Ventriculoperitoneal shunts in children on peritoneal dialysis: a survey of the International Pediatric Peritoneal Dialysis Network.

OBJECTIVE: The aim of this study was to inform best evidence-based practice by collating and disseminating the experiences of members of the International Pediatric Peritoneal Dialysis Network with children having concurrent ventriculoperitoneal shunts (VPS) and peritoneal dialysis catheters (PDC). METHODS: An online questionnaire was created and distributed to all 135 centers participating in the International Pediatric Peritoneal Dialysis Network; the overall response rate was 56 %. RESULTS: A total of 18 patients with a concurrent VPS and PDC were reported. The children were 0-12 (mean 6.8) years old at the time of placement of the second indwelling device (PDC or VPS). In 15 cases, the PDC was inserted post-VPS. On average, the two catheters were present concurrently for 23 (range 1-60) months. There were 20 episodes of peritonitis observed in 11 of the 18 patients during a period of 392 months at risk, which is a peritonitis rate of 1/19.6 months. Only one patient developed both a VPS infection and an episode of peritonitis, and these events were temporally unrelated. No episodes of an ascending shunt infection or meningitis occurred in association with any episode of peritonitis, and no other complications of catheter dysfunction were described. CONCLUSIONS: The rate of peritonitis, the absence of any documented ascending or descending infections and the lack of catheter dysfunction during the period of observation suggests that the presence of, or need for, a VPS should not preclude PD as a safe option for children requiring renal replacement therapy.

Graphene valley filter using a line defect.

With its two degenerate valleys at the Fermi level, the band structure of graphene provides the opportunity to develop unconventional electronic applications. Herein, we show that electron and hole quasiparticles in graphene can be filtered according to which valley they occupy without the need to introduce confinement. The proposed valley filter is based on scattering off a recently observed line defect in graphene. Quantum transport calculations show that the line defect is semitransparent and that quasiparticles arriving at the line defect with a high angle of incidence are transmitted with a valley polarization near 100%.

Perceived number and evoked cortical potentials.

Evoked cortical potentials and the numsber of flashes perceived were compared when subjects were presented with short trains of flashes under conditions where each presented flash could not be counted individually, but the train of flashes appeared to be flickering (1 to 14 flashes at 33.3 flashes per second). The rate at which each successive perceived flash was added appeared to correspond with the rate at which the successive components of the evoked response pattern were added. The temporal nature of this pattern was similar for both single flashes and trains of flashes. The results suggest that the onset of stimulation triggers a process whlich has a marked effect on both the cortical and perceptual response to subsequent stimulation.

Evoked cortical potentials: relation to visual field and handedness.

The amplitiude of evoked responses of occipital cortex in man depends on the visual field in which the stimulus appears. Greater responses occurred repeatedly for two of three subjects, both left-handed. when the stimululs appeared in the left field than in the right. Subsequent tests of 13 right- and 13 left-handed males indicted that the magnitude of the response of the right lobe, relative to that of the left, was greater for left-handed individuals. We conclude that the difference in amplitude between the two lobes is related to handedness.

Reactive molecular dynamics of hypervelocity collisions of PETN molecules.

Born-Oppenheimer direct dynamics classical trajectory simulations of bimolecular collisions of PETN molecules have been performed to investigate the fundamental mechanisms of hypervelocity chemistry relevant to initiating reactions immediately behind the shock wavefront in energetic molecular crystals. The solid-state environment specifies the initial orientations of colliding molecules. The threshold velocities for initiating chemistry for a variety of crystallographic orientations were correlated with available experimental data on anisotropic shock sensitivity of PETN. Collisions normal to the planes (001) and (110) were found to be most sensitive with threshold velocities on the order of characteristic particle velocities in detonating PETN. The production of NO2 is the dominant reaction pathway in most of the reactive cases. The simulations show that the reactive chemistry, driven by dynamics rather than temperature during hypervelocity collisions, can occur at a very short time scale (10(-13) s) under highly nonequilibrium conditions.

Density functional theory calculations of solid nitromethane under hydrostatic and uniaxial compressions with empirical van der Waals correction.

