Clinical predictors of methicillin-resistant Staphylococcus aureus in nosocomial and healthcare-associated pneumonia: a multicenter, matched case-control study.

The situations in which coverage for methicillin-resistant Staphylococcus aureus (MRSA) in the empirical treatment of nosocomial pneumonia (NP) or severe healthcare-associated pneumonia (HCAP) is needed are poorly defined, particularly outside intensive care units (ICUs). Our aim was to characterize if the risk of MRSA NP/HCAP can be defined by clinical variables. We designed an observational, retrospective, multicenter, case-control study to analyze the association between defined clinical variables and risk of MRSA NP/HCAP in non-ICU patients using conditional multivariable logistic regression. Cases and controls (1:2) with microbiological diagnosis were included. Controls were matched for hospital, type of pneumonia (NP or HCAP), and date of isolation. A total of 140 cases (77 NP and 63 HCAP) and 280 controls were studied. The variables associated with the risk of MRSA pneumonia were: (i) respiratory infection/colonization caused by MRSA in the previous year [odds ratio (OR) 14.81, 95% confidence interval (CI) 4.13-53.13, p < 0.001]; (ii) hospitalization in the previous 90 days (OR 2.41, 95% CI 1.21-4.81, p = 0.012); and (iii) age (OR 1.02, 95% CI 1.001-1.05, p = 0.040). The area under the receiver operating characteristic (ROC) curve for the multivariable model was 0.72 (95% CI 0.66-0.78). The multivariate model had a sensitivity of 74.5% (95% CI 65.3-83.6), a specificity of 63.3% (95% CI 56.0-70.6), a positive predictive value of 52.5% (95% CI 43.9-61.2), and a negative predictive value of 82.0% (95% CI 75.3-88.8) for the observed data. Clinical predictors of MRSA NP/HCAP can be used to define a low-risk population in whom coverage against MRSA may not be needed.

Simvastatin exerts antiproliferative and differentiating effects on MG63 osteoblast-like cells: Morphological and immunocytochemical study.

BACKGROUND AND OBJECTIVE: Current evidence suggests that statins exert an anabolic effect on bone and may therefore impact on osteogenic differentiation and proliferation. These effects can be useful for their use in guided bone regeneration. The objective of this study was to determine the in vitro effects of simvastatin on the differentiation and proliferation of MG63 human osteoblast tumor cells. MATERIAL AND METHODS: MG63 human osteosarcoma cells were cultured in the presence of simvastatin or solvent alone for 72 hours, and their proliferation was assessed by MTT assay. Cells from the culture were prepared for light, transmission and scanning electron microscopy studies. immunocytochemical was used to analyze the differentiation and proliferation markers Musashi-1, Ki-67, CD56 and CD44. RESULTS: Cultured MG63 control cells showed spheroid morphology with numerous secretion vesicles accumulated on the surface, observing no cytoplasmic projections with intercellular connections. However, cells cultured with simvastatin had a polygonal and spindle-shaped morphology, with cytoplasmic projections that interconnected cells. There were numerous microvilli-like filamentous projections on the surface with no defined pattern. At 72 hours of culture, CD56, Ki-67 and Musashi-1 expression was significantly reduced (P < .001) in simvastatin-treated cells. CD44 expression was intense in both groups and was not affected by simvastatin treatment. CONCLUSION: MG63 cells cultured with simvastatin for 72 hours undergo morphological and surface changes. Simvastatin treatment exerts antiproliferative and differentiating effects on these cells as well as promoting recovery of cellular homeostasis.

Complementary clinical effects of red complex bacteria on generalized periodontitis in a caucasian population.

OBJECTIVES: To relate five periodontopathogenic bacteria, including the red complex, to the severity, extent, and inflammation of the periodontal lesion in Caucasian patients with generalized aggressive and chronic periodontitis and to explore whether tobacco use is associated with a specific bacterial profile. MATERIALS AND METHODS: A cross-sectional and analytic study was conducted in patients with aggressive and chronic periodontitis. Data were gathered on socio-demographic and periodontal variables, and RH-PCR was used to determine subgingival bacterial profile. Linear and logistic regression analyses were performed. RESULTS: The study included 60 patients with aggressive and 123 with chronic periodontitis. Total red complex bacteria count was higher in aggressive periodontitis, mainly due to T. denticola (P = 0.015). In both periodontitis types, models showed an association between T. forsythia count and probing depth (B = 0.157, P = 0.030) and between T. denticola count and higher bleeding scores (B = 2.371, P = 0.027). Smoking did not affect the red complex bacteria count in either disease. CONCLUSIONS: The prevalence of red complex bacteria was similar between aggressive and chronic periodontitis, but their count was higher in the former. In both diseases, T. forsythia was associated with greater severity and T. denticola with more severe bleeding. Tobacco smoking was not associated with the presence of red complex bacteria in either disease.

