Determining possible thrombus sites in an extracorporeal device, using computational fluid dynamics-derived relative residence time

The prediction of conditions that may result in thrombus formation is a useful application of computational fluid dynamics. A number of techniques exist, based on the consideration of wall shear stress and regions of low blood flow; however, no clear guideline exists for the best practice of their use. In this paper, the sensitivity of each parameter and the specific mechanical forces are explained, before the optimal indicator of thrombosis risk is outlined. An extracorporeal access device cavity provides a suitable geometry to test the methodology. The recommended method for thrombus prediction considers areas with a calculated residence time (RT) and shear strain rate (SSR) thresholds, here set to RT>1 and SSR<10s(-1). Evidence of thrombosis was found for physiological waveforms with an absence of reverse flow, which is expected to 'wash out' the cavity. The predicted thrombosis sites compare well with evidence collected from explanted devices.