Biomedical subjects

H Heuer

Publications and source records attributed to H Heuer.

At least 55 records · Page 3Linked to original sources

PubMed1998

Task-dependent mixtures of coordinate systems in visuomotor transformations.

In two experiments the involvement of relative and fixed coordinate systems in visuomotor transformations was examined. The experimental task required the successive performance of two movements in each trial, which had to "correspond" to different visual stimuli. One kind of visual display indicated target positions by way of different horizontal positions of a vertical line on a monitor (position mode), while the other indicated movement amplitudes by way of different lengths of a horizontal line (amplitude mode). Formal analysis of variances and covariances of successive individual movements led to the conclusion that in the position mode visuomotor transformations were based on a mixture of relative and fixed coordinate systems, while in the amplitude mode only a relative coordinate system was involved. Thus, visuomotor transformations can be characterized as mixtures of different coordinate systems, and their respective weights in the mixtures are task-dependent.

Adolescent↗

PubMed1998

Effects of sleep loss, time of day, and extended mental work on implicit and explicit learning of sequences.

Tacit knowledge is part of many professional skills and can be studied experimentally with implicit-learning paradigms. The authors explored the effects of 2 different stressors, loss of sleep and mental fatigue, on implicit learning in a serial-response time (RT) task. In the 1st experiment, 1 night of sleep deprivation was shown to impair implicit but not explicit sequence learning. In the 2nd experiment, no impairment of both types of sequence learning was found after 1.5 hr of mental work. Serial-RT performance, in contrast, suffered from both stressors. These findings suggest that sleep deprivation induces specific risks for automatic, skill-based behavior that are not present in consciously controlled performance.

Adolescent↗

PubMed1998

Region-specific expression of thyrotrophin-releasing hormone-degrading ectoenzyme in the rat central nervous system and pituitary gland.

Thyrotrophin-releasing hormone (TRH), a hypothalamic neuropeptide hormone and a putative neuromodulator/ neurotransmitter in the central nervous system is inactivated by the TRH-degrading ectoenzyme (TRH-DE), a TRH-specific metallopeptidase localized on the surface of neuronal brain cells in culture and on lactotrophic cells of the pituitary. After succeeding in cloning the cDNA of TRH-DE we now report on the cellular distribution pattern of this enzyme in rat brain, spinal cord and pituitary gland using in situ hybridization histochemistry. In the pituitary, TRH-DE mRNA was found both in the anterior and the neural lobe but not in the intermediate lobe. After treatment with triiodothyronine (T3) a dramatic increase in the mRNA levels of the TRH-DE and a decrease in the intensity of the TRH receptor could be observed in the anterior lobe of the pituitary. In brain, TRH-DE transcripts were predominantly found in neo- and allocortical regions with strongest signals in the olfactory bulb, the piriform cortex, the cerebral cortex, the granular layer of the cerebellar cortex and the pyramidal cells of the Ammon's horn. In the diencephalon, the highest TRH-DE mRNA levels were observed in the medial habenulae followed by several hypothalamic subregions. In the mesencephalon and brainstem, moderate signals were present in the superior colliculi, substantia nigra, dorsal raphe and in the periolivar region. In the spinal cord, TRH-DE mRNA positive neurons were present in all layers. The very distinct distribution of TRH-DE in the brain and the hormonal regulation of the adenohypophyseal enzyme support the concept that this peptidase serves very specialized functions.

Aminopeptidases↗

PubMed1998

Preferred position of visual displays relative to the eyes: a field study of visual strain and individual differences.

At office workplaces equipped with visual display units (VDU) that were adjustable to various positions relative to the eyes short and long viewing distances from the eyes to the screen were imposed (mean value of about 63 and 92 cm) at two levels of screen height so that the visual target was either at eye level or 18 cm below, on the average. The change from far to near viewing distance produced a larger increase in eyestrain when the VDUs were at eye level. High screens resulted in greater eyestrain than low screens, as shown by correlations over subjects. When operators were free to adjust the most comfortable screen position, the group of 22 participants preferred viewing distances between 60 and 100 cm and vertical inclination of gaze direction between horizontal and -16 degrees downwards. However, within most subjects the range of preferred screen positions was much smaller. Between 3 days during a 1-month period the test-retest correlations of the preferred screen positions were highly significant, both for viewing distance and vertical gaze inclination. When operators were forced to work at a shorter distance than their preferred viewing distance they reported more visual strain. Thus, operators appear to prefer an individual adjustment of the screen relative to the eyes in order to avoid visual strain and discomfort at VDU work.

