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J A Varela

Publications and source records attributed to J A Varela.

15 recordsLinked to original sources
PubMed2006

Breath-holding test in subjects with near-fatal asthma. A new index for dyspnea perception.

RATIONALE: Identification of asthmatic subjects with low perception of dyspnea (POD) that are at higher risk of hospitalization, near-fatal and fatal asthma could improve their management. OBJECTIVE: Create a simple procedure that facilitate the recognition of low POD. METHODS: We enrolled near fatal asthma (NFA) subjects and a wide spectrum of non-NFA subjects. Each subject was asked to stop breathing at end-expiration. Dyspnea was assesssed by a modified Borg scale. To design the new index, we combined the Borg score at the end of the voluntary breath-holding maneuver with the airway limitation. The equation was as follows: FEV(1)/FVC%/(breath-holding time in seconds/final Borg score minus basal Borg score). RESULTS: Eleven NFA subjects (4 females) aged 21-73yr and 55 non-NFA (14 severe, 18 moderate and 23 mild asthmatic subjects) completed the study. The threshold value of the index that could predict POD is <12. The mean (+/-sd) of the new index perception was significantly lower in NFA group (n=11; 5.21+/-3.59; vs. n=55; 13.67+/-11.08; P=0.006). This threshold value had 100% sensitivity and it best discriminated between mild and NFA groups. The negative likelihood ratio (when the index > or = 12) was zero. A result > or = 12 represented an almost null probability of poor POD. CONCLUSION: The breath-holding test is simple and rapid. Its negative likelihood ratio was zero. Accordingly, a test result of 12 or greater might exclude the probability of poor perception of dyspnea in subjects with stable asthma.

Adult↗
PubMed2004

[Prevalence of the HIV infection in patients seen at specialized diagnosis centers in 9 cities in Spain from 1992 to 2001].

OBJECTIVE: To describe the prevalence of HIV infection in persons tested between 1992 and 2001. DESIGN: Descriptive, cross-sectional epidemiological study. SETTING: 10 ambulatory centers specialized in diagnosing HIV, located in 9 cities in Spain. PARTICIPANTS: 53,183 persons older than 12 years, tested for the first time for HIV. MAIN MEASURES: Number of persons tested per year, number of persons diagnosed as seropositive for HIV according to sex, age group and category of exposure. RESULTS: The number of persons tested increased from 4401 in 1992 to 6407 in 2001. Approximately half reported heterosexual risk exposure/exposure through high-risk heterosexual behaviors, excluding prostitution. Intravenous drug users (IVDU) increased from 15.3% in 1992-1993 to 1.4% in 2000-2001, and women prostitutes/female sex workers increased from 6.7% to 25.1%. A total of 2898 persons were diagnosed as having HIV infection; 78% of them were men. The number of diagnoses decreased from a high of 1058 in 1992-1993 to 304 in 2000-2001, and this trend was seen for all categories of exposure except female prostitutes and men with heterosexual risk factors. The prevalence decreased from 14% in 1992 to 2% in 2001. There were decreases in all categories of exposure, especially during the first years of the study, with a tendency to level off. In 2001 the prevalence figures were 23.8% for IVDU, 7.9% for homosexual men and women, 0.8% for female sex workers and 1% for other heterosexual men and women. CONCLUSIONS: The specialized diagnostic centers play an important role in diagnosing HIV, and this service complements primary care services. Greater efforts are needed in the prevention of HIV infection.

Adult↗
PubMed2004

Sentinel surveillance of HIV infection in HIV test clinics, Spain 1992-2002.

HIV infection in Spain was monitored in persons undergoing voluntary HIV testing in ten sentinel clinics between 1992 and 2002. Only patients on their first visit were considered for inclusion, and their numbers rose from 4426 in 1992 to 6649 in 2002. Most of them recognised their risk exposure as heterosexual. The proportion of injecting drug users decreased from 19% to 2% of the study population, and the proportion of female sex workers increased from 6% to 26%. The number of patients diagnosed with HIV infection declined from 604 in 1992 to 153 in 2002, and HIV prevalence fell from 13.6% to 2.3% in the same period. In all risk exposure categories, a decrease in HIV prevalence was observed, more pronounced during the first few years and stabilised in the later years. In 2002, the highest HIV prevalence was found in injecting drug users (IDUs) (14.2%), homo/bisexual men (7.5%) and individuals who had an HIV infected heterosexual partner (10.2%).

Adult↗
PubMed2002

[HIV prevalence among homosexual and bisexual men in Spain, 1992-2000].