Nosocomial pneumonia caused by methicillin-resistant Staphylococcus aureus treated with linezolid or vancomycin: A secondary economic analysis of resource use from a Spanish perspective.

OBJECTIVES: Adopting a unique Spanish perspective, this study aims to assess healthcare resource utilization (HCRU) and the costs of treating nosocomial pneumonia (NP) produced by methicillin-resistant Staphylococcus aureus (MRSA) in hospitalized adults using linezolid or vancomycin. An evaluation is also made of the renal failure rate and related economic outcomes between study groups. DESIGN: An economic post hoc evaluation of a randomized, double-blind, multicenter phase 4 study was carried out. SCOPE: Nosocomial pneumonia due to MRSA in hospitalized adults. PARTICIPANTS: The modified intent to treat (mITT) population comprised 224 linezolid- and 224 vancomycin-treated patients. INTERVENTIONS: Costs and HCRU were evaluated between patients administered either linezolid or vancomycin, and between patients who developed renal failure and those who did not. PRIMARY ENDPOINTS: Analysis of HCRU outcomes and costs. RESULTS: Total costs were similar between the linezolid- (€17,782±€9,615) and vancomycin-treated patients (€17,423±€9,460) (P=.69). The renal failure rate was significantly lower in the linezolid-treated patients (4% vs. 15%; P<.001). The total costs tended to be higher in patients who developed renal failure (€19,626±€10,840 vs. €17,388±€9,369; P=.14). Among the patients who developed renal failure, HCRU (days on mechanical ventilation: 13.2±10.7 vs. 7.6±3.6 days; P=.21; ICU stay: 14.4±10.5 vs. 9.9±6.6 days; P=.30; hospital stay: 19.5±9.5 vs. 16.1±11.0 days; P=.26) and cost (€17,219±€8,792 vs. €20,263±€11,350; P=.51) tended to be lower in the linezolid- vs. vancomycin-treated patients. There were no statistically significant differences in costs per patient-day between cohorts after correcting for mortality (€1000 vs. €1,010; P=.98). CONCLUSIONS: From a Spanish perspective, there were no statistically significant differences in total costs between the linezolid and vancomycin pneumonia cohorts. The drug cost corresponding to linezolid was partially offset by fewer renal failure adverse events.

Effect of root planing on surface topography: an in-vivo randomized experimental trial.

BACKGROUND AND OBJECTIVE: The root surface topography exerts a major influence on clinical attachment and bacterial recolonization after root planing. In-vitro topographic studies have yielded variable results, and clinical studies are necessary to compare root surface topography after planing with current ultrasonic devices and with traditional manual instrumentation. The aim of this study was to compare the topography of untreated single-rooted teeth planed in vivo with a curette, a piezoelectric ultrasonic (PU) scraper or a vertically oscillating ultrasonic (VOU) scraper. MATERIAL AND METHODS: In a randomized experimental trial of 19 patients, 44 single-rooted teeth were randomly assigned to one of four groups for: no treatment; manual root planing with a curette; root planing with a PU scraper; or root planing with a VOU scraper. Post-treatment, the teeth were extracted and their topography was analyzed in 124 observations with white-light confocal microscopy, measuring the roughness parameters arithmetic average height, root-mean-square roughness, maximum height of peaks, maximum depth of valleys, absolute height, skewness and kurtosis. RESULTS: The roughness values arithmetic average height and root-mean-square roughness were similar after each treatment and lower than after no treatment ( p < 0.05). Absolute height was lower in the VOU group than in the untreated ( p = 0.0026) and PU (p = 0.045) groups. Surface morphology was similar after the three treatments and was less irregular than in the untreated group. Values for the remaining roughness parameters were similar among all treatment groups ( p > 0.05). CONCLUSION: Both ultrasonic devices reduce the roughness, producing a similar topography to that observed after manual instrumentation with a curette, to which they appear to represent a valid alternative.

