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Biomedical subjects

M H Johnson

Publications and source records attributed to M H Johnson.

At least 91 records · Page 5Linked to original sources
PubMed1998

Kinetics of fluid delivery from methylcellulose sponges.

PURPOSE: The authors quantitatively evaluate the kinetics of fluid transfer from microsurgical sponges in a laboratory model to understand the kinetics of mitomycin C (MMC) delivery. METHODS: The amount of fluid transferred from soaked methylcellulose (Weck-cel, Weck Inc., Durham, NC, U.S.A.) sponges to small pieces of hydrated or dry filter paper used to simulate episcleral tissue and Tenon fascia was measured as a function of time, sponge size, hydration status of the filter paper, and technique of sponge application. RESULTS: The time course of fluid delivery from methylcellulose sponges to filter paper was nonlinear and characterized by a rapid delivery phase over the first 15 to 30 seconds, followed by a slow phase extending to at least 5 minutes. Sponge size and baseline hydration of the paper significantly influenced the rate and amount of fluid delivered, as did replacing the sponge every minute with a new sponge. CONCLUSION: The transfer of fluid from a microsurgical sponge displays nonlinear kinetics, with the majority of delivery occurring in the first 15 to 30 seconds. Sponge size, hydration of the recipient tissue, and technique of sponge application are significant variables influencing the amount of fluid, and therefore mitomycin C, delivered.

Antibiotics, Antineoplastic↗
PubMed1998

Needle biopsies of the prostate: what constitutes adequate histologic sampling?

OBJECTIVE: The automated biopsy gun and increased screening for adenocarcinoma of the prostate have led to increased numbers of biopsies with only tiny foci of prostatic carcinoma. Consequently, the risk of failing to sample a small focus of carcinoma histologically has increased as well. Most pathologists routinely sample prostatic needle biopsies at more than 1 level. An expert panel has recently suggested that prostatic needle biopsies be sampled at at least 2 levels. However, there have been no studies measuring the amount of additional tissue sampled by multiple levels versus 1 level. METHODS: Forty-two prostatic needle biopsies were serially sectioned at 4-microm levels. Hematoxylin-eosin-stained slides were prepared from every fifth section. The total length of each biopsy was compared with the length sampled by 1 level (50% through the block) and 3 levels (25%, 50%, and 75% through the block). RESULTS: Sampling the tissue at 1 level missed an average of 23.4% of the total biopsy length. Sampling the tissue at 3 levels significantly improved this average to 7% (P = .0001). CONCLUSIONS: This study shows that a single histologic section of a prostatic needle biopsy often fails to sample a significant portion of available tissue. This could occasionally result in failure to sample a small focus of prostatic carcinoma. The authors recommend that prostatic needle biopsies be routinely sampled at 3 levels (approximately 25%, 50%, and 75% through the block).

Adenocarcinoma↗
PubMed1997

The emergence of perceptual category representations in young infants: a connectionist analysis.

There has been recent interest in the idea that principles governing learning in connectionist networks can form the basis for an alternative understanding of developmental processes (Elman, Bates, Karmiloff-Smith, Johnson, Parisi, & Plunkett, 1996). The present paper can be viewed as a case example of the usefulness (and limitations) of connectionist modeling for the study of infant cognition. Specifically, the paper reports on a series of connectionist models designed to analyze the factors responsible for the emergence of global-level and basic-level category representations in young infants. The models (1) simulated the formation of global-level and basic-level representations, (2) revealed a global-to-basic order of category emergence, (3) uncovered the formation of two distinct global-level representations-an initial "self-organizing" perceptual global level and a subsequently "trained" arbitrary (i.e., nonperceptual) global level, and (4) displayed a gradual transition from perceptual global-level to perceptual basic-level representation with increasing exposure to training stimuli. Hypotheses for empirical investigations of category development in infants that follow from the modeling efforts are discussed.

Child Development↗
PubMed1997

"How do you remember you ate...?": a Delphi technique study to identify retrieval categories from fourth-grade children.

