Valeriano Comincioli

Thiamine content and turnover rates of some rat nervous regions, using labeled thiamine as a tracer

The content of total thiamine radioactivity in some nervous structures and liver of the rat was determined in a steady state condition, using [thiazole-2-14C]thiamine as a tracer. The contents were analyzed by a mamillary type compartmental model which enabled us to calculate the influx and efflux fractional rate constants, turnover times, turnover rates and relative accuracy. Total thiamine turnover rates of the central nervous system regions were found to be ordered in the following sequence: cerebellum (0.55 microgram/g.h) greater than medullar and pons greater than spinal cord and hypothalamus greater than midbrain (plus thalamic area) and corpus striatum greater than cerebral cortex (0.16 microgram/g.h). Sciatic nerve turnover rate was 0.58 microgram/g.h. The turnover times were mainly between 5 and 10 h (range 2.4--16.4 h). The influx rate constants could be ordered as follows: cerebellum greater than hypothalamus, pons and medulla greater than corpus striatum, spinal cord, midbrain (plus thalamic area) and sciatic nerve greater than cerebral cortex. The results show in general a good agreement between turnover rate values and brain regional sensitivity to thiamine deficiency, the most vulnerable areas to thiamine depletion being those with the highest turnover rates.

Nervous tissue thiamine metabolism in vivo. II: Thiamine and its phosphoesters dynamics in different brain regions and sciatic nerve of the rat

Different steps of the metabolism of thiamine (T), thiamine mono- (TMP), pyro- (TPP) and triphosphate (TTP) in the cerebellum, brainstem, cerebral cortex and the sciatic nerve were evaluated in the rat in vivo. The radioactivity of T and its phosphoesters was determined at fixed time intervals (0.5-240 h) after an intraperitoneal injection of [14C]T (30 micrograms:1.25 muCi), under steady state conditions. The dynamics of thiamine compounds was evaluated using a compartmental mathematical model that allowed the fractional rate constants (FRC), turnover rates (TR) and turnover times to be calculated. The phosphorylation of T to TPP and the dephosphorylations of TPP to TMP and TMP to T could be estimated in all the structures investigated. Their turnover rates were found to be ordered in the sequence: cerebellum greater than brainstem greater than cerebral cortex greater than sciatic nerve. The transphosphorylation of TPP to TTP was so small that it could not be determined in a reliable way. Regional differences were found both the rate and in the composition of T and TMP mixture released from nervous structures. The shortest turnover time of TPP was found in the cerebellum, while the sciatic nerve exhibited the fastest renewal of T and TMP. In all the structures investigated TPP had a rather short turnover time, suggesting that its function might be associated to a rapid conversion into chemically different forms. The possible relationships between the rates of turnover of T compounds are the sensitivity of the nervous structures to T deficiency are discussed.

A wavelet-based method for numerical solution of nonlinear evolution equations

Abstract We describe an adaptive algorithm for solving one-dimensional system of nonlinear partial differential equations. Different strategies are considered for the discretization in time while a multiscale collocation method is applied for the discretization in space. In particular we look at the so called Rothe method which is based on first time then space discretization. Numerical experiments are presented for a set of nonlinear problems from the literature.

Cluster analysis of nutritional and immunological indicators for identification of high risk surgical patients.

In spite of the many anthropometric, biohumoral, and immunologic parameters employed in the nutritional assessment of hospitalized patients, it is difficult in clinical practice to evaluate accurately the degree and type of malnutrition and to assess the prognostic significance of this determination. The purpose of this study is to evaluate nutritional status of surgical patients by means of cluster analysis in orderr to identify different nutritional patterns and to evaluate their clinical and prognostic significance. Nutritional assessment of 71 surgical patients was carried out at admission, and the sets of data were evaluated by means of cluster analysis. Four clusters with different nutritional patterns were identified. The incidence of clinical variables (type of disease, postoperative sepsis, palliative procedures, mortality at 6 months, etc.) in each cluster was determined in order to evaluate their clinical and prognostic significance. Cluster 1 showed minor variations of the indicators, including most of the controls presented the lowest incidence of sepsis, palliative procedures, and mortality at 6 months. It was then considered as a reference group representative of the normal nutritional condition at our institution. The other three clusters showed major variations of nutritional indicators and represent poorer risk clinical conditions. Sepsis, palliative procedures and mortality rate were significantly more frequent in these clusters (p less than 0.05, p less than 0.001, p less than 0.05). A different distribution in the clusters was recorded in gastrointestinal tract cancers and other neoplasms. Only the incidence of gastrointestinal tract cancers increases progressively in the clusters with poorer prognosis, suggesting that this type of neoplasia is more frequently associated with major changes of nutritional status.

