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Biomedical subjects

H Weber

Publications and source records attributed to H Weber.

At least 289 records · Page 16Linked to original sources
PubMed1989

[The wear behavior of capsules and heads of CoCrMo casts in long-term implanted all-metal hip prostheses].

We conducted an investigation on total hip prostheses with cups and balls made of cast CoCrMo alloy that were implanted 10-20 years ago; our results showed that this metal/metal alloy showed very low wear and tear. In comparison, the polyethylen/metal alloy showed a 40 times higher wear in the polyethylene part. Based on these promising long-term clinical results, the metal/metal alloy is again of great interest for total hip prostheses.

Acetabulum↗
PubMed1988

[Return to work following myocardial infarct].

The aim of this retrospective study involving 471 patients was to investigate the percentage of patients who returned to work after acute myocardial infarction. In the group of 350 patients who did not undergo subsequent aortocoronary bypass operation 70% returned to work, whereby half of these patients started work again within 6 months after infarction. A significantly higher number of patients who were enrolled in a cardiac rehabilitation programme returned to work as compared with patients not participating in such a programme (72% vs. 59%, respectively; p less than 0.04). There was, however, no difference between these 2 groups with respect to either the time point of resumption of work after myocardial infarction or the duration of employment between infarction and eventual retirement. Of the 121 patients who underwent an aortocoronary bypass operation, only 38% returned to work (p less than 0.001 vs. patients without bypass surgery).

Coronary Artery Bypass↗
PubMed1988

[Value of computer-assisted, digital long-term ECG analysis in clinical routine practice].

At present the Holter method (HM) is a frequently used investigational procedure in the clinical routine. It was the aim of a prospective study to evaluate the HM from the user's point of view. Therefore a questionnaire was attached to each analysis report including two main questions, which should be answered by the referring physician: Does the analysis result fulfill the consumer's needs? What consequences are drawn due to the HM results? Among 675 questionnaires returned to the laboratory 75% of the referring physicians felt satisfied by the HM result. Disappointments were predominantly related to too infrequently occurring episodes, which did not appear during one 24-hour recording period. Evaluation of therapy (89%), recording prior to antiarrhythmic therapy (84%) and quantification of well-known arrhythmias were the most successful indications of HM. The tremendous daily variability of infrequent symptoms or arrhythmias were the main causes for unsatisfactory results. A successful HM led predominantly to therapeutic consequences (begin, continuation, change or withdrawal of anti-arrhythmic drugs). In 25% HM was not followed by further therapeutic or diagnostic consequences, so that the indication for the HM should be reevaluated! Diagnostic consequences included repeated HM, ECG-Telephone-Transmission consequences heart catheterisation or electrophysiological procedures. In summary the Holter method satisfies the physician's demands if the expectations do not exceed the limitations of the method.

Adolescent↗
PubMed1988

[Variability of arrhythmias and symptoms--their effect on long-term ECG analysis].

The variability of variables influences conclusions in the measurement of biologic variables particularly if the variability of methodological variables are unidentified or of unknown range. Therefore prior the interpretation of Holter-results the interobserver variability of measured parameters (e. g. arrhythmias) and the system-dependent variables (e. g. reproducibility) have to be recognized. Measuring biologic variables like arrhythmias or symptoms using the Holter method the spontaneous variability of infrequent occurring phenomena has to be taken into account and also their relationship to the recording duration: Infrequent occurring phenomena demonstrate an enormous variability, which could be reduced by lengthening the recording duration beyond 24 hours, especially in the evaluation of an antiarrhythmic therapy to avoid a mimicked therapeutic effect. In symptomatic patients their symptoms can be related to arrhythmias or not if an ECG will be recorded during a typical symptomatic period. This depends on the frequency and on the duration of the symptoms, so that other methods than Holter-monitoring should be considered like event-recording, ECG-telephone-telemetry or electrophysiological investigations. In summary the variability of phenomena captured by the Holter method (e. g. arrhythmias, symptoms) is a major factor, which has to be taken into account to avoid unsatisfactorial use of the Holter method.

Anti-Arrhythmia Agents↗
PubMed1988

Significance of attentive fixation for the selection of saccade targets in different parts of the visual field of the rhesus monkey.

Two monkeys were presented with a task in which they were free to make a saccade to one of two simultaneously presented targets. The data from both animals show that the preference for one of the targets depends on at least two factors: (i) active and attentive fixation of the central fixation point at the time when the two targets occur; (ii) relative position of the two targets in the visual field. The results were different for the two monkeys with respect to the role of stimulus position in the visual field. However, both animals changed their preference systematically when the fixation point was turned off before the two targets occurred as compared to the case in which the fixation point remained visible. With respect to the paradigm (fixation point off versus fixation point on) the stimulus selection of either animal was constant throughout the several weeks of testing.

Animals↗
PubMed1988

Genotoxic activities of benzamidine and its N-hydroxylated metabolite benzamidoxime in Salmonella typhimurium and mammalian cells.

