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Biomedical subjects

R Johnson

Publications and source records attributed to R Johnson.

At least 109 records · Page 6Linked to original sources
PubMed1999

Predicting body composition from anthropometry in pre-adolescent children.

The objectives of this paper were to: a) evaluate the accuracy and precision of previously published pediatric body composition prediction equations and b) develop additional prediction equations from a large, heterogeneous group of Caucasian (n = 133) and African-American (n = 69) children. The combined cohort of 202 children included a wide range of ages (4.0-10.9 y), weights (14.0-70.8 kg), fat mass (FM: 1.2-28.5 kg) and percent body fat (% body fat: 6.2-49.6%). Skinfold measurements were obtained using a Lange caliper and body fat was measured with a Lunar DPX-L densitometer. The previously published equations of Slaughter et al and Goran et al did not accurately predict body fat. The entire cohort was randomly divided into two sub-groups for purposes of deriving and cross-validating a new prediction equation. In stepwise regression analysis in the development group (n = 135), weight, triceps skinfold, gender, ethnicity and abdominal skinfold estimated FM measured by dual energy x-ray absorptiometry (DEXA) with a model R2 of 0.95. The new prediction equation was cross-validated in the control group (n = 67) and each ethnic and gender subgroup. We conclude that a) the equations of Slaughter et al and Goran et al did not accurately predict FM in a heterogeneous group of children and b) a new anthropometric prediction equation is proposed that may provide accurate estimates of FM in both Caucasian and African-American children aged 4-10 y with a wide range of FM and body composition.

Alabama↗
PubMed1999

Congenital orbital teratoma.

A case of congenital orbital teratoma is described in which there was no organized eye only microscopic evidence of ocular tissues within the disorganized teratoma. A baby boy presented at birth with a 10-x-8-cm mass extruding from the left orbit. Magnetic resonance imaging (MRI) showed a mixed cystic-solid orbital mass containing areas of calcification and deforming the bony orbit around its margins. There was no organized eye and no intracranial extension. The eye was removed with reconstruction of the eyelids. Histopathology showed representation from all three germ cell layers consistent with a teratoma. There was no organized eye, but some disorganized ocular structures within the teratoma. Follow-up has been uneventful. Neonatologists and pediatricians should be aware of the possible diagnoses in a newborn presenting with an orbital mass, so that early definitive surgery can be performed with preservation of the globe where possible.

Anophthalmos↗
PubMed1999

Influence of lower limb pneumatic compression on pulmonary artery temperature: effect on cardiac output measurements.

OBJECTIVES: To characterize the decreases in pulmonary artery temperature that coincide with the inflation cycle of pneumatic calf compression stockings and to examine their effects on the thermodilution measurement of cardiac output. DESIGN: Three-part observational study. SETTING: University hospital surgical intensive care unit. PATIENTS: Postoperative patients with indwelling pulmonary artery catheters. INTERVENTION: Thermodilution cardiac output measurements with and without pneumatic calf compression. MEASUREMENTS AND MAIN RESULTS: Phase 1 (n = 18) examined the effects of pneumatic compression on pulmonary artery temperature. There was no effect on pulmonary artery temperature (device off, 37.468+/-0.008 degrees C; device on, 37.458+/-0.014 degrees C), but the difference between the maximum and minimum pulmonary artery temperatures was increased (off, 0.031+/-0.006 degrees C; on, 0.055+/-0.012 degrees C [p < .001]). Phase 2 (n = 12) found that the mean thermodilution cardiac output with 10 mL of cold (0-5 degrees C) injectate was unchanged by pneumatic compression (off, 7.00+/-2.28 L/min; on, 6.89+/-2.22 L/min). However, when the compression devices were operating, the variability between the individual measurements was increased, as reflected by larger coefficients of variation (off, 3.19+/-1.96; on, 8.72+/-6.56 [p < .02]). Similar results were obtained during phase 3 (n = 5), when cardiac output was measured with room temperature Injectate. CONCLUSIONS: Intermittent pneumatic calf compression increased lower limb venous return, causing acute but transient decreases in pulmonary artery blood temperature. This did not affect the accuracy of thermodilution cardiac output measurements that were made using 10 mL of either cold or room temperature injectate.

