Biomedical subjects

Jan Sikora

Publications and source records attributed to Jan Sikora.

7 recordsLinked to original sources

PubMed2006

Diffuse photon propagation in multilayered geometries.

Diffuse optical tomography (DOT) is an emerging functional medical imaging modality which aims to recover the optical properties of biological tissue. The forward problem of the light propagation of DOT can be modelled in the frequency domain as a diffusion equation with Robin boundary conditions. In the case of multilayered geometries with piecewise constant parameters, the forward problem is equivalent to a set of coupled Helmholtz equations. In this paper, we present solutions for the multilayered diffuse light propagation for a three-layer concentric sphere model using a series expansion method and for a general layered geometry using the boundary element method (BEM). Results are presented comparing these solutions to an independent Monte Carlo model, and for an example three layered head model.

Algorithms↗

PubMed2006

Distribution of antidepressants between plasma and red blood cells.

OBJECTIVE: The distribution of different antidepressants between plasma and red blood cells (RBCs) or between water and erythrocyte membranes (ghosts) has not been sufficiently compared so far. MATERIALS AND METHODS: Distribution of seven antidepressants (amitriptyline, nortriptyline, imipramine, desipramine, didesmethylimipramine, dothiepin, and citalopram) was measured in vitro in small volumes of blood or erythrocyte membrane suspension using radiolabeled drugs. Blood samples were taken from healthy subjects. RESULTS: The distribution of antidepressants between plasma and RBCs is strongly affected by temperature; however, it does not depend on the antidepressant concentration in the range of their therapeutic concentrations. The data analysis proved that the ratio of RBCs to plasma volume concentrations is the suitable parameter characterizing antidepressant distribution in whole blood. Significantly higher ratios of RBCs to plasma concentrations were found for demethylated metabolites of tricyclic antidepressants and in the case of citalopram. Citalopram showed the highest accumulation in intact RBCs and at the same time the lowest binding to isolated membranes. The binding of drugs to isolated erythrocyte membranes was much higher than in whole blood. CONCLUSION: The concentration ratio of antidepressant in RBCs and in plasma is sensitive not only to the binding properties of plasma proteins and cell membranes, but also to changes in drug molecule, both in aminopropyl chain and in aromatic rings. This ratio is to a large extent characteristic of a particular antidepressant.

Antidepressive Agents, Second-Generation↗

PubMed2005

Flow cytometric analysis of CD55 and CD59 expression on blood cells in paroxysmal nocturnal haemoglobinuria.

PNH is a rare clonal disorder of hematopoietic stem cells, therefore all blood cells lineages are involved. The main feature is an increased sensitivity of erythrocytes to complement-mediated cell lysis due to deficiency of membrane-bound GPI (glycosylphosphatidylinositol)-anchored proteins which normally function as inhibitors of reactive hemolysis. In the present study, we performed flow cytometric analysis using monoclonal antibodies against CD55 and CD59 for the detection of PNH-type clone in the blood of 50 patients (28 females and 22 males, age range 7-67 yrs). In one patient only we found a large population (95%) of granulocytes with decreased expression of both CD55 and CD59 molecules (type I PNH) and in two others with partial loss of CD55 expression (type II PNH). The expression was determined chiefly on granulocytes which in the control group showed reliable and high expression of CD55 and CD59.

Adolescent↗

PubMed2004

[Expression of factors inducing apoptosis of peripheral blood lymphocytes in oral cavity cancers].

One of possible immunosuppression mechanisms during cancer disease is apoptotic death of immunology system cells. Factor FAS and xi chain of TCR-CD3 complex take part in induction of apoptosis of lymphocyte which infiltrate neoplasm as well as lymphocytes of peripheral blood (PBL). Expression of the two factors was estimated in PBL of patients with cancer of bottom of oral cavity and granuloma fissuratum (control group). During cancer disease higher level of FAS factor in PBL was observed in comparison to control group. Lymphocytes of peripheral blood in cases of cancer disease shown lower expression of TCR-xi.

Adult↗

PubMed2003

Anisotropic effects in highly scattering media.

In this paper, we study anisotropic scattering and light propagation models applicable to diffuse optical tomography. We propose a model for anisotropic scattering in the radiative transfer framework and derive the corresponding anisotropic diffusion model. To verify the anisotropic diffusion model, we consider the case of a simple anisotropic scattering model also presentable within the diffusion approximation. For numerical computations, we present a three-dimensional (3D) anisotropic Monte Carlo model and 2D finite element and boundary element solutions of the anisotropic diffusion model, and compare the results of the simulations.

Journal Article↗

PubMed2002

Neural networks method for identification of the objects behind the screen.

The possibilities of identification of intraventricular haemorrhage with the aid of electrical impedance tomography are presented in this paper. On the base of the tomographic image of a human brain (see Fig. 1) a simplified two-dimensional mathematical model of the human head is proposed. The mathematical model is relatively poor, but the main purpose of this paper is to investigate the possibility and precision of the identification procedure. This task is particularly difficult because the object is hidden behind the skull, which becomes a low-conductivity screen when the scalp electrodes are used.

Algorithms↗

PubMed2002

Expression of TCR-zeta chain and apoptosis in subpopulations of tumor-associated lymphocytes (TALs) from malignant pleural effusions.

Malignant effusions in serous cavities represent suspension of tumors and inflammatory cells and therefore present an attractive model for studying tumor-host interactions. T cell functional ability is linked to proper signal transduction via T cell receptor (TCR-CD3 complex), especially its zeta chain. The latter has been found to be often depressed in malignancy. Aim of this study was to assess alterations of zeta chain expression and its relation to apoptosis of T lymphocytes. T lymphocytes obtained from pleural effusions of 20 cancer patients and 9 patients with nonmalignant effusions serving as a control were studied. The analysis was performed using flow cytometry combining CD3, CD 4, CD8, CD 16/56, TCR-zeta and TUNEL reaction. In the control group, T lymphocytes obtained from pure lymphocyte effusions had constantly high level of zeta chain while those from malignant pleural effusions had a decreased zeta chain expression. Lymphocytes with low zeta chain expression were the main subpopulation of T cells undergoing apoptosis.

Apoptosis↗