How good are the fits to the experimental velocity profiles in vivo?

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.A new velocity profile equation for the description of microcirculatory blood flow in vivo was proposed in 2009. However various recently published papers still use the assumption of parabolic velocity profile (Poiseuille flow). The purpose of this work was to evaluate the performance of 3 different fitting cases: 1) best parabolic fit, 2) axial fit with the proposed equation and 3) best fit with the proposed equation. Twelve experimental velocity profiles measured by particle image velocimetry in mouse venules were used to compare the fitting efficiency of the 3 cases on the basis of the velocity relative error (RE) expressed as average ± SE (standard error) at ten different radial segments (REj with 1 ≤ j ≤ 10). The parabolic best fit (case 1) leads to serious deviations from the real velocity distribution (RE10 = - 65% ± 2%). The proposed equation axial fit (case 2) slightly overestimates blood velocity distribution near the vessel wall but the was below + 12% and it requires only one experimental value near the vessel axis, measurable using the Doppler Effect. The proposed equation best fit (case 3) approximates the experimental data without any serious bias but requires a complete velocity profile data set

Fluid shear stress modulation of hepatocyte like cell function

Freshly isolated human adult hepatocytes are considered to be the gold standard tool for in vitro studies. However, primary hepatocyte scarcity, cell cycle arrest and the rapid loss of cell phenotype limit their widespread deployment. Human embryonic stem cells and induced pluripotent stem cells provide renewable sources of hepatocyte-like cells (HLCs). Despite the use of various differentiation methodologies, HLCs like primary human hepatocytes exhibit unstable phenotype in culture. It has been shown that the functional capacity can be improved by adding back elements of human physiology, such as cell co-culture or through the use of natural and/or synthetic surfaces. In this study, the effect of fluid shear stress on HLC performance was investigated. We studied two important liver functions, cytochrome P450 drug metabolism and serum protein secretion, in static cultures and those exposed to fluid shear stress. Our study demonstrates that fluid shear stress improved Cyp1A2 activity by approximately fivefold. This was paralleled by an approximate ninefold increase in sensitivity to a drug, primarily metabolised by Cyp2D6. In addition to metabolic capacity, fluid shear stress also improved hepatocyte phenotype with an approximate fourfold reduction in the secretion of a foetal marker, alpha-fetoprotein. We believe these studies highlight the importance of introducing physiologic cues in cell-based models to improve somatic cell phenotype

Impaired retinal microcirculation in multiple sclerosis

BACKGROUND: The transparent ocular structure enables quantitative analysis of microvasculature of retina, a neuronal tissue affected by multiple sclerosis. OBJECTIVE: To determine whether the retinal blood flow velocity and flow volume at the macula are impaired in patients with relapsing remitting multiple sclerosis (RRMS). METHODS: Seventeen RRMS patients and 17 age- and gender-matched healthy subjects were assessed. A Retinal Function Imager was used to measure the blood flow velocity of retinal arterioles and venules, and to calculate the total perifoveal blood flow volume. RESULTS: The blood flow velocities of the retinal arterioles (3.34 ± 0.89 mm/s) and venules (2.61 ± 0.6 mm/s) were significantly lower in MS patients than normal subjects (arteriole: 4.10 ± 0.87 mm/s; venule: 3.22 ± 0.65 mm/s, both P = 0.01). In addition, the total perifoveal blood flow volume in arterioles (3.74 ± 1.64 nl/s) and venules (3.81 ± 1.60 nl/s) were significantly lower in MS patients than in normal subjects (arteriole: 4.87 ± 1.41 nl/s, P = 0.02; venule: 4.71 ± 1.64 nl/s, P = 0.04). CONCLUSION: The impaired retinal microcirculation in RRMS patients indicates microvascular dysfunction in MS