Bandages↗
PubMed1999

Multiple layers of cooperativity regulate enhanceosome-responsive RNA polymerase II transcription complex assembly.

Two coordinate forms of transcriptional synergy mediate eukaryotic gene regulation: the greater-than-additive transcriptional response to multiple promoter-bound activators, and the sigmoidal response to increasing activator concentration. The mechanism underlying the sigmoidal response has not been elucidated but is almost certainly founded on the cooperative binding of activators and the general machinery to DNA. Here we explore that mechanism by using highly purified transcription factor preparations and a strong Epstein-Barr virus promoter, BHLF-1, regulated by the virally encoded activator ZEBRA. We demonstrate that two layers of cooperative binding govern transcription complex assembly. First, the architectural proteins HMG-1 and -2 mediate cooperative formation of an enhanceosome containing ZEBRA and cellular Sp1. This enhanceosome then recruits transcription factor IIA (TFIIA) and TFIID to the promoter to form the DA complex. The DA complex, however, stimulates assembly of the enhanceosome itself such that the entire reaction can occur in a highly concerted manner. The data reveal the importance of reciprocal cooperative interactions among activators and the general machinery in eukaryotic gene regulation.

Allosteric Regulation↗
PubMed1999

Caffeine overdose in a premature infant: clinical course and pharmacokinetics.

The elimination of caffeine was investigated in a 1860 g, 31 week gestation neonate, following the accidental administration of a 160 mg.kg-1 dose. The first serum concentration measured was 217.5 mg.l-1 at 36.5 h after dosing. Fitting of time-concentration data was performed using non-linear regression with MKMODEL. A first order elimination model was superior to a mixed order model. Parameter estimates were: clearance 0.01 l.h-1, volume of distribution 1.17 litres, elimination half-life 81 h. Toxic manifestations included hypertonia, sweating, tachycardia, cardiac failure, pulmonary oedema and metabolic disturbances (metabolic acidosis, hyperglycaemia and creatine kinase elevation). An unusual feature of this infant's illness course was gastric dilatation. These signs resolved by day 7 at a serum concentration of 60-70 mg.l-1. Caffeine clearance has traditionally been reported as either an absolute value or as directly proportional to body weight. The per kilogram model gives an erroneous impression that clearance is greatest in early childhood and then decreases with age until adult rates are reached in late adolescence. Age-related clearance values reported in the literature were reviewed using an allometric 3/4 power model. This size model demonstrates that clearance increases in infancy and reaches adult rates within the first three months of life.

Age Factors↗
PubMed1999

Factor structure and subtest differences on the Preschool Behavior Questionnaire in a Latino, African-American, Euro-American, and Asian preschool population.

This study examined the factor structure of the Preschool Behavior Questionnaire in a sample of African-American, Euro-American, Asian, and Hispanic children. The sample consisted of 304 children (141 boys, 163 girls) 3- and 4-yr.-old and enrolled in Head Start. A principal component analysis with a varimax rotation was conducted and two- and three-factor solutions were extracted. A two-factor solution produced a clear interpretive structure representing Fowler and Park's 1979 Aggressive-Hyperactive-Distractible and Anxious-Fearful factors. Even though a three-factor solution was statistically appropriate, extracting more than two factors yielded dimensions difficult to interpret. Examination of subscale differences among ethnic groups indicated significant group effect for ethnicity. Further examination showed that Euro-American children are rated significantly higher on the Anxious subtest than Latino, African-American, and Asian children, but there were no other subscale differences. Clinical and research implications are discussed.

Black or African American↗
PubMed1999

Scaling is necessary when making comparisons between shapes of event-related potential topographies: a reply to Haig et al.

