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Biomedical subjects

K Pfeifer

Publications and source records attributed to K Pfeifer.

At least 19 recordsLinked to original sources
PubMed2006

Reliability and performance-dependent variations of muscle function variables during isometric knee extension.

Despite the common use of standardised methods analysing neuromuscular function during knee extension, there is a lack of test-retest reliability studies. Furthermore, for most of the investigated variables it is unknown which changes of values indicate an enhancement of performance. The aim of the present study was to investigate performance-dependent variations of muscle functions during isometric contraction of knee extensors and to examine test-retest reliability of their measurement methods. For test-retest reliability sports students completed three test sessions. Highly skilled athletes, sports students and untrained subjects were investigated to determine the performance-dependent variations. The following variables were analysed: maximal voluntary contraction (MVC), voluntary activation (VA), absolute muscle reaction time (AR), muscle endurance (ME), and EMG frequency analysis (MF) of m. vastus lateralis (VL), m. vastus medialis (VM) and m. rectus femoris (RF). RESULTS TEST-RETEST-RELIABILITY: A high reliability between session 1 vs. 2 and session 2 vs. 3 was shown for MVC (ICC=0.92 and .97), VA (0.92/0.95) and ME (0.87/0.95). ICC in AR (0.23) was low between the first and second session and moderate between the second and third session (0.74). MF of VL, VM and RF showed low ICC between sessions. PERFORMANCE DEPENDENT VARIATIONS: Significant differences in nearly all variables (except VA) were found between trained (athletes and sports students) and untrained subjects.

Adult↗
PubMed2003

Walking patterns of hip arthroplasty patients: some observations on the medio-lateral excursions of the trunk.

PURPOSE: This study examined the angular gait kinematics of the trunk and the pelvis in the frontal plane and their amount of side-to-side asymmetry in patients after total hip replacement arthroplasty. METHOD: The angular gait kinematics of 12 male hip arthroplasty patients (53-70 years) were compared to ten age-matched and ten young (24-35 years) male control subjects. Average step times and medio-lateral oscillation amplitudes of the pelvic and thoracic recordings were calculated for each step. Between successive steps the asymmetry ratio was computed and the mean angle around which the side-to-side oscillations occurred was compared to the angle in a symmetrical standing trial. RESULTS: ANOVA indicated no significant side differences in relative step cycle durations. Patients and senior controls had significantly (p<0.01) less pelvis side-to-side displacements than the younger controls. No significant between-group differences could be detected for the average asymmetry ratio. However, during walking the patients showed a significantly (p<0.01) increased lateral thorax and pelvis deviation. CONCLUSIONS: Hip replacement patients' thoracic and pelvic position is characterized by a lateral shift throughout the gait cycle, while left and right symmetry of angular movements amplitudes remain at about the same value of unimpaired subjects.

Aged↗
PubMed2003

Neuromuscular control of walking with chronic low-back pain.

The reported association of low-back pain and musculoskeletal disorders contributed to the examination of the lumbar spine and hip extensor activation patterns in back pain sufferers during walking. Seventeen idiopathic low-back pain male subjects and 16 healthy volunteers participated in the study. Hip joint ROMs in the sagittal plane and neuromuscular activities of erector spinae [L3, T12], gluteus maximus and biceps femoris were recorded on one randomly selected body side in each group. Analysis using the Student's t-test revealed significant differences for hip joint range of motion, stride time and significantly earlier onsets of the lumbar spine and hip extensors of the back pain sufferers compared with the healthy controls. It is assumed, that low-back disorders are related to changes of the lumbar spine and hip extensor recruitment pattern.

Adult↗
PubMed2003

[Chemoprevention of breast cancer: a literature review and report on the current status in Germany].