Application of a topical vapocoolant spray decreases pain at the site of initial intradermal anaesthetic injection during ultrasound-guided breast needle biopsy.

AIM: To assess whether the application of a topical vapocoolant spray immediately prior to initial intradermal anaesthetic injection during ultrasound-guided breast biopsy decreases pain at the site of the initial injection. MATERIALS AND METHODS: In this institutional review board-approved, Health Insurance Portability and Accountability Act (HIPAA)-compliant study, 50 women aged 49.1 ± 1.6 years (mean ± standard error) were recruited and provided written informed consent. Participants served as their own controls and were blinded as to whether a topical vapocoolant spray or a placebo was used immediately prior to the initial local anaesthetic injection at two separate biopsy sites. With the exception of the application of vapocoolant or placebo, the entire ultrasound-guided procedure was performed according to a routine protocol. Participants recorded pain at initial injection site on a visual analogue scale. General linear mixed models for repeated measures analysis of variance and a 0.05 significance level were used. RESULTS: Application of topical vapocoolant spray was shown to significantly decrease pain at the site of initial intradermal anaesthetic injection as compared to placebo (p<0.001). Treatment effect was independent of age of the subject, race/ethnicity, operator, type of biopsy device, and histopathology result. No complications from vapocoolant spray use were reported. CONCLUSION: Application of a topical vapocoolant spray immediately prior to initial intradermal anaesthetic injection during ultrasound-guided breast biopsy significantly decreases pain at the site of the initial injection and could contribute to improve the patient's overall procedural experience.

Oral bacteria in placental tissues: increased molecular detection in pregnant periodontitis patients.

OBJECTIVES: The objective of this study was to identify the DNA of oral bacteria in placental samples from women with and without periodontitis who had or had not had preterm births and/or low birthweight (PB/LBW) neonates. METHODS: Data were gathered from 57 puerperal women in relation to socio-demographic, gynaecological, and periodontal variables and to placental histomorphology. Fifty-seven biopsies, 28 from mothers with periodontitis, were taken aseptically from preterm placentas (n = 36) and from full-term placentas (n = 21). Total DNA was extracted, and the presence of 15 oral bacteria was assessed using Nested-PCR. RESULTS: The placentas from women with periodontitis showed a higher prevalence of periodontopathogens compared to those from women without periodontitis (P = 0.009). Samples showed low prevalences of Actinomyces israelii, Parvimonas micra and Tannerella forsythia. An association was found between Eikenella corrodens in placenta and periodontitis (P = 0.002). The most ubiquitous bacterium, Fusobacterium nucleatum, was more prevalent in mothers with periodontitis and PB/LBW (P = 0.033). Porphyromonas gingivalis, Treponema denticola, Prevotella intermedia and Aggregatibacter actinomycetemcomitans were not detected. CONCLUSIONS: These results, along with previous findings, show that oral bacteria may be normally present in the placenta, however, the levels of certain oral pathogens in the placenta would highly depend on the mother's periodontal state.

Temperature effects on the calculation of the functional derivative of Tc with respect to α2F(ω).

The functional derivative of the superconducting transition temperature Tc with respect to the electron-phonon coupling function [Formula: see text] permits identifying the frequency regions where phonons are most effective in raising Tc. This work presents an analysis of temperature effects on the calculation of the δTc/δα2F(ω) and µ* parameters. The results may permit establishing that the variation of the temperature in the δTc/δα2F(ω) and µ* parameter allows establishing patterns and conditions that are possibly related to the physical conditions in the superconducting state, with implications on the theoretical estimation of the Tc.

Assessment of surface and electrical properties of the TiO2@zeolite hybrid materials.

Degradation of pollutants in aqueous medium is of high interest due to the impact on environment and human health, therefore, design and study of the physico-chemical properties of photocatalysts for water remediation are of major significance. Among properties of photocatalyst, those related to the surface and electrical mechanism are crucial to the photocatalyst´s performance. Here we report the chemical and morphological characteristics of TiO2@zeolite photocatalyst by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) respectively, and a coherent electrical conduction mechanism was proposed based on data obtained from assisted laser impedance spectroscopy (ALIS), in which the zeolite was synthesized from recycled coal fly ash. The results obtained by SEM and XPS verified the presence of spherical particles of TiO2 anatase with presence of Ti3+ state. ALIS results showed that impedance of the entire system increases when the amount of TiO2 increases and the samples with lower capacitive performance allowed a larger transfer of the charges between the solid-liquid interface. All results showed that higher photocatalytic performance of TiO2 growth over hydroxysodalite with 8.7 wt% and 25 wt% of TiO2 can be explained in terms of the morphology of TiO2 and the interactions between substrate-TiO2 mainly.

