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Biomedical subjects

C Seibert

Publications and source records attributed to C Seibert.

17 recordsLinked to original sources
PubMed2006

Distorted perceptions of competence and incompetence are more than regression effects.

Students inaccurately assess their own skills, especially high- or low-performers on exams. This study assessed whether regression effects account for this observation. After completing the Infection and Immunity course final exam (IIF), second year medical students (N = 143) estimated their performance on the IIF in terms of percent correct and percentile rank. Second year grade point averages (M2GPAs) were combined with the IIF results to form five subgroups: 1 = true-low (lowest third on both IIF and M2GPA, 2 = false-low (lowest third on IIF only), 3 = middle (neither lowest nor highest third on IIF), 4 = false-high (highest third on IIF only), 5 = true-high (highest third on IIF and M2GPA). The false-low and false-high groups were considered more susceptible to regression effects due to likely group misclassification. Differences between self-assessment and actual performance within each group and between the five groups were used to estimate what portion of observed differences is due to general tendencies versus regression effects. Results found that students accurately assessed their percent correct, but inaccurately assessed their percentile rank. No statistically significant differences existed between the true and false-low subgroups nor the true- and false-high subgroups. Percentages of mean differences suggest that while regression effects resulted in 50-75% over/under-estimates of scores by students who were misclassified, when they were merged with the true-low/high groups, they do not account for more than 14% of low performer over-estimates of their performance and high performer under-estimates of their performance. Accurate percent correct assessments and distorted percentile rank assessments are challenges in using instructional methods dependent on student self-assessments of their learning needs. Identifying and helping students with distorted perceptions of their test performances may be a key issue in such instructional approaches.

Data Interpretation, Statistical↗
PubMed2006

Proteomic analysis of cytochromes P450: a mass spectrometry approach.

In human, the CYP (cytochrome P450) superfamily comprises 57 genes arranged in 18 families and 42 subfamiles. These genes encode for enzymes involved in the metabolism of drugs, foreign chemicals, fatty acids, eicosanoids and cholesterol. Additionally, they play roles in bile acid biosynthesis, steroid synthesis and metabolism, and vitamin D(3) synthesis and metabolism. Mutations in many CYP genes cause inborn errors of metabolism and contribute to increased risk of cancer. MS provides a convenient method for the identification and quantification of CYP enzymes, and in the present paper we will review the current state of the technology for such an analysis.

Amino Acid Sequence↗
PubMed1999

Activation of the rod G-protein Gt by the thrombin receptor (PAR1) expressed in Sf9 cells.

Functional coupling of the human thrombin receptor PAR1 (protease-activated receptor 1) with the retinal rod G-protein transducin (Gt, a member of the Gi family) was studied in a reconstituted system of membranes from Sf9 cells expressing the thrombin receptor and purified Gt from bovine rod outer segments. TRAP6-agonist-activated PAR1 interacts productively with the distant G-protein. Agonist-dependent Gt activation was measured using a real-time fluorimetric GTP[S]-binding assay and membranes from Sf9 cells. To characterize nucleotide-exchange catalysis by PAR1, we analyzed dependence on nucleotides, temperature and pH. Activation was inhibited by low GDP concentrations (IC50 = 5.2 +/- 1.5 microM at 5 microM GTP[S]), indicating that receptor-Gt coupling, followed by instantaneous GDP release, is rate limiting under the conditions (25 degrees C). Arrhenius plots of the temperature dependence reflect an apparent Ea of 60 +/- 3.5 kJ.mol-1. Evaluation of the pH/rate profiles of Gt activation indicates that the activating conformation of the receptor is determined by protonation of a titratable group with an apparent pKa of 6.4. This supports the idea that the active state of agonist-bound PAR1 depends on forced protonation, indicating possible analogies to the scheme established for rhodopsin.

Animals↗
PubMed1999

Precepting preclinical students.

Preclinical preceptors have an opportunity to imprint students with good clinical work habits, professionalism, and excitement for medical education. While attention to the multiple roles of the preclinical preceptor can add responsibilities to a busy physician's day, the chance to influence the development of future physicians is deeply gratifying.

Education, Medical, Undergraduate↗
PubMed1995

A nontransportable substrate for lactose permease.

