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Biomedical subjects

F Mas

Publications and source records attributed to F Mas.

10 recordsLinked to original sources
PubMed2001

Voltammetric analysis of heterogeneity in metal ion binding by humics.

The complexation of Cd, Pb, and Cu by fulvic acids at a fixed pH and ionic strength is studied by means of different voltammetric techniques at any metal-to-ligand ratio. When using Reverse Pulse Polarography (RPP) the complex species are electrochemically labile and not subject to significant electrodic adsorption. RPP titrations of fulvic acid with metal ions are interpreted on the basis of a recently proposed analytical expression for limiting currents valid for fully labile heterogeneous complexation. The voltammetric data are transformed into the corresponding binding curve, i.e., the fraction of occupied sites vs free metal concentration. Finally, the competition between metal ions and protons in their interaction with the fulvic binding sites as well as the concomitant polyelectrolytic effects are analyzed in terms of the NICCA-Donnan model. The results show that voltammetric techniques can be applied to the studies of heterogeneous complex systems in a broad range of metal-to-ligand ratios.

Benzopyrans↗
PubMed1998

Physical constraints in the synthesis of glycogen that influence its structural homogeneity: a two-dimensional approach.

Several aspects of glycogen optimization as an efficient fuel storage molecule have been studied in previous works: the chain length and the branching degree. These results demonstrated that the values of these variables in the cellular molecule are those that optimize the structure-function relationship. In the present work we show that structural homogeneity of the glycogen molecule is also an optimized variable that plays an important role in its metabolic function. This problem was studied by means of a two-dimensional approach, which allowed us to simplify the very complicated structure of glycogen. Our results demonstrate that there is a molecular size limit that guarantees the structural homogeneity, beyond which the structure of the molecule degenerates, as many chains do not grow. This strongly suggests that such a size limit is precisely what the molecule possesses in the cell.

Biophysical Phenomena↗
PubMed1993

Quantitative electroencephalographic subtyping of obsessive-compulsive disorder.

Current neuropsychological, electrophysiological, and other imaging data strongly suggest the existence of a neurobiological basis for obsessive-compulsive disorder (OCD), which was long considered to be exclusively of psychogenic origin. The positive response of some OCD patients to neurosurgery, as well as the efficacy of agents that selectively block serotonin reuptake, lends further support to a biological involvement. However, a survey of the treatment literature reveals that only 45-62% of OCD patients improve with these specific medications. In a pilot study using a quantitative electroencephalographic (QEEG) method known as neurometrics, in which QEEG data from OCD patients were compared statistically with those from an age-appropriate normative population, we previously reported the existence of two subtypes of OCD patients within a clinically homogeneous group of patients who met DSM-III-R criteria for OCD. Following pharmacological treatment, a clear relationship was found between treatment response and neurometric cluster membership. In this study, we have expanded the OCD population, adding patients from a second site, and have replicated the existence of two clusters of patients in an enlarged, statistically more robust population. Cluster 1 was characterized by excess relative power in theta, especially in the frontal and frontotemporal regions; cluster 2 was characterized by increased relative power in alpha. Further, 80.0% of the members of cluster 1 were found to be nonresponders to drug treatment, while 82.4% of the members of cluster 2 were found to be treatment responders.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1993

Treatment resistant depression in a case of minor head injury: an electrophysiological hypothesis.

A relatively small but highly concordant literature suggests that manic depressive psychoses may include familial as well as nonfamilial subtypes. The latter, which appears to be an acquired form, follows brain injury of various etiology, displays EEG abnormalities and tends to respond well to anticonvulsant therapy. In this study we postulate an extension of this dichotomy to a larger spectrum of affective disorder, including milder but "treatment resistant" forms often associated with a high degree of dysfunction. Central to this hypothesis is information gathered from the longitudinal study of a well defined case in which precise clinical and electrophysiological data have been obtained at critical junctures. This data also leads us to suggest the existence of a latent vulnerability to psychosocial stressors in a subgroup of minor head injured patients. Once triggered, the resulting psychopathological state may be clinically indistinguishable from similar but etiologically distinct conditions. However, they respond poorly, if at all, to the treatments usually effective for mood disorders, often causing puzzlement and frustration among clinicians as well as mounting hopelessness in patients. This organic mood disorder subtype, which can be described as "neuro-sensitization mood disorder," may be identified by combining a thorough history, including perinatal events and putative brain injury, with electrophysiological data consisting of quantitative EEG (QEEG) in association with evoked potentials. In cases with positive findings, anticonvulsants such as carbamazepine, clonazepam and valproic acid can be a treatment of choice.

Adult↗
PubMed1990

A theoretical approach to describe monolayer-liposome lipid interaction.

It is known from several studies on the interaction between membrane models that mechanisms such as fusion or lipid exchange can play an important role in the process of internalization by cells of lipid vesicles and also in the physical stability of liposomes. In this paper it is shown that a simple monolayer-liposome model can be used to simulate experimentally observed interactions between lipid vesicles and cell surfaces. From experimental data, a simple theoretical model is formulated to interpret the variation with time of surface pressure as a function of liposome concentration. The congruency of the physico-chemical hypothesis and its validity are studied and correlated with results from experimental systems.

Calcium↗
PubMedDate not supplied

Multisyringe flow injection analysis of stable and radioactive strontium in samples of environmental interest.

A multisyringe flow injection (MSFIA) method for the determination of stable and radioactive strontium, using a solid phase resin (Sr-Resin), has been developed. Strontium concentrations are determined by atomic emission spectroscopy and by a low background proportional counter. The method has been applied to different samples (water, milk and soil) of environmental interest. The LLD of the stable and radioactive Sr were 10 microg/l and 0.01 Bq, respectively. The standard deviation of the separation procedure is 2% (n=10).

Animals↗
PubMedDate not supplied

[A descriptive analysis of 81 patients referred to a neurology clinic for syncope].

INTRODUCTION: Syncope is a frequent medical problem which is disabling, potentially serious and difficult to treat. Although patients with syncope are often sent to Neurology clinics for investigation we have found no published report analysing this. OBJECTIVE: To analyze the aetiology of the cases of syncope referred to a Neurology Clinic and also the diagnostic usefulness of the investigations requested, particularly those of neuroimaging, electroencephalogram (EEG) and vascular studies. PATIENTS AND METHODS: A prospective study of the patients referred for syncope to a Neurology Outpatient Clinic. The patients were classified into three groups: 1. Epileptic seizure, if the clinical history suggested the possibility of a convulsion rather than a syncope. 2. Syncope of neurological origin, when the syncope is due to a neurological disorder. 3. Non neurological cause of the syncope when the syncope was not due to neurological disease. RESULTS: We included 81 patients, who made up 4.3% of the patients seen in the Neurology Clinic. Epileptic seizures made up 10% and the other 90% were due to non neurological causes. There was 0% usefulness of neuroimaging investigations and vascular studies. The EEG showed epileptiform changes in 9% of the patients, with non neurological syncopes. CONCLUSION: In patients with syncope neurological investigations are not very useful.

Adolescent↗