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PubMedDate not supplied

Factors that limit the use of flash visual evoked potentials for surgical monitoring.

A study was conducted comparing the incidence with which the N2/P2/N3 was obtained after flash VEP in 3 groups: anterior visual pathway lesions, non-tumor craniotomies and non-cranial surgery. These groups allowed evaluation of the effects of anesthesia, visual pathway lesions and craniotomy on the stability of the flash VEP. It was found that the latency was not significantly affected in the 3 groups, whereas the incidence of obtainable peaks and the amplitudes were adversely affected by anesthesia, cranial surgical manipulation and especially by the presence of a visual pathway lesion. These adverse effects were so marked that the application of flash VEP for intraoperative monitoring seems of little use.

Brain Neoplasms↗
PubMed1993

Use of laser flash photolysis time-resolved spectrophotometry to investigate interprotein and intraprotein electron transfer mechanisms.

A description is given of the methodology developed in our laboratory for the application of laser flash photolysis to the elucidation of the kinetics and mechanism of electron transfer processes which occur intermolecularly between two protein molecules within a collisional complex, or intramolecularly between two redox centers within a single multisubunit or multidomain protein. This involves the use of flavin analogs, excited to their lowest triplet state by a laser flash, to initiate electron transfer, either by oxidation of a sacrificial donor followed by redox protein reduction via the flavin semiquinone, or by direct oxidation of a reduced redox protein by the flavin triplet. Time-resolved spectrophotometry is used to follow the course of the sequence of electron transfer events initiated by the laser flash. The application of this methodology to the following systems is described: cytochrome c/cytochrome c peroxidase; ferredoxin/ferredoxin NADP+ reductase; cytochrome c/plastocyanin; flavocytochrome b2; and sulfite oxidase.

Animals↗
PubMed1993

Flash and pattern reversal visual evoked potentials in C57BL/6J and B6CBAF1/J mice.

Visual system responses (visual evoked potentials) to flash (FVEP) and pattern reversal (PRVEP) stimuli were recorded in mice. Two strains were used: black C57BL/6J mice and agouti B6CBAF1/J mice (first generation offspring of C57BL/6J females and CBA/J males.) Subjects were sedated with ketamine and xylazine. Flash rate (FVEP) and stimulus spatial frequency and pattern reversal rate (PRVEP) were varied to determine optimum stimulus parameters. Normative FVEP and PRVEP data were collected from mice of both strains after determination of optimum parameters. Five positive and four negative alternating peaks were routinely observed in the FVEP, while three positive and three negative alternating peaks were seen with the PRVEP. Varying the flash rate, the pattern reversal rate, and spatial frequency significantly affected nearly all amplitude and latency measures in the responses. Significant differences between strains were seen on some, but not all, latency and amplitude measures when the stimulus parameters were varied.

Animals↗
PubMed1992

Effect of flash photoreactivation on Escherichia coli recA induction by ultraviolet light.

Excision-deficient Escherichia coli, carrying the gene for the photolyase on a multicopy plasmid, were irradiated with ultraviolet (UV) light then photoreactivated by illumination delivered from a camera flash unit. Such instantaneous illumination monomerizes only cyclobutane pyrimidine dimers already bound by the photolyase. Whereas the lethal effect of UV light and the number of C-to-T transition-type mutations induced by UV irradiation were both significantly reduced by subsequent irradiation with a single flash of light, single-flash photoreactivation did not reverse the induction of the recA gene by UV light. The results indicate, therefore, that non-photoreactivable DNA lesions play a role in recA induction.

Escherichia coli↗
PubMed1981

Thyrotropin-releasing hormone and the menopausal hot flash.

The possibility that the sudden discharge of thyrotropin-releasing hormone (TRH) in the brain triggers the climacteric hot flash was tested (double-blind) by an intra-venous, bolus injection of 500 microgram of TRH into 7 post-menopausal women and 1 menstruating control. Temperatures and sweating were recorded continuously on the recumbent subject during the 2-h test. None of the women reacted either subjectively or objectively to the placebo. TRH induced gastric pain in 1 post-menopausal subject. In another subject TRH elicited no response during the first test, but a week later in a second test it evoked transient nausea and a series of hot flashes with bursts of sweating. Published results of animal studies suggest that a higher dose of TRH would probably stimulate hot flash-like responses in more women.

