Bartlett, Matthew; (2025) Predicting haemodialysis access failure through non-invasive haemodynamic surveillance. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Over 30,000 people in the UK rely on regular haemodialysis to compensate for reduced kidney function, and filter toxins from their blood. Vascular access complications remain the leading cause of hospitalisation amongst these patients and are associated with increased morbidity and mortality, as well as considerable social and economic burdens. Despite years of global research and investment into this topic there is still no consensus on an optimum surveillance and maintenance regimen. This thesis details the development, testing and application of a non-invasive surveillance technique, which enables quantification of deleterious flow patterns associated with proliferative neointimal hyperplasia. Intrinsic, physical limitations of diagnostic ultrasound are discussed, along with suggested methods for system optimisation, based on clinical observations and bench-top testing. A novel method for estimating angle independent, turbulence intensity is provided, which can be semi-automated, eliminating much of the user variability associated with traditional ultrasound flow surveillance. This metric is proposed as a surrogate for identification of regions of wall shear stress with high directional variability. The proposed technique is validated against a patient specific in silico model. Computational fluid dynamics enables mapping of oscillatory shear forces and reduced time-averaged wall shear stress, both of which are associated with smooth muscle cell proliferation and migration. The validation case presented shows good correlation between the computational results and the ultrasound-based surrogate, with both techniques successfully identifying segments of the vein where stenotic lesions developed, leading to the need for radiological intervention. A pilot study was conducted, in which 30 patients with newly created arterio-venous fistulas received pre and post-maturation ultrasound assessments. Ultrasound based turbulence intensity ratio recorded on the pre-maturation scan, successfully predicted development of neointimal hyperplasia, resulting in haemodynamically significant lesions at 10 weeks post-surgery, with a sensitivity of 87.5% and specificity of 80%.

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