Adult↗

PubMed1998

Period duration of physical and imaginary movement sequences affects contralateral amplitude modulation.

The hypothesis was tested that the strength of cross-manual effects of voluntary amplitude modulations in bimanual tasks increases when less preparation time is available during the execution of a sequence of movements. By means of the continuation procedure, various period durations (600, 800, 1200, and 1800 msec) of movement sequences were imposed. Subjects performed bimanual periodic arm movements on two digitizers: constant-amplitude movements (short or long) with the one hand, and movements of constant short or constant long amplitudes and movements of alternating short and long amplitudes with the other hand. Period-duration-dependent modulations of the amplitude were observed in movements of instructed constant amplitudes when the other hand performed alternating-amplitude movements, but not when the other hand performed constant-amplitude movements. Not only physical performance, but also the imaginary production of alternating-amplitude movements resulted in period-duration-dependent cross-manual effects, though reduced in size. The pattern of results is in agreement with a recently proposed two-level model of cross-manual effects according to which cross-talk can occur at the programming level as well as at the execution level.

Adolescent↗

PubMed1998

The thyrotropin-releasing hormone-degrading ectoenzyme: the third element of the thyrotropin-releasing hormone-signaling system.

The peptidergic signal substance thyrotropin-releasing hormone (TRH) is inactivated by the TRH-degrading ectoenzyme (TRH-DE), a peptidase that exhibits an extraordinary high degree of substrate specificity and other unusual characteristics. There is no other ectopeptidase known capable of degrading this tripeptideamide, and vice versa, TRH is the only known substrate of this unique enzyme. Thus, studies on this enzyme may reveal new aspects on the function of the TRH signaling system. After succeeding in purifying this enzyme to homogeneity and cloning the cDNA encoding rat TRH-DE, molecular tools became available to study the expression of this enzyme by Northern blot analysis and in situ hybridization histochemistry. The stringent and tissue-specific regulation of the adenohypophyseal TRH-DE by estradiol and thyroid hormones strongly suggests that this enzyme may act as a regulatory element modulating pituitary hormone secretion. In brain, the expression of TRH-DE is not influenced by peripheral hormones but the distinct distribution pattern, and the high activities support the concept that in this tissue TRH-DE may act as a terminator of TRH signals.

Aminopeptidases↗

PubMed1998

Analysis of BIOLOG GN Substrate Utilization Patterns by Microbial Communities.

BIOLOG GN plates are increasingly used to characterize microbial communities by determining the ability of the communities to oxidize various carbon sources. Studies were done to determine whether the BIOLOG GN plate assay accurately reflects the catabolic potential of the inoculum used. To gain insight into which populations of microbial communities contribute to the BIOLOG patterns, denaturing gradient gel electrophoresis and temperature gradient gel electrophoresis (TGGE) were used to assess the diversity of ribotypes in the inocula and individual wells of BIOLOG plates following incubation. These studies were done with microbial communities from the rhizosphere of potatoes and an activated sludge reactor fed with glucose and peptone. TGGE analyses of BIOLOG wells inoculated with cell suspensions from the potato rhizosphere revealed that, compared with the inoculum, there was a decrease in the number of 16S rRNA gene fragments obtained from various wells, as well as a concomitant loss of populations that had been numerically dominant in the inoculum. The dominant fragments in TGGE gels could be assigned to the gamma subclass of the class Proteobacteria, suggesting that fast-growing bacteria adapted to high substrate concentrations were numerically dominant in the wells and may have been primarily responsible for the patterns of substrate use that were observed. Similarly, the community structure changed in wells inoculated with cells from activated sludge; one or more populations were enriched, but all dominant populations of the inoculum could be detected in at least one well. This study showed that carbon source utilization profiles obtained with BIOLOG GN plates do not necessarily reflect the functional potential of the numerically dominant members of the microbial community used as the inoculum.

Journal Article↗

PubMed1998

Monitoring impact of a pesticide treatment on bacterial soil communities by metabolic and genetic fingerprinting in addition to conventional testing procedures.

