PubMed Health⌕ Search

Biomedical subjects

M Wehr

Publications and source records attributed to M Wehr.

At least 19 recordsLinked to original sources
PubMed2004

Antibody levels against Chlamydia pneumoniae and outcome of roxithromycin therapy in patients with acute myocardial infarction. Results from a sub-study of the randomised Antibiotic Therapy in Acute Myocardial Infarction (ANTIBIO) trial.

BACKGROUND: Results of studies concerning prevention of cardiovascular disease by treatment with macrolide antibiotics targeting C. pneumoniae infection are still controversial. This study describes the results of different tests for infection with C. pneumoniae as well as the effect of treatment with roxithromycin in patients with acute myocardial infarction (AMI) in relation to their serostatus against C. pneumoniae. METHODS: We analysed blood of 160 patients who came from the ANTIBIOtic therapy after an AMI ( ANTIBIO-) study, a prospective, randomised, placebo-controlled, double-blind study to investigate the effect of roxithromycin 300 mg/OD for 6 weeks in patients with an AMI. Anti- Chlamydia IgG-, IgA-, and IgM-antibodies of these patients were analysed by means of different test systems. RESULTS: There was a good correlation between the two IgG and IgA methods (r = 0.900, p < 0.001 and r = 0.878, p < 0.001, respectively), but marked differences in the prevalence of positive tests. This resulted in only moderate concordance values, as expressed by the Kappa coefficients, for IgG kappa = 0.611 (95% CI = 0.498-0.724, p < 0.001) and for IgA kappa = 0.431 (95% CI: 0.322-0.540, p < 0.001). No significant association between positive C. pneumonia titers and the combined clinical endpoint during the 12 month follow-up could be found. In all test systems used, patients with positive anti- C. pneumoniae titers did not benefit from roxithromycin therapy (p = ns). CONCLUSION: Depending on the test system used, there are large differences in the prevalence of anti- C. pneumoniae seropositive patients. Clinical events during the 12 month follow-up after AMI did not depend on serostatus against C. pneumoniae and treatment with roxithromycin did not influence these events, independently of the serostatus against C. pneumoniae. However, the power of this subgroup analysis was low to detect small but significant differences.

Anti-Bacterial Agents↗
PubMed2000

Changes of QT dispersion in patients with coronary artery disease dependent on different methods of stress induction.

BACKGROUND: Episodes of stress-induced myocardial ischemia in patients with coronary artery disease (CAD) may cause increases of QT dispersion (QTd). HYPOTHESIS: Aim of this study was to analyze the effect of increasing heart rates on QTd and to compare the effect of different methods of stress induction in patients with varying degrees of CAD when estimating QTd. METHODS: We studied 58 patients, 22 with prior myocardial infarction (MI), 25 without MI or wall motion disturbances at rest, and 11 patients without evidence of CAD. Prior to coronary angiography, standard 12-lead ECGs were obtained at rest as well as during dynamic exercise and pharmacologic stress using arbutamine simultaneously with echocardiography. QTd was determined at each stress level by subtracting minimal from maximal QT interval duration. RESULTS: QTd values at rest were not consistently higher in the patients with CAD. At maximal heart rate, QTd was statistically significantly higher in patients with CAD with a better discrimination between groups for pharmacologic stress (p < 0.005 for exercise, p < 0.0001 for arbutamine). Patients after MI had higher QTd values under all conditions than did the groups without MI. As in patients with CAD, the values of this group changed more radically as a result of pharmacologic stress. CONCLUSION: Patients with CAD can be identified on the basis of QTd under stress. These changes were not as marked in patients with MI as their rest values were already increased. Overall, drug-induced stress produced greater differences than dynamic exercise, suggesting that the ischemic threshold might be lower in the former.

Adrenergic beta-Agonists↗
PubMed2000

Myocardial "hybrid" revascularisation with minimally invasive direct coronary artery bypass grafting combined with coronary angioplasty: preliminary results of a multicentre study.

