Machine Design
Dialysis Technology Lifts Off with Aeronautics Software Peter Vincent/Imperial College London

Dialysis Technology Lifts Off with Aeronautics Software

Patients with kidney failure depend on dialysis machines to replace most renal functions. A dialysis machine is responsible for filtering creatinine and urea from the blood, and moderating water content to control blood volume.

Now, aeronautic software will be used to significantly improve kidney dialysis technology, and no modest bioengineer can shrug off the achievement with “it’s not rocket science” because, well, that’s exactly what it is.

A team consisting of bioengineers, aeronautic engineers, circulatory specialist, and cardiovascular surgeons in the U.K. are using aerospace fluid-dynamic software to simulate blood flow for different arteriovenous-fistula (AVF) configurations. An AVF is necessary to increase blood flow from the patient’s arm to the dialysis machine.

Before dialysis, a vein and an artery in a patient’s arm are surgically connected to create an AVF, where blood flows directly from an artery into the vein, instead of passing through capillaries. The software, which caters specifically to a patient’s blood vessels, analyzes the shear flow for different artery curvatures and vein-artery alignments to create the optimal AVF configuration for that person. Pictures of the patient’s circulatory anatomy can be produced using ultrasound techniques.

Lowering Shear stress

AFV surgery can be problematic because the surgeon alters the trajectory of normal blood flow though the vessels. If the transition between the vein and artery is not smooth, eddies may develop, and the laminar flow becomes turbulent. Such an imperfection could cause shear stress on the blood cells during blood flow. Shear stress is a key instigator for blood clotting, so when AVF surgery goes wrong, it can sometimes result in a clot.

Shear stress on the blood cells during flow can also be triggered by an extreme curvature of the artery when connecting it to the vein. The blood cells hit the edge of the artery wall during flow, producing shear stress and possibly resulting in a clot. Furthermore, AFV configuration could affect oxygen transport. 

For these reasons, surgeons require a way to predict the blood flow profile in different AVF configurations. Blood flow is also different from patient to patient. “Our ultimate aim is to use computational simulation tools to design tailored, patient-specific arteriovenous-fistulae configurations that won’t block and fail,” says Peter Vincent, a senior lecturer and fellow of the Engineering and Physical Sciences Research Council (EPSRC) in the Department of Aeronautics at Imperial College London. 

After analyzing many different AVF configurations with the aeronautic software, the team found the optimal setup for stabilizing blood flow and reducing shear. “We discovered that if an arteriovenous fistula is formed via connection of a vein onto the outside of an arterial bend, it stabilizes the flow,” says Vincent. The process has yet to be tested clinically, but so far, it seems that rocket science and bioengineering have more in common than we thought.

To learn more, read the published report in the AIP Physics of Fluids journal. 

What is AVF surgery?

An arteriovenous fistula (AVF) is surgically created by conjoining a vein and an artery. Normally, the high pressure in arterial blood is decreased gradually as the blood flows from the single artery to small, but numerous, arterioles that branch into smaller and more numerous capillaries. (Although capillaries and arterioles have smaller cross-sectional areas, the high number of them yields a large total cross-sectional area, therefore reducing blood pressure.) From the capillaries, the blood flows into larger venules and then into a single vein, where the pressure remains relatively low.

By creating a fistula, the gradual decrease in blood pressure is replaced with direct high-pressure blood flow from the artery into the vein. Before the patient starts dialysis, he/she must wait several months for the vein to strengthen itself against the direct high pressure. This creates a strong flow from the artery to the machine, and allows the same flow rate back into the vein.

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