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Biomedical subjects

M J Bravo

Publications and source records attributed to M J Bravo.

At least 19 recordsLinked to original sources
PubMed2001

Differences in severity of heroin dependence by route of administration: the importance of length of heroin use.

To explore differences in the severity of heroin dependence by route of administration, we interviewed 909 heroin users in three Spanish cities. Dependence was measured with the severity dependence scale (SDS). No major differences in the severity of heroin dependence were detected among users with 5 or more years of heroin use (long-term users), but differences were found among newer users (SDS mean scores, 7.3 in heroin injectors; 7.9 in smokers and 4.6 in sniffers; P = 0.006), especially those with fewer than 3 years of use. Similar differences by route of administration were found when frequency of heroin use (days/month) was considered rather than severity of dependence. However, in the latter case major differences were also found among long-term users. These findings suggest that the route of administration probably influences the rate of progression to dependence but has little influence on the long-run level of dependence. They also help explain some aspects of the transition between routes of heroin administration, which is occurring in different areas.

Adolescent↗
PubMed2001

The perception of texture on folded surfaces.

Do judgments of texture similarity reflect surface texture or image texture? To find out, we had observers view a rectangular surface that was folded into three panels, much like a brochure. Each panel was textured with an oriented noise pattern and the observers' task was to determine which side panel matched the center panel in surface texture. Information about surface geometry was conveyed by binocular disparity and by the boundaries of the rectangular surface. We found that observers were often consistently wrong, selecting the texture that differed in the image and not on the surface. In sharp contrast, when observers judged the texture orientation on each panel individually, their judgments were accurate reflections of the surface texture. So even when observers can recover surface texture, their judgments of texture similarity may still be based on image texture.

Adolescent↗
PubMed2000

The effect of 3D structure on motion segmentation.

A smooth surface imaged on the retina produces a smooth flow field. Thus, the visual system may group regions of smoothly varying flow to segment surfaces. We tested this idea by having observers perform a segmentation task on several stimuli that differed in their 3D interpretations but were all matched in the smoothness of their 2D flow fields. Performance varied across conditions with the best performance occurring when the stimulus stimulated a rigid plane. This result suggests that while observers may use deviations from smoothness to segment a broad class of motion stimuli, they use a more precise strategy to segment stimuli with a familiar 3D interpretation.

Depth Perception↗
PubMed2000

TNFA promoter polymorphism and susceptibility to brucellosis.

The aim of this study was to investigate the possible influence of the tumor necrosis factor alpha (TNFA) gene promoter polymorphisms and HLA class II genes on the susceptibility to or development of human brucellosis. TNFA genotypes (at positions -308 and -238) were determined in 59 patients with brucellosis and 160 healthy controls by polymerase chain reaction-restriction fragment length polymorphism. There were no significant differences between the patients and the controls for the TNFA-238 genotypes. However, when the overall TNFA-308 genotype distribution of the brucella patients was compared with that of the control subjects, a significant skewing was observed (P = 0.02). The TNFA-308.1/2 genotype was present at significantly higher frequency in the total patient as a whole compared with control subjects (30% versus 15%; P = 0.01, odds ratio (OR) 2.49, 95% confidence interval (CI) 1.16-5.33). No statistically significant differences in the distribution of HLA-DRB1 or DQB1 alleles were observed between brucella patients and control subjects. Stratification to correct for interdependence of TNFA-308.2 and HLA-DR3 alleles confirmed that, in spite of their strong linkage disequilibrium, the association of TNFA-308.2 with brucellosis was independent of HLA-DR3.

Adolescent↗
PubMed1999

[The prevalence of human immunodeficiency virus infection and the risk behaviors in the heroin addicts of Barcelona, Madrid and Seville: an example of the advantages of centering studies on addicts and not just on intravenous users].

