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Biomedical subjects

C T White

Publications and source records attributed to C T White.

At least 19 recordsLinked to original sources
PubMed2001

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.

Age Factors↗
PubMed1996

BioSCAN: a network sharable computational resource for searching biosequence databases.

We describe a network sharable, interactive computational tool for rapid and sensitive search and analysis of biomolecular sequence databases such as GenBank, GenPept, Protein Identification Resource, and SWISS-PROT. The resource is accessible via the World Wide Web using popular client software such as Mosaic and Netscape. The client software is freely available on a number of computing platforms including Macintosh, IBM-PC, and Unix workstations.

Algorithms↗
PubMed1995

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.

Attention↗
PubMed1986

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.

Adult↗
PubMed1986

Synergistic toxicity of endotoxin and hemoglobin.

Stroma-free hemoglobin (SFH) is advocated as an oxygen-transporting resuscitation solution. Hemoglobin has been shown to enhance endotoxin lethality when given intraperitoneally. It is possible that SFH could interact with endotoxin when used as an oxygen-transporting resuscitation system for trauma victims with contaminating wounds. To assess the effects of these two agents when given intravascularly, rabbits were infused with SFH (1.75 gm/kg) or albumin (controls; 1.75 gm/kg) with and without endotoxin. Two doses of endotoxin were used. At 14.5 ng/kg of Salmonella enteritidis endotoxin, no effect was seen in the albumin group. However, 50% of the hemoglobin group died. At 14.5 micrograms/kg, the albumin group showed hematologic alterations, but all animals lived. All SFH-treated animals died at the higher endotoxin dose. SFH alone caused cardiac abnormalities (bradycardia in 100%, sinus arrhythmias in 30%, and ventricular arrhythmias in 20%), liver abnormalities (necrosis in 40% and 240% increase in alanine aminotransferase activity by 6 hours), and intravascular thrombi (30%). The only hemoglobin-induced abnormality that was more frequent in the presence of endotoxin was ventricular arrhythmias (up to 75% of animals). Thrombin times were approximately 20% larger in all SFH groups compared with the albumin groups. By 6 hours after infusion, endotoxin prolonged the thrombin time even further, despite the lack of fibrinogen consumption. This study shows that endotoxin and SFH exert synergistic toxicity when SFH is given in a clinically relevant dose for an oxygen-transporting resuscitation system. Only minute quantities of endotoxin are needed to produce this phenomenon. We hypothesize that this synergism is endotoxin enhancement of hemoglobin toxicity.

Animals↗
PubMed1986

Toxicity of human hemoglobin solution infused into rabbits.

Aqueous human hemoglobin is being considered as an oxygen-transporting resuscitation solution. However, there are some indications that such solutions may be toxic. We report here that at a clinically significant dose (20% to 30% of the estimated blood volume) of hemoglobin solution (10 gm/dl), toxicity similar to that reported in humans is produced in rabbits. This toxicity is characterized by cardiac rhythm disturbances (25%) and coagulation abnormalities, manifested as intravascular thrombi. Hypoxia, tissue necrosis (brain 29%, liver 25%), and death (22%) were seen. Hypoxia appears to be the cause of death, because the arterial PO2 of rabbits that died was significantly lower (43 +/- 8 mm Hg) than that of rabbits that lived (80 +/- 12 mm Hg). We also report the effect of the method of preparation or degree of purity on the observed toxicity. Stroma-free red blood cell hemolysate, stroma-free hemoglobin, zinc-precipitated hemoglobin, and chromatographically purified hemoglobin were infused. Purification of these solutions ranged from removal of stroma to removal of all detectable nonhemoglobin protein components. In addition, the nonhemoglobin proteins were concentrated and infused into rabbits to compare their effects. All of these hemoglobin solutions induced similar toxicity for rabbits infused with stroma-free hemoglobin. The nonhemoglobin proteins, as well as human serum albumin, exhibited no toxicity. These results demonstrate that, at the clinically relevant dose, hemoglobin or something inherently associated with hemoglobin is toxic.

Animals↗
PubMed1984

The diagonal-traverse homology search algorithm for locating similarities between two sequences.

We present a fast computer algorithm for finding homology between two DNA sequences. It generates a two-dimensional display in which a diagonal string of dots represents a stretch of homology between the two sequences. Our algorithm performs the search very rapidly, and has no internal data storage requirement except for the sequences themselves. These characteristics make it particularly well suited for execution on microcomputers. Without slowing execution, the matching criterion can be that a specified fraction of contiguous bases must be identical. Even with gapped sequences, we have found large search windows to be surprisingly good for detecting poor homologies with nearly complete background suppression. A diagonal search pattern is used that reports the finds in a compact and logically ordered form. A simple and rapid plotting algorithm for unsophisticated printers is also reported.

Base Sequence↗
PubMed1983

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.

Adult↗
PubMed1983

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.

Evoked Potentials, Visual↗
PubMed1980

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.

Bacillus↗
PubMed1979

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.

Adolescent↗
PubMed1975

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.

Accommodation, Ocular↗