In Silico Evaluation
- Dylan Lightbody
Background
The aim of in silico evaluation is to access the performance of systems or devices using computer simulation allowing a quick and cost-effective assessment of a simplified system before pursuing in vitro and in vivo evaluation. By using in silico evaluation, significant product development can occur without risk. For example, CFD modelling is an effective mode of 3D in silico evaluation which has drastically changed the development of stents, valve prostheses, and ventricular assist devices [2].
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Modelling Blood Flow
Whole blood consists of plasma and blood cells. Plasma is a Newtonian fluid due to the majority of its contents being water [4]. However, whole blood is far more complex as the suspension of blood cells in plasma results in non-Newtonian fluid properties [4]. Blood experiences shear thinning where the viscosity decreases with increasing shear rate [1].
Majority of in silico CFD and FSI studies model blood as a simplified Newtonian fluid [1].
Lumped Element Models
Zero dimensional models (otherwise known as lumped element models or lumped parameter models) in mechanical circulatory support include the following parameters; systemic circulations, pulmonary circulations, heart chambers and heart valves [1]. The systemic and pulmonary circulations are often analogously represented using a single resistance, capacitance and inductance values.
Distributed Parameter Models
One dimensional (distributed parameter) models are often created in MATLAB, CellML and Labview [1]. When modelling blood flow with a distributed parameter model, it is common to describe the pressure and cross sectional area relationship using simple linear or non-linear constitutive equations [3].
Three Dimensional Models
3D CFD or FSI models can be used to investigate flow in the supported circulatory system. Models can be created using tomography scan slices to accurate represent the geometry of human organs.
Multiscale Models
Due to CFD models being computationally expensive, it is possible to couple lumped element models with CFD. This can be achieved through coupling the flows and pressures at each model's boundaries [1].
References
[1] Gregory, S. et al. (2018). Mechanical Circulatory and Respiratory Support. London. United Kingdom. Elsevier Inc.
[2] Morris PD, Narracott A, von Tengg-Kobligk H, et al. Computational fluid dynamics modelling in cardiovascular medicine Heart 2016;102:18-28.
[3] Shi Y, Lawford P, Hose R. (2011). Review of 0D and 1D Models of Blood Flow in the Cardiovascular System. BioMedical Engineering OnLine 2011;10:33.
[4] Bessonov, N. et al. (2016). Methods of Blood Flow Modelling. Mathematical Modelling of Natural Phenomena. 11. 1-25.