OBJECTIVE: To develop and validate a consensus set of retrieval categories for how children remember what they have eaten, and to relate retrieval categories to accuracy of reporting items eaten during school lunch. DESIGN: A Delphi technique study was conducted using 10 psychologists. The subject matter consisted of responses transcribed from interviews conducted with 89 randomly selected fourth graders within 90 minutes of eating. Retrieval categories were evaluated for accuracy by comparing students' self-reported lunch intake with observation. STATISTICAL ANALYSES: For round 1, a centroid hierarchical cluster analysis was used to identify common sets of rating pairs to propose categories for reaching consensus. For rounds 2 and 3, percent of agreement was calculated. Accuracy was tabulated across meal items and student use by retrieval category. RESULTS: After round 3, we found that 23 "near-consensus" categories were used by at least eight raters. Six categories were used 60% of the time, 4 were used 20% of the time, and 5 were used 15% of the time. Less frequently used categories were combined with similar, more frequently used categories for a total of 16 categories. Students used a large variety of retrieval categories when accurately reporting consumption. Of the 16 categories, 12 were used similarly by both accurate and inaccurate students. Where there were differences in accuracy by retrieval category, the more accurate students used "taste/smell/texture" and "visual" in deference to "order items consumed" and "oral cue still present." APPLICATIONS: These categories provide insight into the broad range of retrieval categories that children use and provide direction for researchers to design and study specific cues to enhance the accuracy of children's self-reports of diet.

Child↗
PubMed1997

Impact of gender, ethnicity, meal component, and time interval between eating and reporting on accuracy of fourth-graders' self-reports of school lunch.

OBJECTIVE: To validate fourth-graders' self-reports of school lunch by comparing their reports to lunch observations, and to determine the impact on accuracy of gender, ethnicity, meal component, and time interval between eating and reporting. DESIGN: Students were randomly selected, observed eating lunch, and interviewed the same day, next day, or Monday regarding Friday's lunch. Accuracy of reporting items was determined by tallying matched foods (items reported and observed), phantom foods (items reported but not observed), and omitted foods (items not reported but observed). Accuracy of reporting amount eaten was determined by calculating absolute and arithmetic differences. SUBJECTS: Subjects were 260 students: 89 same-day, 148 next-day, and 23 Monday recalls; 59 whites (30 boys) and 201 blacks (103 boys) from four schools. STATISTICAL ANALYSES: Rates for matched, phantom, and omitted foods; analysis of variance; Friedman's nonparametric analog of analysis of variance; Student-Newman-Keuls' post hoc comparisons. RESULTS: In regard to reporting items, the respective rates for matched, phantom, and omitted foods were 84%, 5%, and 16% for same-day recalls; 68%, 13%, and 32% for next-day recalls; and 38%, 48%, and 62% for Monday recalls. Rates for omitted and phantom foods were higher for Monday recalls than for next-day recalls, which were higher than for same-day recalls (P < .05 for all). In regard to reporting amounts, analysis by gender, ethnicity, and time interval failed to yield significant main or interaction effects. When children correctly reported items eaten, they were quite accurate in reporting amounts eaten. Omitted food rates were lowest for beverage, followed by entree, and highest for miscellaneous and condiment. APPLICATIONS: Even under the best conditions (ie, reporting within 90 minutes after eating school lunch), children have difficulty accurately reporting what they have eaten. As the time interval between eating and reporting increases, accuracy decreases markedly. Techniques that improve reporting of items eaten should result in improved accuracy of reporting amounts eaten.

Analysis of Variance↗
PubMed1997

Body-centered representations for visually-guided action emerge during early infancy.

The nature of the spatial representations that underlie simple visually guided actions early in life were investigated through the application of a 'double-step' saccade paradigm to 3- and 7-month-old infants. Saccades in the older infants, like those observed in adults, were executed within body-centered spatial coordinates that take into account the effects of intervening eye movements. In contrast, younger infants tended to respond according to the targets' retinocentric locations and did not incorporate the effects of displacements caused by previous saccades. These results indicate that contrary to prevailing views, body-centered representations for action are not present from birth but emerge, probably through experience, over the first few months of life.

Body Image↗
PubMed1997

Attention and oculomotor control: a high-density ERP study of the gap effect.

In a gap paradigm, healthy adult subjects performed visually triggered saccades to peripheral targets either with the fixation stimulus remaining on (overlap trials) or going off before target onset (gap trials). All subjects showed faster reaction times in the gap trials (the gap effect). High density scalp event-related potentials were recorded time-locked to both the target stimuli and the eye movement onset. We observed three neural correlates of the gap effect: (i) a prefrontal positivity that precedes the target presentation which may reflect specific preparatory processes, (ii) an enhancement of the early cortical visual responses (PI) to the peripheral target in the gap trials, and (iii) a prolongation of parietal activity in the overlap trials relative to the gap trials prior to the saccade execution. These results suggest that several factors contribute to the gap effect, each having its own neural basis.