Herbogil (dinoterb), a reference herbicide, the mineral oil Oleo (paraffin oil used as an additive to herbicides), and Goltix (metamitron) were taken as model compounds for the study of impacts on microbial soil communities. After the treatment of soil samples, effects on metabolic sum parameters were determined by monitoring substrate-induced respiration (SIR) and dehydrogenase activity, as well as carbon and nitrogen mineralization. These conventional ecotoxicological testing procedures are used in pesticide registration. Inhibition of biomass-related activities and stimulation of nitrogen mineralization were the most significant effects caused by the application of Herbogil. Even though Goltix and Oleo were used at a higher dosage (10 times higher), the application of Goltix resulted in smaller effects and the additive Oleo was the least-active compound, with minor stimulation of test parameters at later observation times. The results served as a background for investigation of the power of "fingerprinting" methods in microbial ecology. Changes in catabolic activities induced by treatments were analyzed by using the 95 carbon sources provided by the BIOLOG system. Variations in the complex metabolic fingerprints demonstrated inhibition of many catabolic pathways after the application of Herbogil. Again, the effects of the other compounds were expressed at much lower levels and comprised stimulations as well as inhibitions. Testing for significance by a multivariate t test indicated that the sensitivity of this method was similar to the sensitivities of the conventional testing procedures. The variation of sensitive carbon sources, as determined by factor weights at different observation times, indicated the dynamics of the community shift induced by the Herbogil treatment in more detail. DNA extractions from soil resulted in a collection of molecules representing the genetic composition of total bacterial communities. Distinct and highly reproducible community patterns, or genetic fingerprints, resulting from application of the different herbicides were obtained by the sequence-specific separation of partial 16S rDNA amplification products in temperature gradient gel electrophoresis. Significant pattern variations were quantified. For detailed analysis, application-responsive bands from the Herbogil and Oleo treatments were sequenced and their tentative phylogenetic positions were identified. Data interpretation and the potentials and biases of the additional observation windows on microbial communities are discussed.

Bacteria↗

PubMed1998

Fixation disparity, accommodation, dark vergence and dark focus during inclined gaze.

We investigated several oculomotor functions at different angles of vertical inclination of the gaze direction from 15 deg upwards to 45 deg downwards. The mean accommodative resting state (measured in a dark visual field) increased when the eyes or the head were declined from 0 to 45 deg. Fixation disparity (the vergence error in minutes of arc relative to the principle visual directions) became more eso when a fusion target at a viewing distance of 40 cm was lowered: declining the gaze by 45 deg changed mean fixation disparity by 1.8 min arc with eye inclination (keeping the head upright), and by 0.9 min arc with head inclination (with eye position unchanged relative to the head). When the eyes were lowered, the individual rate of eso change in fixation disparity was correlated with the amount of the subjects' near shifts in the resting position of vergence, measured in darkness. Significant test-retest correlations between repeated measurements showed that the effects of eye inclination on vergence varied in a reproducible way among individuals with good binocular vision.

Accommodation, Ocular↗

PubMed1997

[Reduction of the left ventricular outflow tract gradient in hypertrophic, obstructive cardiomyopathy after myocardial infarct].

A 73-year old female patient is known to have hypertrophic obstructive cardiomyopathy (HOCM) since 1989. After a transmural anterolateral myocardial infarction with the development of a large apical aneurysms of the anterior wall, a previously measured gradient of 110 mm Hg in the LVOT is no longer detected. As a consequence of this casuistry, "pseudomyectomy" caused by myocardial infarction is described as an example of an uncommon spontaneous course of HOCM.

Aged↗

PubMed1997

Analysis of actinomycete communities by specific amplification of genes encoding 16S rRNA and gel-electrophoretic separation in denaturing gradients.

A group-specific primer, F243 (positions 226 to 243, Escherichia coli numbering), was developed by comparison of sequences of genes encoding 16S rRNA (16S rDNA) for the detection of actinomycetes in the environment with PCR and temperature or denaturing gradient gel electrophoresis (TGGE or DGGE, respectively). The specificity of the forward primer in combination with different reverse ones was tested with genomic DNA from a variety of bacterial strains. Most actinomycetes investigated could be separated by TGGE and DGGE, with both techniques giving similar results. Two strategies were employed to study natural microbial communities. First, we used the selective amplification of actinomycete sequences (E. coli positions 226 to 528) for direct analysis of the products in denaturing gradients. Second, a nested PCR providing actinomycete-specific fragments (E. coli positions 226 to 1401) was used which served as template for a PCR when conserved primers were used. The products (E. coli positions 968 to 1401) of this indirect approach were then separated by use of gradient gels. Both approaches allowed detection of actinomycete communities in soil. The second strategy allowed the estimation of the relative abundance of actinomycetes within the bacterial community. Mixtures of PCR-derived 16S rDNA fragments were used as model communities consisting of five actinomycetes and five other bacterial species. Actinomycete products were obtained over a 100-fold dilution range of the actinomycete DNA in the model community by specific PCR; detection of the diluted actinomycete DNA was not possible when conserved primers were used. The methods tested for detection were applied to monitor actinomycete community changes in potato rhizosphere and to investigate actinomycete diversity in different soils.

