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Biomedical subjects

R Riera

Publications and source records attributed to R Riera.

18 recordsLinked to original sources
PubMed2005

Additive-multiplicative stochastic models of financial mean-reverting processes.

We investigate a generalized stochastic model with the property known as mean reversion, that is, the tendency to relax towards a historical reference level. Besides this property, the dynamics is driven by multiplicative and additive Wiener processes. While the former is modulated by the internal behavior of the system, the latter is purely exogenous. We focus on the stochastic dynamics of volatilities, but our model may also be suitable for other financial random variables exhibiting the mean reversion property. The generalized model contains, as particular cases, many early approaches in the literature of volatilities or, more generally, of mean-reverting financial processes. We analyze the long-time probability density function associated to the model defined through an Itô-Langevin equation. We obtain a rich spectrum of shapes for the probability function according to the model parameters. We show that additive-multiplicative processes provide realistic models to describe empirical distributions, for the whole range of data.

Journal Article↗
PubMed1999

Thrombotic pulmonary arteriopathy in polycythemia vera.

Pulmonary infarction and hemorrhage are important differential diagnoses in pulmonary coin lesions, especially in patients with underlying hematologic malignancies. We report a 58-year-old female patient suffering from polycythemia vera presenting with multiple pulmonary coin lesions. Open lung biopsy and subsequent histologic investigations showed organized pulmonary infarction and primary pulmonary thrombotic arteriopathy. Although histologic features are non-contributory in distinguishing organized thrombosis from organized thromboembolism, the clinical setting and localization of the lesions suggest that in the present case the vascular lesions are due to organized thrombosis.

Biopsy↗
PubMed1998

Abnormal pattern of tyrosine phosphorylation in unstimulated peripheral blood T lymphocytes from patients with systemic lupus erythematosus.

Previous reports have shown abnormal responses mediated via the TCR/CD3 pathway in T lymphocytes from systemic lupus erythematosus (SLE) patients. Recently, we and others have reported augmented TCR/CD3-mediated responses in lupus T cells. It is possible that the pattern of downstream biochemical signals triggered by TCR/CD3 ligation may be altered in T lymphocytes from patients with SLE, thus leading to abnormal distal cell responses. In this paper we have examined the phosphorylation of proteins on tyrosine residues in peripheral blood T lymphocytes from a group of SLE patients and controls. We found a lower frequency of constitutively tyrosine-phosphorylated 119- and 113-kDa substrates and an enhanced frequency of tyrosine-phosphorylated 66- and 25-kDa proteins in unstimulated cultures of SLE T lymphocytes, suggesting an altered pattern of tyrosine phosphorylation in T cells from patients in vivo. Additionally, the protein tyrosine phosphatase (PTP) activity of CD45 immunoprecipitates was lower in unstimulated lupus T cells and was enhanced after stimulation via the CD3 pathway in lupus but not control T lymphocytes. The present results seem to suggest abnormal regulation of in-vivo tyrosine phosphorylation in T cells from patients with SLE.

Adolescent↗
PubMed1998

[Hydatid cyst in the hepatic hilum causing a cavernous transformation in the portal vein].

Portal cavernomatosis consists in the substitution of the portal vein by many fine, twisting venules leading to the liver. This phenomenon is produced as a consequence of anterior thrombosis of the portal vein and is associated with chronic pancreatitis, cancer of the pancreas, intraabdominal sepsis and cholelithiasis. The symptomatology may be nul or present as obstructive jaundice or portal hypertension. Diagnosis is made by Doppler echography. The treatment is portal shunt when symptomatology is produced. In patients with cholelithiasis requiring surgery, the shunt is advised prior to biliary surgery since perioperative hemorrhage, if present, may be incoercible as in the case herein described. We present a 84-year-old woman with portal cavernomatosis the etiology of which was a hydatidic cyst located in the hepatic bifurcation and treated with mebendazol 10 years previously. This etiology has not been previously reported.

Aged↗
PubMed1986

Massive cerebral calcifications associated with increased renal phosphate reabsorption.

Extensive bilateral cerebral cortical calcifications were demonstrated in a young patient with a history of convulsions since the age of 4 years. Initial metabolic workup showed normal serum calcium levels, hyperphosphatemia, normal renal function, low urinary calcium excretion, and normal serum immunoreactive parathyroid hormone levels. The intravenous infusion of edetate disodium (disodium EDTA) showed a normal phosphaturic and cyclic adenosine monophosphate response, ruling out the diagnosis of pseudohypoparathyroidism. The infusion of acetazolamide produced a blunted phosphaturia with almost no change in the renal phosphorus threshold, suggesting a tubular defect that allows enhanced proximal tubular reabsorption of phosphorus. Although the exact mechanisms responsible for the localized calcifications remain obscure, we suggest that an enhanced proximal tubular reabsorption of phosphorus could be involved in the pathophysiologic basis of this abnormality.

Absorption↗
PubMed1977

Orciprenaline and fetal lung maturation in rabbits.

The palmitic and stearic acids and the palmitic/stearic ratio in fetal rabbit lungs were studied after orciprenaline administration to the mother from the 26th to the 31st day of gestation. The results were significantly higher in the treated groups than in the control group for the palmitic acid and palmitic/stearic ratio.

Animals↗
PubMed1975

The use of urokinase in acute myocardial infarction: report of two cases.

In the course of a study (now including 53 patients) on the effectiveness of urokinase in the treatment of acute coronary occlusion, coronary angiography was performed in 2 patients before and after the use of this drug. In both instances the angiograms demonstrated obstruction in the coronary-artery branches, with additional narrowing and some collateral circulation. After urokinase therapy, blood flow was restored in the areas previously obstructed. These 2 case reports are presented because they demonstrate this favorable change in coronary blood flow in association with this particular form of therapy. It is hoped that the completed urokinase study may add some information concerning the effect of thrombolysis in the management of myocardial infarction.

Acute Disease↗