Adult↗
PubMed1982

Ethnography of the menopause-related hot flash.

Research was conducted to learn how women of two ethnic groups in the United States experience and describe menopause-related hot flashes, their reports of associated events and activities, and the ways in which they cope with the occurrence of the flashes. The women's cognitive ordering of events was learned through ethnographic inquiry, using questions which were derived from respondent-generated topics. Descriptions and responses to this physiological event were similar, but interpretation differed. Middle-class Anglo American women spoke of the sensations negatively, but for Mexican American women, the menopausal hot flash had positive components of meaning.

Adult↗
PubMed1987

Maximizing signal-to-noise and contrast-to-noise ratios in FLASH imaging.

This paper presents an analysis of signal-to-noise and contrast-to-noise ratios from small tip angle, gradient reversal (FLASH) imaging. Analytic and numerical techniques are used to determine the delay times and tip angles that maximize signal-to-noise per unit time from a single tissue. Similar procedures are used to determine the delay times and tip angles that maximize both T1-induced and T-2*-induced contrast-to-noise per unit time for a pair of tissues as a function of tissue characteristics and pulse sequence sampling times. The advantage of optimized FLASH imaging over optimized spin-echo imaging is quantitated by comparing signal-to-noise and contrast-to-noise ratios per unit time from the two sequences. Images are used to confirm these numerical results, to compare noise levels resulting from gradient reversals versus 180 degrees rephasing pulses and to assess the possible adverse effects of static magnetic field inhomogeneities on FLASH imaging.

Humans↗
PubMed1990

3D-snapshot flash NMR imaging of the human heart.

SNAPSHOT-FLASH is a recently developed, ultrafast imaging technique, based on conventional FLASH imaging. The application of this new variant to 3D imaging allows the acquisition of a 128 x 128 x 32 data set in 12.5 seconds without triggering, or for cardiac imaging with gating within 32 heartbeats. Compared to standard 3D-FLASH this is 128 times faster, because triggering is only required when the 3D phase-encoding gradient is incremented. The method depicts for the first time fast three-dimensional views of the human heart without motional artifacts. The images are spin-density weighted. Using suitable prepulses any desired T1- or T2-contrast may be achieved. The generation of 3D movies is possible without an increase of the total scan time.

Heart↗
PubMed1991

Magnetization transfer contrast (MTC) in flash MR imaging.

Magnetization transfer between bound and free protons was used as a source of contrast in high speed MR imaging using the FLASH technique. Contrast in FLASH MR images was found to depend upon the reduced magnetization and the spin lattice relaxation rate of free protons in the presence of bound proton radio-frequency saturation. MTC FLASH imaging was thus used to estimate the variation with saturation frequency of free proton spin-lattice relaxation during magnetization transfer.

Animals↗
PubMed1987

Ontogeny of flash-evoked potentials in unanesthetized rats.

The effects of age and stimulation frequency (0.2/sec, 1.0/sec, 2.0/sec, or 4.0/sec) on flash-evoked potentials (FEPs) were investigated in awake, unsedated, unrestrained rats. Animals were tested daily from postnatal day (PND) 8 to PND 20, and every 3 or 4 days thereafter until PND 41. On PND 9, a single negative wave (N1a) was observed following 0.2/sec flash presentation. Animals tested on PND 10 exhibited a positive wave (P2) following the return of peak N1a to baseline. On PND 13 another negative wave (N1) appeared on the leading shoulder of peak N1a. Peak N1 became the dominant negative wave on PND 14. Peak N1a merged into N1 and had disappeared by PND 19. Peak N3 was first observed as a negative shift following peak P2 on PND 15. Peaks N2 and P3 were not observed in the group average waveforms until PND 34. Peak latencies decreased through the fifth postnatal week. Peak amplitudes increased with age until after eye opening (PND 15), but were variable thereafter. No FEPs were observed following higher than 0.2/sec flash presentation until PND 13. Increasing stimulation frequency decreased N1 and P2 peak amplitudes, but had no effect on peak latencies.

Aging↗
PubMed1994

Quenching of merocyanine 540 triplet state by nitroxyl radicals in liposomal systems: a laser flash photolysis study.

