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Biomedical subjects

Fernando Silva

Publications and source records attributed to Fernando Silva.

8 recordsLinked to original sources
PubMed2006

Mathematical calculation of pedicle subtraction osteotomy size to allow precision correction of fixed sagittal deformity.

STUDY DESIGN: This is a retrospective review of 15 consecutive fixed sagittal plane deformity patients who have undergone pedicle subtraction osteotomies. The focus of this article is the application of a trigonometric equation that calculates the degree of correction needed to achieve sagittal balance. The intraoperative predictive accuracy and clinical radiographic results of using this mathematical equation are discussed. OBJECTIVE: The need for a precise and reproducible planning tool for the correction of sagittal imbalance prompted us to apply a simple trigonometric equation to achieve the desired sagittal alignment of the spine. SUMMARY OF BACKGROUND DATA: Establishing sagittal balance has been widely recognized as one of the most important parameters in optimizing outcomes for spinal reconstruction patients. Preoperative planning for sagittal plane correction in adult spinal deformity has traditionally been done by estimation or with cumbersome film cutouts. To our knowledge, there has not been a consistent method of calculating the exact number of degrees needed to reestablish spinal balance. METHODS: Patients' C7 plumb lines are measured on a 36-inch radiograph to assess the degree of sagittal imbalance and determine how many degrees of correction (and subsequent millimeters of wedge resection) are needed. Applying a basic trigonometric formula for the tangent to the sagittal alignment is used to do this. RESULTS: We have used this technique reliably in a series of 15 consecutive patients to reestablish sagittal balance. The predicted degree of correction was compared to the achieved degree of correction at the site of the osteotomy. This comparison was accurate to within 3 degrees (the standard error of measurement for the method of Cobb) in all cases except 2. CONCLUSIONS: By using a simple mathematical equation, one can reliably determine the degree of pedicle subtraction osteotomy needed for correction of sagittal deformity. This technique is reproducible and has led to successful clinical outcomes.

Adult↗
PubMed2005

Electrochemical characterization of polyelectrolyte/gold nanoparticle multilayers self-assembled on gold electrodes.

Polyelectrolyte/gold nanoparticle multilayers composed of poly(l-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN)(6)](3-/4-) and [Ru(NH(3))(6)](3+/2+). This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN)(6)](3-/4-) species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH(3))(6)](3+/2+) pair.

Electrochemistry↗
PubMed2005

Electrochemical study of interfacial composite nanostructures: polyelectrolyte/gold nanoparticle multilayers assembled on phospholipid/dextran sulfate monolayers at a liquid-liquid interface.

The build up and electrochemical characterization of interfacial composite nanostructures containing a cationic polyelectrolyte and negatively charged mercaptosuccinic acid stabilized gold nanoparticles (AuNPs) is reported. The nanostructures were formed at the interface between two immiscible electrolyte solutions in which the organic phase is an immobilized 2-nitrophenyl octyl ether/PVC gel. The growth of the multilayer was verified with UV-vis spectra, and approximately a linear increase in UV-vis absorbance with increasing number of layers was observed. The interfacial capacitance of the multilayers was measured as a function of the potential and a theoretical model was developed to explain the results. The excellent agreement between theoretical and experimental capacitance curves allows us to conclude that nanocomposites behave similarly to polyelectrolyte multilayers, with the outmost layer determining the alternating sign of the outer surface charge density. Cyclic voltammograms were used to evaluate the transfer rate constant across the multilayers of a model drug, metoprolol, and the standard probe tetraethylammonium cation. The apparent rate constants were slightly larger than in other studies in the literature and decrease with the increasing number of layers.

Catalysis↗
PubMed2005

Electrochemical impedance spectroscopy of polyelectrolyte multilayer modified gold electrodes: influence of supporting electrolyte and temperature.

Electrochemical impedance spectroscopy and cyclic voltammetry are employed to characterize poly(styrenesulfonate)/poly(allylamine hydrochloride) multilayers assembled onto cysteamine-modified gold surfaces. The influence of the supporting electrolyte and temperature on the impedance response is studied because of both its practical interest and the need to test further the capillary membrane model recently developed by Barreira et al. [J. Phys. Chem. B 2004, 108, 17973]. The results obtained are interpreted quite satisfactorily in terms of this model, thus providing additional support to its usefulness for the description of ionic transport through polyelectrolyte multilayers. It is observed that the nature of the supporting electrolyte affects the film resistance and the electrode coverage. The temperature dependence of the diffusion coefficient is shown to follow the Arrhenius law, and the activation energy is estimated as 61 kJ/mol. Experiments with a large number of layers are also included to show that the impedance response of the multilayer then resembles that of a homogeneous membrane.

Biosensing Techniques↗
PubMed2005

Domain wall dynamics in an optical Kerr cavity.

An anisotropic (dichroic) optical cavity containing a self-focusing Kerr medium is shown to display a bifurcation between static--Ising--and moving--Bloch--domain walls, the so-called nonequilibrium Ising-Bloch transition (NIB). Bloch walls can show regular or irregular temporal behavior, in particular, bursting and spiking. These phenomena are interpreted in terms of the spatiotemporal dynamics of the extended patterns connected by the wall, which display complex dynamical behavior as well. Domain wall interaction, including the formation of bound states is also addressed.

Journal Article↗
PubMed2004

Amperometric glucose biosensor based on assisted ion transfer through gel-supported microinterfaces.

A novel amperometric glucose sensor was developed based on the facilitated proton transfer across microinterfaces between two immiscible electrolyte solutions. The combination of a 1,3:2,4-dibenzylidene sorbitol/2-nitrophenyl octyl ether gel membrane and 3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine as the ionophore allows the transfer of protons from water to the gellified organic phase; the gel membrane is supported on arrays of microholes drilled on a polyester film. The protons are generated as the result of the dissociation of gluconic acid produced during the enzymatic degradation of glucose by glucose oxidase. The characteristics of the glucose sensor were investigated using several experimental conditions, namely, the concentration of ligand and enzyme. The electrochemical response is typical of an enzymatic electrode and displays a linear behavior in the range 0.2-3 mM glucose. The effect of the experimental parameters of the voltammetric technique was also optimized with the aim of improving sensor sensitivity.

Biosensing Techniques↗
PubMed2003

Use of an implantable loop recorder: initial experience.

OBJECTIVE: Retrospective analysis of the initial experience at our department with an implantable loop recorder (ILR) for the evaluation of patients with recurrent syncope, palpitations or dizziness. METHODS: We studied ten patients aged 31-65 (52.3) years referred to our center after an inconclusive evaluation that included ECG, Holter monitoring, events recorder, stress test, echocardiogram and electrophysiological study. Seven patients had structural heart disease. We used a Reveal Plus (Medtronic, USA) ILR, which allows up to 41 minutes of electrocardiographic recording, over a period of 24 months, patient or device activated, according to the programmed parameters. Follow-up was scheduled every three months or after every event activated by the patient. Symptoms and recorded events were analyzed. RESULTS: Eight patients activated events, out of a total of 45 episodes, and five patients reported two or more symptoms. Dizziness was reported by five patients (24 episodes), palpitations by three (seven episodes), syncope by three (seven episodes) and nonspecific symptoms by five patients (seven episodes). The first symptom occurred between the twelfth day and the sixth month after implantation. Four episodes (three syncope and one dizziness) occurred with significant AV conduction disturbance (complete or high grade AV block) and in 41 episodes no rhythm or AV disturbance was recorded. Thirty events were automatically activated. There were no device-related complications. None of the patients died during follow-up.

Adult↗