The prevention of breast cancer is increasingly of focus in health-politics policies and has gained a valid position in the area of medical intervention. Data from a current meta-analysis of all four randomised Tamoxifen prevention studies illustrate a reduction of 38 % (Odds ratio 0.62; 95 % CI 0.42-0.89) in the incidence of breast cancer. This observation lead to registration of this drug in the USA for the prevention of breast cancer in women with a calculated 5-year risk of > 1.66 %. In addition to Tamoxifen, further substances are currently being tested with the aim of improving the therapeutic index whilst reducing incidence and mortality rates. These are primarily substances which have proven efficacy in the treatment of breast cancer (other antioestrogens, aromatase inhibitors and GnRH-analogues) or those whose mechanism of action predict a preventative effect (retinoids, phytooestrogens, substitution preparations e. g. Tibolone). In Germany, chemoprevention is currently only to be recommended within study protocols, as to date no substance is approved in the indication 'prevention of breast cancer'. A essential contribution to the accrual of valid data is the conduct of breast cancer prevention trials. The participation of women with high risk of breast cancer in Germany is, in contrast to comparable international studies, problematic. Data on the current knowledge and attitude of the female population towards such trials (gathered via a questionnaire of the DACH in 7 000 women) show that only 19.5 % of the women questioned during a consultation with a gynaecologist were aware of the possibility of active chemoprevention. However, 55.3 % stated that they would be prepared to take such a substance, were chemoprevention possible. Studies for both pre- and post-menopausal women with increased risk of breast cancer are currently active in Germany (GISS and IBIS-II of the study group GABG - German Adjuvant Breast cancer Group). An intensive information campaign to raise public awareness of breast cancer risk amongst women and their physicians is planned in conjunction with the IBIS-II study (www.brustkrebsvorbeugen.de). Latest literature recommendations for prevention of breast cancer (Chlebowski et al.) have been assessed.

Anticarcinogenic Agents↗
PubMed2003

Early detection of hepatitis B surface antigen--prototype of a new fully automated HBsAg microparticle enzyme immunoassay (MEIA).

HBsAg is the most important serological marker of acute and chronic hepatitis B infection. Therefore, sensitivity of the currently used detection systems for HBsAg is of major importance for blood screening, diagnosis of HBV infection and therapy monitoring of HBV infected individuals. A Prototype Microparticle Enzyme Immunoassay (MEIA) for qualitative determination of hepatitis B surface antigen (HBsAg) has recently been developed for the fully automated AxSYM analyzer with the intention to provide a test displaying improved sensitivity when compared to the currently marketed HBsAg assays. The present study was conducted to demonstrate sensitivity of the new Prototype AxSYM HBsAg MEIA and the corresponding, fully automated Prototype AxSYM HBsAg Confirmatory MEIA. Analytical sensitivity of the Prototype AxSYM HBsAg MEIA was assessed by testing quantitative HBsAg panels. Sensitivity for HBsAg subtypes ad and ay was found to be 0.15 ng/ml and 0.09 ng/ml, respectively. The detection level for HBsAg subtype ad Standard provided by the Paul Ehrlich Institute was estimated to be 0.03 PEI U/ml. Analysis of hepatitis B seroconversion panels suggests that the new Prototype AxSYM HBsAg MEIA significantly reduces the seroconversion window when being compared to other highly sensitive commercial HBsAg assays. The corresponding Prototype AxSYM HBsAg Confirmatory MEIA demonstrated the ability to confirm low titer seroconverters found reactive with the Prototype AxSYM HBsAg Screening MEIA.

Hepatitis B↗
PubMed2002

Comparison of angular lumbar spine and pelvis kinematics during treadmill and overground locomotion.

OBJECTIVE: To determine the differences between angular oscillation curves of the lumbar spine and pelvis during walkway and treadmill ambulation. DESIGN: An in vivo observation of walking in overground and treadmill conditions. BACKGROUND: Angular movements of the lumbar spine and pelvis have been obtained during overground and treadmill walking. No data are available to indicate whether lumbar spine treadmill findings may be compared or generalized to overground readings. METHODS: Nine male subjects walked at their natural cadence along an 8 m walkway positioned over a motorized treadmill. During each of 20 walking trials, kinematic data of one full gait cycle were collected in the middle segment of the walkway. Following the overground readings the walkway was removed and treadmill recordings were taken at the subjects' preferred walking speed and at an imposed speed of 1.25 m/s. Movement patterns and maximum oscillation angles were calculated in each plane. RESULTS: Cross-correlation values of pairwise comparisons demonstrated almost comparable movement patterns between walking conditions (r > or =0.891; p<0.001) except for the movement in the sagittal plane (r=0.642, p<0.01). ANOVA for repeated measures revealed significant (p<0.05) differences in the gait cycle duration as well as reductions in oscillation amplitudes of the upper lumbar region and the pelvis in both the frontal and transverse plane during treadmill walking compared to walkway locomotion. CONCLUSIONS: Statistically significant differences exist for some angular lumbar spine movement parameters between walkway and treadmill locomotion. RELEVANCE: The observed differences between overground and treadmill locomotion should be taken in account when treadmill-based lumbar spine and pelvis kinematics want to be extended or compared to overground recordings.

Adult↗
PubMed2002

Performance characteristics of an improved version of the ABBOTT IMx HBsAg (V2) MEIA.

