Biorheology - Volume 40, issue 6

Authors: Tami, A.E. | Schaffler, M.B. | Knothe Tate, M.L.

Article Type: Research Article

Abstract: Transport of fluorescent probes between 300 and 2,000,000 Da was studied in mechanically loaded and unloaded ulnae of skeletally mature rats to characterize the permeability of the pericellular space of the lacunocanalicular system (LCS), and the microporosity of the bony matrix. The mineral matrix porosity allowed for penetration of the 300 Da probe but impeded transport of larger probes. The pericellular space of the LCS was permeable up to 10 kDa; above 10 kDa, diffusion was ineffective for transport through the pericellular space. Convective transport via load‐induced fluid flow increased penetration of all probes up to 70 kDa. Above this …threshold, probes were excluded from bone, both with and without loading. This exploratory study suggests that bone acts as a molecular sieve and that mechanical loading modulates transport of solutes through the pericellular space that links osteocytes deep within the tissue to the blood supply and to osteoblasts and osteoclasts on bone forming and resorbing surfaces. This provides support for the postulate of transport modulated bone remodeling in which osteocytes are influenced by and modulate the local permeability of their surroundings as a means for survival (Knothe Tate et al. 1998, [28]) and has profound implications for osteocyte viability and intercellular communication in bone. Show more

Keywords: Osteocytes, fluid flow, mechanotransduction, molecular sieve, mass transport

Citation: Biorheology, vol. 40, no. 6, pp. 577-590, 2003

Authors: Reilly, Gwendolen C. | Haut, Traci R. | Yellowley, Clare E. | J. Donahue, Henry | Jacobs, Christopher R.

Article Type: Research Article

Abstract: It has been hypothesized that bone cells have a hyaluronic acid (HA) rich glycocalyx (cell coat or pericellular matrix) and that this contributes to bone cell mechanotransduction via fluid flow. The glycocalyx of bone cells of the MC3T3‐E1 osteoblastic cell line and the MLO‐Y4 osteocytic cell line were characterized. Alcian blue staining and lectin binding experiments suggested that these cells have a glycocalyx rich in HA. Sulphated proteoglycans were not detected. Staining with hyaluronic acid binding protein and degradation by hyaluronidase confirmed that HA was a major component of the glycocalyx. We subjected cells, with and without hyaluronidase treatment, to …oscillating fluid flow under standardized in vitro conditions. There was no effect of glycocalyx degradation on the intracellular calcium signal, in either cell type, in terms of the percentage of cells responding (40–80%) or the magnitude of the response (2–5 times baseline). However, a 4‐fold fluid flow induced increase in PGE2 was eliminated by hyaluronidase pre‐treatment in MLO‐Y4 cells. We conclude that under these conditions the calcium and PGE2 responses occur via different pathways. An intact glycocalyx is not necessary in order to initiate a calcium signal in response to oscillating fluid flow. However, in osteocyte‐like cells the PGE2 pathway is more dependent on mechanical signals transmitted through the glycocalyx. Show more

Keywords: Pericellular matrix, osteoblast, osteocyte, mechanical loading, cell signaling, proteoglycans

Citation: Biorheology, vol. 40, no. 6, pp. 591-603, 2003

Authors: Liu, Der‐Zen | Chien, Shu‐Chen | Tseng, Li‐Ping | Yang, Charng‐Bin

Article Type: Research Article

Abstract: The effect of hyperbaric oxygen (HBO2 ) treatment on hemorheological parameters of diabetic rats was investigated. This study is a placebo‐controlled, in vivo animal study. 30 streptozocin‐induced diabetic rats were divided into two groups; one group received hyperbaric oxygen treatment while the other did not. Hematological and hemorheological parameters were tested with blood samples collected directly from the heart using surgical procedures. Student t‐tests with a type I (α) error at 0.05 was used to test any significant difference between means of the hematologic and hemorheological parameters of the control (CON) and the HBO2 groups. Compared with the placebo …group, hyperbaric oxygen resulted in significant higher lipid peroxidation stress of the erythrocytes and resistance of erythrocytes to deformation in rats of the HBO2 group. Whole blood viscosities measured at shear rates of 5, 150 and 400 s−1 were all higher for the rats in the HBO2 group than those for rats in the control group. In addition, the oxygen delivery index was found to be significantly lower in rats of the HBO2 group. Thus, our work demonstrates that hyperbaric oxygen treatment significantly changes the hemorheological parameters in diabetic rats. Show more

Keywords: Hyperbaric oxygen, diabetic rats, blood viscosity, blood viscoelasticity, erythrocyte deformability

Citation: Biorheology, vol. 40, no. 6, pp. 605-612, 2003

Authors: Banerjee, Rupak K. | Back, Lloyd H. | Back, Martin R.