A. R. Haig, E. Gordon, and S. Hook (1997) disputed G. McCarthy and C. C. Wood's (1985) contention that scaling should be used when assessing the statistical significance of between condition (or group) differences in the shapes of event-related potential (ERP) scalp topographies. Haig et al. based their contention upon the lack of empirical realism in McCarthy and Wood's model of within-group ERP noise, claiming that McCarthy and Wood's results could not be generalized to realistic ERP data. We argue, on both empirical and theoretical grounds, that Haig et al. do not make a compelling case against generalization of McCarthy and Wood's results. Moreover, Haig et al.'s conclusion is based upon a misconception of how scaling should be used. We conclude that when a quantitative measure of differences between topographic shapes is needed, scaling is not an option--it is a requirement.

Analysis of Variance↗
PubMed1998

Inadequate control of lipid levels in patients with a previous myocardial infarction.

AIM: To access the current lipid management of late survivors of acute myocardial infarction. METHODS: A systematic follow-up of all survivors who had previously been screened for enrolment into one of three randomised clinical trials in Auckland was undertaken from December 1995 to January 1997. All contacted survivors were asked to answer a questionnaire regarding their current therapy and were invited to undergo venepuncture for a lipid assay. RESULTS: Of the 1036 patients with acute myocardial infarction screened for enrolment in the three trials there were 984 (95%) who survived 30 days. At a median of 5.5 years (interquartile range 3.2-8.5) follow-up, 641 (86%) survivors agreed to have a fasting lipid test. The mean total cholesterol level was 5.7 +/- 1.1 mmol/L high density lipoprotein cholesterol 1.1 +/- 0.3 mmol/L, low density lipoprotein cholesterol 3.8 +/- 0.9 mmol/L and triglyceride level 1.9 +/- 1.1 mmol/L. Two hundred and seven (32%) patients were treated with a lipid-modifying agent. Four hundred and forty-five (69%) patients had a cholesterol level > or = 5.2 mmol/L 381 (59%) patients had a level > or = 5.5 mmol/L and 72 (11%) patients had a level > or = 7.0 mmol/L of whom 62 patients were not being treated with a lipid-modifying agent. For the 107 patients with coronary artery bypass grafts, the mean cholesterol level was 5.4 mmol/L and the mean low density lipoprotein cholesterol level was 3.7 +/- 0.9 mmol/L, with 57 (53%) patients not being treated with a "statin" or "fibrate". CONCLUSION: Lipid management is suboptimal in this high risk population of patients post-infarction and greater efforts need to be made to achieve better control. Diet is frequently inadequate in these patients at high risk and statin therapy is indicated.

Aged↗
PubMed1998

Accuracy of three automated compounding systems determined by end-product laboratory testing and comparison with manual preparation.

The accuracy of three parenteral nutrient (PN) automated compounding systems and the usefulness of end-product laboratory testing of PN solutions were evaluated. Ten identical PN solutions were prepared by the Nutrimix (Abbott), MicroMacro 23 (Baxa), and Automix-Micromix (Clintec) compounders and manually. Three samples were removed from each of the 40 solutions. Dextrose was measured by high-performance liquid chromatography using a modified sorbitol assay; sodium, potassium, calcium, and magnesium were measured by atomic absorption spectroscopy. Theoretical concentrations of ingredients in the PN solution were adjusted by the actual concentrations in the source containers. The solutions differed significantly in their concentrations of glucose, calcium, and magnesium but not in their concentrations of sodium and potassium. The mean glucose concentrations produced by the manual method and Nutrimix system matched the adjusted theoretical values and by the MicroMacro and Automix-Micromix compounders were within the manufactures' accuracy specifications. The sodium concentrations of all solutions were higher than the adjusted theoretical concentration but within the manufacturers' specifications. Potassium and magnesium concentrations were lower in all solutions than the adjusted theoretical concentrations. Calcium concentrations were above the adjusted theoretical value in all solutions. Differences in compounder accuracy, even when significant, were not consistent and not appreciable. Multiple samples of the same solution should be tested if laboratory analysis is part of quality control.

