PubMed Health⌕ Search

Biomedical subjects

O Baffa

Publications and source records attributed to O Baffa.

At least 37 records · Page 2Linked to original sources
PubMed1998

Increased dexamethasone-induced apoptosis of thymocytes from mice exposed to long-term extremely low frequency magnetic fields.

To address the effect of extremely low frequency electromagnetic fields on programmed cell death we assessed both the spontaneous and dexamethasone (Dex)-induced apoptosis of thymocytes and spleen cells from mice submitted to a long-term continuous exposure of a 0.4-1.0 microT 60 Hz magnetic field or an 8-20 microT direct current (DC) magnetic field. Dex-induced apoptosis but not spontaneous apoptosis was substantially increased in thymocytes from 0.4 to 1.0 microT 60 Hz field-exposed animals. Spontaneous apoptosis and Dex-induced apoptosis of spleen cells were not affected by the 0.4-1.0 microT 60 Hz field exposure. In addition, spontaneous apoptosis and Dex-induced apoptosis of thymocytes and spleen cells from mice exposed to an 8-20 microT DC field were similar to the controls. These findings represent the first demonstration that thymocytes from mice exposed to a long-term 0.4-1.0 microT 60 Hz field may show abnormal response to Dex apoptotic stimuli.

Animals↗
PubMed1998

Oesophageal transit time evaluated by a biomagnetic method.

The aim of this work was to determine the oesophageal transit time (OTT) of a bolus using the biomagnetic technique and compare the results to those obtained by means of scintigraphy. For the biomagnetic evaluation, a test meal (yoghurt) uniformly labelled with 5 g of powder ferrite was swallowed in a single gulp by 19 normal volunteers in the upright position. One sensor (first order gradiometer) was placed at the furcula and a second one at the xiphoid process to detect the passage of the test meal and the magnetic signal output was recorded in a computer. The OTT was determined by plotting the voltage signal against time. The scintigraphic technique was used in the same volunteers: the test meal was labelled with less than 350 MBq of 99mTc-phytate and swallowed in the same way. The bolus transit was recorded at 4 frames s(-1) (100-120 frames acquisition) and the OTT was determined by drawing two regions of interest in the same areas as the sensors. The results were determined by plotting counts against time. The averages for OTTs were 3.8 +/- 0.8 s for the scintigraphic technique and 4.6 +/- 0.9 s for the biomagnetic technique. Although scintigraphic OTT was significantly shorter than magnetic OTT, there was a significant correlation between them. We conclude that the biomagnetic study may be used to evaluate OTT.

Adult↗
PubMed1997

A novel biomagnetic method to study gastric antral contractions.

A novel non-invasive method to study the motion associated with gastric antral contractions is discussed. The method is based on magnetic flux changes detected by an a.c. biosusceptometer, produced by a magnetic test meal within the stomach. Measurements are made at the surface of the torso and are easy to perform. Simultaneous measurements were made with electrogastrography and scintigraphy showing remarkable coincidence. The effect of a drug on the amplitude of antral contractions was also assayed with the new method.

Adult↗
PubMed1996

Evaluation of a biomagnetic technique for measurement of orocaecal transit time.

OBJECTIVE: To evaluate a novel non-invasive and harmless biomagnetic technique to measure orocaecal transit time. DESIGN: A biomagnetic method was employed to measure orocaecal transit time in 26 healthy volunteers, 12 patients presumed to have rapid small intestine transit and six volunteers with slow intestinal transit induced by loperamide. Results were compared to those obtained with a standard H2 breath test performed simultaneously. METHODS: Subjects ingested a test meal consisting of a chocolate-flavoured custard (120 g, 120 kcal) containing 18 g of lactulose and 3 g of ferrite powder as a magnetic tracer. External measurements of the magnetic signal on the caecal area and determination of H2 concentrations on samples of end-expiratory air were performed at 5-10-min intervals for 4 h after test meal ingestion. RESULTS: The biomagnetic method yielded reliable values for orocaecal transit time in all healthy volunteers and 11 out of 12 patients with diarrhoea, whereas the H2 test was uninterpretable in two volunteers and five patients, because of either high fasting H2 levels or absolute lack of H2 excretion. Transit time values determined by the biomagnetic method (mean +/- SD = 93 +/- 32 min) were generally higher than those assessed by H2 breath analysis (77 +/- 22 min). Thus, although results obtained by the two methods were significantly correlated (R = 0.56, P < 0.01), calculated agreement between them was poor. Nevertheless, the two methods were equally effective in detecting both abnormally fast transit associated with diarrhoea and slow transit induced by loperamide. CONCLUSION: The simple and harmless biomagnetic technique for measuring orocaecal transit time is as effective as the H2 breath test in detecting abnormal transit rates, and may provide reliable measurements in circumstances where H2 breath profiles are uninterpretable.

