Modeling deformation-induced fluid flow in cortical bone's canalicular-lacunar system.

To explore the potential role that load-induced fluid flow plays as a mechano-transduction mechanism in bone adaptation, a lacunar-canalicular scale bone poroelasticity model is developed and implemented. The model uses micromechanics to homogenize the pericanalicular bone matrix, a system of straight circular cylinders in the bone matrix through which bone fluids can flow, as a locally anisotropic poroelastic medium. In this work, a simplified two-dimensional model of a periodic array of lacunae and their surrounding systems of canaliculi is used to quantify local fluid flow characteristics in the vicinity of a single lacuna. When the cortical bone model is loaded, microscale stress, and strain concentrations occur in the vicinity of individual lacunae and give rise to microscale spatial variations in the pore fluid pressure field. Furthermore, loading of the bone matrix containing canaliculi generates fluid pressures in the contained fluids. Consequently, loading of cortical bone induces fluid flow in the canaliculi and exchange of fluid between canaliculi and lacunae. For realistic bone morphology parameters, and a range of loading frequencies, fluid pressures and fluid-solid drag forces in the canalicular bone are computed and the associated energy dissipation in the models compared to that measured in physical in vitro experiments on human cortical bone. The proposed model indicates that deformation-induced fluid pressures in the lacunar-canalicular system have relaxation times on the order of milliseconds as opposed to the much shorter times (hundredths of milliseconds) associated with deformation-induced pressures in the Haversian system.

The prevalence of hepatitis C virus antibodies among the voluntary blood donors of New Delhi, India.

Infection with hepatitis C virus (HCV) is a major cause of transfusion-associated hepatitis, cirrhosis and hepatocellular carcinoma. The present study was conducted with an objective to evaluate the prevalence of anti-HCV antibody in New Delhi, India using a large number of healthy voluntary blood donors. A total of 15,898 healthy voluntary blood donors were subjected to anti-HCV testing (using a commercially available third generation anti-HCV ELISA kit) and 249 were found to be reactive for anti-HCV antibody, yielding an overall prevalence of 1.57%. No significant difference was found between the HCV positivity rate of male (1.57%; 238/15,152) vs. female (1.47%; 11/746) donors, family (1.58%; 213/13,521) vs. altruistic (1.51%; 36/2377) donors and first-time (1.55%; 180/11,605) vs. repeat (1.61%; 69/4293) donors. The age distribution of anti-HCV reactivity showed a maximum prevalence rate of 1.8% in the age group of 20-29 years. In addition, there was a clear trend of decreasing positivity for anti-HCV with increasing age and this trend was statistically significant. The results of the present study show that the prevalence of anti-HCV antibodies in the healthy voluntary blood donors of New Delhi, India is considerably higher than the reported seroprevalence of HCV in majority of the industrialized nations and this represents a large reservoir of infection capable of inflicting significant disease burden on the society. In addition, donors of New Delhi, India showed a trend of decreasing seroprevalence with increasing age, possibly implying a higher exposure rate to HCV in younger subjects.

Transfusion-associated hepatitis in a tertiary referral hospital in India. A prospective study.

BACKGROUND AND OBJECTIVES: In Indian blood banks, screening for hepatitis B virus (HBV) is currently done by the EIA method, but no routine screening is done for hepatitis C virus (HCV). MATERIALS AND METHODS: To determine the incidence of transfusion-associated HCV hepatitis, and of any residual transfusion-associated hepatitis (TAH) after HBsAg screening, we prospectively studied 182 patients who underwent surgery and received blood transfusion. These recipients had normal alanine aminotransferase (ALT) and were negative for HBsAg (monoclonal EIA), and anti-HCV (third-generation EIA) before receiving transfusion. RESULTS: Of the 818 blood units transfused after routine screening (average 4.49+/-3.3 U/patient, range 1-14), 14 (1.7% of units) were found to be infected. Of the 182 recipients, 14 (7.69%) developed TAH during a follow-up of 6 months, 3 (21.4%) from HBV, 10 (71.5%) from HCV, and 1 (1.7%) from a coinfection of HBV and HCV. All patients with TAH due to HCV were asymptomatic. One patient with TAH due to HBV (33%) and 5 with TAH due to HCV (50%) developed chronic infection with persistently elevated ALT at 6 months. CONCLUSIONS: With the current screening practices, the incidence of TAH remains high in India and is mainly due to HCV infection. Furthermore, the screening methods for HBV also need to be improved.