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S Cavalcanti

Publications and source records attributed to S Cavalcanti.

34 records · Page 2Linked to original sources
PubMed1995

Identification of apolipoproteins A-I and B using high resolution electrophoresis on supported cellulose acetate.

A simple modification of high resolution electrophoresis on supported cellulose acetate is described. This modification is made by adding the surfactant Tween 20 to the buffer and permits the identification of apolipoproteins A-I and B as well as the usually detected serum proteins. The procedure is reproducible using various supported cellulose acetate plates with manual and automated procedures. Furthermore, this improved high resolution electrophoresis allows the semiquantitative evaluation of these apolipoproteins both on freshly collected and on -20 degrees C stored serum samples.

Apolipoprotein A-I↗
PubMed1992

Theoretical analysis of pressure pulse propagation in arterial vessels.

An original mathematical model of viscous fluid motion in a tapered and distensible tube is presented. The model equations are deduced by assuming a two-dimensional flow and taking into account the nonlinear terms in the fluid motion equations, as well as the nonlinear deformation of the tube wall. One distinctive feature of the model is the formal integration with respect to the radial coordinate of the Navier-Stokes equations by power series expansion. The consequent computational frame allows an easy, accurate evaluation of the effects produced by changing the values of all physical and geometrical tube parameters. The model is employed to study the propagation along an arterial vessel of a pressure pulse produced by a single flow pulse applied at the proximal vessel extremity. In particular, the effects of the natural taper angle of the arterial wall on pulse propagation are investigated. The simulation results show that tapering considerably influences wave attenuation but not wave velocity. The substantially different behavior of pulse propagation, depending upon whether it travels towards the distal extremity or in the opposite direction, is observed: natural tapering causes a continuous increase in the pulse amplitude as it moves towards the distal extremity; on the contrary, the reflected pulse, running in the opposite direction, is greatly damped. For a vessel with physical and geometrical properties similar to those of a canine femoral artery and 0.1 degree taper angle, the forward amplification is about 0.9 m-1 and the backward attenuation is 1.4 m-1, so that the overall tapering effect gives a remarkably damped pressure response. For a natural taper angle of 0.14 degrees the perturbation is almost extinct when the pulse wave returns to the proximal extremity.

Arteries↗
PubMed1992

Pressure drops through arterial stenosis models in steady flow condition.

Measures of pressure drops were made in two different plexiglass models of axial-symmetric arterial stenoses. The stenosis models had the same area reduction (86 percent) but were of different length so as to have a different tapering degree. Pressures were measured in steady flow condition at three equidistant points of the stenosis: upstream, in the middle, and downstream. Results indicate that: the upstream-middle pressure drop is independent of tapering degree but is highly influenced by area reduction; moreover it is much greater than the middle-downstream drop. The upstream-middle pressure drop can be accurately predicted by means of a relationship deduced by the momentum equation.

Arteriosclerosis↗
PubMed1991

A new nonlinear two-dimensional model of blood motion in tapered and elastic vessels.

An original mathematical model for the local study of blood motion in tapered and distensible arteries was developed. The theory takes into account the nonlinear terms of the Navier-Stokes equations, as well as wall motion and instantaneous taper angle, and allows the calculation of axial and radial velocity profiles with low computational complexity. The relationship between instantaneous flow and the pressure gradient in steady and dynamic conditions is evaluated by means of the mathematical model. The results obtained by simulation agree with experimental evidence and also indicate that the anatomic tapering of arteries and pulsatile changes in diameter highly influence blood motion.

Arteries↗
PubMed1980

Mammary carcinoma--multidisciplinary treatment with bilateral mastectomy and immediate reconstruction.

The classical concepts pertaining to the natural history of mammary carcinoma and its treatment must be reviewed if survival rate is to be improved. By the time diagnosis is established, a fair amount of cases of carcinoma of the breast present distant, clinically undetectable micrometastases, which will not be affected by local therapy (surgery or radiation). Increasing evidence shows that mammary carcinoma nowadays must be looked upon as a diffuse disease affecting both breasts. Postoperative radiation does not improve the 5- and 10-year survival rates and has a negative effect upon the immunological defense of the patient. Immunology plays an important role in the evolution and cure of the patient with carcinoma of the breast. The mutilation produced by radical or ultraradical mastectomy may throw the patient into mental depression which, as a consequence, may decrease the immunological competence of the patient. Multiple drug chemotherapy, started at the time of surgery and continued for several months thereafter, may kill micrometastases. Preventive immunotherapy seems to be beneficial to the patient in attempting control of metastases.

