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At least 199 records · Page 11Linked to original sources

[Implantable defibrillators].

Automatic implantable defibrillator therapy has changed the approach to life-threatening ventricular tachycardia completely and essentially improved survival after aborted sudden cardiac death. Since the first implantation of a defibrillator in 1980, 20,000 patients have received such a device. Nonetheless, in Germany still too many patients die of sudden cardiac death because defibrillator therapy fails to be known enough and keeps not being made use of (no more than 1,000 implants to date). In this group of patients characterized by poor ventricular function, antiarrhythmic drug therapy proved to be unreliable or even dangerous in many cases, while electrophysiologically-guided surgical interventions use to be impossible. The introduction of the implantable defibrillator enabled the incidence of sudden cardiac death to be reduced to about 2% during the first year after implant, and to 5% in the third year, respectively. In most centers with more extensive experience in defibrillator implantations, operative mortality is about 2-3%. Long-term results with defibrillator patients are controlled by the course of the underlying disease, which is coronary artery disease with large scars due to infarction in some 75% of cases. In a large group of about 10,000 patients, total mortality has been calculated to be 15% after three years. Defibrillator systems of the latest generation offer multiple programmability of tachycardia identification parameters and permit differentiated modification of therapeutic intervention. Defibrillator therapy has now been improved essentially by the introduction of endocardial lead systems and, in addition, by the defibrillator being combined with an antitachycardia pacing system.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac Pacing, Artificial↗

[Time-series analysis on road traffic injury in China].

OBJECTIVE: To establish the predictive models of road traffic injury(RTI) in China, to know the trend of RTI, and to provide the reference data for controlling RTI in China. METHODS: The China RTI data from 1951 to 2003 were collected, and in view of the problem of missing values, the method of intrapolation was adopted. The Box-Jenkins technique was used to analyze and predict the trend of RTI in China. Following the process for stationary time-series analysis, model identification, parameter estimation and model diagnosis, the predictive equation for RTI would be established. RESULTS: A series of predictive equations on RTI were finally established based on ARIMA models. The curve fitting is effective and the predictive data of RTI in 2003 are close to the true statistical data. CONCLUSION: The time-series model thus established proves to be of significant usefulness in RTI prediction.

Accidents, Traffic↗

[Mathematical model of radioactive colloid transport in the evaluation of the functional state of the reticuloendothelial system].

The authors assess the functional potentialities of a mathematical model of transport of labeled colloids in the body. Some additions to and modifications of the model were analyzed. They made it possible to get 4 diagnostically important indices: the rate of colloid excretion from the vascular bed, the rate phagocytosis, RES volume, and the rate of RP accumulation by the liver. Besides, the authors presented the results of a computerized experiment for the determination of maintenance characteristics of a program developed for computer. The iteration algorithm for parameter identification based on a method of linearization of minimized function, was used in the program. They also formulated recommendations for a choice of arbitrary components of a calculation procedure and the use of a method of barrier functions, developed as a result of prolonged maintenance of the program.

Algorithms↗

[Evaluation of the effect of cardiotropic agents using a mathematical model of electromechanical coupling].

An assessment of the ionic action mechanism of cardiotropic substances with the aid of a mathematical model for excitation-contraction coupling in myocardium is proved to be possible. The technique developed consists in the model parameter identification from the experimental data on electrical and mechanical activity of myocardial strip. The validity of the technique is tested using the known mechanism drugs. An example is given of analysis by the technique suggested of the action mechanism of diltiazem on the rat papillary muscle.

Animals↗

[Relations between antioxidant activity and lipid state of blood as an indicator of the effect of tumor on the body].

Studies on antioxidant activity and lipid profile of erythrocytes and blood plasma in patients with fibroadenoma, fibrous-cystic mastopathy and neoplasia at different stages of progression showed each pathology to be associated with certain changes in the said parameters. Identification of signs of systemic effect of cancer growth was attempted. Malignant tumor was shown to involve at certain stage pronounced quantitative changes in lipid metabolism and erythrocyte membrane properties. These included changes in cholesterol/phospholipids molar ratio, presence of phosphatidylinositides and dissociation of regulatory links between antioxidant activity and cellular lipid profile in erythrocytes.

