been demonstrated to localize to regions of atherosclerotic plaque development while each quantifying a different aspect of the flow field as a function of WSS magnitude, direction or both. These metrics include the wall shear stress angle deviation (SAD; a metric of the spatial change in flow direction) [24], relative residence time (RRT; a metric of species transport) [25], oscillatory shear index (OSI; a metric of flow reversal) [26] and the recently developed transverse wall shear stress (tSS; a metric of flow multidirectionality) [27,28]. In addition to these established metrics, we developed two new WSS metrics, the low shear index (LSI) and the high shear index (HSI) [1], which quantify changes in time-averaged WSS (TAWSS) magnitude on a continuous scale.…”

Endothelial fluid shear stress sensing in vascular health and disease

“…This finding has generally been attributed to low and/or oscillatory shear (49). Recently, however, it has been suggested that transverse flow (i.e., flow at 90° to the vessel axis) shows the best correlation with plaque formation over a range of conditions in animal models (52). This in vivo result fits well with an in vitro study showing that flow perpendicular to the morphological and cytoskeletal axis of ECs activated inflammatory pathways, whereas flow that was parallel was antiinflammatory, even if it reversed direction (54).…”