A substrate for lactose permease of Escherichia coli was synthesized that binds to the protein with a relatively high affinity, but is not transported to any detectable extent. This substrate, 6'-[(N-phenylalanylphenylalanyl)amino]hexyl 1-thio-beta-D-galactoside, is a peptide galactoside composed of a bulky aromatic dipeptide that is linked to galactose via an aminohexyl spacer. Binding of the peptide galactoside to lactose permease in cytoplasmic membranes was determined in a competition assay yielding a dissociation constant of 150 microM. Transport was measured by a counterflow assay using lipid vesicles with reconstituted lactose permease. An upper limit for the rate constant of transport was obtained as 0.02 s-1, 3 orders of magnitude smaller than the value for lactose.

Biological Transport↗
PubMed1995

[Focal and diffuse lesions in dynamic MR-mammography of healthy probands].

PURPOSE: To evaluate the range of normal contrast enhancement behaviour in dynamic MR mammography of healthy breast parenchyma, and to reduce false-positive results caused by incidental contrast enhancing lesions. MATERIALS AND METHODS: We performed a prospective two-armed study on 20 healthy premenopausal volunteers who were examined four times within one month (Group 1) or during four consecutive months (Group 2). Incidence, prevalence, morphology, and contrast enhancement pattern of lesions were evaluated. RESULTS: 82% (9/11 of Group 1) and 78% (7/9 of Group 2) showed at least one of a total of 60 contrast enhancing lesions. In 54% or 33% (Group 1 or 2), lesions with enhancement velocity beyond the malignancy threshold were found. 72% or 75% of lesions resolved completely during follow-ups. 69% of lesions were focal with irregular border. Time/signal intensity diagrams were almost always not suspicious; no wash-out phenomenon was seen. CONCLUSION: In MR mammography of premenopausal breast parenchyma, focal contrast enhancing lesions-even with enhancement beyond the malignancy threshold-may occur without any underlying pathology.

Adult↗
PubMed1990

Comparison of lymphangiography and computed tomography scanning in evaluating abdominal disease in stages III and IV Hodgkin's disease. A Southwest Oncology Group study.

The authors reviewed the records of 139 patients who had laparotomy plus computed tomography (CT) and/or lymphangiograms (LAG) as part of a their staging workup for Hodgkin's disease, in accordance with Southwest Oncology Group (SWOG) protocol 7808. They evaluated the relative ability of CT and LAG to detect disease in the abdomen. Two regions of the abdomen were designated, the upper and the lower, to further examine the capabilities of CT and LAG in the lower abdomen and CT in the upper abdomen. A LAG was more sensitive (P less than 0.05) than CT in detecting positive lower abdominal nodes. In the upper abdomen, CT scan had low sensitivity for detecting positive nodes, liver, or spleen. This study suggests that LAG of the lower abdomen provided more information than CT, and therefore should not be abandoned as a valid method for detecting nodal disease.

Abdomen↗
PubMed1989

Development of tolerance in brain mitochondria for calcium uptake following chronic ethanol ingestion.

Brain mitochondria isolated from rats following 10 weeks of chronic exposure to ethanol were not deficient in respiratory function or in rates of calcium uptake under control conditions. Ethanol (80 mM) in the incubation medium caused significant depression in the respiratory and ATP-dependent rates of calcium uptake in control mitochondria, but did not affect mitochondria from ethanol-tolerant rats. Chronic exposure to ethanol causes mitochondria to take calcium up at a normal rate when challenged acutely by ethanol.

Animals↗
PubMed1989

A cross-sectional prevalence study of lumbar disc degeneration in a working population.

The prevalence of lumbar degenerative discs (LDD) was determined in 38 ambulating and 21 sedentary employees of a Rocky Mountain company. Lumbar degenerative discs were identified by magnetic resonance imaging (MRI) performed with a sagittal T2 image of the lumbar spine using a .5 Tesla unit. The L5-S1 level was the most common disc with degenerative changes. Analysis of the two groups showed a significant association at the L5-S1 level between occupation and LDD, as evidenced by the ambulating females having no degenerative lumbar discs and sedentary females having a large number of degenerative discs. The males in the study did not demonstrate a significant difference in prevalence of LDD. Lumbar degenerative discs may be increased in less active females at the L5-S1 level.

Adult↗
PubMed1988

Correlation of neuropsychological and MRI findings in chronic/progressive multiple sclerosis.