Adenofibroma↗

Heat and mass transfer of a thermal indicator in pulsatile flow through the cardio-pulmonary system. I. Modeling.

The construction of a physico-mathematical model which describes the mechanism of indicator dispersion in the circulation and which fits the thermal dilution curves (TDC) is presented. Because of its more evident physical meaning, formulation of the problem in terms of heat and mass transfer is preferred to stochastic theory. Hypotheses necessary to simplify the general system of governing equations are clearly defined and discussed. This deductive method leads to a one-dimensional convective heat transfer model in which pulsatility and form of injection appear naturally. Simulations of TDC in constant and pulsatile flow cases are performed on a digital mini-computer which demonstrates the model's ability to represent different experimental or clinical observations. This will facilitate hemodynamic parameter identification from TD techniques and will increase the accuracy of this identification.

Aorta↗

[Mathematical modelling in medicine and biology. Theoretical basis and fundamentals].

Mathematical modelling is currently a common tool in the study of physiological and biochemical systems. Its basis and fundaments are not, however, well known by the non-specialist. Its aims are to describe, explain and predict physiological and biochemical phenomena. Mathematical models provide a concise and objective description of complex dynamic processes by defining, through mathematical equations, the relationships between quantitative measurements; they indicate, also, ways to improve experimental designs, and allow the testing of hypotheses about physiological or biochemical phenomena. Mathematical models can be developed from simple non-compartmental representations to large scale multi-compartmental models. The basic steps in the formulation of a model include conceptualization, realization and solution of the model. Each step has to be verified and validated. In the case of compartmental models, mass-balance equations are used to represent each compartment. A brief review of the theory of system's analysis and the general aims of mathematical modelling is presented here. The modelling process is usually started with a definition of the problem and a parameter identification followed by the setting up of a clear conceptual model of the system. The model consists of the description of the principal flows of material (in and out) and of the main components which store, convert or transmit these flows. A selection of the class of mathematical representation follows, i.e. linear or non-linear, in order to formulate the equations relating the input and output flows of material for each individual component of the system.(ABSTRACT TRUNCATED AT 250 WORDS)

Models, Biological↗

A non-linear mathematical model for the in vivo evaluation of the RES phagocytic function.

A new non-linear mathematical model was constructed in order to perform in vivo quantification of the RES phagocytic function. This method is based on the same technical facilities as used for the routine liver-spleen scintigraphy with radiocolloids [1, 2]. But kinetic modeling of dynamic Tc-99m-sulfur colloid data produced estimations of the functional RE-parameters: the clearance rate of the colloidal particles, the rate of phagocytosis, and the RES functional volume, which can not be obtained by classical approaches. This non-linear model was designed on the basis of the principal characteristics of particulate material interaction with macrophages (attachment, phagocytosis, digestion) [3, 4, 5]. The theoretically examined behavior of this in vivo mathematical model corresponds with the experimental behavior of the RES. The mathematical expression of the dynamics is the system of non-linear differential equations with constant coefficients that have no analytical solution. Fitting of the normalized heart blood time-activity curve was obtained to identify the unknown model parameters via non-linear regression. For this purpose general interactive PASCAL procedure IDPAR for a PDP-11/34 computer was used (an IBM PC version is also available). Two to three iterations were needed to estimate the set of unknown parameters for any patient study (1-1.5 min). A very good fitting was obtained between experimental and model curves in every case of different pathologies (error of the approximation is about 2-3%). Studies were performed using an in vivo bolus injection of 3.6 mg/80 kg commercially available colloid KOREN labeled with 3m-Ci 99m-Tc (analog of TCK-1). Our method was used to determine the RES functional parameters for patient groups with different levels of the RES dysfunction. Obtained results illustrate the possibilities of our technique to quantitatively estimate not only great pathology (portal cirrhosis), but also small changes of the RE-function (case of hyperlipidemia and ulcer gaster). In all patient groups marked changes of Tc-99m-sulfur colloid turnover were observed. In general, tracer clearance from the circulation was decreased, and the rate of phagocytosis and the RES volume were diminished compared with controls. The effect of a reduction of phagocytosis increases when the RES dysfunction becomes stronger. It can be shown that a non-parametric Wilcoxon-Mann-Whitney test gives a significant difference (P95%) for these patient groups. Further, we represent the possibility of using the model for monitoring changes of the RES-function parameters during and after therapy. The quantitative test of the RES function can significantly enhance the diagnosis and management of different diseases. Serial colloidal studies may document changes in the RES-function for the tumors, cirrhosis, hyperlipidemia, reticulosis, hepatitis, thrombosis, infection, AIDS, burn injury, shock and trauma patients. The technique may be useful for the different RES investigations with laboratory animals. Created computer software can be used as a tool for kinetic models, simulation, and unknown parameters identification.