OBJECTIVE: To expand the benefits of the minimally invasive direct coronary artery bypass (MIDCAB) concept to patients with multivessel disease, a hybrid procedure combining surgical revascularisation of the left anterior descending artery with interventional procedures for additional coronary lesions has recently been introduced. Preliminary results in patients undergoing this hybrid procedure are presented. DESIGN AND PATIENTS: Since December 1996, 35 patients (29 male, 6 female, mean (SD) age 56.7 (17) years) underwent a hybrid revascularisation performed as a primary MIDCAB procedure for grafting of the left anterior descending artery with the left internal mammary artery, followed by staged angioplasty and stenting of additional coronary lesions. RESULTS: After MIDCAB grafting the postoperative course was uneventful in all patients. Coronary reangiography after a median of seven days revealed patent and functioning left internal mammary artery grafts in all patients. Applying subsequent percutaneous transluminal coronary angioplasty and occasional stenting (n = 14), a total of 47 lesions were treated successfully. Procedure related complications did not occur. All patients remained free from angina and no stress ECG changes were recorded. CONCLUSIONS: The preliminary results of this hybrid approach to myocardial revascularisation suggest that this is a safe and effective procedure for complete revascularisation in selected patients with multivessel disease. Elderly and reoperative patients with significant comorbidity may benefit especially from such hybrid procedures by avoiding cardiopulmonary bypass and mid sternotomy.

Adult↗
PubMed1999

Relationship between afferent and central temporal patterns in the locust olfactory system.

Odors evoke synchronized oscillations and slow temporal patterns in antennal lobe neurons and fast oscillations in the mushroom body local field potential (LFP) of the locust. What is the contribution of primary afferents in the generation of these dynamics? We addressed this question in two ways. First, we recorded odor-evoked afferent activity in both isolated antennae and intact preparations. Odor-evoked population activity in the antenna and the antennal nerve consisted of a slow potential deflection, similar for many odors. This deflection contained neither oscillatory nor odor-specific slow temporal patterns, whereas simultaneously recorded mushroom body LFPs exhibited clear 20-30 Hz oscillations. This suggests that the temporal patterning of antennal lobe and mushroom body neurons is generated downstream of the olfactory receptor axons. Second, we electrically stimulated arrays of primary afferents in vivo. A brief shock to the antennal nerve produced compound PSPs in antennal lobe projection neurons, with two peaks at an approximately 50 msec interval. Prolonged afferent stimulation with step, ramp, or slow sine-shaped voltage waveforms evoked sustained 20-30 Hz oscillations in projection neuron membrane potential and in the mushroom body LFP. Projection neuron and mushroom body oscillations were phase-locked and reliable across trials. Synchronization of projection neurons was seen directly in paired intracellular recordings. Pressure injection of picrotoxin into the antennal lobe eliminated the oscillations evoked by electrical stimulation. Different projection neurons could express different temporal patterns in response to the same electrical stimulus, as seen for odor-evoked responses. Conversely, individual projection neurons could express different temporal patterns of activity in response to step stimulation of different spatial arrays of olfactory afferents. These patterns were reliable and remained distinct across different stimulus intensities. We conclude that oscillatory synchronization of olfactory neurons originates in the antennal lobe and that slow temporal patterns in projection neurons can arise in the absence of temporal patterning of the afferent input.

Afferent Pathways↗
PubMed1999

[Hybrid technique for myocardial revascularization: value of combined minimal invasive bypass technique (MIDCAB) with interventional therapy (PTCA)].