BACKGROUND: Our purpose was to describe the time trend in HIV seroprevalence among homo/ bisexual men. SUBJECTS AND METHOD: We analyzed 9,383 homo/ bisexual men who had a first voluntary test for HIV in 10 Spanish clinics from 1992 to 2000. RESULTS: HIV prevalence decreased from 20.3% in 1992 to 8.4% in 2000. In the multivariate analysis this decline appeared independently associated with the testing year and the birth cohort. CONCLUSIONS: New generations of voluntarily tested homo/bisexual men are less infected by HIV, but it is yet necessary to intensify the prevention programs.

Adolescent↗
PubMed2002

Synthesis of SnO2 nanoribbons by a carbothermal reduction process.

This communication describes, for the first time, the growth of SnO2 nanoribbons by a controlled carbothermal reduction process. An analysis of the transmission electron microscopy image revealed that these nanoribbons have a well-defined shape, with a typical width in the range of 70-300 nm. In general, the nanostructured ribbons were more than 100 microns in length. The results reported here support the hypothesis that this ribbon-like nanostructured material grows by a vapor-solid process. This study introduces two hypotheses to explain the SnO2 nanoribbon growth process.

Carbon↗
PubMed2001

Regiocontrolled one-step synthesis of 3,3'-disubstituted 2,2'-bipyridine ligands by cobalt(I)-catalyzed cyclotrimerization.

A one-step, regioselective synthesis of annelated symmetric and asymmetric 3,3'-disubstituted 2,2'-bipyridines by cobalt(I)-catalyzed [2+2+2] cycloadditions between 5-hexynenitrile and 1,3-diynes is described. In the symmetric case, the total regioselectivity of the first cycloaddition is ensured electronically by the conjugation of the triple bonds, and for aminomethylated diynes that of the second is ensured by the cobalt coordinating to the aminomethyl rather than to the hexynenitrile nitrogen. In the asymmetric case, the first cycloaddition took place chemoselectively, which in the case of bis(trimethylsilyl)-1,3,5-hexatriyne (viewed as a 1,3-diyne) is explained by semiempirical calculation of LUMO coefficients. The copper(I) complex of 6b, constituting the first reported complex of the form ML2 (L is a symmetric 3,3'-disubstituted 2,2'-bipyridine), has been prepared. It had UV/Vis and NMR spectra reflecting the 3-substituent-induced mutual torsion of the bipyridine rings in the cis conformation, as was confirmed by x-ray diffractometric determination. The bipyridine 6c forms the dinuclear complex [Cu2(6c)2(CH3CN)2]2+ in the solid state.

2,2'-Dipyridyl↗
PubMed2001

Remote C-H activation of phenyl-substituted alkenes by BH(3).THF: mechanism and applications.

[reaction: see text] The hydroboration of tetrasubstituted alkenes and, in particular, bicyclic alkenes with BH(3).THF at 50 degrees C provides, via a highly stereoselective 1,2-rearrangement and a remote C-H activation, a diol in which the relative stereochemistry of three centers has been controlled. A mechanistic study provides general rules for remote C-H activation and leads to new synthetic applications.

Journal Article↗
PubMed2001

Herpes simplex virus type 2 seroepidemiology in Spain: prevalence and seroconversion rate among sexually transmitted disease clinic attendees.

BACKGROUND: Only limited data on the seroprevalence of herpes simplex virus type 2 (HSV-2) are available from European countries. Until recently, serologic tests for HSV-2 serotyping have been hampered by cross-reactivity to type-common antigens. The present study aims at providing data on the prevalence of HSV-2 infection in a group of STD clinic attendees using a reliable type-specific immunoassay. GOAL: To evaluate the seroprevalence of HSV-2 and the accumulated incidence of clinical genital herpes infection in a sample of Spanish sexually transmitted disease (STD) clinic attendees. STUDY DESIGN: The study consisted of two parts. First, a cross-sectional study of HSV-2 seroprevalence was conducted in patients with STDs. Second, a prospective cohort study was undertaken to evaluate the accumulated incidence of infection by HSV-2 and of clinical episodes of genital herpes in HSV-2-negative patients included in the first study during a follow-up period of 6 to 18 months. RESULTS: Of the 374 patients (129 men, 245 women) studied, 25% were seropositive for HSV-2 (12% of men, 30% of women). Antibodies to HSV-2 were related to female gender (odds ratio, 2.7; P < 0.001) and to the number of sexual partners (odds ratio, 4.1; P < 0.001). Fifty-two percent of patients (145 of 281 patients) who were initially seronegative returned to the clinic for a second serologic testing, of whom 1% (2 of 145 patients) had seroconverted. None of the patients developed genital herpes during the follow-up period. CONCLUSION: The relatively high seroprevalence (25%) and the low rate (4%) of HSV-2 previously reported in the general population in Spain suggest that the virus circulation may be restricted to certain risk groups. Therefore, future healthcare measures may target specific groups, such as patients with STDs.