Humans↗

Comparison of measured parameters from a 24-keV and a broad spectrum epithermal neutron beam for neutron capture therapy: an identification of consequential parameters.

Epithermal neutron beams are under development in a number of locations in the U.S. and abroad. The increased penetration in tissue provided by these neurons should circumvent problems associated with the rapid attenuation of thermal neutron beams encountered in previous clinical trials of neutron capture therapy (NCT). Physical and radiobiological experiments with two "intermediate energy" or "epithermal" beams have been reported. A comparison is made here between the 24-keV iron-filtered beam at Harwell, England, and the broad-spectrum Al2 O3 moderated beam at the Brookhaven Medical Research Reactor (BMRR). In addition, parameters which are relevant for NCT, and which are best suited for evaluation and comparison of beams, are discussed. Particular attention is paid to the mean neutron energy which can be tolerated without significant reduction of therapeutic gain (TG), where TG is the ratio of tumor dose to maximum normal tissue dose. It is suggested that the simplest and most meaningful parameters for comparison of beam intensity and purity are the epithermal neutron fluence rate, and the fast neutron dose per epithermal neutron (4.2 X 10(-11) rad/neutron for the broad-spectrum beam and 29 X 10(-11) rad/neutron for the 24-keV beam). While the Al2O3 beam is close to optimal, the 24-keV beam produces a significant fast neutron dose which results in a lower TG.(ABSTRACT TRUNCATED AT 250 WORDS)

Biophysical Phenomena↗

Toward an identification of mechanical parameters initiating periosteal remodeling: a combined experimental and analytic approach.

The ability of bone to adapt to its mechanical environment is well recognized, although the specific mechanical parameters initiating or maintaining the adaptive responses have yet to be identified. Recently introduced mathematical models offer the potential to aid in the identification of such parameters, although these models have not been well validated experimentally or clinically. We formulated a complementary experimental/analytic approach, using an animal model with a well-controlled mechanical environment combined with finite element modeling (FEM). We selected the functionally isolated turkey ulna, since the loading could be completely characterized and the periosteal adaptive responses subsequently monitored and quantified after four and eight weeks of loading. Known loads input into a three-dimensional, linearly elastic FEM of the ulna then permitted full-field mechanical characterization of the ulna. The FEM was validated against a normal strain-gaged turkey ulna, loaded in vivo in an identical fashion to the experimental ulnae. Twenty-four candidate mechanical parameters were then compared to the quantified adaptive responses, using statistical techniques. The data supported strain energy density, longitudinal shear stress, and tensile principal stress/strain as the mechanical parameters most likely related to the initiation of the remodeling response. Model predictions can now suggest new experiments, against which the predictions can be supported or falsified.