Actinomycetales↗

PubMed1997

Thyrotropin-releasing hormone gene expression by anterior pituitary cells in long-term cultures is influenced by the culture conditions and cell-to-cell interactions.

It has been suggested that TRH, synthesized by anterior pituitary (AP) cells in long-term monolayer cultures, may act as a paracrine or autocrine regulator. Because local control through messenger molecules depends on the cellular microenvironment, we were interested in studying the synthesis of TRH by AP cells in different culture systems and under various conditions. When AP cells were cultured as monolayers in medium containing 10% FCS for long periods of time (up to 3 weeks), a considerable increase in TRH content and prepro-TRHmessengerRNA (preproTRHmRNA) levels could be demonstrated by RIA and Northern blot analysis, whereas the cellular content of the TRH-like peptide pyroGlu-Glu-Pro-NH2 decreased with time in culture to undetectable levels. The release of TRH could be stimulated by depolarizing concentrations of K+ (55 mM), by the Ca++ ionophore A23187, and by GnRH, but not by CRH or GRF, indicating that TRH is stored in gonadotropes. Moreover, a combined in situ hybridization and immunocytochemical analysis demonstrated colocalization of LH in preproTRHmRNA-positive AP cells. When AP cells were cultured as reaggregates in the same (FCS-containing) medium, only a marginal increase in TRH content and preproTRHmRNA levels was observed. Irrespective of the culture systems and the culture conditions used, TRH gene expression was not observed when FCS was omitted. These results indicate that TRH gene expression more likely reflects derepression, rather than induction, of the TRH gene.

Animals↗

PubMed1996

[Percutaneous transluminal coronary angioplasty (PTCA) as primary therapy in acute myocardial infarct].

BASIC PROBLEM AND OBJECTIVE: Percutaneous transluminal coronary angioplasty (PTCA) is being increasingly considered as an alternative to thrombolytic treatment of acute myocardial infarction. Studies performed so far, some on selected groups of patients, have produced high initial results of success. This prospective study was undertaken to determined primary success, complications and recurrence after primary PTCA in acute myocardial infarction (AMI). PATIENTS AND METHODS: Primary treatment in the form of immediate PTCA of the infarct vessel was undertaken in 111 patients (84 men, 27 women; mean age 58.6 +/- 10.3 years) with AMI. PTCA was judged successful if the infarct vessel had been reopened to perfusion grade 3 and restenosis was < 50%. No thrombolytic treatment was given, but heparin infusions were given during and for 24-48 hours after the procedure. 13 patients (11.7%) were in cardiogenic shock or required cardiopulmonary resuscitation for infarct-related arrhythmias. RESULTS: The primary success rate of PTCA for the whole group was 91% (101 of 111 patients), but only 77% (ten of 13) among patients in cardiogenic shock and (or) after resuscitation. Acute re-occlusion (0-6 days after PTCA) occurred in seven patients. Eight patients (7.2%) died during the hospital phase (0-4 weeks), seven of whom had been in shock or required resuscitation (death rate 54%). The overall complication rate of the intervention was 6.3%. No emergency aortocoronary bypass was necessary. Repeat coronary angiography was performed in 71 of the 101 successfully treated patients 6 or 12 weeks after the PTCA. Re-occlusion was demonstrated in four (5.6%), a restenosis of more than 50% in 25% of patients. Mean left ventricular ejection fraction, obtained by planimetry from the levocardiogram was 58.6 +/- 9.3%. CONCLUSION: PTCA, performed immediately after acute myocardial infarction is an effective therapeutic measure with a high primary success rate.

Aged↗

PubMed1996

Secondary-task effects on sequence learning.

With a repeated sequence of stimuli, performance in a serial reaction-time task improves more than with a random sequence. The difference has been taken as a measure of implicit sequence learning. Implicit sequence learning is impaired when a secondary task is added to the serial RT task. In the first experiment, secondary-task effects on different types of sequences were studied to test the hypothesis that the learning of unique sequences (where each sequence element has a unique relation to the following one) is not impaired by the secondary task, while the learning of ambiguous sequences is. The sequences were random up to a certain order of sequential dependencies, where they became deterministic. Contrary to the hypothesis, secondary-task effects on the learning of unique sequences were as strong or stronger than such effects on the learning of ambiguous sequences. In the second experiment a hybrid sequence (with unique as well as ambiguous transitions) was used with different secondary tasks. A visuo-spatial and a verbal memory task did not interfere with the learning of the sequence, but interference was observed with an auditory go/no-go task in which high- and low-pitched tones were presented after each manual response and a foot pedal had to be pressed in response to high-pitched tones. Thus, interference seems to be specific to certain secondary tasks and may be related to memory processes (but most likely not to visuo-spatial and verbal memory) or to the organizations of sequences, consistent with previous suggestions.