Nervous tissue thiamine metabolism in vivo. III. Influence of ethanol intake on the dynamics of thiamine and its phosphoesters in different brain regions and sciatic nerve of the rat

The effects of chronic ethanol administration on different steps of the metabolism of thiamine (T), thiamine mono- (TMP) and thiamine pyrophosphate (TPP) in the cerebellum, brainstem, cerebral cortex and sciatic nerve were evaluated in vivo. The radioactivity of T and its phosphoesters was determined in plasma and in the selected nervous structures under steady-state conditions and at fixed time intervals (0.5-192 h) after an i.p. injection of [14C]T (30 micrograms: 1.25 microCi) to rats chronically (35 days) ethanol-treated (daily dose of 4.7 g X kg-1 b.wt. by gastric gavage) and pair-fed controls similarly treated with a sucrose solution isoenergetic with ethanol. All rats were given a nutritionally adequate diet supplying an excess of thiamine, which produced a virtually steady content of thiamine compounds in the tissues. By using a compartmental mathematical model, fractional rate constants, turnover rates and turnover times were calculated. Ethanol caused a reduction of the rate of thiamine compound enzymatic transformations (T phosphorylation to TPP, TPP dephosphorylation to TMP and TMP to T), and a facilitation of the regional uptake of T and TMP, associated to a less relevant influence on their release. Isoenergetic sucrose prevailingly caused an increased rate of thiamine metabolic steps (except phosphorylation in the brainstem and cerebral cortex), with negligible modifications of T and TMP uptake and release. Thus the changes induced by ethanol were virtually opposite to those caused by sucrose.

A wavelet-like Galerkin method for numerical solution of variational inequalities arising in elastoplasticity

The well-known problem of elasticity that may be written as a variational equation [4] has been recently extended to non-linear elastoplastic behaviours [13] giving rise to a class of variational inequalities of second kind [9]. This paper presents a wavelet Galerkin method for the numerical solution of such a class of problems, extensively studied and solved in the past by means of more traditional approaches. The novelty of the scheme presented herein is represented by the capability of wavelets to locate regions where plasticity is growing without the need of any further indicator. This is useful for adaptive remeshing as well as for gaining insight into internal variable models with applications to dynamic analysis and damage identification. Copyright

A four-state cross bridge model for muscle contraction. Mathematical study and validation

A mathematical model of contracting skeletal muscle is studied. The model is composed by an elastic element (SE) in series with a contractile element (CE) that describes the cross bridge kinetics with a formulation derived by that proposed by Eisenberg and Hill (1978).An analytical study of the system of nonlinear partial differential equations of the model allows the existence and the uniqueness of the solution to be proved.A suitable approach to the numerical solution is defined and a series of numerical tests are performed. These tests lead to select an appropriate set of parameters and allow to compare model predictions and experimental observations on frog skeletal muscle.

Numerical solution of free boundary problems in seepage flow with capillary fringe

Abstract A free boundary problem related to the stationary flow in a porous medium in which the capillary fringe is taken account of is analyzed and solved numerically. In particular two different numerical methods are applied. With the first method by means of a suitable transformation the solution of the problem is equivalent to the search for the minimum of a quadratic functional on a fixed domain. The second method applies a classical idea and determines the free boundary by means of successive approximations. The results of the two methods are compared with each other and with those obtained by means of an analogous model and found to be in good agreement. The first method, which is a new one, is better justified on a theoretical level and moreover is more convenient with regard to the programming effort and the execution time needed to carry it out on a computer.

On the solution of transient free-surface flow problems in porous media by a fixed-domain method

Abstract The numerical model presented here is the solution to the exact initial-boundary-value problems arising in recharge fluid flow through porous media having a free surface. Since the problem is nonlinear and includes a moving boundary, a numerical solution is obtained by using a fixed-domain approach. The Baiocchi transformation and method are used to develop a boundary-value problem which is then solved by an iterative method of successive over-relaxation type. Transient free-surface seepage through a two-dimensional dam with accretion is presented as an example problem. The effects of hydraulic conductivity, specific storativity and accretion on the seepage flow are studied. Two modified cases are satisfactorily compared with published results.

Mathematical modelling for contracting muscle (

An overview of the results obtained from the collaboration of mathematicians and physiologists in mathematical simulation of muscle contraction is presented. Next a mathematical model taking into account the heterogeneity of the muscle, is presented. A mathematical analysis of the model is given along with a numerical approach and some physiological implications.