Adaptation, Physiological↗

Faecal coliform bacteria in Febros river (northwest Portugal): temporal variation, correlation with water parameters, and species identification.

Febros river water was sampled weekly, during 35 successive weeks, and analyzed for microbiological (total coliforms, faecal coliforms, faecal streptococci and enterococci) and chemical-physical (ammonia and temperature) parameters. All microbiological parameters were highly correlated with each other and with ammonia, suggesting that the simultaneous determination of all variables currently in use in the evaluation of the microbiological quality of waters is probably redundant, and could be simplified, and that ammonia should be tested as a sentinel parameter of the microbiological pollution load of Febros river. From the strains isolated from positive tubes of the faecal coliforms test (multiple tube fermentation technique) and retested in this assay, Escherichia coli, Klebsiella oxytoca and Klebsiella pneumoniae subsp. pneumoniae strains were positive, indicating that the faecal coliforms test is not totally specific for Escherichia coli, and can detect other bacteria. Considering that these Klebsiella spp. are not necessarily of faecal origin, it was concluded that the faecal coliforms test can overestimate true faecal pollution. From the strains isolated from positive tubes of the faecal coliforms procedure, only Escherichia coli strains were clearly positive in the beta-D-glucuronidase test. All other species were negative or very weakly positive, suggesting that the assay of the beta-D-glucuronidase activity is less prone to false positives than the faecal coliforms test in the quantification of Escherichia coli in environmental waters.

Ammonia↗

[Identification of prognostic parameters for renal cell carcinoma by cDNA arrays and cell chips].

We report here an example of how the combined application of cDNA and tumor array can lead to the identification of a novel prognostic marker within a very short time. A cDNA array analysis was performed on 5184 cDNA clones on a filter to screen for genes with differential expression between the renal cancer cell line CRL-1933 and normal kidney tissue to identify genes with relevance in RCC. There were 89 differentially expressed genes in the cancer cell line, one of them coding for vimentin, a cytoplasmic intermediate filament. To determine the in vivo prevalence and prognostic significance of vimentin expression, a renal cancer tissue micro array containing 532 RCC specimen was constructed and vimentin expression was determined by immunohistochemistry. Vimentin expression was frequently seen in clear-cell (51%) and papillary RCC (61%), but rarely in chromophobe RCC (4%) and oncocytomas (12%). These results obtained from minute arrayed tumor samples match with previous findings on vimentin expression in renal tumors. Furthermore, vimentin expression was significantly associated with poor patient prognosis (p < 0.007) independently of grade and stage. These results suggest that tissue microarray analysis provides a rapid and powerful method to determine the prevalence and prognostic significance of novel candidate genes discovered to be involved in cancer development with large-scale cDNA expression arrays. The tissue array can be adapted as a routine tool in research laboratories for analyses of large tumor series at the DNA, RNA or protein level. With such a tool, cancer researchers can study vast numbers of tumor samples in a short time and can generate a wealth of data on the application of tumor markers.

Biomarkers, Tumor↗

Selection of pre-operative haematobiochemical parameters for the identification of patients 'at risk of infection' undergoing surgery for gastro-intestinal cancer.

Sixty-three patients were given a complete laboratory screening before undergoing surgical treatment for cancer of the digestive tract. The values of all these parameters were correlated with the incidence of postoperative infections, with the aim of identifying those markers which could be useful for the pre-operative selection of the patients at risk of infection. Patients who developed postoperative infections showed a significant pre-operative reduction of total serum proteins (P less than 0.02), albumins (P less than 0.02), beta-globulins (P less than 0.01) and C3c (P less than 0.05), while alpha 1-globulins were slightly, but not significantly, increased. The possible clinical applications of these parameters, to develop a predictive model which may help identify the patients at risk of infection, are discussed.

Aged↗

Intraoperative identification and neurophysiologic parameters to verify pelvic autonomic nerve function during total mesorectal excision for rectal cancer.