Adult↗
PubMed1993

Liver injury and generation of hydroxyl free radicals in experimental secondary hemochromatosis.

An experimental model of secondary hemochromatosis is described. Saccharated iron was administered i.v. to rats for 7 months in total doses in the range 1.0-1.7 g per kg body weight. After the completion of iron loading, the biochemical measurements revealed elevation of alanine aminotransferase (ALT), slight reduction of plasma glucose concentration, and significant reduction of both plasma and liver ascorbic-acid levels. The mean liver iron concentration was 50 times higher in iron-loaded animals than in controls. High concentrations of inorganic iron were also observed in spleen, pancreas, and heart. Histologic analysis revealed marked hepatic fibrosis in most animals in the experimental group. These results demonstrate this animal model presents some pathologic findings observed in human transfusional hemochromatosis. Additionally, hydroxyl free radicals were detected by electron paramagnetic resonance (EPR) spectroscopy in the iron-overloaded liver tissue processed at pH 5.0. No free radicals were detected at pH 7.4. These results suggest the possible participation of hydroxyl free radicals in the cellular toxicity of iron overload.

Animals↗
PubMed1993

Rheological studies of photopolymerized dental composites.

An oscillating rheometer was constructed to study the polymerization of light-cured dental composites. The instrument is based on the forced harmonic oscillator, where the polymerization of the sample leads to a reduction of amplitude of oscillations. The polymerization time as determined for different materials seemed to be influenced by the filler particle size. The results obtained for the viscosity and shear modulus for a class of samples agreed with values published using other instruments and methods.

Composite Resins↗
PubMed1992

Magnetic and electric characteristics of the electric fish Gymnotus carapó.

The fresh water fish Gymnotus carapó produces a continuous series of weak pulsed electric fields in its surroundings and senses disturbances of this field as part of its sensory system. The electric and magnetic properties of the electric organ of this fish were studied. Magnetic fields close to the fish on the order of nT are produced by currents on the order of 10(-4) A in the electric organ of the fish. The electromotive force, the internal resistance, the current, and the electric power of the equivalent circuit were determined noninvasively.

Animals↗
PubMed1992

Optical transmittance of reflecting wedges.

This study quantified the light intensity transmitted by the reflecting wedges perpendicularly to the growth axis. The results demonstrated that the cervical wedges did reflect the light of 180 degrees and original light intensity diminished by 83.9%. The maximal light intensity transmitted to the resin by the wedge was less than 8% of that receiving direct exposure to the curing wand. Differential measurements made on points closely spaced along the sides of the wedge indicated a maximal intensity at approximately 2 mm from the base of the wedge.

Composite Resins↗
PubMed1990

An ESR study of pathologic red blood cell membranes (RBCM).

A comparative study of red blood cell membranes from normal subjects and beta-thalassemia and sickle cell anemia patients was performed by spin labeling at the lipidic and protein phase. The results show that the quantity of bound spin label is the same for sickle, thalassemic, and normal membranes. The data from 5-doxyl stearic acid suggest an increase in fluidity for the thalassemic membrane.

Adult↗
PubMed1988

Hemichrome formation during hemoglobin Zurich denaturation.

Electron paramagnetic resonance (EPR) spectrum of hemoglobin Zurich, after oxidation, storage and heating, showed several absorption derivatives in the high field region (g approximately equal to 2) which are indicative of hemichrome formation. Characteristic visible spectra of hemichromes were observed for oxidized Hb Zurich and for its spontaneous precipitate. The proportional increase of EPR signals at g approximately equal to 2 and decrease at g = 6.37, the constant ratio of absorbance at 540 nm to 280 nm during heating, and the similarity of this ratio for spontaneously precipitated HbA and for Hb Zurich indicate that heme is not lost during the first steps of Hb Zurich denaturation.

Electron Spin Resonance Spectroscopy↗
PubMed1985

The acid-alkaline transition of a sea turtle myoglobin: coexistence at high pH of high- and low-spin forms.

