Blood flow in stented coronary artery: numerical fluid dynamics analysis.

Recent generalization of stent implantation in interventional cardiology require full understanding of blood flow cartography. Interdepency between fluid stresses and in vivo cells covering lumen artery are regularly accused to be one of the instigator of neointimal proliferation (thickening of the inner layer of blood vessels) and mid-term restenosis. This study purpose to numericaly investigate the three dimensional flow in vicinity of an endoprothesis. We used a finite element method to simulate a steady flow of non-Newtonian fluid in a coronary artery using a rigid wall approximation. Results on the velocities, wall shear stress and wall shear stress gradients are presented. Theses simulations allow identification of stagnation site and low wall shear stress area that may be prone to clot formation and neointimal hyperplasia. Intra stent flow knowledge can potentially contribute to optimization of prothesis design and decreasing second intervention rate.

Relationship between ankle frontal muscle powers and three-d gait patterns.

OBJECTIVE: This study was undertaken to demonstrate that the ankle frontal muscle power absorption and generation at push-off are related to the foot's initial position at heel-strike with respect to the body center of mass. DESIGN: Nineteen able-bodied male subjects participated in this study and were divided into two groups according to ankle frontal plane power generation or absorption at push-off. RESULTS: At heel-strike, the group that absorbed had a center of pressure that was located on average 25% more anteriorly and 36% more laterally to the body center of mass. Moreover, at push-off, the center of pressure was closer (26%) to the center of mass than in the generating group. The absorbing group compensated by increasing their sagittal plane hip energy by 30% to pull the lower limb forward and their knee power absorption by 47% to slow down the leg before the subsequent heel-strike. CONCLUSIONS: The foot's initial position at heel-strike explains in part the ankle frontal power generation or absorption at push-off. Increasing hip and knee sagittal joint powers and mechanical energies were the main contributors in compensating and providing a broader base of support and frontal plane ankle power absorption.

Main functional roles of knee flexors/extensors in able-bodied gait using principal component analysis (I).

This study was undertaken to demonstrate how principal component analysis (PCA) can be used to detect the main functional structure of actions taken by knee flexors/extensors during able-bodied gait. PCA was applied as a classification and curve structure detection method for knee sagittal muscle moment developed during walking of 20 young, healthy male subjects. Over 90% of the information provided by the first three principal components (PCs) was chosen for further biomechanical interpretation. PCA was able to identify the three main functional contributions of knee sagittal muscle moment during able-bodied gait, namely control balance, foot clearance/limb preparation and shock absorption.

RPA facilitates rejoining of DNA double-strand breaks in an in vitro assay utilizing genomic DNA as substrate.

PURPOSE: Replication protein-A (RPA) is a heterotrimeric single-stranded DNA-binding protein playing essential roles in many aspects of nucleic acid metabolism, including DNA replication, nucleotide excision repair and homologous recombination. Here, the role of RPA in the rejoining of radiation-induced DNA double-strand breaks (DSB) by non-homologous end-joining (NHEJ) was investigated. METHODS AND MATERIALS: A previously described in vitro assay for DSB rejoining was employed. The assay used 'naked' genomic DNA prepared from agarose-embedded G(1)-phase A549 cells as a substrate and extracts prepared from HeLa cells as a source of enzymes. Rejoining of DSB in this assay is absolutely dependent on cell extract and proceeds, under optimal reaction conditions, to an extent similar to that observed in intact cells. For experiments, extracts were supplemented with excess purified recombinant RPA. Alternatively, RPA was removed from the extracts either by fractionation or immunodepletion. RESULTS: Although the rejoining of DSB in vitro was not absolutely dependent on RPA, it proceeded faster and to higher levels of completion when recombinant protein was added to the extracts. Depletion of RPA from extracts reduced the rejoining half-times and addition of purified recombinant protein restored the kinetics of DSB rejoining. Extract fractionation indicated the operation of at least two pathways in DSB rejoining, only one of which was facilitated by RPA. CONCLUSIONS: The results suggest that in addition to its role in homologous recombination, RPA may also have a supportive role in some forms of non-homologous end-joining.

