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At least 1,207 records · Page 67Linked to original sources
PubMed1999

An experimental study and mathematical simulation of adrenergic control of hindlimb vessels in rats after 3-week tail suspension.

Adrenoreactivity of rat hindlimb vessels was studied in experiments with constant-pressure saline perfusion. An original mathematical model was applied to evaluate the mechanism of changes in vascular tone regulation. A 3-week suspension resulted in decreased responses to sympathetic nerve stimulation, as well as to exogenous noradrenaline, the latter effect being registered when the pressure level was close to normal. Mathematical simulation indicated that long-term suspension induces both structural and functional changes in the vascular bed of the hind limbs, one of which is a disorder in the myogenic mechanisms of vascular tone regulation. In suspended rats, suppression of the myogenic response can be one of the reasons for decreased vessel reactivity to constrictor stimuli and, consequently, for disturbances in blood flow regulation in skeletal muscles of the hind limbs.

Animals↗
PubMed2003

[Dosage regimen optimization in cancer chemotherapy using a mathematical model].

In cancer chemotherapy, it is important to design treatment strategies that ensure a desired rate of tumor cell kill without unacceptable toxicity. To optimize treatment, we used a mathematical model describing the pharmacokinetics of anticancer drugs, antitumor efficacy, and drug toxicity. This model was associated with constraints on the allowed plasma concentrations, drug exposure, and leukopenia. Given a schedule of drug administrations, the mathematical model optimized the drug doses that could minimize the tumor burden while limiting toxicity on the white blood cells. Simulation suggests that the optimal drug administration is an initial high dose chemotherapy up to saturation of constraints associated with normal cell toxicity followed by a maintenance continuous infusion at a moderate rate. Data related to etoposide investigations were next used in a feasibility study. Simulations made with the usual clinical protocols and optimized protocols revealed that model-based optimal drug doses lead to greater cytoreduction. Also, examples showed how to use this new approach for the dose ranging problem and they evaluated the sensitivity of the optimized protocols with respect to the clinical constraints.

Antineoplastic Agents↗
PubMed2002

[Mathematical modeling -- an objective assessment of new medicines and treatment technologies].

An objective method of studying effectiveness of new medicines and methods of treatment is mathematical modeling. On the basis of mathematical processing of the pooled data obtained in the control group of patients an individual prognostic formula can be made which predicts the only outcome for each patient. When studying a new medicine or method of treatment in each patient under test his prognostic outcome is compared to the real one. An improvement of the real outcome as compared to the prognostic one points to the effectiveness of the new medicine used. An objective and individual approach to the assessment of the result after the end of each case of treatment allows the further perspectiveness of the work done and the number of necessary tests to be efficiently estimated.

Drug Therapy↗
PubMed2003

Mathematical analysis of calcifications in stented, antibiotic sterilized and cryopreserved sheep biological valves implanted for one year in tricuspid position.

UNLABELLED: The aim of the study was morphometric and mathematic analysis of calcification profiles present in the leaflets of a cryopreserved and alive heart valve depending on the diagnosed pathologic process. Sheep antibiotic sterilised and cryopreserved biological valves were implanted in tricuspid position in young sheeps for one-year period. After this time the valves removed and studied morphologically. The control group consisted of 7 intact valves, the comparative group, so called group of valves after the processing antibiotic sterilization and cryopreservation consisted of 7 valves after mentioned procedures. Histologic investigations were based on paraffin sections of formalin-fixed valve cusps, stained with H&E and Masson trichrome, calcium deposits were stained von Kossa technique. The measured values included: 1. area and equivalent diameter, 2. length, 3. breadth, 4. perimeter, 5. elongation, 6. roundness, 7. fullness coefficient. CONCLUSIONS: 1. A process of initial processing and cryopreservation of biological valve increases a dimension and disturbs a shape of microcalcifications. 2. Cryopreserved biological valves explanted after one-year implantation into an animal in a tricuspid position possess microcalcifications and calcification foci. The size of microcalcifications decreases together with an intensification of degenerative processes of the connective tissue, especially in hyalinization. Hyalinization of the biological valve tissue seems to be favorable for a valve durability and as a pathological process decreasing calcification. 3. Mathematic analysis of morphometric features defining differences in size and shape of each calcification indicate morphologic and morphometric autonomy of calcifications, characteristic for the analyzed group of valve pathologic changes.

Animals↗
PubMed2003

[Importance of mathematical analysis of the retinal image in diabetic retinopathy].