The ABBOTT IMx HBsAg (V2) microparticle enzyme immunoassay (MEIA) is a fully automated two-step assay for the qualitative determination of hepatitis B surface antigen (HBsAg). HBsAg is the most important serological marker of acute and chronic hepatitis B infection. Therefore, sensitivity of the currently used detection systems for HBsAg is critical to blood screening, diagnosis of HBV infection and therapy monitoring of HBV infected individuals. The design of the assay has been modified and performance characteristics of the modified test were compared to its predecessor. Precision and specificity of the modified assay are comparable to its predecessor. PEI standard subtype ad is detected at 0.026 U/ml versus 0.053 U/ml with the previous assay version. HBsAg subtypes ad and ay are detected at 0.22 ng/ml and 0.17 ng/ml, respectively. The seroconversion window is reduced by 2-28 days versus the predecessor test. The modified assay has the capability to detect HBsAg mutants not detected by some other commercial assays. The modified version of the ABBOTT IMx HBsAg (V2) MEIA provides significantly improved sensitivity combined with the capability to detect prevalent and less prevalent HBsAg mutants.

Electronic Data Processing↗
PubMed2001

Influences of nonspecific low back pain on three-dimensional lumbar spine kinematics in locomotion.

STUDY DESIGN: A three-dimensional kinematic analysis of lumbar spinal movements with an ultrasonic measuring system was used to distinguish patients with chronic low back pain from those without such pain. OBJECTIVES: To investigate the effects of chronic low back pain on the three-dimensional movements of the lumbar spine, and to identify variables that would allow discrimination among patients with chronic low back pain and control subjects. SUMMARY OF BACKGROUND DATA: To the authors' knowledge, no previous studies have described or identified altered spinal and pelvic gait kinematics caused by nonspecific chronic low back pain in all anatomic planes. METHODS: In this study, 34 participants with chronic low back pain and 22 subjects without such pain were monitored during treadmill gait. Data from the measuring system operating at 30 Hz were low-pass filtered and normalized to a percentage of the gait cycle. RESULTS: Cross-correlations showed almost identical patterns of pelvic (S1) and thoracic (T12) movement curves in all anatomic planes between groups. No statistical group differences were detected for either pelvic or thoracic oscillation amplitudes. However, Student's t test showed significantly higher coefficients of variation (P < 0.01) in all anatomic planes of patients with chronic low back pain than in healthy control patients. CONCLUSIONS: The phasic patterns and angular spinal displacements of patients with nonspecific low back pain were shown to be within normal limits. However, the patients demonstrated higher degrees of stride-to-stride variability, representing increased fluctuations in dynamic thoracic and pelvic oscillations. These findings, resulting in less than optimal gait patterns, must be considered in the rehabilitation of patients with chronic low back pain.

Adult↗
PubMed2001

Targeted disruption of the Kcnq1 gene produces a mouse model of Jervell and Lange-Nielsen Syndrome.

KCNQ1 encodes KCNQ1, which belongs to a family of voltage-dependent K(+) ion channel proteins. KCNQ1 associates with a regulatory subunit, KCNE1, to produce the cardiac repolarizing current, I(Ks). Loss-of-function mutations in the human KCNQ1 gene have been linked to Jervell and Lange-Nielsen Syndrome (JLNS), a disorder characterized by profound bilateral deafness and a cardiac phenotype. To generate a mouse model for JLNS, we created a line of transgenic mice that have a targeted disruption in the Kcnq1 gene. Behavioral analysis revealed that the Kcnq1(-/-) mice are deaf and exhibit a shaker/waltzer phenotype. Histological analysis of the inner ear structures of Kcnq1(-/-) mice revealed gross morphological anomalies because of the drastic reduction in the volume of endolymph. ECGs recorded from Kcnq1(-/-) mice demonstrated abnormal T- and P-wave morphologies and prolongation of the QT and JT intervals when measured in vivo, but not in isolated hearts. These changes are indicative of cardiac repolarization defects that appear to be induced by extracardiac signals. Together, these data suggest that Kcnq1(-/-) mice are a potentially valuable animal model of JLNS.

Action Potentials↗
PubMed2001

[Inline skating in school--perspectives from the sports medicine viewpoint].