[The interdiction of tobacco sales to minors: a concerted effort is necessary]. / L'interdiction de la vente de tabac aux mineurs: une concertation est nécessaire.

We discuss the feasibility of an intervention involving retailers of over-the-counter tobacco sales to minors in a multi-ethnic Montreal neighbourhood. An overview of the literature on the efficacy of such interventions and an analysis of the present sociopolitical situation have influenced our decision to delay this intervention. The community should be made aware of this problem prior to intervention.

[Experimental simulation of blood flow perturbations induced by the placement of caval filters and thrombi]. / Simulation expérimentale des perturbations de l'écoulement sanguin engendrées par la pose de filtres caves et par les thrombi.

Implantation of caval filters to prevent thrombo-embolism is a common medical option for twenty years, since the standard Greenfield model. The numerous new models with various geometries have been the subject of many studies aimed at testing their effectiveness in clot capture and the stability of their fixation to the vein, but very few ones are dedicated to the influence of their shape on blood flow, and to the flow disturbances induced by trapped clots shape and location. So, we have designed a caval blood flow simulation test bench of different filters and clot models. Opcetra and LGM filters were furnished with a reference regular input flow of physiological viscosity fluid. Rigid thrombus model, trapped in filter middle, was a one centimetre diameter sphere; and a recent soft one, which could model itself on the final part of the capture zone, was a two centimetres high cone. Perturbations, eddies, trajectories and velocities were recorded by particles visualization and ultrasound velocimetry. Downstream the Opcetra, velocity vectors were practically axial, no eddies could be seen; the central cylinder had changed the input parabolic flow into a one with two symmetrical maxima. For LGM, on the one hand, from the middle, the sheet branches perturbed the flow and induced several jets. On the other hand, the end ring had created an helicoïdal wake which extended up to three centimetres. With thrombi models, for Opcetra, a central spherical clot induced eddies inside the filter, but smoothed the two maxima of the profile, which vanished more rapidly. For the LGM, a central spherical clot increased the perturbations, whereas a final conical one decreased them. Finally, it was clear that filter shape, capture location and clot aspect were the leading causes of the hydrodynamic induced disturbances and might be important for the trapped clots evolution.

Unrelated bone marrow transplantation in Canada, the national experience.

The Canadian Unrelated Bone Marrow Donor Registry (UBMDR) of the Canadian Red Cross Society (CRCS) Blood Transfusion Service (BTS) was officially funded as of April 1, 1989 for an initial three year period with a mandate to recruit 50,000 unrelated bone marrow donors and conduct the search activities for unrelated bone marrow donors worldwide on behalf of Canadian patients (1). All provinces of Canada agreed to fund the Registry and it was unanimously adopted to locate the Canadian National Coordinating Centre (CNCC) of the Registry in Vancouver. Since February of 1988, 64 unrelated bone marrow transplants have been carried out in Canada. Over half of the unrelated donors have come from other countries. Canada has established working relationships with the United States, the United Kingdom and France. Recruitment of unrelated bone marrow donors is now established in twelve Canadian cities with more to follow. It is anticipated that the size of the registries world wide will continue to increase, that their ethnic makeup will become diversified and that the indications for unrelated bone marrow transplantation will broaden in the years to come.

The Canadian Red Cross plasmapheresis donor safety program: changes in plasma proteins after long-term plasmapheresis.