The authors test whether for evaluation of the severity of diabetic retinopathy it is possible to use the method of computer assisted mathematical processing of the retinal image. This method is based on the identification of vascular endings in the visualized part of the retina. It is assumed that with the severity of the finding the number of vascular endings increases in conjunction with the process of neogenesis. For assessment of the number of vascular endings the authors use the Adaptive Contrast Control (ACC) method. By a special procedure the vascular endings are identified and their number is assessed in the investigated area of the retina. The method makes it possible to assess in addition to the number of vascular endings also the total length of the vessels, their volume, surface, area they cover and the histogram of the diameter of the vessels. The authors examined 19 patients (38 eyes) with a quite normal finding on the retina. The mean age of the group was 37.3 years. Moreover they examined 10 patients (20 eyes) with middle advanced and advanced non-proliferative diabetic retinopathy and 10 patients (20 eyes) with risk proliferative diabetic retinopathy. In every patient a standard digital photograph of the fundus of both eyes size "tif" was made and each picture was subjected to mathematical analysis. The group of patients was divided into three sub-groups (patients with a normal finding, a non-proliferative finding and a finding of proliferative diabetic retinopathy). In the conclusion the authors provide evidence that with increasing severity of the finding on the retina also the number of vascular endings increases.

Adolescent↗
PubMed2003

[Mathematical model for study the reliability of organism function in extreme conditions of high altitude].

The health of a person and his capacity for work under conditions of high mountains in many respects is determined by the reliability of the function of physiological systems. Mathematical methods of both the reliability theory and mathematical simulation of basic functional systems are proposed to be used for investigating the reliability. It is shown that the most suitable reliability model for living systems is a chain model-a successive connection of links representing separate functional systems of organism. Besides, the weakest links determining the reliability of functioning of the whole organism under the extreme conditions of high mountains even for a healthy person are-respiration, blood circulation, thermoregulation and psychophysiological systems. Quantitative characteristics of the reliability of these systems are determined through the main indicators. The influence of non-sufficient contents of oxygen in respiration mixture, low atmospheric pressure, low temperatures of the environment are simulated by computer models of organism. An analyses of modeling data shows that moderate physical loading improves indicators of organisms adaptively to external conditions of high mountains and promotes the increasing of persons capacity for work and the reliability of his functioning.

Adaptation, Physiological↗
PubMedDate not supplied

[Assessment of the potential impact in Italy of extensive varicella vaccination programs based on a mathematical model].

A mathematical model has been developed in order to assess the effect of extended programs of varicella vaccination on the epidemiology of the disease in Italy. The effect of different vaccination options have been estimated by the change in incidence of the disease and age distribution of cases over a short and long period of time. The developed mathematical model reproduces chickenpox transmission and immunisation; five strategies different for target age of vaccination and/or proportion of vaccinated subjects have been considered. In all scenarios the model pointed out an initial decrease of case frequency observed in the first 3-5 years, followed by a series of epidemic peaks, variable in number and size by vaccination strategy. Moreover, as the number of cases among infants decreases, the number of cases among adults increases. Such event is minimised only by very high vaccination coverage (80% in the first year of life and 50% at 12 years of age). Extensive programmes of vaccination against chickenpox must reach a high coverage as soon as possible in order to avoid undesirable effects that may move forward the age of cases and therefore should be offered to target age groups easy to reach.

Chickenpox↗
PubMed1990

[The role of static-dynamic factors in genesis of femoral head and neck deformation in dysplastic hips. A physical-mathematical interpretation ].

The clinical material for a physical-mathematical analysis of femoral head and neck deformations in subluxated and luxated hips consisted of 1.574 case histories of children operated on in 1954-1988. In that material 21.9 per cent of the children had preoperative growth disorders of the head, and in the half of the cases also the femoral neck was involved. In 10.79 per cent of the children pre- and postoperative trophic disorders were also observed. On the basis of the physical-mathematical analysis of static-dynamic factors of the hip, it has been determined that the disordered shape of the femoral head and neck is most of all the result of defective formation of the roof. The oblique roof changes the static and dynamic forces acting on the femoral head and neck in such a way that large overloading of the growth zones of the medial side occurs and is followed by development of proximal femur deformation.

Biomechanical Phenomena↗
PubMed1992

[Molecular basis of regulation of contraction of skeletal muscle cells and the role of calcium. Mathematical modeling].

The review summarizes recent knowledge concerning regulatory mechanisms of skeletal muscle cell contraction. Calcium ions are the essential mediator of these processes. Their primary function is signal transmission from the sarcoplasmic reticulum to contractile proteins. A large variety of methods is available for the investigation of such complex molecular processes, ranging from physiological through biochemical and morphological to biophysical and mathematical approaches. Mathematical modelling is assessed comprehensively in the last part of the review. (Fig. 3, Ref. 58.)