First-principles density functional theory calculations have been performed with and without an empirical van der Waals (vdW) correction to obtain constitutive relationships of solid nitromethane under hydrostatic and uniaxial compressions. The unit-cell parameters at zero pressure and the hydrostatic equation of state at 0 K are in reasonable agreement with experimental data using pure DFT, and the agreement is significantly improved with the inclusion of the vdW dispersion correction. Uniaxial compressions normal to the {100}, {010}, {001}, {110}, {101}, {011}, and {111} planes were performed, and a comparison of the principal stresses, changes in energy, and shear stresses for different compression directions clearly indicate anisotropic behavior of solid nitromethane upon compression. The calculated anisotropic constitutive relationships might help to link the anisotropic shock sensitivity and the underlying atomic-scale properties of solid nitromethane.

The recognition site of type II restriction enzyme BglI is interrupted.

The Type II restriction endonuclease BglI recognizes the interrupted DNA sequence 5'-G-C-C-N-N-N-N-N-G-G-C-. This sequence occurs at all locations in over 33 000 base pairs of DNA sequence where the enzyme was found to cut DNA and nowhere else. All six of the specified bases are essential parts of the site since all groups of five of the six bases occur in the DNA sequences tested and none of them are cut by BglI. The length of the block of intervening unspecified positions must be exactly five since all other sizes between zero and 15 occur in the DNA sequences searched and none are cut by BglI. The 5'-terminal nucleotides of BglI cleaved phage G4 replicative form DNA and plasmid pER18 DNA were compared with the DNA sequences near the BglI sites on these DNAs. These results indicated that BglI cuts within the intervening unspecified region and produces single-stranded 3' termini that are three bases long. The BglI recognition site and cleavage points can thus be represented as follows: (Formula: see text). This study of the BglI recognition site was facilitated by the use of inexpensive microcomputers. A system of programs was developed that allowed analysis of over 33 kb of DNA sequences stored on flexible magnetic disks or audio cassettes. While these programs were generally written in the higher level language BASIC, some assembly language subroutines were utilized to reduce execution time.

Reflections on visual evoked cortical potentials and selective attention: methodological and historical.

Details of research in which Russ Harter participated in his formative years are reviewed. Harter's participation in the early work on Visual Selective Attention (Eason, Harter & White, 1969) probably contributed most importantly to his career. While reviewing Russ's early experience with basic vision research and pioneer visual evoked potentials (VEPs), there is reference to extensive information regarding stimulus effects on VEPs (exogenous components of the ERP). There can be complex early and late waveforms and waveform changes with changes in certain stimulus conditions. There are critical peripheral vision effects at various loci over the visual field on VEP and reaction time. Special emphasis is given to effects of individual differences in training and skill of experienced subjects, as well differences in ability. These observations may suggest methods for optimizing sensitivity of ERPs and possibly some clues toward further understanding of ERPs.

Children's UTIs in the new millennium. Diagnosis, investigation, and treatment of childhood urinary tract infections in the year 2001.

OBJECTIVE: To provide an effective approach for family physicians treating children presenting with urinary tract infections (UTIs). QUALITY OF EVIDENCE: The information presented, and articles quoted, are drawn from both review of the literature and recent consensus guidelines. Data and recommendations come from prospective multicentre trials; retrospective reviews; expert consensus statements; and some smaller trials, commentaries, and editorials. MAIN MESSAGE: Urinary tract infections are often seen in family practice. Diagnosis requires suspicion and a realization that children, especially those younger than 2 years, often have very few, nonspecific signs of infection. Obtaining a proper urine sample is vital, because true infections require radiographic studies. Antibiotic prophylaxis is promoted because of the link between vesicoureteral reflux, recurrent UTIs, and renal scarring and hypertension. We generally provide prophylaxis until children are 3 or 4 years, when risk of damage from reflux is lessened and timely urine samples are easier to obtain for prompt therapy. Surgical opinion is sought only when medical management has failed. Failure is defined as either recurrent infections and pyelonephritis or poor renal growth. CONCLUSION: To diagnose UTIs in children, physicians must suspect them, obtain proper urine samples, order appropriate investigations to rule out underlying anatomic abnormalities, and treat with appropriate antibiotics considering both organism sensitivities and length of therapy.

Complex binocular interaction and other effects in the visual evoked response.

One article dealing with some of the research on binocular interaction effects being carried out in our laboratory has appeared previously in this Journal (White and Bonelli). In that study, it was found that the amplitude of the visually evoked cortical potential (VER) produced by patterned stimuli viewed with both eyes was directly related to the quality of the retina image. Furthermore, the degree of binocular summation shown by the VERs was also related to image quality, with marked summation occurring when sharply focused patterns were presented but much less evidence of it when the patterns were blurred. In that study the retinal images were reasonably similar, since the degree of blur desired was produced by placing ophthalmic lenses of equal strength before the two eyes. The next situation we decided to test was that in which the images presented to the two eyes were not of the same quality. This paper will deal briefly with some work we have done on that topic, and will also present some other examples of work dealing with binocular interaction and related topics.