Adult↗
PubMed1997

Detection and localization of steel intraocular foreign bodies using computed tomography. A comparison of helical and conventional axial scanning.

PURPOSE: To compare the sensitivity and specificity of detection, and accuracy of localization, of small steel intraocular and episcleral foreign bodies, using conventional axial and helical computed tomographic scanning in an experimental model. METHODS: Small steel foreign bodies ranging in size from 0.048 to 0.179 mm3 were placed in intraocular and episcleral locations in eye bank eyes mounted in the orbits of a human skull and scanned using helical and conventional axial techniques. Helical scanning was performed using 1-mm and 3-mm thick sections. Conventional axial scanning was performed using 3-mm thick sections. Images were reviewed by masked observers to determine sensitivity, specificity, and accuracy of localization for each imaging method. RESULTS: Steel foreign bodies as small as 0.048 mm3 were detectable with each scanning protocol. Although the helical scans appeared to provide higher levels of sensitivity compared to conventional axial scanning, the difference in outcome between the scan types was not statistically significant. Sensitivity was dependent on the size of the foreign body and ranged from 45% to 65% for the smaller ones (< 0.06 mm3) to 100% for the larger ones (> 0.06 mm3). Multiplanar reformatting of images was helpful in achieving optimal accuracy. CONCLUSION: In an experimental model of steel intraocular foreign body, helical computed tomographic scanning provided images of high quality similar to that of conventional axial scanning.

Cadaver↗
PubMed1997

The effects of distraction on exercise and cold pressor tolerance for chronic low back pain sufferers.

Distraction has been found to be effective for the attenuation of experimental and acute clinical pain but its efficacy for chronic pain management remains unclear. There are even some suggestions that distraction may be a counterproductive strategy for chronic pain sufferers. In this study we found that a word shadowing distraction task increased the ability of a group of 12 female and eight male chronic low back pain (CLBP) sufferers to carry out a brief (maximum 300 s) step-up exercise that temporarily increased their pain (P < 0.05). This 15% increase in exercise time was not accompanied by an increase in reported pain after the exercise. Interestingly, the same distraction task did not increase the cold pressor (CP) tolerance time for the CLBP group but produced a 26% increase in tolerance time for a pain-free control group consisting of nine females and nine males (P < 0.05). Also, performance on the distraction task during the CP was worse for the CLBP group than the controls (P < 0.05). Although these findings should be interpreted cautiously because of the parameters of the experiment, they do suggest that distraction is a potentially useful technique to assist chronic pain sufferers.

Adolescent↗
PubMed1997

An ophthalmic surgeon's view of orbital imaging techniques.

Selection of an orbital imaging technique requires a thorough understanding of pertinent anatomy applied to relevant clinical history and detailed ophthalmic examination. The clinical finding should direct the clinician to the imaging study that provides maximum information and narrows diagnostic considerations for the individual patient. Clinical examples are provided to illustrate the rationale in ordering magnetic resonance images, computed tomography, ocular ultrasound, and color Doppler arteriography of orbital processes.

Adolescent↗
PubMed1997

Rethinking infant knowledge: toward an adaptive process account of successes and failures in object permanence tasks.

Infants seem sensitive to hidden objects in habituation tasks at 3.5 months but fail to retrieve hidden objects until 8 months. The authors first consider principle-based accounts of these successes and failures, in which early successes imply knowledge of principles and failures are attributed to ancillary deficits. One account is that infants younger than 8 months have the object permanence principle but lack means-ends abilities. To test this, 7-month-olds were trained on means-ends behaviors and were tested on retrieval of visible and occluded toys. Means-ends demands were the same, yet infants made more toy-guided retrievals in the visible case. The authors offer an adaptive process account in which knowledge is graded and embedded in specific behavioral processes. Simulation models that learn gradually to represent occluded objects show how this approach can account for success and failure in object permanence tasks without assuming principles and ancillary deficits.