BACKGROUND: Minimally invasive direct coronary artery bypass (MIDCAB) grafting without cardiopulmonary bypass (CPB) through an anterolateral minithoracotomy has become a promising therapeutical option especially in multimorbid, elderly and reoperative patients with single vessel disease. However, this procedure precludes complete revascularization in multivessel disease because the minithoracotomy limits the surgical access either to anterior or lateral or posterior vessels of the beating heart. To expand the benefits of the MIDCAB concept to patients with multivessel disease, new interdisciplinary approaches have recently been introduced. METHODS: Since December 1996, 26 patients (21 male, 5 female, mean age 56.6 +/- 18.8 years) underwent a "hybrid" revascularization performed as a primary MIDCAB procedure for grafting of the left anterior descending artery (LAD) with the left internal mammary artery (LIMA) followed by staged angioplasty and stenting of additional coronary lesions. RESULTS: After MIDCAB grafting, the postoperative course was uneventful in all patients. Coronary re-angiography after a median of 7 days revealed patent and functioning LIMA grafts in all patients. Applying subsequent percutaneous transluminal coronary angioplasty (PTCA) and occasional stenting (n = 8), a total of 31 lesions were treated successfully. Procedure related complications did not occur. All patients remained angina-free and no stress electrocardiographic changes were recorded. CONCLUSION: Our preliminary results of a "hybrid" approach to myocardial revascularization suggest that this concept is a safe and effective approach of complete revascularization for selected patients with multivessel involvement. Especially elderly and reoperative patients with significant comorbidity may benefit from hybrid procedures avoiding cardiopulmonary bypass and midsternotomy.

Adult↗
PubMed1999

Spatial distribution of QT dispersion measured by magnetocardiography under stress in coronary artery disease.

This study investigated changes in spatial distribution of QT duration in patients with and without coronary artery disease (CAD) using magnetocardiography. Thirty-six-channel magnetocardiograms (MCGs) were registered at rest and under stress in 15 patients with chest pain, seven of whom had significant coronary stenosis. QT dispersion (QTd) was calculated for MCG and 12-lead electrocardiogram (ECG) under both conditions. For MCG, homogeneity of repolarization was measured using a smoothness index (SI). Also, at each registration site, the intraindividual difference between QT at rest and under stress was determined (deltaQT). QTd values as determined by standard 12-lead configurations were not significantly different between groups. MCG QTd values were significantly higher in the CAD group at rest only when all available channels were taken into consideration (P < .05); SI values differed significantly between groups under both conditions (rest, P < .005; stress, P < .01). Good separation between groups was possible using the range of deltaQT (P < .05) and SI (deltaQT) (P < .005). Consideration of the spatial distribution of QTd increases its sensitivity in the detection of CAD, suggesting that CAD involves complex changes in repolarization, not apparent in limited lead sets such as standard 12-lead configurations.

Adrenergic beta-Agonists↗
PubMed1996

Odour encoding by temporal sequences of firing in oscillating neural assemblies.

Stimulus-evoked oscillatory synchronization of activity has been observed in many neural systems, including the cerebral cortex of mammals and the brain of insects. The possible functions of such rhythmic synchronization in neural coding, however, remain largely speculative. In the locust, odours evoke activity in dynamic (evolving) ensembles of transiently synchronized neurons. We report here that the active neurons composing these ensembles change in a stimulus-specific manner and with a high degree of reliability on a cycle-by-cycle basis during an odour response. Hence, information about an odour is contained not only in the neural assembly active at each oscillation cycle, but also in the precise temporal sequence in which these assemblies are updated during an odour response. Neural coding with oscillations thus allows combinatorial representations in time as well as in space.

Action Potentials↗
PubMed1996

Temporal representations of odors in an olfactory network.

The responses of projection neurons in the antennal lobe of the locust brain (the functional analog of mitral-tufted cells in the vertebrate olfactory bulb) to natural blends and simple odors were studied with multiple intra- and extracellular recordings in vivo. Individual odors evoked complex temporal response patterns in many neurons. These patterns differed across odors for a given neuron and across neurons for a given odor, but were stable for each neuron over repeated presentations (separated by seconds to minutes) of the same odor. The response of individual neurons to an odor was superimposed on an odor-specific coherent oscillatory population activity. Each neuron usually participated in the coherent oscillations during one or more specific epochs of the ensemble activity. These epochs of phase locking were reliable for each neuron over tens of repeated presentations of one odor. The timing of these epochs of synchronization differed across neurons and odors. Correlated activity of specific pairs of neurons, hence, generally occurred transiently during the population response, at times that were specific to these pairs and to the odor smelled. The field potential oscillations, therefore, fail to reveal a progressive transformation of the synchronized ensemble as the response to the odor unfolds. We propose that (1) odors are represented by spatially and temporally distributed ensembles of coherently firing neurons, and (2) the field potential oscillations that characterize odor responses in the olfactory system occur, at least in this animal, in parallel with a slower dynamic odor representation.

