Keita Nakaaki

Quantification of red blood cell deformation at high-hematocrit blood flow in microvessels

The deformation of red blood cells in microvessels was investigated numerically for various vessel diameters, hematocrits, and shear rates. We simulated blood flow in circular channels with diameters ranging from 9 to 50 μm, hematocrits from 20% to 45%, and shear rates from 20 to 150 s(-1) using a particle-based model with parallel computing. The apparent viscosity predicted by the simulation was in good agreement with previous experimental results. We quantified the deformation of red blood cells as a function of radial position. The numerical results demonstrated that because of the shape transition in response to local shear stress and the wall effect, the radial variation of red blood cell deformation in relatively large microvessels could be classified into three different regions: near-center, middle, and near-wall regions. Effects of the local shear stress and wall varied with vessel diameter, hematocrit, and shear rate.

Leukocyte margination at arteriole shear rate

We numerically investigated margination of leukocytes at arteriole shear rate in straight circular channels with diameters ranging from 10 to 22 μm. Our results demonstrated that passing motion of RBCs effectively induces leukocyte margination not only in small channels but also in large channels. A longer time is needed for margination to occur in a larger channel, but once a leukocyte has marginated, passing motion of RBCs occurs continuously independent of the channel diameter, and leukocyte margination is sustained for a long duration. We also show that leukocytes rarely approach the wall surface to within a microvillus length at arteriole shear rate.

Development of a Numerical Model for Micro-Scale Blood Flow Simulation Using GPGPU

Computational fluid dynamics (CFD) study of the behavior of red blood cells (RBCs) in flow provides us informative insight into the mechanics of blood flow in microvessels. However, the size of computational domain is limited due to computational expense. Recently, we proposed a graphics processing unit (GPU) computing method for patient-specific pulmonary airflow simulations (Miki et al., in press). In this study, we extend this method to micro-scale blood flow simulations, where a lattice Boltzmann method (LBM) of fluid mechanics is coupled with a finite element method (FEM) of membrane mechanics by an immersed boundary method (IBM). We also present validation and performance of our method for micro-scale blood flow simulations.Copyright

Numerical Modeling of Microvascular Hemodynamics in Plasmodium Falciparum Malaria

High concentrations of nitric oxide (NO) have previously been measured in human maxillary sinuses, but the transport rates between the sinus and the nose during normal breathing have not been quantified. In this study, NO transport has been investigated using published NO concentrations and production rates, computational fluid dynamics (CFD) and first-order modeling in stylised physiological, pathological and post-surgical geometries. The results indicate that physiological sinus geometries cannot supply all the NO found in the nasal cavity. Pathological and post-surgical geometries have higher NO transport and lower steady-state NO concentrations than physiological geometries, but no difference was found between the two surgical techniques considered (inferior and middle meatal antrostomy). All the steady state concentrations are also above the level required for bacteriostatic effects.