Blood flow dynamics assessment within the Supera stent in the common femoral and popliteal arteries

Project reference:  SIE_14_22 
1st supervisor:  Prof. Pablo Lamata

2nd supervisor: Dr Jordi Alastruey

3rd supervisor: Mr Hany Zayed

Start date:  February 2023

Aim of the project: Endovascular treatment of atherosclerotic arterial disease affecting the lower limb arteries has become the first-line treatment in patients with symptomatic peripheral arterial disease. This commonly involves stenting the treated arterial segment where the stent acts as a scaffold to maintain vessel patency. Biomimetic stents (Supera) have shown satisfactory patency rates and freedom from re-interventions in the femoro-popliteal segment (superficial femoral artery and proximal popliteal artery). However, endovascular treatment of certain arterial territories – namely the common femoral artery (CFA) and distal popliteal artery (Pop A) – remains controversial because both arterial segments are located across an active joint (e.g., the hip and knee). There are unproven theories that joint movements will produce compression and deformity of the stents with consequent stent damage and occlusion. The aim of this project is to examine whether joint movements have an impact on the flow dynamics within Supera stents inserted into the CFA and Pop A.   

 
Project description:  
A 1:1 scale cardiovascular simulator rig of the lower limb arteries around the hip and knee joints will be produced to experimentally calculate the net flow reduction and pressure drop across the joints, under different scenarios; e.g. with/ without the stent and with the joint extension and flexion at variable angles. The following two tasks will be carried out to fulfil the project’s objective:  

 

Task 1 – Model set up: Blood flow in the lower limb arteries around the hip and knee joints will be simulated using an experimental model with arteries made of silicone tubes, blood modelled as a water–glycerol mixture to reproduce its rheological properties (i.e. blood density and viscosity), and a pulsatile pump connected to upstream to the joint to produce physiological blood flow waveforms. Similar experimental set-ups have been produced by Prof. Lamata’s lab to characterise pressure differences across the aortic valve [1] and aortic coarctations [2]. Anatomically correct CFA and Pop A arteries will be produced from segmented computed tomography (CT) images.  

 

Task 2 – Flow and pressure drop measurements: Existing equipment enables highly accurate measurements of flow waves using ultrasonic perivascular probes and pressure waves using Millar intravascular pressure-tip wires. This equipment will be used to measure the flow and pressure of the fluid in the in vitro model proximal and distal to the joint, for different bending angles of the joint (see Figure 1) simulated mechanically. Measurements will be taken with and without the Supera stent inserted into the silicone tube. Joint movements create transient narrowing to the lumen which will be measured using an ultrasound dimension gauge that tracks the movement of sonomicrometry crystals attached to the silicone tubes. These measurements will provide a complete characterisation of flow dynamics across the joint that will allow us to (i) understand the effects of joint movements on the local blood flow around the joint and (ii) quantify how much these movements reduce the net blood flow to distal vessels with and without the Supera stent. 

 

 

Figure 1. Computed tomography of the limb flexion states demonstrating standing (180 degrees), walking (110 degrees), sitting (90 degrees), and gardening (60 degrees) postures. Bending angle is defined as the inner angle between the femur and tibia. Note severe deformations at the adductor hiatus (AH) and below the knee. Intra-arterial markers are blue. PA, Popliteal artery; SFA, superficial femoral artery. (Taken from Poulson et al, J Vasc Surg, 2018). 

 

This project will run in parallel with the project titled Blood flow dynamics assessment distal to knee and hip arteries stented with the Supera stent. The net flow reductions and pressure drops across the joint obtained experimentally in the present project will be used to inform a computational model of blood flow in the lower-limb arteries developed in the parallel study to investigate the flow dynamics distal to the joint. 

 

References 

[1] Beyond Bernoulli | Circulation: Cardiovascular Imaging (ahajournals.org) 

[2] Flow profile for a better non-invasive pressure drop in CoA | European Heart Journal