Front microrheology of the non-Newtonian behaviour of blood: scaling theory of erythrocyte aggregation by aging.

We introduce a new framework to study the non-Newtonian behaviour of fluids at the microscale based on the analysis of front advancement. We apply this methodology to study the non-linear rheology of blood in microchannels. We carry out experiments in which the non-linear viscosity of blood samples is quantified at different haematocrits and ages. Under these conditions, blood exhibits a power-law dependence on the shear rate. In order to analyse our experimental data, we put forward a scaling theory which allows us to define an adhesion scaling number. This theory yields a scaling behaviour of the viscosity expressed as a function of the adhesion capillary number. By applying this scaling theory to samples of different ages, we are able to quantify how the characteristic adhesion energy varies as time progresses. This connection between microscopic and mesoscopic properties allows us to estimate quantitatively the change in the cell-cell adhesion energies as the sample ages.

Capillary Filling at the Microscale: Control of Fluid Front Using Geometry.

We propose an experimental and theoretical framework for the study of capillary filling at the micro-scale. Our methodology enables us to control the fluid flow regime so that we can characterise properties of Newtonian fluids such as their viscosity. In particular, we study a viscous, non-inertial, non-Washburn regime in which the position of the fluid front increases linearly with time for the whole duration of the experiment. The operating shear-rate range of our apparatus extends over nearly two orders of magnitude. Further, we analyse the advancement of a fluid front within a microcapillary in a system of two immiscible Newtonian liquids. We observe a non-Washburn regime in which the front can accelerate or decelerate depending on the viscosity contrast between the two liquids. We then propose a theoretical model which enables us to study and explain both non-Washburn regimes. Furthermore, our theoretical model allows us to put forward ways to control the emergence of these regimes by means of geometrical parameters of the experimental set-up. Our methodology allows us to design and calibrate a micro-viscosimetre which works at constant pressure.

[Clinical and biochemical characteristics of predialysis patients in terms of 25 hydroxy vitamin D levels]. / Características clínicas y bioquímicas de pacientes en prediálisis con respecto a los niveles de 25 hidroxivitamina D.

INTRODUCTION: Decreased levels of 25 hydroxyvitamin D (25[OH]D) have been reported in patients with chronic kidney disease (CKD). The pleiotropic effects of vitamin D are known to go beyond mineral metabolism. OBJECTIVES: The aims of this study were to: 1) Determine the 25(OH)D levels in predialysis outpatients. 2) Find out the clinical and biochemical characteristics of patients with 25(OH)D deficiency, and predictive factors for the deficiency. PATIENTS AND METHODS: An observational study in 79 predialysis outpatients was performed. Clinical and biochemical parameters were analysed in terms of nutrition, inflammation and mineral metabolism in relation to serum levels of 25(OH)D. Levels of 25(OH)D lower than 15ng/ml were considered to be deficient. RESULTS: Serum levels of 25(OH)D were deficient in 41 patients (52%). The comparative study regarding levels of vitamin 25(OH)D showed the group of patients with a deficiency, i.e. those with less than 15ng/ml, were older (70 ± 11.97 vs. 61 ± 14.5; p = 0.005), had a greater body mass index, BMI, (30±4.06 vs. 27.1 ± 5.08; p = 0.003) and increased proteinuria (1.42g/24h (0.53-2.96) vs. 0.51 (0.20-1.48), p = 0.009). This group included a greater number of diabetic patients: 20 (76.9%) vs. 6 (23%), p = 0.002. They had a higher level of parathyroid hormone (PTH): 359 (239-658) vs. 233 (129-323), p = 0.000; and more patients were under treatment with Calcitriol: 28 (62.2%) vs. 17 (37.8%), p = 0.024. In the multivariate analysis, high levels of PTH (OR 13.38; CI 95% [2.94-60.89]; p=0.001), increased proteinuria (OR 4.41; CI 95% [1.12-17.25]; p = 0.033); and being diabetic (OR 5.713; CI 95% [1.43-22.77]; p = 0.014) were independent predictor factors for patients with 25(OH)D deficiency. CONCLUSIONS: In our study, we observed a high prevalence of 25(OH)D deficiency among patients with CKD. The increased levels of PTH, the increase of proteinuria and the presence of diabetes were independent predictors for 25(OH)D deficiency.