Breast Neoplasms↗
PubMedDate not supplied

Digital processing of the current noise evoked by kainate in cerebellar granule cells.

Current induced in cultured cerebellar granule cells by the bath application of kainate (500 microM) was measured using the conventional patch-clamp technique. Two different kinds of responses were observed after the agonist perfusion. Some cells exhibited small inward whole-cell currents: 116 +/- 40 pA (7 cells) at a clamp potential of -60 mV; in other cells, the agonist induced significantly larger currents: 420 +/- 35 pA (6 cells) at a clamp potential of -60 mV. The current flowing in the agonist-activated ionic channels was indirectly estimated by processing the fluctuations of whole-cell current by means of an original parametric method. Mean conductance of the underlying channels was then determined from the single-channel current estimated at different clamp potentials. In the cells exhibiting small inward currents, the mean conductance was equal to 0.5 +/- 0.2 pS (7 cells), whereas in the cells with large inward currents it was 3 +/- 0.4 pS (6 cells). This result gives a coherent explanation of the different kinds of responses observed at macroscopic level in the whole-cell current and confirms that kainate-activated channels can exhibit different levels of conductance.

Animals↗
PubMedDate not supplied

Chaotic oscillations in microvessel arterial networks.

A mathematical model of a multibranched microvascular network was used to study the mechanisms underlying irregular oscillations (vasomotion) observed in arteriolar microvessels. The network's layout included three distinct terminal arteriolar branches originating from a common parent arteriole. The biomechanical model of the single microvessel was constructed to reproduce the time pattern of the passive and active (myogenic) response of arterioles in the hamster cheek pouch to a step-wise arterial pressure change. Simulation results indicate that, as a consequence of the myogenic reflex, each arteriole may behave as an autonomous oscillator, provided its intraluminal pressure lies within a specific range. In the simulated network, the interaction among the various oscillators gave rise to a complex behavior with many different oscillatory patterns. Analysis of model bifurcations, performed with respect to the arterial pressure level, indicated that modest changes in this parameter caused the network to shift between periodic, quasiperiodic, and chaotic behavior. When arterial pressure was changed from approximately 60-150 mm Hg, the model exhibited a classic route toward chaos, as in the Ruelle-Takens scenario. This work reveals that the nonlinear myogenic mechanism is able to produce the multitude of different oscillatory patterns observed in vivo in microvascular beds, and that irregular microvascular fluctuations may be regarded as a form of deterministic chaos.

Animals↗
PubMedDate not supplied

Gene/longevity association studies at four autosomal loci (REN, THO, PARP, SOD2).

The possibility that four loci (REN, THO, PARP, SOD2) are associated with longevity was explored by comparing the genotypic pools of subjects older than 100 years with those of younger subjects matched for sex and geographic area (northern and southern Italy). The markers (all located within the respective gene) were HUMREN4; HUMTHO1; HUMPARP (gt)845nt; SOD2(C/T)401nt. In order to reduce the number of genotypes, multiallelic polymorphisms were recoded as diallelic according to allele size and frequency patterns (small: S, and large: L, alleles). A significant loss of LL homozygous genotypes was found at the THO locus in male but not in female centenarians with respect to matched controls. On the other hand no significant difference was found between case/control genotypic frequencies at REN, PARP, SOD2 loci. The latter loci therefore do not affect inter-individual variability in life expectancy (at least in terms of qualitative variants associated with the tested markers). However, the data is consistent with an association between the THO locus and longevity.

Adolescent↗
PubMedDate not supplied

Model based sensitivity analysis of arterial pressure response to hemodialysis induced hypovolemia.