The microenvironment of the iron in a sea turtle Dermochelys coriacea myoglobin is studied using the spectroscopic techniques EPR and optical absorption. Optical absorption spectra in the visible region suggest a great homology between turtle Mb and other myoglobins, such as those from whale, human and elephant. The pK of the acid-alkaline transition is 8.4 slightly lower than the pK of whale and equal to that of elephant myoglobin. The EPR spectrum at pH 7.0 is characteristic of a high-spin configuration with axial symmetry (gx = gy = 5.95). At higher pH, this signal changes in a way different from that observed for whale myoglobin. We observe for turtle Mb both the formation of a low-spin configuration with rhombic symmetry (gx = 2.56, gy = 2.20, gz = 1.90) and of a high-spin species with rhombic distortion (gx = 6.79, gy = 5.18, gz = 2.12). This suggests a lowering of symmetry at the haem, so that now the x and y directions are no more equivalent. This can be explained by amino acid substitution at the distal positions of haem or to off-axial positioning of distal residues. The coexistence at high pH (pH 11.0) of these two spin forms could be explained by the existence of two protein conformations, in which the crystal field splitting factor, delta, and the electron exchange energy are of the same order, allowing the presence of different configurations simultaneously. The presence of different kinds of haem is ruled out by the experiments with nitrosyl turtle Mb and turtle Mb-F showing spectra very similar to those of whale myoglobin. The pk of the acid-alkaline transition, 8.5, obtained from EPR spectra, agrees very well with results from optical absorption.

Animals↗
PubMed1985

On the interaction of small molecules with hemoglobin: orientational effects of hydration layers in protein crystal.

The spin label TEMPO does not show a binding to hemoglobin molecule in solution. In the crystal however the spin label is bound and a considerable anisotropy in the ESR spectra is observed similar to that with covalent spin labeling. Since TEMPO is a small spherical molecule the anisotropy should be a consequence of the ordering in the crystal packing observed for the hydration layers. Besides the anisotropic sites (one per asymmetric unit) an isotropic signal is apparent. The population of these sites is sensitive to the temperature and above around 30 degrees C a transition is observed of the label from the anisotropic site to the isotropic one. This is consistent with a change in the hydration structure above this temperature so that the spin label is sensitive to the reorganization of water or crystallization. Results of simulations based on the relaxation theory in liquids are compared for different hemoglobin physical states: crystal, powder and solution. It is shown that the ESR parameters obtained in the crystal are very different from those used for spectral stimulation at low temperature.

Crystallization↗
PubMedDate not supplied

Late pain-related magnetic fields and electric potentials evoked by intracutaneous electric finger stimulation.

Surface magnetic and electric recordings were used to localize the sources of late pain-related magnetic fields and electric potentials, evoked by painful intracutaneous electric finger stimulation. We find that the source of the P90m component of the evoked magnetic field lies in the finger area of the primary somatosensory cortex; the sources of the N150m and P250m are found to reside in the frontal operculum. These findings are unexpected from the evoked electric potential data, which suggest a central location for these sources. We also note that the interpretation of the electric data was confounded by the presence of an alpha-like oscillation, which overlapped many components of the evoked potential.

Brain↗
PubMedDate not supplied

A new strategy for easy volume conductor modelling in magnetocardiography.

Modelling the electromagnetic properties of the thorax in magnetocardiographic (MCG) studies is usually performed by the Boundary Element Method (BEM). Magnetic Resonance Imaging (MRI) scans are generally used as the basis for extracting the coordinates for BEM. As MRI is a (time) expensive technique and scanners have a high use demand, in this work a strategy is presented that reduces the costs and the need for additional MRI images. This strategy is based on the use of low resolution and incomplete MRI image sets of the thorax.

Body Surface Potential Mapping↗
PubMedDate not supplied

An AC biosusceptometer to study gastric emptying.

A simple AC susceptometer was developed to study the gastric emptying when test meals labeled with 10% of a harmless magnetic tracer were ingested. The instrument allows the determination of T 1/2 of the stomach emptying with good precision compared to measurements with gamma camera and 99m Tc in the test meal.

Adult↗
PubMedDate not supplied

Magnetocardiography in normal subjects and in patients with right bundle branch block.

The initial results of a magnetocardiographic study comparing normal subjects to patients with right bundle branch block due to Chagas' and other diseases is presented. A quantitative criterion to discriminate normal healthy individuals from patients was proposed based on the amplitude of R and S waves detected by the magnetocardiogram.

Adolescent↗