Animals↗
PubMed1996

Spatial distribution of QT intervals: an alternative approach to QT dispersion.

QT dispersion (QTd) describes the heterogeneity of ventricular repolarization on the basis of the temporal range of QT intervals as measured in the 12-lead ECG. We examined the spatial distribution of QTd using multichannel magnetocardiograms (MCGs), which noninvasively register changes in magnetic field strength at 37 sites over the heart. As in ECG, the MCG signal in each channel may be used to measure QT interval. By calculating QT deviation from QTmin at each site, one can reconstruct the spatial distribution of QTd. Analysis of spatial QTd in ten healthy subjects and ten patients after acute myocardial infarction (MI) showed clear differences in spatial distribution. The healthy subjects generally displayed shorter QT intervals along a line corresponding to the approximate position of the septum with longer intervals in plateaus in the upper right and lower left. Spatial QTd of the post-MI patients deviated from this pattern, often displaying a sharp rise in QT duration over specific areas, which could be related to functional and morphological disturbances. The quantification of local irregularities as well as the overall pattern on the basis of a smoothness index allowed better discrimination between healthy subjects and post-MI patients than QTd. Distribution patterns of QTd which reflect local repolarization alterations may thus represent a more differentiated marker for pathology and risk.

Adult↗
PubMed1994

Distinct rhythmic locomotor patterns can be generated by a simple adaptive neural circuit: biology, simulation, and VLSI implementation.

Rhythmic motor patterns can be induced in leg motor neurons of isolated locust thoracic ganglia by bath application of pilocarpine. We observed that the relative phases of levators and depressors differed in the three thoracic ganglia. Assuming that the central pattern generating circuits underlying these three segmental rhythms are probably very similar, we developed a simple model circuit that can produce any one of the three activity patterns and characteristic phase relationships by modifying a single synaptic weight. We show results of a computer simulation of this circuit using the neuronal simulator NeuraLOG/Spike. We built and tested an analog VLSI circuit implementation of this model circuit that exhibits the same range of "behaviors" as the computer simulation. This multidisciplinary strategy will be useful to explore the dynamics of central pattern generating networks coupled to physical actuators, and ultimately should allow the design of biologically realistic walking robots.

Adaptation, Physiological↗
PubMed1993

Heart rate variability and circulating catecholamine concentrations during steady state exercise in healthy volunteers.

OBJECTIVES: To assess whether exercise induced suppression of heart rate variability in the low frequency domain (0.06-0.15 Hz) is related to the increase in circulating catecholamine concentrations. DESIGN: Randomised crossover trial of three exercise tests characterised by different workloads. Pharmacological simulation of exercise-induced changes in vagal and sympathetic activity. PARTICIPANTS: Six healthy men with a mean age of 31.2 (SD 3.0) years. INTERVENTIONS: Three different workloads of steady state cycling ergometry: control state without cycling, cycling at a target heart rate of 100 beats/min, and cycling at a target heart rate of 150 beats/min. Intravenous infusion of atropine (target heart rate 100 beats/min) followed by the additional infusion of adrenaline and noradrenaline. MAIN OUTCOME MEASURES: Fast Fourier analysis of heart rate variability; blood pressure; and venous plasma concentrations of lactate, adrenaline, and noradrenaline. RESULTS: During the control exercise period there were no changes in the assessed variables compared with the preceding resting period. During exercise at a heart rate of 100 beats/min systolic blood pressure increased and heart rate variability decreased. During exercise at a heart rate of 150 beats/min systolic blood pressure and lactate, adrenaline, and noradrenaline concentrations increased. In addition, low frequency (LF) was lower than during exercise at 100 beats/min, high frequency (HF 0.15-0.80 Hz) resembled that during exercise at 100 beats/min, and diastolic blood pressure was reduced. Infusion of atropine caused no changes in blood pressure or plasma concentrations of lactate, adrenaline, and noradrenaline and decreased heart rate variability. The additional infusion of adrenaline and noradrenaline completely suppressed heart rate variability and increased blood pressure. CONCLUSIONS: The reduction in LF and HF during exercise at a heart rate of 100 beats/min, which is not characterised by increased plasma catecholamine concentrations, and during atropine infusion suggests that heart rate variability in the supine state is largely influenced by vagal activity. The additional reduction in LF during exercise at 150 beats/min and during catecholamine infusion may reflect a negative feedback of circulating catecholamines on the sympathetic control of heart rate.