Laser flash photolysis experiments were undertaken to investigate the interaction between stearic acid nitroxide spin probes and photoexcited merocyanine 540 (MC540) in dimyristoyl-L-alpha-phosphatidylcholine liposomes (membrane model). The measurements of the paramagnetic signal decay kinetics of four different spin-labelled stearic acids (n-DSA) show that the direct interaction between the dye and the probe is affected by the position of the nitroxyl group along the carbon chain. Laser flash photolysis results reveal a significant decrease in the MC540 triplet lifetime in the presence of n-DSA, the effect depending on the depth at which the nitroxyl moiety is localized in the bilayer. Previous results on the rate of disappearance of the electron spin resonance (ESR) nitroxide signal on continuous photolysis of the same systems do not show the same dependence on the localization of the nitroxyl moiety in the liposome. Although the MC540 triplet state seems to be implicated in the reaction process, the results suggest that ESR and laser flash experiments demonstrate two different kinds of mechanism.

Dimyristoylphosphatidylcholine↗
PubMed2006

Aggregation of the 636 nm emitting monomeric protochlorophyllide form into flash-photoactive, oligomeric 644 and 655 nm emitting forms in vitro.

Artificial formation of flash-photoactive oligomeric protochlorophyllide complexes was found in etiolated pea (Pisum sativum L. cv. Zsuzsi) epicotyl homogenates containing glycerol (40% v/v) and sucrose (40% m/v). The 77 K fluorescence emission spectra indicated that the ratio of the 644 and 655 nm emitting forms to the 636 nm form increased during 3 to 5-day incubation in the dark at -14 degrees C. Electron micrographs showed the presence of well-organized prolamellar bodies in the homogenates. The same phenomena were found when the homogenates were frozen into liquid nitrogen and thawed to room temperature in several cycles. Similar treatments of intact epicotyl pieces caused significant membrane destructions. In homogenates, the in vitro produced 644 and 655 nm emitting protochlorophyllide forms were flash-photoactive; the extent of phototransformation increased compared to that in native epicotyls. The newly appeared 692 nm chlorophyllide band showed a blue shift (similar to the Shibata shift in leaves), however this process took place only partially due to the effect of the isolation medium. These results prove that the in vitro accumulated 644 and 655 nm protochlorophyllide forms were produced from the flash-photoactive 636 nm emitting monomeric NADPH:protochlorophyllide oxidoreductase units via aggregation, in connection with structure stabilization properties of glycerol and sucrose.

Freezing↗
PubMed2005

Flash photolysis using a light emitting diode: an efficient, compact, and affordable solution.

Flash photolysis has become an essential technique for dynamic investigations of living cells and tissues. This approach offers several advantages for instantly changing the concentration of bioactive compounds outside and inside living cells with high spatial resolution. Light sources for photolysis need to deliver pulses of high intensity light in the near UV range (300-380 nm), to photoactivate a sufficient amount of molecules in a short time. UV lasers are often required as the light source, making flash photolysis a costly approach. Here we describe the use of a high power 365 nm light emitting diode (UV LED) coupled to an optical fiber to precisely deliver the light to the sample. The ability of the UV LED light source to photoactivate several caged compounds (CMNB-fluorescein, MNI-glutamate, NP-EGTA, DMNPE-ATP) as well as to evoke the associated cellular Ca(2+) responses is demonstrated in both neurons and astrocytes. This report shows that UV LEDs are an efficient light source for flash photolysis and represent an alternative to UV lasers for many applications. A compact, powerful, and low-cost system is described in detail.

Animals↗
PubMed2006

Injury pattern of the Flash-Ball, a less-lethal weapon used for law enforcement: report of two cases and review of the literature.

Less-lethal weapons are used in law enforcement to neutralize combative individuals and to disperse riot crowds. Local police recently used such an impact weapon, the Flash-Ball, in two different situations. This gun fires large rubber bullets with kinetic energies around 200 J. Although it is designed to avoid skin penetration, impacts at such energies may still create major trauma with associated severe injuries to internal organs. This is a report of 2 patients shot with the Flash-Ball who required medical attention. One could be discharged quickly, but the other required hospitalization for heart and lung contusion. Both patients required advanced investigations including computed tomography (CT) scan. The medical literature on injuries induced by less-lethal impact weapons is reviewed. Impacts from the Flash-Ball can cause significant injury to internal organs, even without penetration. Investigations as for other high-energy blunt traumas are called for in these cases.