The Canadian Red Cross Blood Services have been harvesting plasma from whole blood by plasmapheresis procedure for the last 10 years. To date, we have performed approximately 230,000 procedures. To determine whether this procedure is a health hazard to an individual, a donor safety program was established in 1979 at the National Reference Laboratory. Serum levels of total protein, albumin, and immunoglobulins are monitored at intervals set by the Bureau of Biologics, Health and Welfare Canada. In this communication, we present a 10-year evaluation of this program. A comparison of the protein concentration distributions between first-time and long-term plasmapheresis donors showed no significant differences. Therefore, we have demonstrated that the donors are not at risk as the result of changes in the measured plasma protein levels following plasmapheresis procedure as performed over the last 10 years at The Canadian Red Cross Blood Services.

Blood viscosity measurements in both extensional and shear flow by a falling ball viscometer.

A falling ball viscometer is used to measure whole blood and plasma viscosities. The principle of the device is to determine the fall time of a ball contained in a disposable syringe; the periodic run of the sphere prevents blood sedimentation during the measuring cycle but does not prevent the aggregation process which takes place with a short relaxation time. The analysis of the flow field is discussed relative to previous papers. The study of the dynamics of the falling ball provides two characteristic rates of deformation for the mixed extensional and shear flow field. The Reynolds numbers are calculated using different velocities and radii. Results on blood and plasma viscosity of patients suffering from rheumatoid arthritis are given in relation with clinical and biological indexes.

Substitution of the "group-and-screen" for the full crossmatch in elective operations.

For many years, the crossmatch has served as the pretransfusion determinant of compatibility between recipient and donor. The majority of units of blood crossmatched for elective surgical procedures are not used and many antibodies detected in the crossmatch are not of clinical significance. Motivated by the need to eliminate testing that does not significantly enhance the provision of a safe product, the necessity for doing crossmatches has been questioned. Recent studies indicate that the substitution of the "group-and-screen" for the complete crossmatch represents an acceptable approach to the provision of blood for many elective surgical procedures. The benefit of this approach is significant: blood is utilized more efficiently and the blood bank has a reduction in workload. The risk is very minimal: only one of several thousand transfusions will be given to patients with previously undetected alloantibodies; and recent evidence indicates that such incompatibilities have little clinical impact.

Clinical use of blood, blood components and blood products.

The goal of modern transfusion therapy is to provide appropriate replacement therapy with blood components as opposed to whole blood for patients with specific hematologic deficiencies. A prerequisite of component therapy is, therefore, correct identification of the deficiency. Appropriate use of components avoids many of the hazards associated with the use of whole blood, and at the same time makes maximal use of this valuable resource. Blood components separated from whole blood soon after collection and appropriately stored can, in combination, provide all the factors present in fresh whole blood. Red cell concentrates prepared from multiple packs have a hematocrit of approximately 70%. They may be stored for up to 3 weeks at 4 degrees C and are recommended for most situations requiring red cell transfusions. Platelet concentrates, which can be stored for up to 72 hours at 22 degrees C, may be used for thrombocytopenic patients. Fresh frozen plasma, stored plasma, cryoprecipitated factor VIII, factor VIII concentrate and factor IX complex concentrate are available for the proper treatment of patients with hemorrhagic disorders due to coagulation factor deficiencies. Similarly, albumin and immune serum globulin are available for their oncotic and antibody properties respectively. Thus, the availability and appropriate use of the various blood products allows not only optimal transfusion therapy for each patient, but also fuller utilization of national blood resources.

Hepatitis B antigenemia among blood donors: the changing scene.

For the period May 1973 to August 1974 inclusive, the mean prevalence of hepatitis B antigenemia (HBsAg) in all Canadian provinces (per 100,000 population) was, for "first-time" donors, 242 and, for "repeat" donors, 77. A modification of counterimmunoelectrophoresis was used in all 16 regional transfusion centres. The findings confirm the previously noted high prevalence for the Province of Québec and the continuing relatively high prevalence for Canada. The prevalence of HBsAg among donors could be lessened by institution of the following measures: development of a more effective technique for the screening of hepatitis carriers, study of nonparenterally transmitted hepatitis, better reporting of post-transfusion hepatitis, and greater discrimination in prescribing blood and blood components.