Automation↗
PubMed1998

Development of the mouse inner ear and origin of its sensory organs.

The molecular mechanisms dictating the morphogenesis and differentiation of the mammalian inner ear are largely unknown. To better elucidate the normal development of this organ, two approaches were taken. First, the membranous labyrinths of mouse inner ears ranging from 10.25 to 17 d postcoitum (dpc) were filled with paint to reveal their gross development. Particular attention was focused on the developing utricle, saccule, and cochlea. Second, we used bone morphogenetic protein 4 (BMP4) and lunatic fringe (Fng) as molecular markers to identify the origin of the sensory structures. Our data showed that BMP4 was an early marker for the superior, lateral, and posterior cristae, whereas Fng served as an early marker for the macula utriculi, macula sacculi, and the sensory portion of the cochlea. The posterior crista was the first organ to appear at 11.5 dpc and was followed by the superior crista, the lateral crista, and the macula utriculi at 12 dpc. The macula sacculi and the cochlea were present at 12 dpc but became distinguishable from each other by 13 dpc. Based on the gene expression patterns, the anterior and lateral cristae may share a common origin. Similarly, three sensory organs, the macula utriculi, macula sacculi, and cochlea, seem to arise from a single region of the otocyst.

Animals↗
PubMed1998

The medial temporal lobe in dementia with Lewy bodies: a comparative study with Alzheimer's disease.

The usefulness of determining medial temporal lobe (MTL) size in differentiating Alzheimer's disease (AD) from other dementia subtypes is unknown. We compared the cross-sectional areas of the MTLs in histological sections from the brains of 18 patients with dementia with Lewy bodies (DLB) but lacking AD changes, 24 DLB patients with concurrent AD pathology, 20 pure AD cases, and 18 age-matched control cases. Duration and severity of disease were comparable between groups. When data for cross-sectional area were expressed as percentages of the average control area, DLB MTLs were significantly larger than either AD or DLB/AD MTLs at rostral levels (86 +/- 16%, 54 +/- 17%, and 66 +/- 23% of control areas, respectively). At caudal levels, DLB MTLs were larger than AD MTLs (80 +/- 20%, 59 +/- 21%, and 77 +/- 26% of control areas in DLB, AD, and DLB/AD, respectively). MTL cross-sectional area often approaches normal in pure DLB, even when disease duration is prolonged and symptoms are end stage. In contrast, a greatly reduced MTL area mitigates against the diagnosis of DLB, unless there are concurrent AD changes.

Aged↗
PubMed1998

Mutation measurement in mammalian cells. IV: Comparison of gamma-ray and chemical mutagenesis.

The interaction of chemical mutagens with mammalian cells is much more complex than that of gamma-irradiation because of the different ways in which chemical agents react with cell and medium components. Nevertheless, the system previously described for analysis of mutagenesis by gamma-radiation appears applicable to chemical mutagenesis. The approach involves measurement of cell survival, use of caffeine to inhibit repair, analysis of mitotic index changes, and quantitation of microscopically visible structural changes in mitotic chromosomes. The behavior of a variety of chemical mutagens and nonmutagens in this system is described and compared with that of gamma-irradiation. The procedure is simple and the results reasonably quantitative though less so than those of gamma-irradiation. The procedure can be used for environmental monitoring, analysis of mutational events, and individual and epidemiological testing. Mutational events should be classified as primary or secondary depending on whether they represent initial genomic insult, or genomic changes resulting from primary mutation followed by structural changes due to metabolic actions. While caffeine has multiple effects on the mammalian genome, when used under the conditions specified here it appears to act principally as an inhibitor of mutation repair, and so affords a measure of the role of repair in the action of different mutagens on cells in the G2 phase of the life cycle.

Animals↗