Child Development↗
PubMed1997

The interstitial response to renal injury: fibroblast-like cells show phenotypic changes and have reduced potential for erythropoietin gene expression.

To define the potential for erythropoietin gene expression in injured kidneys, marker gene expression was examined in transgenic mice bearing a homologously recombined erythropoietin--simian virus 40 T antigen (Epo-TAg) transgene. Three types of renal injury were studied: ureteric obstruction, global ischemia following clamping of the renal pedicle, and focal needlestick injury. All modes of injury were associated with an expansion of the interstitial space, which contained an increased number of cells. Alterations observed in the interstitial fibroblast-like cells included an increased number and complexity of cellular processes, enhanced expression of contractile elements, particularly of the intermediate filament desmin, and reduced expression of ecto-5'-nucleotidase. Following each type of injury there was a focal or general reduction in the proportion of such cells that could be stimulated to express Epo-TAg. However, some positively staining cells were present even in severely injured regions and more could be recruited to express Epo-TAg by severe anemic or hypoxic stimulation, indicating that cells with the potential for erythropoietin gene expression were neither absent nor completely refractory to stimulation in these regions. In all injured kidneys, Epo-TAg expression was limited to the fibroblast-like population. Double labeling experiments showed that cells expressing Epo-TAg also expressed increased amounts of desmin, demonstrating that the myofibroblast features which develop in response to injury and the capacity for erythropoietin gene expression are not mutually exclusive.

Animals↗
PubMed1997

Using relative value units to measure faculty clinical productivity.

The objective of this project was to compare faculty productivity in teaching and nonteaching clinical settings. We hypothesized that teaching activity would have no impact on productivity. A mixed model, repeated measures analysis of variance was used to analyze average relative value units (RVUs) billed and to test for differences between clinics. Data were drawn from 4,956 clinical encounters made within a student, resident, and faculty clinic. Average RVUs per visit were similar in the three settings. Resident supervision increased faculty productivity, while student supervision had no impact on billed RVUs. Thus, RVUs can be used as a measure of faculty clinical productivity in different settings in an academic medical center. Precepting students does not appear to affect clinical productivity.

Efficiency, Organizational↗
PubMed1997

Connectionism and developmental psychology.

What features of brain processing and neural development support linguistic and cognitive development in young children? To what extent are the profile and timing of development in young children determined by a preordained genetic programme? Does the environment play a crucial role in determining the patterns of change observed in children growing up? These questions have been of central concern to developmental psychologists for well over a century. Yet none of them have received answers that are generally accepted by the profession. This article reviews some recent computational modelling of developmental change in children that promises to contribute to a deeper understanding of the issues behind these questions. The modelling work exploits artificial neural networks that mimic some of the basic properties of neural processing in the brain. These networks involve densely connected webs of simple processing units that propagate and transform complex patterns of activity. When exposed to a training environment, they undergo a process of self-organisation, yielding information processing systems that support new forms of behaviour. The study of the dynamics of these systems and their learning capabilities promises to provide us with important clues as to the nature of the mechanisms underlying development in infants and young children.

Brain↗
PubMed1996

Phospholipase C in mouse oocytes: characterization of beta and gamma isoforms and their possible involvement in sperm-induced Ca2+ spiking.

This study involved an investigation of the role of phospholipase C (PLC) in generating repetitive Ca2+ spikes at fertilization. Using a PCR-based strategy we have demonstrated that mouse oocytes have mRNA coding for PLC beta 1, PLC beta 3 and PLC gamma isoenzymes. Furthermore, immunodetection of PLC gamma 1 using monoclonal antibodies reveals that PLC gamma 1 protein is present in mature mouse oocytes, ruling out the possibility that mRNA was being transcribed but not expressed. We were unsuccessful at detecting the presence of PLC beta protein, but the presence of this isoform can be inferred from functional studies. The PLC inhibitor, U73122, exerted an inhibitory effect on oocytes activated by spermatozoa or acetylcholine at concentrations of 10 and 30 microM respectively, while its inactive analogue had no effect. The soluble tyrosine kinase inhibitors, genistein (100 microM), herbimycin (10 microM) and geldanamycin (0.6 microM) which could affect signalling through PLC gamma hindered but never completely inhibited Ca2+ spiking in response to fertilization. We conclude that the activation of PLC to generate InsP3 may play a critical role in fertilization.

Acetylcholine↗