Biorheology - Volume 41, issue 6

Authors: Akagawa, Eiki | Ookawa, Keiko | Ohshima, Norio

Article Type: Research Article

Abstract: Neointimal hyperplasia influenced by intravascular hemodynamics is considered partly responsible for restenosis after endovascular stenting. To evaluate the effect of stent configuration on fluid flow behavior, we visualized flow near stents, and measured the proliferation of cultured endothelial cells (ECs). A single‐coil stent (coil pitch; CP=2.5, 5, or 10 mm) was inserted into a glass tube and perfused at 30–90 ml/min, while the flow pattern was determined by particle imaging velocimetry. The reduction of the flow velocity near the wall was correlated with the decrease in the coil interval of the stent. In perfusion cultures with stents, the proliferation of …ECs was influenced by the local flow velocity distribution. When a stent with a CP value of 10 mm was used, the doubling time of ECs was 30.7 h, while the doubling time was 38.5 h when the CP was 5 mm. The doubling time of ECs was shorter at sites upstream of the stent wire where the velocity was higher than downstream of the wire. In conclusion, a single‐coil stent can be used to modify hemodynamic factors, suggesting that improved stent design may facilitate rapid endothelialization after stent implantation. Show more

Keywords: Restenosis, wall shear stress, coil pitch, perfusion culture, porcine aortic endothelial cell

Citation: Biorheology, vol. 41, no. 6, pp. 665-680, 2004

Authors: Lippert, Samuel A. | Rang, Elizabeth M. | Grimm, Michele J.

Article Type: Research Article

Abstract: Computer modeling is becoming increasingly important in the realm of brain biomechanics and injury. New computer simulations range from modeling of brain surgery, a low frequency, high strain event, to predicting injury as a result of an impact to the head, a high frequency event with varying strain magnitudes. This range of modeling efforts requires characterization of the tissue over as wide a frequency and strain range as possible. Research done to date has concentrated on the low frequency properties of the tissue. Complex compression and complex shear moduli have been measured at frequencies up to 350 Hz. Impact modeling …requires use of frequency data at significantly higher frequencies than these. The “wave‐in‐a‐tube” ultrasonic method was applied to brain tissue to determine mechanical properties at frequencies between 100 kHz and 10 MHz. Of these properties, only complex bulk modulus |K* | is fairly invariant (2133 MPa) with respect to frequency. Complex shear and complex Young's moduli vary with frequency and approach an asymptotic upper limit. Some variation in complex Poisson's ratio was also observed. Show more

Keywords: Brain tissue, ultrasound, Young's modulus, shear modulus, complex modulus, complex shear modulus

Citation: Biorheology, vol. 41, no. 6, pp. 681-691, 2004

Authors: Neofytou, Panagiotis

Article Type: Research Article

Abstract: The present study investigates the flow effects that different blood constitutive equations induce when employed in numerical simulations in the framework of computational hemodynamics. In accord with experimental studies on the rheological behavior of blood, three blood constitutive equations namely the Casson, Power‐Law and Quemada models were used for simulating the shear flow behavior of blood. The case studied is the flow in a channel with a moving part of the boundary and was selected because it reproduces the flow phenomena occurring in realistic arterial conditions. Flow simulation for every model is carried out assuming the same flow rate at …the inlet of the channel and different Strouhal numbers reflecting different intensities of the boundary movement. Results show that the modeling of blood as non‐Newtonian fluid has marked qualitative and quantitative effects on both the flow field and the wall shear stress whereas comparison of the different models shows good agreement between the flow effects by the Casson and Quemada models. Show more

Keywords: Blood models, non‐Newtonian flow, computational fluid dynamics, moving‐boundary flow, unsteady flow

Citation: Biorheology, vol. 41, no. 6, pp. 693-714, 2004

Article Type: Abstract

Citation: Biorheology, vol. 41, no. 6, pp. 715-733, 2004

Article Type: Other

Citation: Biorheology, vol. 41, no. 6, pp. 735-742, 2004