Search PubMed⌕ Search

Biomedical subjects

R Sánchez

Publications and source records attributed to R Sánchez.

At least 19 recordsLinked to original sources
PubMed2006

Enhanced production of runaway electrons during a disruptive termination of discharges heated with lower hybrid power in the Frascati Tokamak Upgrade.

We report on the observation of a large production of runaway electrons during a disruptive termination of discharges heated with lower-hybrid waves at the Frascati Tokamak Upgrade. The runaway current plateaus, which can carry up to 80% of the predisruptive current, are observed more often than in normal Ohmic disruptions. The largest runaway currents correspond to the slowest plasma current decay rates. This trend is opposite to what is observed in most tokamaks. We attribute this anomalous behavior to the acceleration of the preexistent wave-resonant suprathermal electrons during the disruption decay phase. These results could be relevant for the operation of the ITER tokamak whenever a sizeable amount of lower-hybrid power is made available.

Journal Article↗
PubMed2006

Renormalization of tracer turbulence leading to fractional differential equations.

For many years quasilinear renormalization has been applied to numerous problems in turbulent transport. This scheme relies on the localization hypothesis to derive a linear transport equation from a simplified stochastic description of the underlying microscopic dynamics. However, use of the localization hypothesis narrows the range of transport behaviors that can be captured by the renormalized equations. In this paper, we construct a renormalization procedure that manages to avoid the localization hypothesis completely and produces renormalized transport equations, expressed in terms of fractional differential operators, that exhibit much more of the transport phenomenology observed in nature. This technique provides a first step toward establishing a rigorous link between the microscopic physics of turbulence and the fractional transport models proposed phenomenologically for a wide variety of turbulent systems such as neutral fluids or plasmas.

Journal Article↗
PubMed2006

Nuclear charge radii of 9,11Li: the influence of halo neutrons.

The nuclear charge radius of 11Li has been determined for the first time by high-precision laser spectroscopy. On-line measurements at TRIUMF-ISAC yielded a 7Li-11Li isotope shift (IS) of 25 101.23(13) MHz for the Doppler-free [FORMULA: SEE TEXT]transition. IS accuracy for all other bound Li isotopes was also improved. Differences from calculated mass-based IS yield values for change in charge radius along the isotope chain. The charge radius decreases monotonically from 6Li to 9Li, and then increases from 2.217(35) to 2.467(37) fm for 11Li. This is compared to various models, and it is found that a combination of halo neutron correlation and intrinsic core excitation best reproduces the experimental results.

Journal Article↗
PubMed2006

A new technique to evaluate the ability of cryoprotectors to prevent premature acrosome reaction in human spermatozoa.

Acrosome reaction (AR) induced by low temperature has been used to evaluate sperm function; it correlates adequately with the fertilization percentages in vitro. In this study, the technique of AR induction by low temperature was used to evaluate the effect in the protection of the acrosome by cryopreservatives normally used in human semen cryopreservation. Donor sperm selected by use of the migration sedimentation technique was incubated in human tubal fluid medium, added to dimethyl sulphoxide 1 m, ethylene glycol 0.75 m, glycerol 1 m, incubated at 4 degrees C and 20 degrees C (as a control) for 18 h, and then for 3 h at 37 degrees C in a cell incubator. The AR was evaluated by triple stain in 100 viable spermatozoa. The effect of cryopreservatives on acrosome preservation in samples incubated for 18 h at 4 degrees C was as follows: 78% intact acrosome for glycerol, 77.8% intact acrosome for dimethyl sulphoxide and 96.2% intact acrosome for ethylene glycol (P < 0.0025 compared with glycerol and dimethyl-sulphoxide). The sperm samples incubated with cryopreservatives for 18 h at 20 degrees C did not show an increase in the percentage of AR in samples incubated with glycerol and ethylene glycol, while a significant variation was observed in the sample incubated with dimethyl sulphoxide (P < 0.001). Additional incubation for 3 h at 37 degrees C significantly increased the AR only in the sample incubated with glycerol (P < 0.001). Acrosome preservation is essential in the fertilization process and the evaluation of acrosome reaction induction by low temperature test was satisfactory. This test proves that ethylene glycol presents a greater protective effect on the acrosome preservation of human spermatozoa.

Acrosome Reaction↗
PubMed2006

[Cerebrospinal fluid drainage in endovascular repair of thoracic aortic lesions: preliminary report of experience with 5 patients].

Endovascular repair of thoracic or thoracoabdominal aortic lesions as an alternative to open surgery, to avoid the high complication and mortality rates associated with the conventional approach, does not eliminate the risk of postoperative paraplegia. We report on a series of 5 patients with different thoracic aortic lesions who underwent endovascular stent-graft repair procedures. We describe measures to drain cerebrospinal fluid to prevent ischemic spinal cord injury. We also review the anesthetic management of patients undergoing this type of surgery.

