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Biomedical subjects

M Hammer

Publications and source records attributed to M Hammer.

At least 37 records · Page 2Linked to original sources
PubMed2001

Basic investigations for 2-dimensional time-resolved fluorescence measurements at the fundus.

The decay time is characteristic for several natural fluorophores. The determination of the decay time is independent of the fluorescence intensity. As a consequence, a short living weak fluorescence should be detectable also if it is covered by a intensive long-living fluorescence. As the decay time is influenced by the embedding matrix, information about the cellular stage might be possible. The laser scanning technique in combination with the time correlated single photon counting technique seems to be the optimal method for the discrimination of different fluorophores at the fundus according to the decay time. Fields of an equal decay time are presented as a tau mapping. An experimental set up was developed. Until now, only basic experiments were done on structured fluorescent tests, but under the conditions of the living eye. The results are promising. For the separate detection of the most important short life-time of 120 ps of A2E (excitation at 413 nm. emission 450-600 nm) as a putative precursor of lipofuscin in age-related macular degeneration [11], a light source for pulses in the range of about 50 ps is required.

Eye Proteins↗
PubMed2001

Non-invasive measurement of the concentration of melanin, xanthophyll, and hemoglobin in single fundus layers in vivo by fundus reflectometry.

A new model of the reflection of the human ocular fundus on the basis of the adding-doubling method, an approximate solution of the radiative transport equation, is described. This model enables the calculation of the concentration of xanthophyll in the retina, of melanin in the retinal pigment epithelium and in the choroid, and of hemoglobin in the choroid from fundus reflectance spectra. The concentration values found in 12 healthy subjects are in excellent agreement with literature data. In single cases of pathologic fundus alterations possible benefits to the ophthalmologic diagnostics is demonstrated.

Choroid↗
PubMed2001

[Relationship between illness, rehabilitation and work (ZERA)--an training program for medical-vocational rehabilitation of the mentally ill].

A training programme for rehabilitation of people with mental illness is presented, designed particularly for schizophrenic patients who need occupational rehabilitation. The training goal is to connect aspects of the schizophrenic disorder with vocational issues. It is aimed at supporting the participants in developing a realistic and appropriate vocational perspective in line with their illness related restrictions and current vocational possibilities, seeking to find out the individual's optimal ability to take stress so as to avoid over- or understimulation in vocational respects. The ZERA training has been developed for implementation in different medical and vocational rehabilitation settings for persons with mental illness. An initial control-group study was carried out to evaluate the effectiveness of this group training approach, and preliminary results have revealed changes in the experimental group in accordance with the objectives of the training and encourage further research.

Adult↗
PubMed2001

A scattering phase function for blood with physiological haematocrit.

Though the optics of red blood cells as well as whole blood has been studied extensively, an effective scattering phase function for whole blood is still needed. The interference of waves scattered by neighbouring cells cannot be neglected in highly concentrated suspensions such as whole blood. As a result, the phase function valid for single erythrocytes may fail to describe a single scattering process in whole blood with physiological haematocrit (Hct approximately 0.4). In this study we compared the results obtained in goniophotometric measurements of blood samples with the results of angle-resolved Monte Carlo simulations. The results show that a Henyey-Greenstein phase function with an anisotropy factor of 0.972 is an adequate approximation for the effective scattering phase function of whole blood with high haematocrit at a wavelength of 514 nm.

Blood Physiological Phenomena↗
PubMed2001

Light paths in retinal vessel oxymetry.

The oxygen utilization and, therefore, the metabolic state, of a distinctive area of the retina may be calculated from the diameter of the supplying artery and vein, the haemoglobin oxygenation, and the velocity of the blood. The first two parameters can be determined by imaging spectrometry at the patients ocular fundus. However, the reflected light emerging from a vessel followed different pathways through the ocular fundus layers and the vessel embedded in the retina. The contribution of the single pathways to the vessel reflection profile is investigated by a Monte Carlo simulation. Considering retinal vessels with diameters of 25-200 microm we found the reflection from a thin vessel to be determined by the single and double transmission of light at 560 nm. The backscattering from the blood column determines the reflectance in the case of a thick vessel. However, both components are in the same order of magnitude. This has to be considered in the calculation of the oxygen saturation of blood in retinal vessels from their reflection spectra.

Light↗
PubMed2001

Urinary excretion and bactericidal activities of gemifloxacin and ofloxacin after a single oral dose in healthy volunteers.