[Intracranial tuberculoma simulating a malignant tumor: case report and literature review]. / Tuberculoma intracraneal simulando neoplasia maligna. Caso clinico y revision dela literatura.

INTRODUCTION: Extrapulmonary manifestations of tuberculosis involving the central nervous system (CNS) due to haematogenous spread are not a rare entity. Tuberculoma is a granulomatous inflammatory process mimicking in rare occasions a malignant neoplasm radiologically. The authors report a case of a giant right frontal tuberculoma mimicking a malignant tumor and review the literature. CASE REPORT: A sixty four-year-old women with several weeks of headache and behavior alterations admitted at the hospital with light right hemiparesis. The MRI showed a left frontal tumor suggestive of a malignant tumor. CT showed bone infiltration. At surgery, a nodular, avascular lesion was found and pathological examination confirmed granulomatous inflammation suspecting tuberculoma. Mycobacterium tuberculosis complex-specific PCR assay confirmed diagnosis. Intracranial tuberculoma is an uncommon variety of central nervous system tuberculosis. The prognosis is related to the early diagnosis, surgical resection and the complementary antituberculosis treatment. CONCLUSIONS: We present the unusual presentation of a giant brain tuberculoma which MRI led us to believe was a malignant tumor. Computed Tomography revealed bone infiltration. Positive diagnosis could be established on the basis of the pathology results of a brain biopsy or detection of DNA of Mycobacterium tuberculosis in the PCR study.

Cooper Pairs Distribution function for bcc Niobium under pressure from first-principles.

In this paper, we report Cooper Pairs Distribution function [Formula: see text] for bcc Niobium under pressure. This function reveals information about the superconductor state through the determination of the spectral regions for Cooper-pairs formation. [Formula: see text] is built from the well-established Eliashberg spectral function and phonon density of states, calculated by first-principles. [Formula: see text] for Nb suggests that the low-frequency vibration region [Formula: see text] is where Cooper-pairs are possible. From [Formula: see text], it is possible to obtain the [Formula: see text] parameter, which is proportional to the total number of Cooper-Pairs formed at a temperature [Formula: see text]. The [Formula: see text] parameter allows an approach to the understanding of the Nb [Formula: see text] anomalies, measured around 5 and 50 GPa.

Cooper-pair distribution function [Formula: see text] for superconducting [Formula: see text] and [Formula: see text].

Cooper-pair distribution function, [Formula: see text], is a recent theoretical proposal that reveals information about the superconductor state through the determination of the spectral regions where Cooper pairs are formed. This is built from the well-established Eliashberg spectral function and phonon density of states, calculated by first-principles. From this function is possible to obtain the [Formula: see text] parameter, which is proportional to the total number of Cooper pairs formed at a critical temperature [Formula: see text]. Herein, we reported [Formula: see text] function of the compressed [Formula: see text] and [Formula: see text] high-[Formula: see text] conventional superconductors, including the effect of stable sulfur isotopes in [Formula: see text]. [Formula: see text] suggests that the vibration energy range of 10-70 meV is where the Cooper pairs are possible for these superconductors, pointing out the possible importance of the low-energy region on the electron-phonon superconductivity. This has been confirmed by the fact that a simple variation in the low-frequency region induced for the substitution of S atoms in [Formula: see text] by its stable isotopes can lead to important changes in [Formula: see text]. The results also show proportionality between [Formula: see text] parameter and experimental or theoretical [Formula: see text] values.

The higher superconducting transition temperatureTcand the functional derivative ofTcwithα2F(ω) for electron-phonon superconductors.