Aged↗
PubMed2006

[Treatment of acute lithium intoxication with high-flux haemodialysis membranes].

Lithium carbonate is commonly prescribed for the treatment of bipolar (manic-depressive) disorders. However, because of its narrow therapeutic index an excessive elevation of serum lithium concentration, either during chronic maintenance therapy or after an acute overdose, can result in serious toxicity. In addition to supportive care, the established treatment of severe lithium toxicity is haemodialysis. Conventional haemodialysis can reduce serum lithium rapidly, but post-dialysis rebound elevations with recurrent toxicity have been documented in old publications. High-flux membranes should be capable of removing more lithium per hour of haemodialysis, but published values are not available. We report here three patients with acute lithium intoxication who were treated successfully with bicarbonate and high-flux haemodialysis membranes. Our patients presented with a severe degree of intoxication, based on the amount of drug ingested, the initial serum lithium level, the severity of neurologic symptoms and systemic manifestations. Two patients developed acute renal failure probably as a result of volume depletion since it was rapidly reversible by haemodialysis and infusion therapy. In addition, consecutive haemodialysis sessions and improvement of renal function allowed a rapid decrease in serum lithium levels without haemodynamic instability or rebound elevations in lithium concentration. The effectiveness of the procedure in these cases can be attributed to the use of bicarbonate dialysate and high-efficiency dialysers. This is the first report describing the effect of high-efficiency dialysers on lithium pharmacokinetic. Using this technique the elimination rate of lithium was found to be greater than previously reported with haemodialysis.

Acute Disease↗
PubMed2005

Fluid limit of nonintegrable continuous-time random walks in terms of fractional differential equations.

The fluid limit of a recently introduced family of nonintegrable (nonlinear) continuous-time random walks is derived in terms of fractional differential equations. In this limit, it is shown that the formalism allows for the modeling of the interaction between multiple transport mechanisms with not only disparate spatial scales but also different temporal scales. For this reason, the resulting fluid equations may find application in the study of a large number of nonlinear multiscale transport problems, ranging from the study of self-organized criticality to the modeling of turbulent transport in fluids and plasmas.

Journal Article↗
PubMed2005

Pyrrolidon carboxypeptidase activities in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-ovary axes of rats with mammary gland cancer induced by N-methyl nitrosourea.

Pyrrolidon carboxypeptidase is an omega-peptidase that hydrolyses N-terminal pyroglutamyl residues from biologically active peptides such as gonadotropin-releasing and thyrotrophin-releasing hormones. We previously described a decrease in both rat and human pyrrolidon carboxypeptidase activity with breast cancer, suggesting that gonadotropin-releasing hormone may be an important local intracrine, autocrine and/or paracrine hormonal factor in the pathogenesis of breast cancer while playing a role in the tumoral process. However, the other susceptible substrate of pyrrolidon carboxypeptidase, thyrotrophin-releasing hormone, may also be modified with breast cancer, supporting an association between breast cancer and thyroid disorders. The present work analyses soluble and membrane-bound pyrrolidon carboxypeptidase activities in the hypothalamus-pituitary-thyroid and hypothalamus-pituitary-ovary axes in N-methyl nitrosourea-induced breast cancer in rats. Our aim was to determine the possible relationship between gonadotropin-releasing hormone and thyrotrophin-releasing hormone regulation through pyrrolidon carboxypeptidase activity. We propose that pyrrolidon carboxypeptidase activity dysregulation at various local and systemic levels may participate in the initiation, promotion and progression of breast cancer induced in rat by N-methyl nitrosourea through the increase in gonadotropin-releasing hormone. Since pyrrolidon carboxypeptidase activity also acts on thyrotrophin-releasing hormone, the dysregulation of this enzyme's activity could indirectly affect hypothalamus-pituitary-thyroid axis function, and thus potentially represent a link between the diseases of thyroid and breast cancer.

Animals↗
PubMed2005

Ambulatory blood pressure monitoring in patients with hyperthyroidism before and after control of thyroid function.