BACKGROUND: Preservation of parasympathetic and sympathetic nerves is required to avoid urogenital function disturbances after total mesorectal excision (TME) for rectal carcinoma. This study sought to determine whether intraoperative stimulation of parasympathetic nerves with monitoring of bladder contraction is useful in meeting this demand. STUDY DESIGN: In a prospective pilot study, 17 patients, 11 men and 6 women, underwent TME with pelvic autonomic nerve preservation performed by an experienced surgeon. The parasympathetic nerves were stimulated by an electrostimulation device (Screener 3625, Medronic), and the resulting bladder contraction was measured manometrically in all patients. Variations in pulse rate and voltage were measured to determine optimal stimulation parameters. A standardized questionnaire was used to record urogenital function disturbances. Residual urine volume was measured by ultrasound pre- and postoperatively. Shortterm outcomes data were evaluated to establish a possible association between intraoperative test results and postoperative bladder function. RESULTS: In 15 of 17 patients undergoing TME with pelvic autonomic nerve preservation for rectal carcinoma, the parasympathetic nerves were identified based on nerve stimulation-induced bladder contraction. Two patients with negative results on intraoperative nerve stimulation had persisting bladder dysfunction requiring an indwelling catheter after discharge from hospital. In spite of a short median followup of 2 months (range 1 to 4 months), in 7 of 10 men with intact erectile function prior to surgery, postoperative erectile dysfunction could be excluded. The study showed a pulse rate of 35 Hz and an electric potential of 12 V to be optimal stimulation parameters, associated with a mean intravesical pressure rise of 12.7 cm H(2)O (range 2.8 to 18.0 cm H(2)O). CONCLUSIONS: Intraoperative nerve stimulation with monitoring of intravesical pressure represents a technically simple procedure for the identification and verification of function of pelvic parasympathetic nerves during TME for rectal carcinoma.

Electric Stimulation↗

Dielectric relaxation on the intermediate layer in a bipolar membrane under the water splitting phenomenon. II. Double dielectric relaxation and identification of phase parameters.

In this study, we investigated the impedance spectra of bipolar membranes. Under the application of a reverse-biased voltage, the spectra showed a double dielectric relaxation profile due to the heterogeneous structure and it was analyzed in accordance with the three-layered dielectric model. It is defined that one of the compositions of the heterogeneous structure is situated at the membrane interface region between the negatively and the positively charged membrane with a thickness of less than several micrometers, which has an extraordinarily large electric capacity with a magnitude of sub-microfarads. It is concluded that this layer is identified with the intermediate layer in which the water splitting phenomenon occurs on the bipolar membrane.

Journal Article↗

Genetic transformation of Arabidopsis thaliana zygotic embryos and identification of critical parameters influencing transformation efficiency.

An efficient procedure for Agrobacterium-mediated transformation of zygotic embryos derived from three different Arabidopsis thaliana ecotypes has been developed. This procedure yielded an average transformation rate of 76% for ecotype C24, and 15-20% for ecotypes Landsberg-erecta and Columbia. A critical step for optimal transformation was the preculture of embryos on a phytohormone-containing medium. Light and electron microscopical studies showed that, during preculture, procambium cells of embryos became highly susceptible to Agrobacterium infection. Transformed cells developed calli and regenerated shoots within 4-5 weeks of culture. A total of 1500 fertile transgenic plants were regenerated. In regenerated plants the presence of inserted DNA was verified by genomic Southern blot analysis, assays of enzymatic activities of reporter genes (neomycin phosphotransferase II and beta-glucuronidase) as well as by genetic segregation tests. R1 progenies of 45 randomly chosen transformed lines and 150 independent regenerants did not show any somaclonal variations as ascertained by both morphological and cytological criteria. Short duration (7-8 weeks), high efficiency, reproducibility and low frequency of somaclonal variation makes the zygotic embryo transformation particularly well-suited for T-DNA tagging mutagenesis.

Cells, Cultured↗