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Biomedical subjects

M Fritz

Publications and source records attributed to M Fritz.

At least 37 records · Page 2Linked to original sources
PubMed2000

Bacterial turgor pressure can be measured by atomic force microscopy.

We report a study of the deformability of a bacterial wall with an atomic force microscope (AFM). A theoretical expression is derived for the force exerted by the wall on the cantilever as a function of the depths of indentation generated by the AFM tip. Evidence is provided that this reaction force is a measure for the turgor pressure of the bacterium. The method was applied to magnetotactic bacteria of the species Magnetospirillum gryphiswaldense. Force curves were generated on the substrate and on the bacteria while scanning laterally. With the mechanical properties so gained we obtained the spring constant of the bacterium as a whole. Making use of our theoretical results we determined the turgor pressure to be in the range of 85 to 150 kPa.

Cell Wall↗
PubMed2000

In situ determination of sulfide turnover rates in a meromictic alpine lake.

A push-pull method, previously used in groundwater analyses, was successfully adapted for measuring sulfide turnover rates in situ at different depths in the meromictic Lake Cadagno. In the layer of phototrophic bacteria at about 12 m in depth net sulfide consumption was observed during the day, indicating active bacterial photosynthesis. During the night the sulfide turnover rates were positive, indicating a net sulfide production from the reduction of more-oxidized sulfur compounds. Because of lack of light, no photosynthesis takes place in the monimolimnion; thus, only sulfide formation is observed both during the day and the night. Sulfide turnover rates in the oxic mixolimnion were always positive as sulfide is spontaneously oxidized by oxygen and as the rates of sulfide oxidation depend on the oxygen concentrations present. Sulfide oxidation by chemolithotrophic bacteria may occur at the oxicline, but this cannot be distinguished from spontaneous chemical oxidation.

Bacteria↗
PubMed1999

Effects of modification of the allocation system on ischemia duration and costs of heart transplantation. Transplantation Cooperation UNI-NRW.

BACKGROUND: In order to optimize regional utilization of transplantable thoracic organs, the seven university hospitals in North-Rhine-Westfalia have formed a transplant cooperation meanwhile approved by Eurotransplant. METHODS: Heart transplant and organ donation activities of the cooperating hospitals in the year before the foundation of the cooperation (period A, 7/95 - 6/96) and in the year thereafter (period B, 7/96 - 6/97) were retrospectively analysed. RESULTS: In period A, a total of 39 heart transplants and 74 heart donations were performed, whereas in period B 67 heart transplantations and 78 heart donations could be achieved. The regional utilization of the donor organs increased from 4% to 30% with a significantly shorter ischemia time of regionally or locally allocated donor hearts than of nationally or internationally allocated ones. CONCLUSIONS: A high rate of regional or local heart transplant procedures with short ischemia times clearly demonstrate the benefits of a regionalization of heart transplant medicine for medical as well as economical reasons.

Cost-Benefit Analysis↗
PubMed1998

Three-dimensional biomechanical model for simulating the response of the human body to vibration stress.

Several investigations have revealed that long-term exposure to whole-body vibrations can induce low back pain. In analogy to materials handling, the health risk can be assessed if the forces transmitted in the spine during vibration are known. To estimate the forces a biomechanical model has been developed in which the human trunk, neck, head and arms are represented by 16 rigid bodies. An additional body simulates the vibrating seat. The bodies are connected by visco-elastic joint elements, and 56 force elements imitate the trunk and neck muscles. The motion equations are derived by means of the dynamics of systems of rigid bodies, and the motions are simulated in three directions. The frequency-response functions between the accelerations of the seat and the head satisfactorily correspond to data reported in the literature. The spine forces are composed of a static part, due to body posture, and a vibration-induced part. The relation between the oscillating parts of the forces transmitted from seat to pelvis and the spine forces are also described by frequency-response functions. To assess the health risk the simulated spine forces must be compared with the strength of the spine, bearing in mind that this is dependent on the number of load cycles.

Biomechanical Phenomena↗
PubMed1997

Dominance of the BV17 element in nickel-specific human T cell receptors relates to severity of contact sensitivity.