In a randomized crossover study, 16 volunteers (8 men, 8 women) received single oral doses of 320 mg of gemifloxacin and 400 mg of ofloxacin on two separate occasions in the fasting state to assess the urinary excretion and urinary bactericidal titers (UBTs) at intervals for up to 144 h. Ofloxacin showed higher concentrations in urine compared with those of gemifloxacin. The median (range) cumulative excretion of gemifloxacin was 29.7% (8.4 to 48.7%) of the parent drug administered, and median (range) cumulative excretion of ofloxacin was 84.3% (46.5 to 95.2%) of the parent drug administered. The UBTs, i.e., the highest twofold dilutions (with antibiotic-free urine as the diluent) of urine that were still bactericidal, were determined for a reference strain and nine uropathogens for which the MICs of gemifloxacin and ofloxacin were as follows: Escherichia coli ATCC 25922, 0.016 and 0.06 microg/ml, respectively; Klebsiella pneumoniae, 0.03 and 0.06 microg/ml, respectively; Proteus mirabilis, 0.125 and 0.125 microg/ml, respectively; Escherichia coli, 0.06 and 0.5 microg/ml, respectively; Pseudomonas aeruginosa, 1 and 4 microg/ml, respectively; Staphylococcus aureus, 0.008 and 0.25 microg/ml, respectively; Enterococcus faecalis, 0.06 and 2 microg/ml, respectively; Staphylococcus aureus, 0.25 and 4 microg/ml, respectively; Enterococcus faecalis, 0.5 and 32 microg/ml, respectively; and Staphylococcus aureus, 2 and 32 microg/ml, respectively. Generally, the UBTs for gram-positive uropathogens were higher for gemifloxacin than for ofloxacin and the UBTs for gram-negative uropathogens were higher for ofloxacin than for gemifloxacin. According to the UBTs, ofloxacin-resistant uropathogens (MICs, >or=4 mg/liter) should also be considered gemifloxacin resistant. Although clinical trials have shown that gemifloxacin is effective for the treatment of uncomplicated urinary tract infections, whether an oral dosage of 320 mg of gemifloxacin once daily is also adequate for the treatment of complicated urinary tract infections has yet to be confirmed.

Adolescent↗
PubMed2001

Formation of strong airway irritants in mixtures of isoprene/ozone and isoprene/ozone/nitrogen dioxide.

We evaluated the airway irritation of isoprene, isoprene/ozone, and isoprene/ozone/nitrogen dioxide mixtures using a mouse bioassay, from which we calculated sensory irritation, bronchial constriction, and pulmonary irritation. We observed significant sensory irritation (approximately 50% reduction of mean respiratory rate) by dynamically exposing the mice, over 30 min, to mixtures of isoprene and O3 or isoprene, O3, and NO2. The starting concentrations were approximately 4 ppm O3 and 500 ppm isoprene (+ approximately 4 ppm NO2. The reaction mixtures after approximately 30 sec contained < 0.2 ppm O3. Addition of the effects of the residual reactants and the identified stable irritant products (formaldehyde, formic acid, acetic acid, methacrolein, and methylvinyl ketone) could explain only partially the observed sensory irritation. This suggests that one or more strong airway irritants were formed. It is thus possible that oxidation reactions of common unsaturated compounds may be relevant for indoor air quality.

Air Pollution, Indoor↗
PubMed2001

The superefficient company.

Most companies do a great job promoting efficiency within their own walls, streamlining internal processes wherever possible. But they have less success coordinating cross-company business interactions. When data pass between companies, inconsistencies, errors, and misunderstandings routinely arise, leading to wasted work--for instance, the same sales, order entry, and customer data may be entered repeatedly into different systems. Typically, scores of employees at each company manage these cumbersome interactions. The costs of such inefficiencies are very real and very large. In this article, Michael Hammer outlines the activities and goals used in streamlining cross-company processes. He breaks down the approach into four stages: scoping--identifying the business process for redesign and selecting a partner; organizing--establishing a joint committee to oversee the redesign and convening a design team to implement it; redesigning--taking apart and reassembling the process, with performance goals in mind; and implementing--rolling out the new process and communicating it across the collaborating companies. The author describes how several companies have streamlined their supply-chain and product development processes. Plastics compounder Geon integrated its forecasting and fulfillment processes with those of its main supplier after watching inventories, working capital, and shipping times creep up. General Mills coordinated the delivery of its yogurt with Land O'Lakes; butter and yogurt travel cost effectively in the same trucks to the same stores. Hammer says this new kind of collaboration promises to change the traditional vocabulary of corporate relationships. What if you and I sell different products to the same customer? We're not competitors, but what are we? In the past, we didn't care. Now, we should, the author says.