Antibodies, Viral↗
PubMed1999

Differential depression at excitatory and inhibitory synapses in visual cortex.

The function of cortical circuits depends critically on the balance between excitation and inhibition. This balance reflects not only the relative numbers of excitatory and inhibitory synapses but also their relative strengths. Recent studies of excitatory synapses in visual and somatosensory cortices have emphasized that synaptic strength is not a fixed quantity but is a dynamic variable that reflects recent presynaptic activity. Here, we compare the dynamics of synaptic transmission at excitatory and inhibitory synapses onto visual cortical pyramidal neurons. We find that inhibitory synapses show less overall depression than excitatory synapses and that the kinetics of recovery from depression also differ between the two classes of synapse. When excitatory and inhibitory synapses are stimulated concurrently, this differential depression produces a time- and frequency-dependent shift in the reversal potential of the composite postsynaptic current. These results indicate that the balance between excitation and inhibition can change dynamically as a function of activity.

Analysis of Variance↗
PubMed1997

A quantitative description of short-term plasticity at excitatory synapses in layer 2/3 of rat primary visual cortex.

Cortical synapses exhibit several forms of short-term plasticity, but the contribution of this plasticity to visual response dynamics is unknown. In part, this is because the simple patterns of stimulation used to probe plasticity in vitro do not correspond to patterns of activity that occur in vivo. We have developed a method of quantitatively characterizing short-term plasticity at cortical synapses that permits prediction of responses to arbitrary patterns of stimulation. Synaptic responses were recorded intracellularly as EPSCs and extracellularly as local field potentials in layer 2/3 of rat primary visual cortical slices during stimulation of layer 4 with trains of electrical stimuli containing random mixtures of frequencies. Responses exhibited complex dynamics that were well described by a simple three-component model consisting of facilitation and two forms of depression, a stronger form that decayed exponentially with a time constant of several hundred milliseconds and a weaker, but more persistent, form that decayed with a time constant of several seconds. Parameters obtained from fits to one train were used to predict accurately responses to other random and constant frequency trains. Control experiments revealed that depression was not caused by a decrease in the effectiveness of extracellular stimulation or by a buildup of inhibition. Pharmacological manipulations of transmitter release and postsynaptic sensitivity suggested that both forms of depression are mediated presynaptically. These results indicate that firing evoked by visual stimuli is likely to cause significant depression at cortical synapses. Hence synaptic depression may be an important determinant of the temporal features of visual cortical responses.

Animals↗
PubMed1997

Synaptic depression and cortical gain control.

Cortical neurons receive synaptic inputs from thousands of afferents that fire action potentials at rates ranging from less than 1 hertz to more than 200 hertz. Both the number of afferents and their large dynamic range can mask changes in the spatial and temporal pattern of synaptic activity, limiting the ability of a cortical neuron to respond to its inputs. Modeling work based on experimental measurements indicates that short-term depression of intracortical synapses provides a dynamic gain-control mechanism that allows equal percentage rate changes on rapidly and slowly firing afferents to produce equal postsynaptic responses. Unlike inhibitory and adaptive mechanisms that reduce responsiveness to all inputs, synaptic depression is input-specific, leading to a dramatic increase in the sensitivity of a neuron to subtle changes in the firing patterns of its afferents.

Action Potentials↗
PubMed1984

[Standardization of a microtechnic for passive hemagglutination to detect antibodies against infectious bovine rhinotracheitis].

A micromethod for passive Hemagglutination is described for the detection of IBR antibodies in serum samples of nine herds. The samples correspond to different zones of the province Buenos Aires. In animals without clinical signs the proportion of positives was 43.60%; in herds with signs consistent with the disease, this value attained 66.4% positivity (Tables 1 and 2). The feasibility of this method is discussed. Some variants introduced into the original technique are described.

Animals↗
PubMedDate not supplied

[Incidental carcinoma of the kidney with renal vein thrombosis].

Incidental carcinoma of kidney is an increasingly common pathology as a result of a wider use of high resolution diagnostic methods. The special characteristics of these tumors, usually small and in a low grade or stage, make conservative surgery to be considered as a valid therapeutical option. An incidental carcinoma of kidney with tumoral thrombosis of the renal vein undetected in the pre-surgical study, circumstance which allows to emphasize the malignant potential of these tumors is presented here. Based on this, we believe that a meticulous evaluation of the renal vein condition should be made, in patients considered as possible candidates for conservative surgery. In this sense, selective renal phebography and magnetic resonance could be considered explorative means that play an important role in the introduction of renal preservation surgery, if future studies show that its use allows an early detection of the tumoral condition of renal vein.

Adenocarcinoma↗