Adult↗
PubMed1992

[Poor reproducibility of parameters of heart rate variations].

The analysis of heart rate variability is supposed to be a marker of autonomic cardiac activity and is used for risk stratification of post-infarction patients. Analysis of heart rate variability in the frequency domain may permit a differentiation of vagal and sympathetic control; for such analyses only short time intervals characterized by a steady-state autonomic balance can be used. Yet, it is unclear whether single determinations of heart rate variability indices derived from short time intervals yield reproducible results. Therefore, the reproducibility of heart rate variability indices was studied with weekly measurements in 10 healthy volunteers under the following defined conditions: 13 min supine rest, 10 min standing, 13 min sitting, and 15 min cycle ergometry followed by a 14 min recovery period. Heart rate variability was determined in the frequency domain (fast Fourier transformation) and in the time domain. The reproducibility was estimated by the coefficient of variation (CV). Additionally, the reproducibility of heart rate, blood pressure, and the expiratory-inspiratory ratio of heart rate was determined. The reproducibility of the frequency domain indices (36.6-74.9% CV) and of the time domain indices (19.6-32.8% CV) was considerably worse than that of heart rate (5.2-8.2% CV), blood pressure (5.1-8.2% CV) and the expiratory-inspiratory ratio of heart rate (4.6% CV). The reproducibility of heart rate variability indices was not improved by orthostatic or ergometric challenge. This poor reproducibility does not permit a reliable interpretation of heart rate variability on the basis of single measurements in healthy volunteers. Given the wide range and scatter of the measured parameters, the diagnostic and prognostic value of heart rate variability indices derived from short recording periods appears questionable.

Arrhythmias, Cardiac↗
PubMed1991

[The correlation of duplex sonography and intra-arterial DSA in degenerative vascular diseases in the supra-aortic region].

In 46 patients the common and internal carotid artery were examined by duplex sonography and intraarterial DSA in a prospective study. A correlation of 80% was found in diagnosis and degree of the pathological changes. Small lesions of the vessels are more exactly demonstrated by duplex sonography. In subtotal stenosis duplex sonography is inferior to angiography.

Adult↗
PubMed1990

[Cardiac findings in alcoholic liver disease].

In a prospective study 53 patients with alcohol-induced liver disease (fatty liver in 27, cirrhosis in 26) were studied clinically and with non-invasive techniques (electrocardiogram, systolic time intervals, M-mode echocardiography, upright bicycle stress test) to detect a possible cardiac involvement. Mean daily alcohol consumption was comparable in both groups (136 g/day over 16 years vs 124 g/day over 14 years). 15 to 41% of patients (more patients with fatty liver) complaint of angina pectoris and dyspnea at exercise or had palpitations. Echocardiography and systolic time intervals demonstrated in both groups (in patients with cirrhosis despite of a more intensive therapy with digitalis and diuretics) a marked enlargement of left ventricular dimensions with a significant (p less than 0.05) degree of dysfunction (PEP/LVET). Electrocardiography showed abnormalities in 26 to 44% of patients: signs of right ventricular enlargement in 26% of patients with fatty liver, and a prolongation of myocardial repolarisation (QTc) in 44% of patients with cirrhosis. Patients with alcohol-induced liver disease deserve more attention of their cardiac complaints, clinical and functional findings.

Adult↗