Commerce↗
PubMed2001

Transforaminal ventral epidural adhesiolysis.

Epidural fibrosis with chronic low back pain, nonresponsive to traditional measures of treatment including surgery, is a common entity in modern medicine. Traditionally, epidural steroid injections have been employed to treat chronic low back pain and radiculopathy associated with failed back surgery. Due to the poor effectiveness of epidural steroid injections in post lumbar laminectomy syndrome, epidural adhesiolysis was introduced in the early 1980s. Caudal epidural adhesiolysis with hypertonic saline neurolysis has been described extensively in the literature and has been proven to be relatively successful and safe. To improve the results and reach the target area with steroid, transforaminal ventral epidural adhesiolysis has been utilized. This retrospective case analysis included 14 patients. Transforaminal ventral epidural adhesiolysis was performed on an outpatient basis in all patients. The results showed 93% improvement initially, which decreased to 71% at 1 month, 57% at 3 months, 43% at 6 months and 21% at 1 year. The results of this case study show that ventral epidural lysis of adhesions with hypertonic saline neurolysis is safe and effective in managing chronic low back and lower extremity pain in patients who failed to respond to other conservative modalities of treatments, including fluoroscopically directed transforaminal epidural steroid injections.

Journal Article↗
PubMed2000

[Age-related maculopathy. Comparative studies of patients, their children and healthy controls].

BACKGROUND: The aim of this study was to evaluate prospectively whether there are differences in spectrometrically measurable parameters of the fundus between patients with early and late age-related maculopathy (ARM), the children of the ARM patients (F1 generation) and normals. METHOD: Using the "Jenaer Imaging Spectrometer", retinal oxygen saturation, xanthophyll, and intrinsic fluorescence were measured; the spatial distribution of xanthophyll was determined using the Rodenstock SLO 101 model. RESULTS: Xanthophyll is reduced in late ARM as compared to the F1 generation and the control group (alpha < 0.01). The different fluorescence spectra, measured at shortwave and at longwave excitation, suggest the presence of more than one fluorophore. Furthermore, the components of the fluorophores seem to be different between patients with ARM and their F1 generation. The longwave autofluorescence is age-dependent only in late ARM (r2 = 0.81). For the first time, we found an alteration in oxygen saturation in retinal vessels in patients with ARM. CONCLUSIONS: Xanthophyll is reduced only in late ARM. Autofluorescence and oxygen saturation are different between ARM patients, the F1 generation and normals, however, we were not able to identify a genetically based predisposition concerning the parameters studied.

Adult↗
PubMed2000

Bioluminescence as a classroom tool for scientist volunteers.

There is a great need for practicing scientists to volunteer their time and expertise in the K-12th grade science classroom. We have found that bioluminescence is a fun and exciting way to teach basic science concepts and is an excellent tool for the volunteering scientist. We have had very positive reactions from both teachers and students. The excitement of the students when they first see bioluminescence is contagious. Bioluminescent dinoflagellates are one of the easiest ways to introduce students to this fascinating topic. Many activities and experiments can be done using the bioluminescent dinoflagellates and many students and teachers could benefit from your knowledge and expertise. See you in the classroom.

Luminescent Measurements↗
PubMed2000

Effects of R-(+)- and S-(-)-limonene on the respiratory tract in mice.

The effects of airborne R-(+)- and S-(-)- limonene were studied in conscious BALB/c mice by continuous monitoring respiratory rate (f), tidal volume (VT) and mid-expiratory flow rate (VD) during an exposure period of 30 min. Both enantiomers decreasedf from a trigeminal reflex, i.e., due to sensory irritation. The exposure concentration decreasing f by 50% (RD50) in the first 10 min of the exposure period was estimated to be 1,076 ppm for R-(+)-limonene and 1,467 ppm for S-(-)-limonene. Results for sensory irritation of R-(+)-limonene in BALB/c mice and humans are in close agreement. The reported sensory irritation threshold is above 80 ppm in humans while the no-observed-effect level was estimated to be 100 ppm in mice. The enantiomers were devoid of pulmonary irritation or general anesthetic effects with R-(+)-limonene < or =1,599 ppm and S-(-)-limonene < or =2,421 ppm. R-(+)-limonene did not influence VT below 629 ppm. S-(-)-limonene increased VT above 1,900 ppm. Both enantiomers induced a mild bronchoconstrictive effect above 1,000 ppm.

Administration, Inhalation↗
PubMed2000

Sensory preconditioning in honeybees.