Animals↗
PubMed2003

Mathematical modelling for the study of respiratory mechanics.

The target of this study was the development of mathematical models that best describe the behaviour of respiratory parameters. First of all, we studied lung volume in relation to time both for normal and maximal inspiration/expiration by developing mathematical models. For the construction of these equations the exponential model was used. Then we tried to study the flow-volume of a typical spirometer curve by dividing it into two parts: the first part reaches the Peak Expiratory Flow (PEF) point and the second follows until the volume reaches Vital Capacity (VC). For the first part we built an exponential equation; for the second part a number of existing prediction equations for the flow in various points of VC were used. For the volume-pressure diagram, we built exponential equations that describe the volume-pressure relation below Vo (Vo: lung volume where pressure is zero). The equations were coupled for expiration and inspiration. The modeling of respiratory mechanics led us to the conclusion that the developed models could offer new potentials in the description of other respiratory parameters as well.

Adult↗
PubMed2004

[Mathematical model of epidermal growth factor receptor-mediated lipid phosphatidylinositol(4,5)-bisphosphate hydrolyzation by phospholipase C-gamma1 activity].

OBJECTIVE: To investigate the dynamic characteristics of lipid phosphatidylinositol (4,5)-bisphosphate (PIP(2)) in plasma membrane hydrolyzed by phospholipase C-gamma1 in epidermal growth factor receptor(EGFR)-mediated signal pathway. METHODS: A mathematical model based on the law of mass action was established with differential equations to simulate metabolizable pathway of PIP(2). RESULTS: Differential equations of the key product concentration during hydrolysis of PIP(2) were formulated, and the effects of the parameters on these hydrolyzed products analyzed. CONCLUSION: This mathematical model provides foundation for further investigation of the dynamic changes of biological characteristics and the relations between the key product concentrations in PIP2 hydrolysis.

ErbB Receptors↗
PubMed2003

Mathematical models of fluid and solute transport in peritoneal dialysis.

Three types of mathematical models of peritoneal transport are reviewed: distributed models, membrane models, and pore models. The distributed model described the capillary bed distributed within the tissue with two sets of transport parameters for the capillary wall and for the tissue separately. The membrane and the three pore models consider blood as a compartment separated by a transport barrier from the dialysis fluid in the peritoneal cavity. The membrane model describes the barrier using "black box" transport parameters, whereas the three pore model assumes three types of pores across the barrier (large, small, and ultra small pores) and a mathematical theory of fluid and solute transport through the pore. Each model contributes its specific share to investigations of peritoneal transport. The basic features and specific areas of application of all three types of the models are discussed.

Biological Transport, Active↗
PubMed2004

[Mathematical algorithm for evaluation of the human cardio-respiratory homeostatic function].

Mathematical algorithm of the cardiorespiratory homeostasis was determined by oxygen demand (VO2) and carbon dioxide production (VCO2) during maximal physical loading on the bicycle ergometer; calculated and measured parameters of the physical capacity were compared in experiments with long-term (110- to 240-d) isolation of human subjects. Aerobic capacity was evaluated during incremental physical testing in the sitting position on bicycle Elema-Siemens 380-B. The following parameters were measured: peak (maximal loading) heart rate (HRpeak) and VO2, work time, and VO2 at 15 points on the Borg load scale, total aerobic test time and some others. Analysis of the homeostatic function of the cardiorespiratory system with the integral H = (h(u)du failed to state statistically reliable differences (p > 0.05) before and after isolation in group-1; however, it evidenced an increased homeostatic ability (p < 0.05) in group-2 and a decreased homeostatic ability in group-3 after isolation. Hence, the proposed mathematical algorithm showed a good agreement with the aerobic capacity parameters measured using classic methods. There was a high correlation (p < 0.05) between the homeostatic function and aerobic capacity in the groups of subjects and, therefore, determination of the cardiorespiratory homeostatic function can be considered an additional evaluative criterion.

Algorithms↗
PubMed2004

[Significance of the mathematical model of cardiac electrical field for the interpretation of experimental data].