BACKGROUND: The switch from intravenous heroin administration to smoking of heroin might be changed the trends in the prevalence of HIV infection and risk behaviours among Spanish users. SUBJECTS AND METHODS: Cross-sectional study of 909 regular heroin users, recruited within and outside of drug treatment centres. The prevalence of HIV infection and risk behaviours were studied in the whole sample and among injectors. RESULTS: The proportion of heroin users who had ever injected was 86.7% in Barcelona, 71.1% in Madrid and 56.1% in Seville, while the proportion of those who had injected in the last 30 days was 79.7, 35.6 and 29.2%, respectively. The prevalence of HIV infection among users who had ever injected was 46.2% in Barcelona, 39.6% in Madrid and 47.1% in Seville; in the total population of heroin users the prevalence was 40, 31.1 and 28%, respectively. Among current injectors, 10.9% in Barcelona, 13.9% in Madrid and 23.6% in Seville reported they had injected with used syringes in the last 30 days, while the corresponding proportion among the total population of users was 8.7, 4.9 and 6.9%, respectively. Moreover, 19.2% of injectors in Barcelona, 16.7% in Madrid and 16.9% in Seville admitted to injecting drugs which had been diluted in syringes previously used by others in the last 30 days; of this group, over half stated they had not injected with used syringes during that period. CONCLUSIONS: The prevalence of HIV infection and risk behaviours among heroin users differs depending on whether all users or only injectors are considered. This suggests that the transition from injecting to smoking is one of the major factors contributing to the control of the HIV epidemic in Spain. This contribution, which has little to do with regional prevention policies, must be taken into account when comparing their effectiveness.

Adult↗
PubMed1999

Methadone treatment in Spain, 1994.

The objective of this study was to describe the methadone treatment (MT) network in Spain, and to evaluate compliance with criteria known to influence the spread of human immunodeficiency virus (HIV). During the last 3 months of 1994, a mailed questionnaire was sent to the coordinators of all methadone treatment centers in Spain. A total of 224 centers completed the questionnaire (90% response rate). The total number of patients receiving MT in the studied centers was 13,402. Their mean age was 29 years, 79% were male, and approximately 60% were HIV positive. The rate of patients in MT varied by Region (mean: 6.7 patients in MT per 10,000 inhabitants). Although the global mean of reported daily dose of methadone was 60 mg, in 44% of the centers it was lower than that. Despite the high number of centers involved with MT in Spain, the coverage by regions is unequal. Studied centers revealed only a moderate adherence to procedures considered to be effective in HIV prevention. Given the magnitude of HIV infection in Spain, there is a clear need for improvement.

Adolescent↗
PubMed1999

[Acute respiratory problems and cocaine or heroine smoking].

BACKGROUND: To explore if cocaine or heroin smoking was positively associated to acute respiratory complications (ARC). SUBJECTS AND METHODS: We collected data from medical records for 717 cocaine users who were attended in 14 hospital emergency rooms. The association was studied by logistic regression. RESULTS: The most frequent ARC were respiratory infections and complications with chest pain or dyspnea. Cocaine smokers (OR = 3.3; CI 95% = 1.5-6.9) and cocaine sniffers (OR = 2.5; CI 95% = 1.1-5.6) had greater risk of ARC than cocaine injectors. Heroin smokers (OR = 3.5; COI 95% = 1.8-7.0) and heroin sniffers (OR = 2.8; CI 95% = 1.4-5.6) had greater risk of ARC than non heroin users. CONCLUSIONS: These results suggest that cocaine or heroin smoking increases the risk of ARC.

Acute Disease↗
PubMed1998

A global process in motion segregation.

Observers viewed sparse random dot cinematograms in which the moving dots were confined to eight windows. The motions in seven of the windows were consistent with a global flow pattern, while the direction of motion in the eighth window deviated from this pattern. The observer's task was to determine which of the eight windows contained the inconsistent motion. The task was performed on two types of global flow patterns: spirals, which appear rigid, and deformations, which appear highly non-rigid. Although these patterns produce qualitatively different global percepts, they are exactly matched in their local velocities and velocity differences. Observers were better able to locate an inconsistent motion in spiral patterns than in deformation patterns, indicating that they were using more than just local motion information to find the target. This result is taken as indirect support for a segregation process that involves fitting the stimulus with a global motion pattern and segregating motions inconsistent with this pattern.