Sensory preconditioning means that reinforcement of stimulus A after unreinforced exposure to a compound AB also leads to responses to stimulus B. Here, we describe and analyze sensory preconditioning in an insect, the honeybee Apis mellifera. Using two-element odorant compounds in classical conditioning of the proboscis extension reflex, we found (i) that sensory preconditioning is not due to stimulus generalization, (ii) that paired, but not unpaired, presentation of elements supports sensory preconditioning, (iii) that simultaneous, but not sequential, exposure to the elements of the compound supports sensory preconditioning and (iv) that a single presentation of the compound yields maximal sensory preconditioning. The results are discussed with respect to configural and chain-like associative explanations for sensory preconditioning. We suggest an experience-dependent step of compound processing, establishing configural units, as an additional explanation for sensory preconditioning.

Animals↗
PubMed1999

Pattern learning by honeybees: conditioning procedure and recognition strategy.

In recognizing a pattern, honeybees Apis mellifera, may focus either on its ventral frontal part, or on the whole frontal image. We asked whether the conditioning procedure used to train the bees to a pattern determines the recognition strategy employed. Bees were trained with the same patterns presented vertically on the back walls of a Y maze. Conditioning was either absolute, that is, bees should learn to choose a rewarded pattern when there is no alternative, or differential, that is, bees should learn to choose a rewarded pattern that is paired with a different, nonrewarded one. Bees used different pattern recognition strategies depending on the conditioning procedure: absolute conditioning restricted recognition to the lower half whilst differential conditioning extended it to the whole pattern. Bees trained with absolute conditioning saw and learned the features of the upper part of the trained patterns, but assigned more weight to the lower part. Bees trained with differential conditioning learned not only the features of the reinforced stimulus in an excitatory way, but also those of the nonreinforced one in an inhibitory way. Thus, conditioning tasks that involve not only excitatory acquisition of the conditioned stimulus per se, but also discrimination of nonreinforced stimuli, result in an increase in the visual field assigned to the recognition task. Conditioning tasks that involve only excitatory acquisition of the rewarded stimulus result in a higher weighting of the lower pattern half and thus in a more reduced field assigned to the recognition task. This difference may reflect that existing between a conditioned and an incidental behavioural modification. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

[Oxygen saturation of retinal vessels. Studies for measuring with polarized light].

UNLABELLED: The accuracy of the spectrometric measurement of the oxygen saturation in retinal vessels is limited by its signal-to-noise ratio. The aim of this study was to investigate the possibility of enhancement of the reflection signal by the use of polarized light. MATERIALS AND METHODS: The Jena ophthalmospectrometer was equipped with two polarizing filters: one in the illumination and the other in front of the detector. Reflection spectra of erythrocytes streaming through a cuvette in the focus of an artificial eye were recorded. The influence of the polarization on the reflection spectra was investigated by rotating the polarizer in front of the detector. Furthermore, the degree of polarization of the light reflected from retinal vessels in vivo was determined. RESULTS: The degree of polarization of the light reflected from the erythrocytes was 0.6-0.8, whereas the polarization of light reflected by a standard white reflectance target was virtually zero. CONCLUSION: Polarized light can be used for the reduction of error in retinal vessel oximetry.

Blood Flow Velocity↗
PubMed1999

In vivo measurement of the oxygen saturation of retinal vessels in healthy volunteers.

A new method for the spatially resolved measurement of the oxygen saturation of retinal vessels is described. Imaging spectrometry was used for both measurements of transmission and reflectance spectra of whole blood in cuvettes as well as for fundus reflectance spectra. A model was developed for the calculation of the oxygen saturation, valid in the wavelength range between 510 nm and 586 nm, in that the internal reflectance is constant and only the transmitted light depends on layer thickness and hematocrit. Altogether 265 measurements were performed in different number at 30 eyes. In each measurement, the oxygen saturation was simultaneously determined for 193 locations along a line of 1.5 mm at the fundus. The mean oxygen saturation in retinal arteries was (92.2 +/- 4.1)% and (57.9 +/- 9.9)% in retinal veins. The mean retinal arterio-venous difference of the oxygen saturation was (35.1 +/- 9.5)%. The venous oxygen saturation depended on distance from the optic disc. The measured mean of the arterio-venous difference of the oxygen saturation corresponded well to the value of the brain (34%). The utilization of oxygen in the temporal quadrants (inferior: 39.4 +/- 10.4%) is significantly (p = 0.05) higher than in the nasal quadrants (inferior: 31.3 +/- 6.7%).

Adolescent↗