On the modelling of cell and lipoprotein transport in the thoracic aorta

• Purpose: The purpose of the study is to compare and assess modeling of transport cells and lipoproteins by the blood in the human thoracic aorta.Methods: In the continuum framework, three flux models were considered; Fickian, Zydney-Colton (Z-C) and Leighton-Acrivos (L-A). The transport of spherical particles (cells and lipoprotein of different sizes and densities) under pulsatile flow condition were simulated. The effect of local red blood cell (RBC) concentration (hematocrit) on blood viscosity wasconsidered through Quemada’s model. Lagrangian particle transport (LPT) was assessed and compared to the continuum models. Contribution to RBC flux (diffusion) due to gradients inhematocrit, mixture density and viscosity was assessed. Results were extracted in terms ofmean and variations in concentrations, residence time and path lengths of RBC and six othercells and lipoproteins.Results: The effects of local hematocrit variations on the local blood viscosity is large (a factor of more than 2) but the effect on wall shear stress (WSS) indicators is much more modest (few percent). In terms of mean concentration, the three continuum transport modelsyield local viscosity that deviate by a factor between about 1.3 to 2, as compared to a constantviscosity case. The main contribution to the mass (RBC) flux in the L-A model is from the shear-rate gradient term, followed by the viscosity gradient term and least by the RBC concentration gradient term (low flow rate). The inflow and wall boundary conditions play an important role on the details of the mass transport. The LPT result do converge to the expected concentration at the different outflow boundaries. However, the convergence rate isslow and require more than 30 cardiac periods to get below 2% in outflow hematocrit.Detailed analysis of the RBC paths shows large variations. For the outlet from the thoracicaorta RBC path length and residence time ranging from 0.333 m to 0.0.791 m and from lessthan one to about four cardiac cycles, respectively. The corresponding values for the LCCA are about 0.2 m to more than 0.5 m and about a quarter to about four cardiac cycles,respectively. The LPT results also show that particles are subject to a lift force driven bystrong path curvature and particle to fluid density difference. A simulation with injection ofparticles in the descending aorta indicated the possibility of upstream transport of particlesinto the three main arteries branching from the aortic arch.Conclusions: Continuum transport models depend strongly on calibrated model parametersand the imposed boundary conditions. Counter gradient diffusion may occur as the fluxes aredependent on gradients of shear rate, concentration, and viscosity. LPT has the advantage ofaccounting for temporal effect and are most appropriate for dilute particle suspensions such ascells (except for RBC) and lipoproteins. LPT though, may require substantially longercomputational time when statistical data is sought.

Subject headings

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Strömningsmekanik och akustik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Fluid Mechanics and Acoustics (hsv//eng)

Keyword

Whole blood viscosity

non-Newtonian fluid

Thoracic aorta

LPT

cell and lipoprotein transport.

Engineering Mechanics

Teknisk mekanik

Publication and Content Type

vet (subject category)

ovr (subject category)