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Biomedical subjects

E Rivas

Publications and source records attributed to E Rivas.

At least 37 records · Page 2Linked to original sources
PubMed1995

[Gliomatosis cerebri. Ante-mortem diagnosis].

Gliomatosis Cerebri is an unusual neoplastic entity that affects the central nervous system (C.N.S.); it consists of a marked proliferation of glial cells with variable degrees of differentiation in extensive areas of the brain and/or spinal cord. The process is primarily an infiltrative one rather than destructive. Most of the cases are diagnosed at autopsy. The authors report a new case of Gliomatosis Cerebri in a 46 year old woman, with a long clinical history--15 years--of focal seizures; and during the year prior to her admission: behavioral changes, vertigo, urinary incontinence and frequent falls. C.N.S. imaging revealed extensive involvement of the white matter of both cerebral hemispheres. Stereotactic guided biopsy showed a moderately cellular astrocytic neoplasm. A review of the medical literature led to the conclusion that the present case constitutes one of the very few examples in which the diagnosis of Gliomatosis Cerebri was achieved ante-mortem.

Biopsy↗
PubMed1994

[Resection with primary anastomosis in complicated diverticulitis. Risk analysis].

107 patients operated for complicated diverticulitis 1988 until 1993 were analysed retrospectively regarding perioperative risk of resection with primary anastomosis (n = 94). 53 of them had peridiverticulitis with stenosis (mortality 0), 41 had emergency operations (mortality 14.6%). Hartmann procedure (n = 13, mortality 7.6%) has been accepted only for the following situations: 1. ileus with secondary damage of the bowel, 2. extended diffuse peritonitis with secondary organ failure, 3. poor blood supply of the bowel, 4. the patient under immunosuppression after transplantation. Regarding these recommendations mortality rate in emergency operations (12.9%) has been lower as compared to 15 to 20% in literature. So regarding the recommendations named above resection with primary anastomosis seems to be a safe procedure in complicated diverticulitis.

Adult↗
PubMed1993

A comparative study of azithromycin and amoxycillin in paediatric patients with acute otitis media.

In this open study, a three-day regimen of azithromycin (single daily dose of 10 mg/kg) was compared with a ten-day regimen of amoxycillin paediatric suspension (30 mg/kg/day in three divided doses; children > 20 kg received 250 mg tid daily) in 154 children (aged 2-12 years) with a clinical diagnosis of acute otitis media (13 recurrent). Full clinical, bacteriological and laboratory safety assessments were performed during and after the study. Of the 77 azithromycin patients, 61 (79%) were considered cured, 15 (19%) improved and one (1%) failed, compared with 45 (58%) cured, 28 (36%) improved and four (5%) failed among the 77 amoxycillin patients. Excluding from analysis the 13 patients with recurrent otitis media, azithromycin was found to be significantly superior to amoxycillin (P = 0.003). The incidence of side-effects was low, with only two (3%) and three (4%) patients reporting adverse events with azithromycin and amoxycillin, respectively. These were gastrointestinal in nature and of mild or moderate severity, except for one case of severe diarrhoea in the amoxycillin group. No treatment-related abnormalities in the laboratory safety tests were observed, and no patients withdrew from therapy. A three-day regimen of azithromycin was therefore shown to be more effective than, and as well tolerated as, amoxycillin in the treatment of children with acute otitis media.

Acute Disease↗
PubMed1992

Partial dehydration of phosphatidylethanolamine phosphate groups during hexagonal phase formation, as seen by i.r. spectroscopy.

The gel-to-fluid and lamellar-to-HII-hexagonal thermotropic phase transitions of egg-yolk phosphatidylethanolamine have been examined by Fourier-transform infrared spectroscopy under a variety of conditions, namely excess water at pH 5.0, excess water at pH 9.5 and low hydration. The various lamellar and hexagonal phases have been characterized by X-ray diffraction. At pH 5.0, gel-fluid and lamellar-hexagonal transitions were detected at 10 and 32 degrees C respectively, in accordance with previous data. At pH 9.5, only the first of these two transitions was detected. In the partially hydrated sample a single phenomenon was observed, probably encompassing both transitions, so that, in practice, a gel-HII-hexagonal transition appears to occur. The region of the i.r. spectrum corresponding to the phospholipid phosphate group reveals that the lamellar-hexagonal, but not the gel-fluid, transition is accompanied by a weakening in the shell of hydrogen-bonded water, thus providing direct evidence that, in a pure lipid/water system, hexagonal phase formation requires partial dehydration of the phospholipid phosphate group. X-ray diffraction data support this conclusion, since, at least in the low-hydration system, the average surface area per lipid polar group decreases with the thermotropic lamellar-hexagonal transition.