Adolescent↗

PubMed1995

Generalized motor programs for rapid bimanual tasks: a two-level multiplicative-rate model.

A model is proposed for the timing of rapid bimanual movements. It combines (a) the notion of a generalized motor program (GMP) with invariant relative timing, (b) the two-level concept of timing control with a central level of control and a peripheral level where the observations are made, and (c) the hypothesis that a single GMP simultaneously controls both limbs. Our method is based on the analysis of temporal intervals measured among landmarks taken from the bimanual kinematic traces. We show that sets of tetrad ratios--each composed of two pairs of covariances among four temporal intervals in the actions--should be equal to 1.0 if the hypothesis is correct. In addition, we show that these tetrad ratios should deviate systematically from 1.0 under certain, biologically realizable violations of the model. Data from human subjects show that the results generally conform to the basic model. Simulations are used to illustrate other violations of the model and to explore characteristics of the sampling distribution of the tetrad ratios under the model.

Hand↗

PubMed1994

[The monitor findings of digitalized conventional wrist x-rays].

The study aimed at proving the reliability of monitor systems with the matrix of 1024 x 768 for the detection of scaphoid fractures compared to conventional X-ray. Moreover, we were interested in the significance of procedures of digital imaging post processing, depending in particular on the experience of investigators. 5 investigators with different levels of experience analysed 57 X-rays of the wrist. They compared conventional X-rays with images on a high screen monitor system after the digitalisation of these X-rays by a CCD-scanner and analysed untreated and treated images. A 5-point scale ROC analysis was used for evaluation. The analysis covered a total of 1740 evaluations. The untreated images seen on the monitor system proved slightly better than conventional X-rays. Post-processing has no evident advantage over untreated images. Differing levels of experience had no effect whatsoever on the identification of findings.

Carpal Bones↗

PubMed1994

[Emergency intracoronary stent implantation: complications and experiences with 124 patients].

From January 1990 to February 1993, 88 patients (group 1) received an emergency stent implantation with threatening vascular occlusion within the framework of an elective PTCA or a second emergency PTCA after up to 5 days following a primary successful PTCA. In addition, 36 patients (group 2) received an intracoronary stent during emergency PTCA of instable angina pectoris or acute myocardial infarction. The attempted stent implantation was not successful in 6 other patients. All patients were anticoagulated with heparin, aspirin (100 to 500 mg), and phenprocoumon. Since October 1991, 3 x 75 mg dipyridamole was given and heparinization was stopped after measuring the anticoagulation factor II (prothrombin time < 40%). Main complications within the first 2 to 3 weeks were acute and subacute stent thrombosis (21.8%) and complications of the puncture site (bleeding 19.3%, a. spurium/av-fistula 1.6%). The risk of acute stent thrombosis was significantly higher in patients of group 2 (instable angina pectoris despite of drug therapy or acute myocardial infarction) compared with group 1 (42.4 versus 14.8%). Implantation of multiple stents to stabilize extended dissections had a lower occlusion rate (6.3%). Acute myocardial infarctions were registered in group 1 in 25% (11.4% following implantation, 13.6% following stent occlusion, CK 153 to 3380 U/I, average 826 U/I) and in 58.3% of the high risk patients in group 2 (50% just before or following implantation, 36.1% infarctions or re-infarctions caused by stent occlusion, CK 152 to 1950 U/I, average 657 U/I). The risk of infarction could be limited to approximately 58% of the patients of group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Structural constraints on bimanual movements.

A theoretical framework is outlined, according to which structural constraints on bimanual movements can at least in part be understood as coupling between parameters of generalized motor programs. This framework provides a conceptual link between reaction-time data from experiments with bimanual responses, successive unimanual responses, and choice between left-hand and right-hand responses on the one hand and performance data obtained with concurrently performed continuous movements or sequences of discrete responses on the other. On the basis of data obtained with different methods for the study of intermanual interactions, a distinction is drawn between steady-state and transient constraints, and the hypothesis that the tendency to coactivate homologous muscles originates from a transient coupling of program parameters is applied to a variety of observations on performance in different tasks. Finally, the notion of transient constraints is applied to other types of intermanual interdependencies, and to interpersonal coordination; the possible emergence of transient constraints from steady-state constraints through progressive development of inhibitory pathways in childhood is discussed, as is the potential biological significance of transient constraints.

Attention↗