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Biomedical subjects

A Gorea

Publications and source records attributed to A Gorea.

At least 55 records · Page 3Linked to original sources
PubMed1989

Widespread quinolone resistance among methicillin-resistant Staphylococcus aureus isolates in a general hospital.

Ofloxacin and ciprofloxacin resistance (MIC, greater than 4 micrograms/ml) was encountered in 45 of 50 clinical isolates of methicillin-resistant Staphylococcus aureus. None of 20 methicillin-susceptible strains was resistant to the quinolones (P less than 10(-6). Quinolone-susceptible and -resistant isolates did not differ with respect to culture source or bacteriophage type. The future usefulness of quinolones for S. aureus infection may be limited.

4-Quinolones↗
PubMed1989

Penetration of third-generation cephalosporins into human peritoneal tissue.

Each of 40 patients underwent elective laparotomy following administration of a single 1.0-gram intravenous dose of ceftizoxime, ceftriaxone, cefoperazone or cefotaxime. Therapeutic concentrations of cefoperazone and ceftriaxone were achieved in peritoneal tissue in 20/20 patients. Only 9/20 samples from patients receiving the other two antibiotics had detectable antibiotic activity. The antibiotic concentration in peritoneal fluid (7 samples) was 2.36-11.15 times higher than that of concurrently obtained peritoneal tissue. When adjusted for the in vitro susceptibility (MIC) of potential peritoneal pathogens, our data suggest that ceftriaxone and cefoperazone may be preferable to other third-generation cephalosporins for the prophylaxis and therapy of intraabdominal infection.

Ascitic Fluid↗
PubMed1989

Motion processing by chromatic and achromatic visual pathways.

We describe a family of stimuli consisting of colored bars of different orientations, which, when presented in rapid succession, may elicit unambiguous motion perception. These stimuli permitted the isolation of directional spatiotemporal information extracted from oriented luminance clues, from nonoriented chromatic-plus-luminance clues, or, when the stimuli were presented under equiluminant conditions, from pure chromatic clues. As a general rule, matching of orientation induces weaker motion-detection performances than does matching of color. When the orientation clues are in competition with the chromatic ones, motion perception based on the former is always overridden by motion perception based on the latter. We indirectly isolated an oriented chromatic mechanism that also contributes to motion perception. We finally showed that, under equiluminant conditions, matching of orientation across different colors is inefficient in eliciting motion perception, either because motion information is extracted poorly across different chromatic channels or because such channels show little orientational selectivity. Because motion strength determined by each of the manipulated attributes follows different functions with the displacement (or velocity) of the stimuli, we propose the existence of three underlying mechanisms, a luminance mechanism, a chromatic-plus-luminance mechanism, and a pure chromatic mechanism, each of which provides motion information.

Attention↗
PubMed1988

Bartholin's gland abscess caused by Neisseria sicca.

Neisseria sicca has been reported to cause bacterial meningitis, endocarditis, pneumonia, and spondylitis. Surgical drainage from a Bartholin's gland abscess contained N. sicca in pure culture. Neisseria species recovered from cerebrospinal fluid and gynecologic specimens must be carefully examined to avoid misidentification as meningococci or gonococci.

Abscess↗
PubMed1987

Concentrations of ciprofloxacin in human liver, gallbladder, and bile after oral administration.

We have measured concentrations of ciprofloxacin in serum, hepatic tissue, gallbladder, and bile in 10 patients after a single oral dose of 750 mg given before cholecystectomy. Mean liver and gallbladder tissue concentrations were 12.76 micrograms X g-1 +/- 2.79 (SEM) and 5.94 micrograms X g-1 +/- 1.35, respectively. Concentrations in bile taken from the gallbladder (7 patients) ranged from 68 to 225 micrograms X ml-1, with a mean bile/serum concentration ratio of 49. Concentrations in bile taken from the common bile duct (2 patients) were 17 and 16 micrograms X ml-1.

Administration, Oral↗
PubMed1987

Concentration of norfloxacin in human gallbladder tissue and bile after single-dose oral administration.

Concomitant concentrations of norfloxacin in serum and in gallbladder tissue and bile were determined in 10 patients after a single oral dose of 400 mg given before cholecystectomy. Concentrations in gallbladder bile ranged from 0.6 to 15.6 micrograms/ml, with a mean bile/serum ratio of 7.0. The mean concentration in gallbladder tissue was 1.8 +/- 0.8 (standard error) micrograms/g.

Adult↗
PubMed1987

Masking efficiency as a function of stimulus onset asynchrony for spatial-frequency detection and identification.

Detection and identification thresholds for grating targets were measured in the presence of a compound mask grating as a function of the stimulus onset asynchrony (SOA). The detection and identification SOA functions are both reversed U-shaped but they are not parallel. The detection-to-identification ratio is itself a reversed U-shaped function of SOA, even for stimuli two octaves apart, with a peak between +20 and +60 ms SOA (backward masking). It is argued that these results support the hypothesis according to which detection and identification are serial processes.

Form Perception↗
PubMed1986

Different encoding mechanisms for phase and contrast.