The role of hemodynamic and regulatory factors in the arterial pressure response to hemodialysis induced hypovolemia was investigated by means of a computer model of the cardiovascular system, including the main short-term pressure regulatory mechanisms. The model mimics the arterial and venous systemic circulation, Starling's law and inotropic heart regulation, arterial and cardiopulmonary baroreflex controls of resistance, and capacitance vessels. All of the model parameters have a clear physiologic meaning: 10 represent the systemic circulation, 4 describe cardiac pump performance, and 3 characterize baroreflex regulation. Sensitivity analysis is performed to determine the effect of each parameter on the pressure response to mild hypovolemia (a 10% blood volume reduction after 4 hours). The results demonstrate that circulatory parameters, such as resistances and compliances, have no relevant effect upon the pressure response. Conversely, regulation of venous capacity seems to play a pivotal role in sustaining arterial pressure during hemodialysis induced hypovolemia. Regulation of systemic peripheral resistance exerts a compensatory action only as long as the blood volume reduction is < 5%, but it is inadequate to compensate for a larger blood volume reduction when venous capacity regulation is absent. A paradoxical arterial pressure increase during hypovolemia can be referred to a prevalence of cardiopulmonary afferences in the regulatory process.

Blood Pressure↗
PubMedDate not supplied

Deterministic model of ion channel flipping with fractal scaling of kinetic rates.

The flipping of ion channels in biological membranes has usually been modeled in terms of Markov transitions between open and closed states. The basic assumption of this approach is that channel flipping between open and closed states is an inherent stochastic process, due to random thermal fluctuations of units forming the channel protein. In this paper, we propose a different view of channel flipping, one not involving external stochastic causes. We consider the channel as a physical dynamic system, the unpredictable flipping of which is due to a deterministic mechanism which sustains a chaotic dynamics. In particular, we presume the changes in the channel conformation are due to delayed interaction between the ionic flow through the channel and the protein forming the channel. The model proposed here describes the channel by means of macroscopic physical quantities such as conductance, current, membrane, and reversal potentials and predicts open and closed dwell time distributions consisting of multiple exponential components and exhibiting power-law scaling over a wide range of time scales. The effective kinetic rate computed through use of simulation data shows fractal properties in good agreement with those seen experimentally. This mathematical model of the ion channel is physically consistent in terms of a plausible real system and may provide a novel key to understanding the complex behavior of the flipping process.

Electric Conductivity↗
PubMedDate not supplied

Heart rate response to hemodialysis-induced changes in potassium and calcium levels.

BACKGROUND: It is well known that hemodialysis affects cardiovascular functions, mainly because of excess body water removal. Conversely, the role of hemodialysis-induced modifications in body fluid characteristics is not yet well-grounded. In particular, the impact of modifications in plasma electrolytes on the pacemaking rhythm of the sinus node has not yet been evaluated. METHODS: Eight patients on regular hemodialysis treatment were studied along a two-hour diffusive dialysis study session without fluid removal. Biochemical (metabolic and hormonal) as well as hemodynamic parameters were measured during the treatment. A computer model of the sinus node cell electrical activity was used to analyse the experimental data. The measured changes in electrolyte concentrations and pH were imposed as model inputs and the model-computed heart rate changes were validated against the measured ones. After validation, numerical simulation was used to obtain a quantitative evaluation of the comparative weight of calcium and potassium on heart rate changes, by simulating treatments leading to different changes in plasma concentrations of such electrolytes. RESULTS: A significant heart rate increase (11%) was obtained following potassium, calcium and pH changes, with no significant variations in indices of autonomic activity. Simulation results revealed that calcium load and potassium removal both accelerate sinoatrial pacemaker beating. Concurrent changes in these electrolyte concentrations may cause heart rate to increase up to 30% at the end of hemodialysis. Heart rate sensitivity to extracellular potassium changes appears to be strictly dependent upon calcium concentration. CONCLUSIONS: Hemodialysis-induced changes in calcium and potassium concentrations may greatly affect the rhythm of the sinus node pacemaker.

Aged↗
PubMedDate not supplied

Epidural pressure measurement in the rat.

An original device for the epidural pressure measurement in the rat is presented. The reliability of epidural pressure as an index of intracranial pressure is discussed and several possible causes of error are examined. The device has been tested under conditions both of transient and prolonged cerebral blood volume increase, obtained by venous outflow obstruction.

Animals↗