This work presents an analysis of the functional derivative of the superconducting transition temperatureTcwith respect to the electron-phonon coupling functionα2F(ω) [δTc/δα2F(ω)] andα2F(ω) spectrum of H3S (Im3̄m), in the pressure range where the high-Tcwas measured (155-225 GPa). The calculations are done in the framework of the Migdal-Eliashberg theory. We find for this electron-phonon superconductor, a correlation between the maximums ofδTc/δα2F(ω) andα2F(ω) with its higherTc. We corroborate this behavior in other electron-phonon superconductors by analyzing data available in the literature, which suggests its validity in this type of superconductors. The correlation observed could be considered as a theoretical tool that in an electron-phonon superconductor, allows describing qualitatively the proximity to its highestTc, and determining the optimal physical conditions (pressure, alloying or doping concentration) that lead to the superconductor reaching its highestTcpossible.

The effect of Mn2Sb2 and Mn2Sb secondary phases on magnetism in (GaMn)Sb thin films.

In this work, a detailed study of structural, electrical and magnetic characterization of (GaMn)Sb diluted magnetic semiconductors (DMS) is presented. (GaMn)Sb thin films were grown by DC magnetron co-sputtering method as an innovative procedure to fabricate III-V DMS. The presence of unusual Mn2Sb2 and Mn2Sb secondary phases, induced by substrate temperature and deposition time, were revealed through XRD measurements. Magnetization measurements allow determining crossover between a paramagnetic-like to a ferromagnetic-like behavior controlled by secondary phases. It was found that both, the magnetic remanence and magnetic coercivity, increases with substrate temperature. Interestingly, the magnetic response is paramagnetic at lower deposition times and substrate temperatures, and XRD measurements suggest the absence of Mn2Sb and Mn2Sb2 in secondary phases. For longer deposition times or higher substrate temperature, XRD shows the presence of Mn2Sb2 and Mn2Sb phases and ferromagnetic-like behavior. The DC resistivity of our samples was characterized and the carrier density was determined by Hall measurements and, in contrast with the reported in other studies, found them to be a p-type semiconductor with carrier densities as big as one order of magnitude larger than reported values. From the ferromagnetic-like samples, evidence of an anomalous Hall-effect in the sample was found, with higher magnetic saturation and a anomalous Hall conductivity of 2380 S/cm. All the results point to a contribution of the secondary phases to the overall magnetic response of the samples used, and suggest the importance of studying the formation of secondary phases in the growth of DMS, especially, for the case of (GaMn)Sb where Mn ion can have multiple oxidation states.

Analytical theory of extraordinary transmission through metallic diffraction screens perforated by small holes.

In this letter, the problem of extraordinary (ET) transmission of electromagnetic waves through opaque screens perforated with subwave-length holes is addressed from an analytical point of view. Our purpose was to find a closed-form expression for the transmission coefficient in a simple case in order to explore and clarify, as much as possible, the physical background of the phenomenon. The solution of this canonical example, apart from matching quite well with numerical simulations given by commercial solvers, has provided new insight in extraordinary transmission as well as Wood's anomaly. Thus, our analysis has revealed that one of the key factors behind ET is the continuous increase of excess electric energy around the holes as the frequency approaches the onset of some of the higher-order modes associated with the periodicity of the screen. The same analysis also helps to clarify the role of surface modes -or spoof plasmons- in the onset of ET.

Analytical theory of wave propagation through stacked fishnet metamaterials.

This work analyzes the electromagnetic wave propagation through periodically stacked fishnets from zero frequency to the first Wood's anomaly. It is shown that, apart from Fabry-Perot resonances, these structures support two transmission bands that can be backward under the appropriate conditions. The first band starts at Wood's anomaly and is closely related to the well-known phenomena of extraordinary transmission through a single fishnet. The second band is related to the resonances of the fishnet holes. In both cases, the in-plane periodicity of the fishnet cannot be made electrically small, which prevents any attempt of homogenization of the structure along the fishnet planes. However, along the normal direction, even with very small periodicity transmission is still possible. An homogenization procedure can then be applied along this direction, thus making that the structure can behave as a backward-wave transmission line for such transmission bands. Closed-form design formulas will be provided by the analytical formulation here presented. These formulas have been carefully validated by intensive numerical computations.

Pulsed electromagnetic fields induced femoral metaphyseal bone thickness changes in the rat.