Fourier Analysis↗
PubMed1992

Lipid polymorphism: a correction. The structure of the cubic phase of extinction symbol Fd-- consists of two types of disjointed reverse micelles embedded in a three-dimensional hydrocarbon matrix.

The X-ray scattering study of a cubic phase of extinction symbol Fd--, recently performed on a lipid extract (PFL) from Pseudomonas fluorescens [Mariani et al. (1990) Biochemistry 29, 6799-6810] has been extended to several other systems, all consisting of mixtures of water-miscible (MO, PC, PE, oleate) and of water-immiscible (FA, DG) lipids, plus water. In all of these systems the cubic phase was observed in the presence of excess water. Some inconsistencies observed between PFL and the other systems, the fact that in PFL one of the reflections of the cubic phase happened to coincide with the strongest reflection of the hexagonal phase, and the finding, in one of the original cubic samples of PFL kept in the cold for more than 3 years, that the intensity of one of the reflections had decreased dramatically all indicated that a nonnegligible amount of a hexagonal impurity was in fact present in the samples of PFL originally thought to contain a pure cubic phase. The intensities were corrected for that impurity and analyzed again using a pattern recognition approach based upon the axiom that the histogram of the electron density maps is invariant with respect to physical structure, when different phases are compared whose chemical composition is the same. The hexagonal phase provided the reference phase for the comparison. The moments mean value of (delta rho)n were used to compare the histograms.(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallography↗
PubMed1990

Polymorphism of a lipid extract from Pseudomonas fluorescens: structure analysis of a hexagonal phase and of a novel cubic phase of extinction symbol Fd--.

The phase diagram of the Pseudomonas fluorescens lipid extract is unusual, in the sense that it displays a cubic phase straddled by a hexagonal phase. The hexagonal phase was studied over an extended concentration range, and the reflections were phased on the assumption that the structure contains circular cylinders of known radius. The cubic phase, whose extinction symbol is Fd--, was analyzed by reference to space group No. 227 (Fd3m). The phases of the reflections were determined by using a novel pattern recognition approach, based upon the notion that the average fourth power of the electron density contrast mean value of (delta r)4 is dependent on chemical composition but not on physical structure, provided that the function delta r(r) satisfies the constraints mean value of (delta r) = 0 and mean value of (delta r)2 = 1. As a further constraint, a shape normalization is used, in the form of a Gaussian apodization of the intensities, which has the effect of normalizing the curvature of the autocorrelation function at the origin. We analyzed two cubic samples of different composition: for each of them we generated all the phase combinations compatible with the X-ray scattering data and we searched for those whose mean value of (delta r)4 best agrees with the hexagonal phase. Taking advantage of the favorable properties of the phase diagram, we carefully explored the effects of various parameters; we concluded that the chemical composition of the phases being compared must be identical, that the X-ray scattering data should not be truncated artificially, and that the apodization must be mild so that the curvature takes a value intermediate between those corresponding to the raw data of the two phases. When all these precautions were taken, mean value of (delta r)4 was found to be remarkably invariant; this conclusion is important in view of the possible usefulness of the novel technique in tackling ab initio--and at very low resolution--structural problems of more general interest. The structure of the cubic phase consists of a 3D network of rods joined tetrahedrally 4 by 4 according to a diamond lattice and of a family of quasi-spherical disjointed micelles; the core of the rods and of the micelles is polar, and the interstices are filled by the hydrocarbon chains (structure of type II). All the dimensions (diameter of rods and micelles, area per chain at the polar/apolar interface) are consistent with the chemical properties of the system.(ABSTRACT TRUNCATED AT 400 WORDS)

Lipids↗
PubMed1990

P+QA- and P+QB- charge recombinations in Rhodopseudomonas viridis chromatophores and in reaction centers reconstituted in phosphatidylcholine liposomes. Existence of two conformational states of the reaction centers and effects of pH and o-phenanthroline.