Adult↗
PubMed2006

Semiconductor ultra-violet light-emitting diodes for flash photolysis.

'Caged' compounds are biological molecules that are rendered inactive by a protecting (cage) group. Photocleaving of chemical bonds associated with the cage species with intense UV light results in the release of the active molecules. This technique, called flash photolysis, allows for real-time study of interacting biological molecules and typically involves the use of high intensity lasers or flash lamps to deliver the UV pulse to the biological specimen [Callaway EM, Katz LC. Photostimulation using caged glutamate reveals functional circuitry in living brain slices. Proc Natl Acad Sci USA 1993;90(16):7661-5; Parpura V, Haydon PG. "Uncaging" using optical fibers to deliver UV light directly to the sample. Croat Med J 1999;40(3):340-5; Denk W. Pulsing mercury arc lamps for uncaging and fast imaging. J Neurosci Methods 1997;72(1):39-42]. Here, we introduce compact, custom-designed semiconductor UV light-emitting diodes (LEDs) as a viable and efficient source for performing flash photolysis studies, focusing specifically on the application of these devices for uncaging neurotransmitters locally onto neurons cultured on artificial substrates. The illumination design feature incorporated in these devices allows for direct placement of the UV source in immediate proximity with the neuron of interest and provides a means for optical triggering of activity in the neuronal culture.

Animals↗
PubMed2005

Neural latencies do not explain the auditory and audio-visual flash-lag effect.

A brief flash presented physically aligned with a moving stimulus is perceived to lag behind, a well studied phenomenon termed the Flash-Lag Effect (FLE). It has been recently shown that the FLE also occurs in audition, as well as cross-modally between vision and audition. The present study has two goals: to investigate the acoustic and cross-modal FLE using a random motion technique; and to investigate whether neural latencies may account for the FLE in general. The random motion technique revealed a strong cross-modal FLE for visual motion stimuli and auditory probes, but not for the other conditions. Visual and auditory latencies for stimulus appearance and for motion were measured with three techniques: integration, temporal alignment and reaction times. All three techniques showed that a brief static acoustic stimulus is perceived more rapidly than a brief static visual stimulus, while a sound source in motion is perceived more slowly than a comparable visual stimulus. While the results of these three techniques agreed closely with each other, they were exactly opposite that required to account for the FLE by neural latencies. We conclude that neural latencies do not, in general, explain the flash-lag effect. Rather, our data suggest that neural integration times are more important.

Acoustic Stimulation↗
PubMed2006

Flash lag in depth.

The perceived position of a moving target at a particular point in time, indicated by a flash, is often judged to be different from its actual location. Here, we show that the position of a target moving in depth is also systematically mislocalized. We used three types of targets moving in depth at a range of speeds from 2 to 16 cm/s. (i) A target realistically rendered that included concordant looming, disparity, and perspective cues. (ii) A random dot surface whose depth was defined by disparity, without concordant perspective or looming cues. (iii) A surface of dynamic random dots whose depth was defined by disparity with no consistent motion visible monocularly. Subjects viewed the targets moving either towards or away from them and indicated whether the targets appeared to be nearer or farther than a continuously present reference depth at the moment that a flash was presented. A staircase procedure was used to null, and thus measure, any perceptual displacement from the reference depth. A flash lag in depth was found in which the target appeared ahead of its true position, displaced by a constant amount of time depending on the stimulus type and the direction of motion (towards or away). The time displacement varied from 76 ms (for the realistic target moving away from the observer) to 263 ms (for static random dots moving towards). These effects may depend on the confidence with which subjects were able to judge the location of our various targets: greater confidence leading to a smaller temporal displacement.

Cues↗
PubMed2006

Dividing attention in the flash-lag illusion.

A dual-task paradigm was used to examine the effect of withdrawing attentional and/or cognitive resources from the flash-lag judgment. The flash-lag illusion was larger, and performance in a detection task was generally poorer, under dual-task conditions than in single-task control conditions. These effects were particularly pronounced when decisions in the two tasks were required simultaneously, as compared to when they could be made sequentially. The results suggest that a time-consuming process is involved in the flash-lag decision, of such a nature that prolonging the process increases the magnitude of the illusion.

Attention↗