INTRODUCTION: Children are motivated by new activities in physical education. Inline Skating (ILS) is one of the trend activities of the last years. For the establishment of ILS in school injury risks and the possible preventive transfer in leisure time activities are of interest. The aim of this study was to compare the incidence of injuries in an ILS-program in school with traditional activities of exercise lessons. Furthermore inline skate specific injury incidence in leisure time was evaluated. METHOD: A sample of 47 schools was evaluated by a standardized questionnaire asking for: injury incidence in traditional sports and ILS and the incidence of ILS-injuries in leisure time. RESULTS: The relative injury risk of ILS (% per 100 teaching units) is 14.3%. Basketball e.g. has an injury risk of 16.1%, handball 14.6%, gymnastics 13.9% and other games 9.5%. After the end of the ILS-program 37.3% of the students reported the incidence of an injury due to ILS in leisure time. CONCLUSION: Compared to other activities in physical education ILS shows a moderate risk of injury and may improve the acceptance of active and passive prophylaxis.

Adolescent↗
PubMed2001

Regulatory mechanisms at the mouse Igf2/H19 locus.

The closely linked H19 and Igf2 genes show highly similar patterns of gene expression but are reciprocally imprinted. H19 is expressed almost exclusively from the maternally inherited chromosome, while Igf2 expression is mostly from the paternal chromosome. In humans, loss of imprinting at this locus is associated with tumors and with developmental disorders. Monoallelic expression at the imprinted Igf2/H19 locus occurs by at least two distinct mechanisms: a developmentally regulated silencing of the paternal H19 promoter, and transcriptional insulation of the maternal Igf2 promoters. Both mechanisms of allele-specific silencing are ultimately dependent on a common cis-acting element located just upstream of the H19 promoter. The coordinated expression patterns and some experimental data support the idea that positive regulatory elements are also shared by the two genes. To clarify the organization and function of positive and negative regulatory elements at the H19/Igf2 locus, we analyzed two mouse mutations. First, we generated a deletion allele to localize enhancers used in vivo for expression of both H19 and Igf2 in mesodermal tissues to sequences downstream of the H19 gene. Coincidentally, we demonstrated that some expression of Igf2 is independent of the shared enhancer element. Second, we used this new information to further characterize an ectopic H19 differentially regulated region and the associated insulator. We demonstrated that its activity is parent-of-origin dependent. In contrast to recent results from Drosophila model systems; we showed that this duplication of a mammalian insulator does not interfere with its normal function. Implications of these findings for current models for monoallelic gene expression at this locus are discussed.

Alleles↗
PubMed2000

Mechanisms of genomic imprinting.

Imprinted genes represent a curious defiance of normal Mendelian genetics. Mammals inherit two complete sets of chromosomes, one from the mother and one from the father, and most autosomal genes will be expressed from both the maternal and the paternal alleles. Imprinted genes, however, are expressed from only one chromosome, in a parent-of-origin-dependent manner. Because silent and active promoters are present in a single nucleus, the differences in activity cannot be explained by transcription-factor abundance. Thus, transcription of imprinted genes represents a clear situation in which epigenetic mechanisms restrict gene expression and, therefore, offers a model for understanding the role of DNA modifications and chromatin structure in maintaining appropriate patterns of expression. Furthermore, because of their parent-of-origin-restricted expression, phenotypes determined by imprinted genes are susceptible not only to genetic alterations in the genes but also to disruptions in the epigenetic programs controlling regulation. Imprinted genes are often associated with human diseases, including disorders affecting cell growth, development, and behavior.

Alleles↗
PubMed2000

A transcriptional insulator at the imprinted H19/Igf2 locus.

Igf2 and H19 exhibit parent-of-origin-specific monoallelic expression. H19 is expressed from the maternal chromosome and Igf2 from the paternal. The two genes share enhancer elements and monoallelic expression of both genes is dependent on cis-acting sequences upstream of the H19 promoter. In this work we examine the mechanisms by which this region silences the maternal Igf2 allele and we demonstrate that deletion of this region can result in high levels of activation of both H19 and Igf2 from a single chromosome. Moreover, by inserting this cis element between a promoter and its enhancer at a heterologous position, we demonstrate that the sequences carry both insulator activity and the ability to be stably imprinted. We also characterize the insulator in vitro and show that it is neither enhancer nor promoter specific.

Animals↗
PubMed2000

H19 and Igf2 monoallelic expression is regulated in two distinct ways by a shared cis acting regulatory region upstream of H19.