Hypersensitivity to nickel (Ni) represents the most common manifestation of contact allergy in humans. The role of metal-specific T cells in this disease is well established, but the molecular interactions involved in their activation are poorly understood. We examined the T cell receptor (TCR) repertoire in T cells activated with either NiSO4 or NiSO4-treated human serum albumin from six allergic patients. For the three most hyperreactive donors, we found a strong over-representation of the TCR BV17 element. TCR sequencing for one of these donors revealed an additional skewing for AV1 as well as a selection for an N region encoded argine at position 95 of the BV17 complementarity determining region (CDR)3. Since Arg is not known to participate in Ni complexing, we suppose that this selection is driven by contacts with peptide rather than nickel. However, the CDR1 of BV17 contains a unique combination of amino acids (HDA) that bears similarities to known motifs in Ni-binding proteins or peptides. We therefore propose that the severe hypersensitivity reactions found in BV17 over-expressors may be the result of Ni2+ ions bridging the germ-line-encoded BV17 CDR1 loop to corresponding sites in the major histocompatibility complex/peptide complex and thereby creating a superantigen-like enhancement of weak TCR-peptide contacts.

Amino Acid Sequence↗
PubMed1997

Estimation of spine forces under whole-body vibration by means of a biomechanical model and transfer functions.

BACKGROUND: Several investigations reveal that long-term exposure to whole-body vibrations can induce degenerative changes in the lumbar spine. In analogy to the activities of lifting or carrying loads, an assessment of the health risk should be possible if the forces transmitted in the spine during vibration stress are known. METHODS: To estimate the spine forces a biomechanical model was developed. In the model the human trunk, neck, and head were represented by 10 rigid bodies connected by visco-elastic elements. Some 56 force elements imitated the muscles of the body. The motion equations of the model were derived by means of the dynamics of systems of rigid bodies. RESULTS: The transfer functions of the model accelerations in x- and z-direction satisfactorily corresponded to data reported in the literature. Transfer functions were computed between the forces transmitted from the seat to the pelvis and in the lumbar spine, respectively. CONCLUSION: The forces between seat and pelvis were measured, then the spine forces were computed by means of the transfer functions. To assess the health risk the computed forces must be compared with the strength of the spine because the strength is dependent on the age and gender of the worker and decreases with the number of load cycles.

Acceleration↗
PubMed1996

Measuring the viscoelastic properties of human platelets with the atomic force microscope.

We have measured force curves as a function of the lateral position on top of human platelets with the atomic force microscope. These force curves show the indentation of the cell as the tip loads the sample. By analyzing these force curves we were able to determine the elastic modulus of the platelet with a lateral resolution of approximately 100 nm. The elastic moduli were in a range of 1-50 kPa measured in the frequency range of 1-50 Hz. Loading forces could be controlled with a resolution of 80 pN and indentations of the platelet could be determined with a resolution of 20 nm.

Biophysical Phenomena↗
PubMed1996

Protein tracking and detection of protein motion using atomic force microscopy.

Height fluctuations over three different proteins, immunoglobulin G, urease, and microtubules, have been measured using an atomic force microscope (AFM) operating in fluid tapping mode. This was achieved by using a protein-tracking system, where the AFM tip was periodically repositioned above a single protein molecule (or structure) as thermal drifting occurred. Height (z-piezo signal) data were taken in 1 - or 2-s time slices with the tip over the molecule and compared to data taken on the support. The measured fluctuations were consistently higher when the tip was positioned over the protein, as opposed to the support the protein was adsorbed on. Similar measurements over patches of an amphiphile, where the noise was identical to that on the support, suggest that the noise increase is due to some intrinsic property of proteins and is not a result of different tip-sample interactions over soft samples. The orientation of the adsorbed proteins in these preliminary studies was not known; thus it was not possible to make correlations between the observed motion and specific protein structure or protein function beyond noting that the observed height fluctuations were greater for an antibody (anti-bovine IgG) and an enzyme (urease) than for microtubules.

Animals↗
PubMed1995

Imaging soft samples with the atomic force microscope: gelatin in water and propanol.