BACKGROUND: In concurrence of our recent findings of the elevation of QT dispersion (QTd) in the group of pregnant women, mathematical approaches were developed aimed to give possible geometrical explanation whether the observed changes result from the rotation or from the changed position of the heart. METHODS AND RESULTS: Mathematical model of the cardiac electrical field approximated as a time variable dipole in a homogenous spatial conductor was developed. From the experimental vectocardiographic records, representing time course of the cardiac dipole, body surface potential maps were calculated on the basis of the model. To validate the adequacy of the model, the reconstructed electrocardiograms were compared with the empiric data. To determine the effects of rotation, original empiric VCG data of the control group were transformed accordingly the hypothetic pregnancy related changes. Calculated surface electrocardiograms were then compared with empiric cardiograms of the pregnant women. CONCLUSIONS: Based on the results, several conclusions can be drawn: 1) QT dispersion is associated also with the geometrical relations between the direction of cardiac vector during the terminal phase of repolarization and the direction of axes in the given system of leads. The dispersion then has its typical occurrence at the thoracic surface--minimums of the QT duration are found in the plane perpendicular to the axis of the terminal vector lead. 2) When the duration of repolarization is estimated from the classic thoracic leads within the phisiological variations of terminal-depolarization vector orientations, can exist that in some cases the minimum of QT interval is and in others it is not recorded by the lead system. Value of QT dispersion between these two extremes will be significantly different. 3) In case of the horizontal declination of the heart, the ECG signal in most of the leads of the body surface mapping has a higher voltage than in case of vertical declination due to a smaller angle between axes of the terminal vector and most of the leads. Such fact will contribute to more accurate reading of the T wave end and to the estimation of QT interval, usually with smaller value of QTd. 4) The change of the cardiac electrical field corresponding to the changed position of the heart (rotation) does not result by itself in QTd changes, if it is evaluated from the records from the whole thorax. Obversely, horizontalization of the heart contributes more to the evaluation of lower QTd values, as it is given above. 5) More then the result of geometrical changes, QT dispersion found in the group women in high level of pregnancy is an effect of changes in the T loop morphology, which was observed in this group. Another possible explanation of the observed dispersion is the non-dipolar character of the electrical field changes during pregnancy.

Adult↗
PubMed2004

Optimisation of a large WWTP thanks to mathematical modelling.

Better controlling and optimising the plant's processes has become a priority for WWTP (Wastewater Treatment Plant) managers. The main objective of this project is to develop a simplified mathematical tool able to reproduce and anticipate the behaviour of the Tougas WWTP (Nantes, France). This tool is aimed to be used directly by the managers of the site. The mathematical WWTP model was created using the software WEST. This paper describes the studied site and the modelling results obtained during the stage of the model calibration and validation. The good simulation results have allowed to show that despite a first very simple description of the WWTP, the model was able to correctly predict the nitrogen composition (ammonia and nitrate) of the effluent and the daily sludge extraction. Then, a second more detailed configuration of the WWTP was implemented. It has allowed to independently study the behaviour of each of four biological trains. Once this first stage will be completely achieved, the remainder of the study will focus on the operational use of a simplified simulator with the purpose of optimising the Tougas WWTP operation.

Algorithms↗
PubMed2004

[A mathematical model of determining the knee joint injury].

A mathematical model of determining the injury of human knee joint was established by using structural dynamics method. The results showvered the corresponding shearing displacement and bending angle of the knee joint on the occasion of ligament avulsion, and the shearing force and bending moment which caused tibial condylar fractures under purest shearing and bending condition. The calculated results consisted with the experimental results greatly, suggesting that using mathematical method to determine the injury is feasible and this kind of method can do good to lots of subjects, such as pedestrian protection, athletic medicine and rehabilitation engineering.

Humans↗
PubMedDate not supplied

[An experimental study and a mathematical model of interactions in mixed culture of invertebrates and algae in the "producer-consumer" aquatic biotic cycle].

An experimental investigation was carried out, and a mathematical model of interaction between invertebrates (infusoria Paramecium caudatum and rotifera Brachionus plicatilis) and algae (Chlorella vulgaris and Scenedesmus quadricauda) in the "producer-consumer" aquatic biotic cycle with spatially divided links was constructed. The model describes the dynamics of a mixed culture of infusoria and rotifera in the "consumer" link, when they consume a mixed culture of algae coming from the "producer" link. A negative influence of products of algae Scenedesmus metabolism upon the reproduction of infusoria P. caudatum was revealed. Taking this into account, a qualitative coincidence of the results of mathematical modeling with experimental data was obtained. It was shown that the co-existence of mixed algae culture in the "producer" link with invertebrates in the "consumer" link in the "producer-consumer" aquatic biotic cycle is impossible because of the displacement of infusoria P. caudatum by rotifera Brachionus plicatilis.

Animals↗