Article Type: Research Article

Abstract: This study gains insight on the nature of flow blockage effects of small guidewire catheter sensors in measuring mean trans‐stenotic pressure gradients $\Delta\tilde{p}$ across significant coronary artery stenoses. Detailed pulsatile hemodynamic computations were made in conjunction with previously reported clinical data in a group of patients with clinically significant coronary lesions before angioplasty. Results of this study ascertain changes in hemodynamic conditions due to the insertion of a guidewire catheter (di =0.46 mm) across the lesions used to directly determine the mean pressure gradient $(\Delta\tilde{p})$ and fall in distal mean coronary pressure ($\tilde{p}_{r})$ . For …the 32 patient group of Wilson et al. [1988] (minimal lesion diameter dm =0.95 mm; 90% mean area stenosis; proximal measured coronary flow reserve (CFR) of 2.3 in the abnormal range) the diameter ratio of guidewire catheter to minimal lesion was 0.48, causing a tighter “artifactual” mean area stenosis of 92.1%. The results of the computations indicated a significant shift in the $\Delta\tilde{p}$ –$\widetilde{Q}$ relation due to guidewire induced increases in flow resistances ($\widetilde{R}=\Delta\tilde{p}/\widetilde{Q})$ of 110% for hyperemic flow, a 35% blockage in hyperemic flow $(\widetilde{Q}_{h})$ and a phase shift of the coronary flow waveform to systolic predominance. These alterations in flow resulted in a fall in distal mean coronary pressure (at lower mean flow rates) below the patho‐physiological range of $\tilde{p}_{rh}\sim 55$ mmHg, which is known to cause ischemia in the subendocardium (Brown et al. [1984]) and coincides with symptomatic angina. Transient wall shear stress levels in the narrow throat region (with flow blockage) were of the order of levels during hyperemic conditions for patho‐physiological flow. In the separated flow region along the distal vessel wall, vortical flow cells formed periodically during the systolic phase when instantaneous Reynolds numbers Ree (t) exceeded about 110. For patho‐physiological flow without the presence of the guidewire these vortical flow cells were much stronger than in the more viscous flow regime with the guidewire present. The non‐dimensional pressure data given in tabular form may be useful in interpretation of guidewire measurements done clinically for lesions of similar geometry and severity. Show more

Citation: Biorheology, vol. 40, no. 6, pp. 613-635, 2003

Authors: Ghalichi, Farzan | Deng, Xiaoyan

Article Type: Research Article

Abstract: The pulsatile blood flow in a partially blocked artery is significantly altered as the flow regime changes through the cardiac cycle. This paper reports on the application of a low‐Reynolds turbulence model for computation of physiological pulsatile flow in a healthy and stenosed carotid artery bifurcation. The human carotid artery was chosen since it has received much attention because atherosclerotic lesions are frequently observed. The Wilcox low‐Re k–ω turbulence model was used for the simulation since it has proven to be more accurate in describing transition from laminar to turbulent flow. Using the FIDAP® finite element code a validation …showed very good agreement between experimental and numerical results for a steady laminar to turbulent flow transition as reported in a previous publication by the same authors. Since no experimental or numerical results were available in the literature for a pulsatile and turbulent flow regime, a comparison between laminar and low‐Re turbulent calculations was made to further validate the turbulence model. The results of this study showed a very good agreement for velocity profiles and wall shear stress values for this imposed pulsatile laminar flow regime. To explore further the medical aspect, the calculations showed that even in a healthy or non‐stenosed artery, small instabilities could be found at least for a portion of the pulse cycle and in different sections. The 40% and 55% diameter reduction stenoses did not significantly change the turbulence characteristics. Further results showed that the presence of 75% stenoses changed the flow properties from laminar to turbulent flow for a good portion of the cardiac pulse. A full 3D simulation with this low‐Re‐turbulence model, coupled with Doppler ultrasound, can play a significant role in assessing the degree of stenosis for cardiac patients with mild conditions. Show more

Keywords: Numerical modeling, hemodynamic, pulsatile flow, turbulence

Citation: Biorheology, vol. 40, no. 6, pp. 637-654, 2003

Article Type: Abstract

Citation: Biorheology, vol. 40, no. 6, pp. 655-675, 2003

Article Type: Other

Citation: Biorheology, vol. 40, no. 6, pp. 677-685, 2003