We have imaged mica coated with thin gelatin films in water, propanol, and mixtures of these two liquids by atomic force microscopy (AFM). The elastic modulus (Young's modulus) can be tuned from 20 kPa to more than 0.1 GPa depending on the ratio of propanol to water. The resolution is best in pure propanol, on the order of 20 nm, and becomes worse for the softer samples. The degradation in resolution can be understood by considering the elastic indentation of the gelatin caused by the AFM tip. This indentation becomes larger and thus the contact area becomes larger the softer the sample is. Therefore this study may be used to estimate the resolution to be expected with an AFM on other soft samples, such as cells. Nondestructive imaging was possible only by imaging at forces < 1 nN. This was difficult to achieve in contact mode because of drift in the zero load deflection of the cantilever, supposedly caused by temperature drift, but straightforward in tapping mode.

1-Propanol↗
PubMed1995

High-yield selection criteria for cranial computed tomography after acute trauma.

OBJECTIVE: To develop and prospectively evaluate criteria for selecting head-injured patients requiring cranial CT. METHODS: A two-phased prospective observational study design was implemented at a university ED. Physicians completed a form with 51 variables for 540 patients in Phase I. Ten high-yield variables were identified and prospectively tested on 273 patients in Phase II. Prediction rule performance for identification of patients with abnormal CT scans was determined. RESULTS: The combined criteria had a sensitivity of 97% for CT-scan abnormalities in Phase I; sensitivity was 96% in Phase II. Negative predictive values were 97% and 94%, respectively. Prevalence of disease in Phase I was 17%; prevalence in Phase II was 16%. Had the Phase I criteria been implemented during Phase II, 43 of 273 patients (16%) would not have been scanned, including two patients with positive results who did not require operative intervention. CONCLUSIONS: Fifty-one clinical variables from head-injured patients were narrowed to ten of statistical significance and consistent interpretation for prospective evaluation. Patients with none of these criteria were found to be at low risk of having sustained significant head injury.

Adolescent↗
PubMed1995

Succession of putative peri-implant pathogens after root-form and plate-form implant placement in partially dentate adult monkeys.

This report describes the succession of putative peri-implant pathogens in partially dentate monkeys after dental implantation and prosthetic reconstruction. Tooth and implant (6 root-end form, 4 blade-vent implants) sites in eight monkeys were monitored microbiologically and clinically during the pre-implant stage, abutment connection stage, bridge placement stage, and three and six months after the bridge placement stage. Tooth and implant sites were cleaned monthly post-extraction. Microbiological studies included dark field microscopy, selective and non-selective culture, and primary phenotypic characterization of culture isolates. After implant surgery, the median proportion of several putative peri-implant pathogens studied were significantly elevated. Following fixture placement, P. intermedia replaced P. melaninogenica as the predominant Black Pigmented Anaerobic Bacilli (BPAB) in the mouth. After abutment connection stage, levels of P. intermedia, A. actinomycetemcomitans, F. nucleatun, Haemophilus sp. and spirochetes were significantly elevated at implant and tooth sites. Three months after bridge installations, P. intermedia and A. actinomycetemcomitans remained significantly elevated at implant sites. At six months after bridge installation, levels of P. intermedia, F. nucleatum and A. actinomycetemcomitans declined significantly relative to levels at three months. Porphyromonas sp. and spirochetes were not significantly elevated although their levels correlated with gingival redness. P. intermedia, Porphyromonas sp. and spirochetes levels correlated significantly with probing depth. Correlation was detected between P. gingivalis and spirochetes; and between A. actinomycetemcomitans and F. nucleatum. Our studies show a transitional increase in levels of several organisms resembling putative pathogens of human peri-implant infection, associated with implant placements in partially edentulous mouths and supports early prophylactic interventions to control their levels.

Aggregatibacter actinomycetemcomitans↗
PubMed1995

[Effect of vaginal estrogen therapy on urinary incontinence in postmenopause].

A depot preparation of Estriol (Ortho Gynest D; 3.5 mg Estriol, intravaginal) was applied for 3 months to 135 postmenopausal women with urinary incontinence. Before and after treatment the symptoms of incontinence were scaled by the Gaudenz questionnaire. 8 symptoms were tested for statistical significance. All of them had significantly improved after treatment. 63% of patients showed improvement of their incontinence, urinary stress incontinence improved in 50%. Dysuria was reported by 14 patients before treatment, by none after treatment. Daytime and nighttime micturition frequency both decreased significantly, also subjective impairment by incontinence. Thus the local application of Estriol ovula represents an effective mode of primary treatment (maintenance therapy, one dose per week) in postmenopausal patients with urinary incontinence.

Administration, Intravaginal↗