The P+QA- and P+QB- charge recombination decay kinetics were studied in reaction centers from Rhodopseudomonas viridis reconstituted in phosphatidylcholine bilayer vesicles (proteoliposomes) and in chromatophores. P represents the primary electron donor, a dimer of bacteriochlorophyll; QA and QB are the primary and secondary stable quinone electron acceptors, respectively. In agreement with recent findings for reaction centers isolated in detergent [Sebban, P., & Wraight, C.A. (1989) Biochim. Biophys. Acta 974, 54-65] the P+QA- decay kinetics were biphasic (kfast and kslow). Arrhenius plots of the kinetics were linear, in agreement with the hypothesis of a thermally activated process (probably via P+I-; I is the first electron acceptor, a bacteriopheophytin) for the P+QA- charge recombination. Similar activation free energies (delta G) for this process were found in chromatophores and in proteoliposomes. Significant pH dependences of kfast and kslow were observed in chromtophores and in proteoliposomes. In the pH range 5.5-11, the pH titration curves of kfast and kslow were interpreted in terms of the existence of three protonable groups, situated between I- and QA-, which modulate the free energy difference between P+I- and P+QA-. In proteoliposomes, a marked effect of o-phenanthroline was observed on two of the three pKs, shifting one of them by more than 2 pH units. On the basis of recent structural data, we suggest a possible interpretation for this effect, which is much smaller in Rhodobacter sphaeroides. The decay kinetics of P+QB- were also biphasic. Marked pH dependences of the rate constants and of the relative proportions of both phases were also detected for these decays. The major conclusion of this work comes from the biphasicity of the P+QB- decay kinetics. We had suggested previously that biphasicity of the P+QA- charge recombination in Rps. viridis comes from nonequilibrium between protonation states of the reaction centers due to comparable rates of the protonation events and charge recombination. This hypothesis does not hold since the P+QB- decays occur on a time scale (tau approximately 300 ms at pH 8) much longer than protonation events. This leads to the conclusion that kfast and kslow (for both P+QA- and P+QB-) are related to conformational states of the reaction centers, existing before the flash. In addition, the fast and slow decays of P+QB- are related to those measured for P+QA-, via the calculations of the QA-QB in equilibrium QAQB- apparent equilibrium constants, K2.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacterial Chromatophores↗
PubMed1990

Thickness measurements of single walled dimyristoyl phosphatidylcholine vesicles by neutron scattering.

A method of deriving by neutron scattering thicknesses of lamellae in suspensions has been applied to single-walled vesicles of dimyristoyl phosphatidylcholine. The contrast variation method, based on data obtained for a range of isotope mixtures, has been used to extract a dimension Dw related to the lipid bilayer thickness and a measure alpha of the difference of density within the lamellae. Isotope mixtures for the lipid were used to optimize the information available. Dw is compared with results from multilayer stacks of lipid layers. The thickness for the low temperature L beta, structure has been observed to be higher than for the high temperature L alpha structure. Preliminary experiments on the kinetics of the mixing of the lipid isotope species are reported, and evidence is shown that the species are not segregated for lipids either above or below the transition temperature.

Chemical Phenomena↗
PubMed1982

Detergent extraction of membrane proteins related to the action of antidiuretic hormone.

Antidiuretic hormone (ADH) induces, in the apical plasma membrane of target cells, the insertion of intramembranous particle aggregates that probably contain water channels. A mild attack of this membrane by a polyoxyethylene nonylphenyl detergent, which reversibly depressed ADH-induced water permeability, has been found to modify aggregate structure while extracting additional proteins. This simple procedure could be a valuable approach to the problem of aggregate isolation and characterization.

Animals↗
PubMed1979

Reversion of supraventricular tachyarrhythmias by means of atrial stimulation.

Thirteen patients with different forms of supraventricular tachyarrhythmia were treated by means of right atrial pacing. Reversion of arrhythmia was obtained in nine out of ten patients with atrial tachycardia or flutter. The remaining three patients, with atrial fibrillation, did not respond to the procedure. The effective pacing rate in converting arrhythmia ranged from 110 to 2400/min, however in five cases it was lower than the atrial rate. The duration of pacing at an effective rate ranged from 20 seconds to 5 minutes in 5 cases, while in the remaining patients it lasted 10 minutes. In two patients the original arrhythmia was converted to atrial fibrillation during stimulation, but in one it disappeared with pacing at 110/min, and in the other, reversion to sinus rhythm occurred spontaneously 4 hours later. No complications were observed. It is concluded that atrial pacing may be useful aid to treat paroxysmal atrial tachycardia or flutter, and can be considered as an alternative procedure whenever there is no response to customary medical treatment or when transthoracic direct current cardioversion is potentially dangerous.

Adult↗
PubMed1976

Water permeability and lipid composition of toad urinary bladder: the influence of temperature.

The water diffusional permeability, its activation energy and the lipid composition were studied in urinary bladders from toads adapted to different temperatures. It was observed that the unidirectional water flux greatly depends on the temperature at which the experiments are performed. This dependence is greater in the animals adapted to higher temperatures. Toads adapted to cold show strong reduction in the activation energy for water diffusion permeability (from 11.4+/-1.9 kcal-mol-1 to 4.4+/-1.1kcal-mol-1) and an increase of 30% in the amount of total lipids from bladder epithelial cells. There were no significant changes in the phospholipid/cholesterol ratio, composition of the parafinic chains or protein concentration between toads adapted to both temperatures. The possibility that water translocates through the mucosal border of the toad bladder by partitioning in the polar zone and diffusioning between the hydrocarbon chains of the membrane lipids and that cold adaptation would induce a stronger "packing" of lipids in the membrane is discussed.

Acclimatization↗