The presence of helical flow can suppress areas of disturbed shear in parameterised models of an arteriovenous fistula

• Published in: International journal for numerical methods in biomedical engineering 2019-12, Vol.35 (12), p.e3259-n/a
• Main Authors: Cunnane, Connor V., Cunnane, Eoghan M., Moran, Daniel T., Walsh, Michael T.
• Format: Article
• Language: English
• Subjects: Anastomosis; Angles (geometry); arteriovenous fistula; Arteriovenous Fistula - physiopathology; Blood Flow Velocity; Computational fluid dynamics; Computer applications; Diagnostic systems; disturbed shear; Exposure; Fistula; Fistulae; Fluid dynamics; Helical flow; Humans; Hydrodynamics; Hyperplasia; intimal hyperplasia; Mathematical models; Models, Cardiovascular; parameterised models; Parameterization; Pulsatile Flow; Shear flow; Shear Strength; Ultrasound
• ISSN: 2040-7939; 2040-7947
• DOI: 10.1002/cnm.3259

Areas of disturbed shear that develop following arteriovenous fistula (AVF) creation are believed to trigger the onset of intimal hyperplasia (IH), leading to AVF dysfunction. The presence of helical flow can suppress the flow disturbances that lead to disturbed shear in other areas of the vasculature. However, the relationship between helical flow and disturbed shear remains unevaluated in AVF. In this study, computational fluid dynamics (CFD) is used to evaluate the relationship between geometry, helical flow, and disturbed shear in parameterised models of an AVF characterised by four different anastomosis angles. The AVF models with a small anastomosis angle demonstrate the lowest distribution of low/oscillating shear and are characterised by a high helical intensity coupled with a strong balance between helical structures. Contrastingly, the models with a large anastomosis angle experience the least amount of high shear, multidirectional shear, as well as spatial and temporal gradients of shear. Furthermore, the intensity of helical flow correlates strongly with curvature (r = 0.73, P < .001), whereas it is strongly and inversely associated with taper (r = −0.87, P < .001). In summary, a flow field dominated by a high helical intensity coupled with a strong balance between helical structures can suppress exposure to low/oscillating shear but is ineffective when it comes to other types of shear. This highlights the clinical potential of helical flow as a diagnostic marker of exposure to low/oscillating shear, as helical flow can be identified in vivo with the use of ultrasound imaging. This study found that a flow field characterised by a high helical intensity coupled with a strong balance between helical structures is associated with a reduction in exposure to low/oscillating shear. However, no apparent feature of the bulk flow correlates with a reduction in exposure to high shear, multidirectional shear, or spatial and temporal gradients of shear. Furthermore, the locations of an arteriovenous fistula (AVF) predisposed to stenotic lesions experience multiple patterns of disturbed shear, making it difficult to ascertain if a single wall shear stress metric is capable of accurately predicting the areas of an AVF susceptible to the development of intimal hyperplasia.