Female↗
PubMed1997

The transition from injecting to smoking heroin in three Spanish cities. The Spanish Group for the Study of the Route of Heroin Administration.

AIMS: To measure the current prevalence of different routes of heroin administration among users and to describe the most frequent patterns in the evolution of the main route from the time of first use to the present and their implications for the control of the HIV epidemic. DESIGN: Cross-sectional study. Face-to-face interviews using a structured questionnaire. SETTING AND PARTICIPANTS: Nine hundred and nine regular heroin users from Madrid, Barcelona and Seville (about 300 per city), half of them recruited in treatment centres and the other half out of treatment. MEASUREMENTS: Socio-demographic characteristics, current and historical behaviours related to route of administration. FINDINGS: Before 1980 injection was the first main route of heroin administration for most users in Barcelona and Madrid; in Seville smoking already predominated, although 40% of users began by injecting. Sniffing subsequently became predominant in Barcelona, while smoking became the predominant first route in Madrid and Seville (smoking has been the only first route in Seville since 1991). The prevalence of injection as the main route of administration during the last 30 days was 77.3% in Barcelona, 24.3% in Madrid and 23.9% in Seville; smoking predominated in the latter two cities. The factors most strongly associated with injection as the preferred route were city of recruitment and having a partner who injected. Some 73% of those who stopped injecting in their last change of route stated that the results of their HIV test or fear of becoming infected had been important in making this decision. CONCLUSIONS: The change from injecting to smoking will greatly facilitate the control of HIV infection in Spain. However, the main causal factor does not appear to be the perception of HIV risk, but rather other, ecological factors (cultural or market-related). The absence of these factors in some areas may impede the spread of smoking.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Evidence for two speed signals: a coarse local signal for segregation and a precise global signal for discrimination.

In calculating the precise speed of an object, the visual system must integrate motion measurements across time and space while keeping motion measurements from different objects separate. We examined whether an initial coarse estimate of local speed may be used to segregate the motions of different objects prior to a precise calculation of object speed. Our stimuli consisted of 256 dots that moved upward at two speeds. In Expt 1, each dot alternated between the two speeds every 133 msec. When the speed alternations were asynchronous across dots, subject saw two transparent surfaces moving at different speeds and their ability to discriminate changes in the slow speed were unaffected by the presence of the fast speed. This experiment suggests that before integration, motion measurements may be segregated according to speed. We sought more conclusive evidence for this claim in Expts 2 and 3. In Expt 2, dots with 33 msec lifetimes were used to generate the two speeds. Although individual dots permitted only crude speed discrimination, subjects perceived this stimulus as two surfaces moving at different speeds and they precisely judged the slower speed. Apparently, the coarse local signals generated by the slow dots were segregated from those of the fast dots and then separately integrated to produce a precise speed signal. In Expt 3, the dots again moved at two speeds, but each speed was generated by a range of spatial and temporal displacements. Once more, subjects saw two surfaces and precisely judged the speed of the slower surface, demonstrating that segregation may be based solely on differences in local speed.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential Threshold↗
PubMed1995

The 'uniqueness constraint' and binocular masking.

In stereo-matching algorithms, the 'uniqueness constraint' requires that a feature in one stereo half-image be matched to, at most, one similar feature in the other half-image. Experiments are reported in which binocular contrast thresholds and depth-discrimination judgments have been used to determine whether the human stereo system makes unique matches. A single high-spatial-frequency target in the left eye was paired stereoscopically with two identical targets, presented near retinal correspondence (+/- 3.5 min of disparity), in the right eye. Contrast-increment thresholds were measured for each of the targets in the right eye, and it was found that the target in the left eye masked both. Indeed, the amount of binocular masking for each member of the double target nearly equaled the masking observed when only a single target was presented to the right eye. Depth judgments confirmed that the target in the left eye had been matched to both targets in the right eye. It is concluded that uniqueness is not an absolute constraint on human stereo matching.