The effect of 1 Hz, 30 mT pulsed magnetic fields on young adult rat femoral metaphyseal bone thickness was assessed. Ten same litter, female Wistar rats were studied; five of them underwent 30 min magnetic stimulation sessions for 20 consecutive days. The anterior and posterior cortical, as well as trabecular bone transverse thicknesses were measured. The results obtained under clear field microscopy in stimulated and control histological cuts were (in microm) 398 +/- 32 versus 260 +/- 22 (P = 0.002), 380 +/- 68 versus 252 +/- 21 (P = 0.03), and 168 +/- 11 versus 112 +/- 11 (P = 0.002), respectively. The transcranial magnetic stimulation system, approved for human therapy, generates pulsed electromagnetic fields, which induce a significant thickness increase in cortical and trabecular in vivo stimulated bone tissues. This is the first time this effect in healthy animals is shown.

Synthesis and characterization of porous silicon as hydroxyapatite host matrix of biomedical applications.

In this work, porous-silicon samples were prepared by electrochemical etching on p-type (B-doped) Silicon (Si) wafers. Hydrofluoric acid (HF)-ethanol (C2H5OH) [HF:Et] and Hydrofluoric acid (HF)-dimethylformamide (DMF-C3H7NO) [HF:DMF] solution concentrations were varied between [1:2]-[1:3] and [1:7]-[1:9], respectively. Effects of synthesis parameters, like current density, solution concentrations, reaction time, on morphological properties were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements. Pore sizes varying from 20 nm to micrometers were obtained for long reaction times and [HF:Et] [1:2] concentrations; while pore sizes in the same order were observed for [HF:DMF] [1:7], but for shorter reaction time. Greater surface uniformity and pore distribution was obtained for a current density of around 8 mA/cm2 using solutions with DMF. A correlation between reflectance measurements and pore size is presented. The porous-silicon samples were used as substrate for hydroxyapatite growth by sol-gel method. X-ray diffraction (XRD) and SEM were used to characterize the layers grown. It was found that the layer topography obtained on PS samples was characterized by the evidence of Hydroxyapatite in the inter-pore regions and over the surface.

Mortality of childhood-onset IDDM patients. A cohort study in Havana City Province, Cuba.

OBJECTIVE: To determine the survival pattern and the underlying cause of death in a cohort of childhood-onset IDDm subjects from Havana City Province, Cuba. RESEARCH DESIGN AND METHODS: This was a descriptive study carried out on a historical cohort of IDDM subjects with disease onset before 15 years of age in Havana City Province, Cuba. The cohort was assembled from several sources. Subjects were diagnosed from 1965 to 1980, and their vital status was assessed at 31 December 1991. Cumulative survival rate was calculated by the Kaplan-Meier method, and a univariate analysis was performed. To test survival differences between groups, the Cox-Mantel test was used. To compare the cohort mortality with the general population, standardized mortality ratios by sex and age were calculated. Specific causes of death were determined by a committee examining death certificates, clinical records, and necropsy reports. RESULTS: A total of 504 subjects were identified, and the mean follow-up time was 17.5 years. Of the subjects, 70 (13.9%) had died at 31 December 1991. Overall, the cohort had a 71% cumulative survival rate at 25 years of IDDM duration. There were no survival differences according to sex or calendar period of IDDM diagnosis. Statistically significant differences were found among age-at-diagnosis groups. The group with a peripubertal age at diagnosis showed the worst prognosis. The cohort experienced 8.5 times the all-causes death rate, compared with the general population. Renal disease accounted for almost half the deaths. CONCLUSIONS: IDDM subjects from Havana City Province, Cuba, showed a better survival pattern than IDDM subjects from other developing countries. However, when compared with IDDM populations from developed countries, there is a survival reserve to be achieved by reducing mortality due to renal disease and infections.

[Spatial summation: its topography in the central visual field]. / Topografía de la sumación espacial en el campo visual central.

PURPOSE: Luminance (L) and area (A) of the stimulus are related by the equation LxAk=constant. We evaluated the k value in 66 positions of the central visual field. METHODS: Ten eyes of 10 healthy subjects were examined for conventional luminous thresholds at 66 positions of the central visual field with the TOP strategy using Goldmann sizes 4, 3.5, 3, 2.5 and 1.9 in the PULSAR perimeter. RESULTS: The k value increased in a lineal manner from the centre towards the periphery (slope=0.01 per degree, average k=0.616, r=0.98, p<0.01) but with unequal slopes at the different meridians. In the inferior hemi-fields it was higher (k=0.657) than in the superior hemi-fields (k=0.574). The k value at the supero-nasal hemifields is quite similar to that found at the paracentral region, and maximum at the temporal inferior region. CONCLUSIONS: Spatial summation in the central visual field has specific values for different positions.