Sixty patients with chronic/progressive MS received a newly assembled neuropsychological screening battery (NSB) and a brain MRI. A neuroradiologist blinded to NSB findings quantified cerebral lesions on MRI. We developed weighted brain area lesion scores according to number and size of cerebral lesions. Patients who were impaired on NSB testing had a significantly higher mean bihemispheric lesion score (X = 26.1) than those who were unimpaired (X = 17.4); this MRI lesion rating score correlated significantly with the cognitive summary score of the NSB (r = 0.35, p less than 0.01). However, we did not find a significant correlation between the Kurtzke Expanded Disability Status Scale and any MRI or NSB summary measures. Compared with the Mini-Mental State Exam (MMSE), the NSB cognitive summary score yielded a prevalence estimate for cognitive impairment that is more consistent with previous findings in chronic/progressive MS. The NSB is a useful screening test for cognitive dysfunction in chronic/progressive MS because of its relationship to cerebral lesions on MRI and its greater sensitivity than the frequently used MMSE.

Adult↗
PubMed1984

Radiographic classification of the vestibular and cochlear aqueducts: the paired correlation between normal and abnormal vestibular aqueduct and cochlear aqueduct anatomy.

Multidirectional tomography (MDT) can be useful in determining the caliber, shape, and course of the vestibular aqueduct (VA) and cochlear aqueduct (CA). Clinical decisions have been based on the findings from MDT. Unfortunately, the clinical utility of these observations has been confusing and controversial because similar MDT techniques were not used. This study will address some of the difficult questions and clinical controversies derived from MDT observations. This new perspective has evolved with the use of high resolution computed tomography (HRCT). An analysis of 750 petrous bones for the occurrence of the various types of VAs and CAs using Gado's classification, further vestibular aqueduct and a variation of Gado's classification for the cochlear classification is reported. The distribution of the possible paired types of VA and CA are evaluated. MDT results indicate that the paired analysis in patients with inner ear dysfunction is not useful, cost effective, diagnostic, or of prognostic value. MDT can provide clinically valid observations of periaqueductal and perilabyrinthine pneumatization which is helpful in anticipating the size and position of the endolymphatic sac at the time of surgery for those few patients who may benefit from endolymphatic system surgery. However, when a comparison is made between MDT and CT of 60 ears in those same patients, the clinical limitations of MDT for inner ear diagnosis and prognosis became apparent. The future for HRCT scanning with reformatting holds potential for clinically meaningful visualization of inner and middle ear structures previously expected from MDT imaging.

Cochlea↗
PubMed1972

Model approach to immunological rejuvenation of the aged.

Reconstitution of a damaged or exhausted immune system by injection of genetically compatible immunocompetent cells (immunologic rejuvenation) is a promising approach for restoration of immune activity. By using this model, spleen cells from young-adult mice, previously immunized with Salmonella typhimurium, were transferred to either young-adult or old, syngeneic recipients before or after storage at -196 C. The susceptibility of recipient mice was then determined by challenging them at increasing time intervals after reconstitution with lethal doses of the virulent organisms. The findings, although preliminary in nature, demonstrate that (i) immunological rejuvenation of mice is possible with immunocompetent cells from specifically immunized donors; (ii) prolonged "takes" of these cells can occur even in nonirradiated recipient mice, and (iii) storage at -196 C does not impair their protective capacity.

Aged↗
PubMedDate not supplied

The impact of the Trial Coordinator in the Diabetes Control and Complications Trial (DCCT). The DCCT Research Group.

The Diabetes Control and Complications Trial (DCCT) is a multicenter, randomized clinical trial studying the effects of two different diabetes regimens on the development and progression of early vascular complications in persons with insulin-dependent diabetes mellitus (IDDM). All of the centers have a Trial Coordinator. We administered a self-report questionnaire to each center to document the different activities for which the Trial Coordinator assumed responsibility in successfully orchestrating the trial. All Trial Coordinators were responsible primarily for recruitment, screening, medical management, education and training, and adherence and administration. Although documentation indicated that the Trial Coordinator was responsible for all of the above activities, the original applications reflected that very few of the Principal Investigators anticipated such a wide variety of duties. A Trial Coordinator was named in only 13 of the 21 applications and of these, only 6 actually assumed the position. This study points out the need to develop a means to define characteristics, background, and training appropriate for candidates for a Trial Coordinator position in future studies.

Allied Health Personnel↗