BACKGROUND AND OBJECTIVE: Thyroid hormones have pronounced effects on the cardiovascular system. Thyrotoxicosis affects blood pressure (BP), modifying both diastolic (DBP) and systolic (SBP) pressures. There are no studies examining BP with ambulatory blood pressure monitoring (ABPM) in hyperthyroidism before and after control of thyroid function. Our aims were (1) to analyse ABPM in a group of normotensive hyperthyroid patients before and after normalizing circulating thyroid hormones and (2) to compare these results with those obtained in a group of euthyroid subjects. PATIENTS AND MEASUREMENTS: We studied 20 normotensive hyperthyroid subjects [18 women; age (mean +/- SEM) 49.0 +/- 3.0 years] and 15 healthy subjects. Patients were evaluated by ABPM over 24 h, at diagnosis and after therapy (n = 18). RESULTS: The average 24-h, daytime and night-time SBP was significantly greater in hyperthyroid patients than in controls with no significant differences in DBP. Circadian BP rhythm, estimated by the difference between mean values of SBP, DBP and mean BP during daytime and night-time, was unchanged. The average 24-h and daytime SBP significantly decreased after normalizing thyroid function in the 18 hyperthyroid evaluated patients. Daytime SBP and DBP were higher than night-time values both before and after control of thyroid function. However, no differences in circadian BP rhythm were observed. CONCLUSIONS: Normotensive hyperthyroid patients exhibit higher ambulatory SBP throughout 24 h than normotensive euthyroid subjects. Control of hyperthyroidism decreases ambulatory SBP values. Mean nocturnal fall in BP is comparable in normotensive hyperthyroid patients and control subjects.

Antithyroid Agents↗
PubMed2005

Naevus lipomatosus cutaneous superficialis on the nose.

Naevus lipomatosus cutaneous superficialis (NLCS) is an uncommon hamartomatous lesion with an exceptional presentation on the face. We report the case of an elderly patient who presented with a classic type of NLCS on the right nasal orifice. This patient was taking inhaled steroids for his allergic rhinitis during 35 years.

Administration, Inhalation↗
PubMed2005

[Tubulointerstitial nephritis associated with treatment with selective Cox-2 inhibitors, celecoxib and rofecoxib].

The nephrotoxic effect of nonselective nonsteroidal anti-inflamatory drugs (NSAIDS) has been widely described. The main benefit of the Cox-2 inhibitors in relation to the NSAIDS is the production of a very similar analgesic effect, but with fewer gastrointestinal side effects. However, their effects on renal function are little known as yet and their long-term safety is still pending definition. The use of selective Cox-2 inhibitors as anti-inflamatory analgesic is becoming more and more common in our environment. We report two cases of tubulointersticial nephritis confirmed by renal biopsy, associated with administration of the two Cox-2 inhibitors currently available on the market, celecoxib and rofecoxib. In both cases, we were talking about elderly women, with deterioration of the general condition and acute renal failure. In the former case, renal biopsy showed an acute tubulo-intersticial nephritis (TIN) so highly "variegated" in its histologic expression. In the second case, was associated with strong indications of chronicity. Treatment with steroid was initiated in both patients and improvement of renal function was observed.

Aged↗
PubMed2005

[Role of peritoneal drainage in very low birth weight with enterocolitis].

UNLABELLED: Peritoneal drainage (PD) has been proposed as a temporizing procedure for perforated necrotizing enterocolitis (NEC) in very low birth weight neonates. This operation was designed for patients considered too unstable to undergo laparotomy (LAP). Since the introduction of PD some investigators have suggested that it may serve as a definitive therapy. The aim of our study is to determine the efficacy of PD for the stabilization of patients with complicated NEC and its utility as a definitive surgical treatment. METHODS: We review the clinical records from all the patients treated in our unit because of NEC that required surgical therapy. We analyze the mean blood pressure, cardiac and respiratory rate, inspired oxygen concentration, mean airway pressure, diuresis, and arterial blood gases measured 6 and 12 hours after the initial surgical treatment. We divide patients in two different groups according to the initial surgical procedure, peritoneal drainage (PD) or laparotomy group (LAP). Data is shown as media +/- standard deviation, statistical analyses were performed using analysis of variance (ANOVA) for repeated measures and Mann-Withney test. RESULTS: From January 1997 to January 2001 we treated 13 patients with necrotizing enterocolitis that required surgical treatment. Among this group 6 patients were managed initially with PD and 7 with LAP. The gestational age media was 29.07 +/- 3.81 weeks and the birth weight mean 1199.76 +/- 521 gr., without any significant differences between the two groups DP and LAP. All patients improved haemodynamically and respiratory 6 and 12 hours after the surgical treatment. Nevertheless, the mean blood pressure improved even more in the DP group (p<0.005). The DP group showed an improvement in all parameters 6 hours after the drainage was placed, but this effect wasn't maintained for the next 12 hours onwards. From the 12 hours after PD all patients suffered a steady worsening that required further surgical procedures. The overall mortality was 3 patients (23%), without differences between the two groups. The surgical techniques performed (bowel resection, diversion) were similar for both groups. DISCUSSION: DP allows the stabilization for very critically ill patients with complicated NEC. However, this stabilization is temporary. This improvement lasts for a few hours providing a better status for the definitive surgical treatment for the perforated NEC. In our experience DP could not be considered as a definitive surgical treatment.

Child, Preschool↗