Evoked potentials to dynamic random dot stereograms in upper, center and lower fields.

Dynamic random dot stereograms consisting of square, crossed disparities subtending 3 degrees, exposure duration 100 ms, were presented in the midplane centrally (surrounding the fixation point) and in the upper and lower fields at 3.5 degrees vertical displacement from fixation. Stereoscopic cerebral evoked potentials (EPs) recorded from scalp sites 02, 01, T6 and T5 (10-20 system) were analyzed in a group of normal young adults (N = 28). Fourteen were able to perceive and report the stereophenomenon (perceivers); the other half were unable to do so (nonperceivers). Mean response amplitudes were significantly larger to center field stimuli than to those in the upper field. Responses were larger in perceivers than nonperceivers, maximal at T5, and larger to stimuli with definite than indefinite boundaries. Peak EP latencies were shortest to lower field stimuli (243 ms) but not significantly different than to center (247 ms) or upper (253 ms) field stimuli. A separate experiment comparing EP amplitudes and latencies with crossed and uncrossed disparities of varying magnitudes confirmed greater responses to the crossed.

Cortical and subcortical components of the pattern VEP.

Studies in the past have shown that wavelength related VEPs can be recorded from both cortical and noncortical sites. Elements of pattern-specific VEPs for both transient and pattern-reversal stimuli are also obtained from these sites. From the noncortical montage consistent responses are obtained with a major component at about 100 msec, which has been found for both the wavelength related and pattern related VEP. In contrast, the cortical VEP to both types of stimuli include two major components, at around 100 and 200 msec. In pattern reversal these components react quite differently to changes in spatial frequency. The component around 100 msec reacts strongly to a wide range of spatial frequencies when recorded from either cortical or noncortical sites. In contrast, the component around 200 msec, obtained with cortical recording, reacts very strongly to high spatial frequencies and very weakly to low spatial frequencies. This finding corresponds to recent results of single-cell studies in the macaque LGN and striate cortex.

Pattern component ratio in pattern-reversal VEP: normative data and clinical applications.

It has been well established that there is a reliable implicit time to the VEP positive component (ca 100 msec) in response to pattern reversal. This has become a valuable test of the status of the visual system. Recent data suggest that activity around 200 msec is another useful measure of the cortical response to pattern alternation. We have carried out a normative study of the relative amplitudes of the two components. Among adults with normal visual acuity activity around 200 msec is directly related to the spatial frequency of the stimulus, peaking markedly in amplitude at a narrow range of spatial frequencies. This is in sharp contrast to the earlier component, which does not exhibit such sensitive size differentiation. Recently we have used the ratio between the late and early component amplitudes as a quantitative indicator of the efficiency of higher-level processing of pattern information. We present our normative data and illustrate the effects of decreased visual responses not related to known peripheral optical problems. The results of this work are also interpreted as showing basic characteristics of information processing in the visual system, in that higher spatial frequencies are processed by a continuum of rather sharply tuned cortical processes, with the higher spatial frequencies being processed later in time.

Effect of altered central and peripheral visual field stimulation on correct recognition and visual evoked response.

Hemispheric asymmetry was assessed using combined electrophysiological (visual evoked response) and behavioral (percentage-correct-recognition) techniques. Right-handed, right-eyed, male undergraduates who viewed tachistoscopically exposed CVCs and random shapes in both central and peripheral visual fields were scored for their ability to recognize the stimuli correctly. Latency and amplitude of visual evoked responses were compared with correct recognition. Central and peripheral stimuli produced significant results. Superiority of the left hemisphere for verbal stimulus processing was supported. Small but consistent positive peak latencies of visual evoked responses also indicated language specialization of the left lobe. Results were interpreted as supporting hemispheric functional asymmetry. Additional findings of "cognitive masking" and marked reduction in intersubject variance in postive peak latencies of visual evoked responses by a central stimulus occurring at approximately 300 msec were also obtained. Mechanisms of iconic image storage, neuropsychological attentional theories, and differential hemispheric structural organization were discussed in interpreting results.