Algorithms↗
PubMed1995

The impact of drug-related deaths on mortality among young adults in Madrid.

The trend from 1983 to 1990 of drug-related mortality (defined as the sum of deaths from acute drug reactions and the acquired immuno-deficiency syndrome [AIDS] in drug users) among the population 15 to 39 years of age in Madrid, Spain, was studied and compared with mortality from all causes. All of the mortality rates increased from 1983 to 1990: all causes, from 101/100,000 to 148/100,000; acute drug reactions, from 3/100,000 to 15/100,000; and AIDS, from 0 to 20/100,000. Drug-related mortality represented 60% of the increase in the rate from all causes in males and 170% of the increase in females. The increases in drug-related mortality are likely to continue in the future.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Stereo matching precedes dichoptic masking.

Stereo matching can intervene to prevent dichoptic masking. In a dichoptic masking paradigm we measured the contrast threshold for a bar target, presented to one eye, as a function of the contrast of an identical masking bar, presented at retinal correspondence in the other eye. Confirming previous studies of dichoptic masking with sinusoidal gratings, the test bar thresholds rose proportionally with increasing masking contrast. This threshold elevation was almost nullified when an extra bar was presented to the eye seeing the test stimulus. Release from masking occurred when the disparity between the masking bar and extra bar was < 20 min arc over a range of contrast levels (8-45%), and for bars containing either broad spatial frequency spectra or bars with only high spatial frequencies (peak = 12 c/deg). The latter result rules out an explanation for the release from masking based on contrast discrimination in low spatial frequency channels. The extra bar was effective in releasing the test bar from masking as long as the extra bar's contrast was greater than about one-fifth the contrast of the mask, a result that suggests that there is a contrast threshold for stereo matching. We interpret our findings to indicate that a stage of stereo matching occurs prior to the neural site limiting dichoptic contrast discrimination.

Contrast Sensitivity↗
PubMed1994

HIV-transmission knowledge in drug users from outpatient facilities in Spain. A national survey.

Knowledge of AIDS and its transmission was studied in patients undergoing drug-dependence treatment for opiates and/or cocaine. The study area included all of Spain and was carried out via a questionnaire assessing information about risk practices, HIV serostatus, etc, and 13 true or false questions concerning HIV-transmission knowledge. The main purpose of the present study was to analyse the relationship between the level of information found in patients and factors potentially related to it, including the practice of high-risk activities for HIV transmission, the sources of information and behaviour modification. Findings indicate that poor information was associated with the use of non-sterile needles, anal-penis sexual relations, non-use of condoms, lack of preventive measures in daily cohabitation, and lack of previous drug-dependence treatment. Determining factors of being well-informed were a high level of education, a longer duration of intravenous drug use, and contact with the Health Service as a source of information. These findings partially support the need to implement programs aimed at improving knowledge about HIV in the population of drug users.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Intravenous administration among heroin users having treatment in Spain.

BACKGROUND: Of critical importance to AIDS control in Spain is the analysis of geographical variation and trend over time in the prevalence of intravenous administration in heroin users, as well as the factors associated with the use of this route. METHODS: We carried out a cross-sectional study of 27,655 people admitted to outpatient treatment for heroin dependence in 15 of the 17 Autonomous Communities of Spain during 1991, using data provided by the State Information System on Drug Abuse (SEIT). To assess the association of some factors with use of the intravenous route crude and logistic analysis was performed. RESULTS: The prevalence of intravenous administration in this population was 64.4% with regional differences ranging between 33% and 90%. Crude and logistic analysis demonstrated a strong association with two factors in addition to geography: the year of first use and the age at first use (the earlier the first use, the greater the strength of the association). CONCLUSIONS: These findings are of paramount importance for the control of the HIV epidemic in Spain and further study in this area could help to guide policy development.

Acquired Immunodeficiency Syndrome↗