H19 and Igf2 are expressed in a monoallelic fashion from the maternal and paternal chromosomes, respectively. A region upstream of H19 has been shown to regulate such imprinted expression of both genes in cis. We have taken advantage of a loxP/cre recombinase-based strategy to delete this region in mice in a conditional manner to determine the temporal requirement of the upstream region in initiating and maintaining the imprinted expression of H19 and Igf2. Analysis of allele-specific expression of H19 and Igf2 and DNA methylation at the H19 promoter demonstrates that this region controls the monoallelic expression of the two genes in different ways, suggesting that it harbors two functionally distinct regulatory elements. Continued presence of the region is required to silence maternal Igf2 in accordance with its proposed role as an insulator. However, it does not have a direct role in keeping the paternal H19 promoter silenced. Instead, on the paternal chromosome, the upstream element mediates epigenetic modifications of the H19 promoter region during development, leading to transcriptional silencing of H19. Thereafter, its presence is redundant for preventing transcription. Presently, this temporal requirement of the silencing element appears to be a unique cis activity in the mammalian system. However, it is likely that other cis-acting elements, positive and negative, have the ability to effect stable changes in the chromatin structure and are not constantly required to give signals to the transcriptional machinery.

Alleles↗
PubMed2000

Identification of specific BRCA1 and BRCA2 variants by DHPLC.

Denaturing high performance liquid chromatography (DHPLC) is generating increasing interest in clinical genetics as a reliable tool for the analysis of genetic alterations. In the work presented here our intentions were to optimize primer design and DHPLC analysis conditions for a qualitative detection of BRCA1 and BRCA2 variations. The BRCA1 and BRAC2 genes display a high proportion of polymorphisms. Sequencing efforts geared towards the distinction of tumor-related mutations and benign variants still remain time-consuming and expensive. DHPLC elution profiles, however, permit the correlation of a characteristic chromatographic profile with a specific sequence alteration. In this study we evaluate the sensitivity of DHPLC for the identification of unique polymorphisms, which are frequent in the Caucasian population, in lieu of sequence analysis. The complete BRCA1 gene and parts of BRCA2 were examined. In the case of BRCA1, 431 out of 432 heterozygotes were identified correctly. In addition, 18 new profiles were identified which had not been detected previously in our studies and which represented new mutations or rare polymorphisms. For BRCA2, 135 out of 137 simple sequence variants were classified correctly. In addition, six new profiles were identified which represented new mutations or rare polymorphisms.

BRCA2 Protein↗
PubMed2000

[Reproducibility of lumbar spine kinematics in clinical gait analysis].

The objective measurement of functional lumbopelvical movements enables the evaluation of the quantity and quality of movements referring to functional disorders in dynamic test-situations. The goal of the present study is the determination of the reproducibility of time-continuous movement analysis of the pelvic region during walking and the determination of possible errors. The movements of the thoracic (Th12), lumbar and sacrum-region (S1) of 17 healthy subjects (age: 32.1 +/- 2.3 years) during walking on a treadmill (4.5 km/h) were investigated twice in an interval of 24 hours by means of a 3D ultrasonic movement analysis system. The ensemble averages of the low-pass filtered and time-normalized angle-time sequences of all anatomical planes and regions showed high test-retest correlations (r > or = 0.92, p < 0.01) except fo the lumbar movement in the sagittal plane (r = 0.79, p < 0.01). A paired t-test showed no significant differences for the amplitudes of test and retest measurements except for the thoracolumbar movement in the sagittal plane (p < .05). The results show that the evaluation of lumbar movement patterns can be regarded as admissible and desirable for clinical movement analysis. The data can be used as a diagnostic tool for the planning and control of therapeutic interventions.

Adult↗
PubMed1999

Characterization of maternal influence on teratogenicity: an assessment of developmental toxicity studies for the herbicide cyanazine.

The contribution of maternal toxicity to the teratogenic effects of the herbicide cyanazine has been assessed to determine whether it may be a hazard to development. Eye defects such as anophthalmia and microphthalmia were observed in rat fetuses and pups. Maternal toxicity was determined from body weight data and clinical signs. Two approaches were used. First, the timing of maternal toxicity was correlated with the specific period of gestation during which the observed fetal defect was most likely to have occurred. Second, individual dams, as well as mean values for each group, were evaluated. The data at the individual level, i.e., in dams with affected litters, did not support conclusions based on the group means. Instead, it is suggested that the developmental effects were not a direct result of maternal toxicity of cyanazine. Data from a rabbit developmental toxicity study supported the findings from the Fischer 344 rat studies. The strategy employed may thus enable direct toxicity to the fetus to be distinguished from developmental toxicity arising as a secondary consequence of maternal toxicity.

Abnormalities, Drug-Induced↗