Cardiovascular haemodynamics: Advancement of numerical and experimental diagnostic tools

Overview

Cardiovascular diseases (CVDs) are the main cause of death in developed world. After a few decades of research, the clear anatomic functional and haemodynamic interdependency of cardiovascular assemblies and the use of various simulation tools to analyse such interactions are well recognized and documented.^1–4 In line with this recent advances in computational fluid dynamics (CFD), laser diagnostics and imagining processing have introduced new methodologies to study the CVDs and the mechanisms underlying their pathology.^5–11 Knowledge gained from implementing these tools has led to the development of successful therapies and novel tools to characterize these clinical conditions and assist in the development of a precise, preventive and predictive treatment for CVDs. Moreover, new designs of various artificial devices to aid the functionality of the heart and main blood vessels, such as ventricular assist devices (VADs), stents and valves, have been widely proposed and implemented with various degrees of success.^12–18 However, research is still ongoing as there is a need to develop a rigorous synergy between advanced simulation tools and experimental diagnostic methodologies.

In this Special Issue of CVDs, a total of 12 articles were submitted of which only 5 have been accepted after rigorous reviewing. We are pleased to present such excellent work in our journal. The 5 articles include the work of Hu and Cai, who investigated the flexible deformation of the guide wire in a force feedback device of virtual cardiovascular surgery to determine the optimal length of the guide wire. The authors experimentally determined the performance of force transmission by varying the length of the guide wire and determined the optimal length of the wire that gave maximum force to the actuator. Such approach can be equally applied to optimize and enhance the dynamic performance of other catheter-type surgery instruments.

Gårdhagen et al. used large eddy simulation (LES) method to examine the haemodynamic of the coartation of the aorta (CoA) and post-stenosis dilatation. In this study, different haemodynamic parameters associated with the vascular dysfunction risk factors before and after CoA repair were used in the analysis. They confirmed that turbulence fluctuations, the direct jet impact and/or the combination of both could lead to initiation of post-stenosis dilatation which may instigate thrombus formation in patients with CoA. Moreover, they found that the risk factors for the vascular dysfunction appeared to be considerably higher before the CoA which was attributed to the elevated turbulence fluctuations and the high oscillating and unstable flow patterns in this region. In addition, their results showed that intervention reduced the effect of the haemodynamic risk factors which are critically abnormal before the CoA. Ma et al. numerically studied the left pulmonary artery stenosis with different degree of stenosis, using the multi-scale method to determine the effect of the unilateral pulmonary artery stenosis after the Glenn procedure. In this study, different haemodynamic parameters such as the wall shear stress, oscillatory shear index and the blood flow distributions were examined to evaluate the influence of the pulmonary stenosis after the Glenn surgery. The authors found that the stenosis of more than 75% significantly influences the haemodynamic parameters of the pulmonary arteries which could lead to considerable unbalanced blood perfusion to each lung and the blood power loss. The study recommended treating severe stenosis before the Glenn operation, but such treatment is not necessary for the mid-range stenosis. Another interesting study in this Special Issue is the one by Shcherbakova et al., where the authors developed a simple ex-vivo setup to evaluate the feasibility of using the supersonic shear wave imaging (SSI) techniques to determine the mechanical property of the artery. It should be noted, however, that although in this non-invasive techniques the stiffness and other mechanical properties of the bulk tissues can be measured by the ultrasound waves, there are some technical limitations that affect the accuracy of the obtained mechanical property of the arteries. It is also noted that to quantify the mechanical property of the artery, it is necessary to develop more complex setup, and such uni-axial mechanical setup incorporating the hysteresis effects in the excised equine aorta was proposed for the consideration of the viscoelastic property of the sample investigated. Moreover, as expected in the collagen fibres, experimental results showed that the shear waves along the circumferential direction of the sample are found to be higher than in the axial direction. Li et al. numerically investigated the haemodynamic of four patient-specific artery aneurysms aiming at determining the risk factors for the cerebral aneurysms rupture. The authors analysed different haemodynamic parameter distributions in the aneurysms to determine the link between the haemodynamic parameters and the rupture risks. Their results showed that the aneurysms rupture risk is found to be significantly high when the maximum wall shear stress and the oscillatory shear index located at the neck and dome, respectively.

In Table 1, the findings from the 5 articles in this issue that support the utilization of CFD coupled with experimental diagnostic techniques for the examination of CVDs are summarized.

Table 1.

Summary of published articles in this issue.

Authors	The research theme	Methodology	Main findings
Hu and Cai 19	Structure optimization of force feedback device in virtual cardiovascular surgery	Experimental	The length of the guide wire was experimentally optimized by measuring the flexible deformation of the guide wire in the force feedback device of virtual cardiovascular surgery
Gårdhagen et al. 20	Simulation of pulsating flow before and after CoA repair by using the LES	Numerical techniques	The findings indicated that the risk factors for the vascular dysfunction are found to be considerably higher before the CoA due to the elevated turbulence fluctuations and the high oscillating and unstable flow patterns there. Moreover, the haemodynamic risk factors are found to be critically abnormal before the CoA, but they can be considerably decreased by restoring the normal blood flow after the intervention
Ma et al. 21	Analysis of the haemodynamic of stenosis pulmonary artery after Glenn surgery	Numerical techniques	The study showed that the stenosis of more than 75% significantly influences the haemodynamic parameters of the pulmonary arteries and can lead to considerable unbalanced blood perfusion to both lung and the blood power loss. It was recommended that severe stenosis must be treated before the Glenn operation, and this treatment is not necessary for the mid-range stenosis
Shcherbakova et al. 22	SSI	Ex-vivo using the SSI techniques	Successful development of a simple uni-axial mechanical setup to measure the mechanical property of the artery
Li et al. 23	Analysis of the haemodynamic of anterior communicating artery aneurysms	Numerical	The numerical results showed that that the aneurysms rupture risk is significantly high when the maximum wall shear stress and the oscillatory shear index are in the neck and dome regions, respectively

CoA: coartation of the aorta; LES: large eddy simulation; SSI: supersonic shear wave imaging.

It is worth noting that the advancement of computational and experimental techniques, including image analysis and so on is ongoing worldwide with continuous new refinements and evaluation. This issue highlights the importance of such techniques to assist clinician in diagnostic and subsequent treatment of CVDs.