Phase sensitivity was assessed over a large range of exposure durations by means of a 2AFC staircase procedure where the observer had to detect the relative position of sinusoidal gratings relative to a superimposed thin, dark line. Phase discrimination thresholds decreased as a function of exposure duration although the contrast of the stimuli was weighted for equal detectability at all durations. Phase sensitivity improved markedly with contrast, as opposed to the degradation with contrast seen in contrast discrimination paradigms. The contrast and time functions of phase sensitivity both support the hypothesis that phase is processed separately from contrast by a pathway with different temporal and contrast characteristics. We propose a model where phase sensitivity depends on a luminance subtraction process with a time constant of about 130 msec.

Discrimination, Psychological↗
PubMed1986

Temporal integration characteristics in spatial frequency identification.

Spatial frequency detection and identification performances were measured simultaneously as a function of exposure duration. Detection and identification sensitivity/duration functions appeared to be parallel over durations ranging from 10 to 1000 msec, independent of both spatial frequency and spatial frequency difference between the stimuli to be discriminated. The results are compatible with both a simultaneous or a serial processing of the two types of tasks. In the former case, detection and identification would take place at the same neural level and they would, therefore, be indistinguishable. The second alternative implies that the identification stage must have a time-constant substantially shorter than the detection stage. Both possibilities are compatible with the concept of spatial frequency labelled detectors.

Discrimination, Psychological↗
PubMed1986

Concentration of ciprofloxacin in human prostatic tissue after oral administration.

Concomitant concentrations of ciprofloxacin in serum, urine, and prostatic tissue were determined in 15 patients after single oral doses of 750 mg. Levels in tissue ranged from 0.6 to 4.18 micrograms/g, and therapeutic concentrations were demonstrable for up to 9 h after administration. The mean ratio of tissue to serum concentration was 0.93 +/- 0.08 (standard error).

Administration, Oral↗
PubMed1986

New look at Bloch's law for contrast.

It has been commonly reported that the temporal integration of grating contrast proceeds more slowly as spatial frequency is increased. Such results have been based on the critical duration for sensitivity to contrast pulses varying in duration, but the analyses have not assumed full integration at short durations and have neglected the effects of probability summation over time. To take such effects into account, we discuss a class of analytical models based on nonlinear temporal integration. On the assumption that the temporal impulse response of the visual system determines contrast integration over time, we develop both a high-threshold model and a signal-detection approach involving multiple and independent nonlinear signal detectors with a time-limited integration span. The redefined critical durations predicted by the models and verified by the data are about 35 msec and vary by no more than 10 msec across spatial frequency. This variation is entirely attributable to a change in the strength of inhibition with spatial frequency, and the analysis implies that the excitatory component is constant at all spatial frequencies, contrary to previous accounts.

Humans↗
PubMed1985

Spatial integration characteristics in motion detection and direction identification.

Spatial integration characteristics were assessed with drifting gratings for both detection and direction-identification contrast thresholds. Thresholds were measured while stimulus width, length or both were varied. It was found that: (1) the shape of the size/sensitivity functions changes with spatial, but not with temporal, frequency; (2) direction-identification thresholds diverge from the detection thresholds below 1 cycle but can be reliably measured for stimulus widths as small as 0.1275 cycles; (3) the integration characteristics are slightly anisotropic for the identification but not for the detection process, and (4) the two-dimensional spatial integration cannot be directly predicted from its one-dimensional characteristics. Width/sensitivity detection functions are well fitted by predictions of Wilson and Bergen's four-channel model. Predictions from a temporal covariance model provide a poor fit to the identification data. It is argued that classes of detection and direction-identification models must involve identical nonlinearities prior to their respective thresholds. It is concluded that the hypothesis according to which both performances are determined by the same spatial integration stage cannot be rejected.

Humans↗
PubMed1984

Perceptual bistability with counterphase gratings.

Suprathreshold counterphase modulated gratings induce a bistable percept of drift or flicker. It is argued that these perceptual alternations might provide a new means for the investigation of directional selective mechanisms. The prevalance of either of the two perceptions has been studied as a function of the spatio-temporal characteristics of the stimulus and compared with: (1) the spatio-temporal contrast sensitivity surface for counterphase modulated gratings; (2) the motion/counterphase sensitivity ratio. Drift perception elicited by suprathreshold counterphase gratings attains a maximum for 8 c/deg, 12 Hz stimuli and decreases for any other experimental condition. For spatial frequencies below 1 c/deg, or temporal frequencies below 2 Hz, only flicker perception is reported. These phenomenal experiences do not show any systematic dependence on the involuntary eye movements of the observer. Comparison with the threshold measurements does not support their explanation in terms of the transient-sustained dichotomy, nor does it allow for a straightforward equivalance between the spatio-temporal characteristics of direction-selective mechanisms at threshold and at suprathreshold levels. It is suggested that the balance between flicker and motion is the perceptual outcome of the competition between lower and higher order motion detectors.

Eye Movements↗
PubMed1984

Recurrent breast abscesses caused by Corynebacterium minutissimum.

A 42-year-old woman developed severe, recurrent breast abscesses caused by Corynebacterium minutissimum. Prior reports of C. minutissimum infection have been limited to erythrasma, a minor dermatosis. The microbiological and clinical features of this species were reviewed.

Abscess↗