The genotoxic potentials of benzamidine and benzamidoxime were determined to study the toxicological relevance of the metabolic N-oxygenation (N-hydroxylation) of benzamidines to benzamidoximes. Benzamidoxime induced DNA single-strand breaks (in rat hepatocytes) and DNA amplification in SV40-transformed hamster cells. In the experiments performed, benzamidine itself was only marginally positive in the hepatocyte/DNA single-strand break assay. Since these cells possess an intact metabolization apparatus, the biological activities may be attributed to toxic and genotoxic metabolites formed by biotransformation. In the Salmonella typhimurium mutagenicity test (TA 98 and TA 100) benzamidoxime alone exhibited a low mutagenicity in the TA 98 strain in the presence of rabbit liver S-9 fractions. These results permit recognition of the metabolic N-hydroxylation of benzamidines to benzamidoximes as a process to toxication. Indirect evidence for the formation of a glucuronide of benzamidoxime has been obtained from in vitro experiments, but it could not be established that this process was a decisive factor in the genotoxicity of benzamidoxime.

Amidines↗
PubMed1988

Steroidogenic properties of isolated adrenocortical cells from Japanese quail selected for high serum corticosterone response to immobilization.

The effect of selection for high stress response on adrenocortical function was examined by measuring the corticosterone response of adrenocortical cells isolated from random-bred Japanese quail and quail selected for high serum corticosterone response to immobilization (high-stress). Highly enriched adrenocortical cells were incubated with various concentrations of ACTH1-24 (ACTH), 8-bromo-cyclic AMP (8Br-cAMP) and pregnenolone for 2 hr. Corticosterone production was measured by radioimmunoassay. Basal corticosterone production values by cells from random-bred and high-stress birds were not different. In contrast, the average maximal ACTH- and 8Br-cAMP-induced corticosterone production by cells from high-stress quail was 89% greater than that of cells from random-bred quail. However, the average pregnenolone-supported corticosterone production by cells from high-stress birds was 34% less than that of cells from random-bred birds. Thus, the data suggest that although random-bred quail cells had a greater potential capacity for corticosterone production, high-stress quail cells had a greater ability to couple ACTH, ACTH-transmembrane-signaling factors and subsequent second messengers with the available steroidogenic enzyme pool. The magnitude of the differences in function between cells from high-stress and random-bred birds was greater for female cells compared to male cells. In addition to differences in cellular function, there were also differences in adrenal and relative adrenal weights between random-bred and high-stress quail. The average, adrenal and relative (mg/100 g body weight) adrenal weights of high-stress quail were 14-16% greater than those of random-bred quail. It is concluded that the enhanced serum corticosterone response of the high-stress quail line is, in part, due to an increase in relative adrenal weight and an increase in adrenocortical cell responsiveness to ACTH.

Adrenal Cortex↗
PubMed1988

Intraoperative assessment of in situ saphenous vein bypass grafts by vascular endoscopy.

Intraoperative vascular endoscopy was used in 20 femorocrural in situ saphenous vein bypass procedures in order to control valvular incompetence, to localize side branches and to assess the integrity of the distal anastomosis. We used an Olympus Fiberscope (PF-27L) with a diameter of 2.7 mm and a working length of 80 cm, which had fixed illuminating and viewing fibers and a steerable tip, Valvulotomy was performed according to the technique described by R. Leather using a valve-cutter. In 8 out of 20 patients, partly retained valve leaflets were found by intraluminal inspection and could be immediately corrected. The integrity of the distal anastomosis was verified angioscopically in 14 patients. In addition, venous side branches, which had to be ligated, were easily identified under direct vision and localized by transillumination of the endoscopic light through the skin. Vascular endoscopy seems to be a practicable and time saving method to control in situ vein bypass procedures. The steps of the procedure and early results after 20 bypasses for limb salvage are presented.

Anastomosis, Surgical↗
PubMed1988

The influence of nitroglycerine on the inducibility of sustained ventricular tachycardia in coronary artery disease.

To investigate the influence of nitroglycerine on the inducibility of sustained ventricular tachycardia, 11 patients with documented sustained ventricular tachycardia were studied (mean age 59 years, range 52-70 years, eight posterior wall infarctions, three anterior wall infarctions). After the induction of sustained ventricular tachycardia using a standard protocol (three ventricular premature beats triggered on the R wave, three ventricular premature beats to the refractory period during basic driving rate up to 180 beats min-1), 0.8 mg nitroglycerine was given and when the wedge pressure started dropping (after about 3 min) the EPS was repeated. The mode of the initiation of sustained ventricular tachycardia was almost identical before and after application of nitroglycerine. In addition the heart rate before (mean 186 beats min-1) and after nitroglycerine (mean 187 beats min-1) and the morphology of sustained ventricular tachycardia were the same. It is therefore concluded that anti-ischaemic interventions by nitroglycerine treating silent ischaemia and improving ventricular function respectively does not influence the initiation of sustained ventricular tachycardia during EPS. Silent ischaemia obviously does not play a role in sustained ventricular tachycardia and therefore anti-ischaemic interventions cannot be expected to influence the recurrence of sustained ventricular tachycardia.

Aged↗
PubMed1988

Increase in plasma atrial natriuretic factor and right atrial area during endogenous and exogenous volume loading in healthy volunteers: effect on plasma renin activity, aldosterone and antidiuretic hormone.

The mechanisms of atrial natriuretic factor (ANF) release and the effects of ANF on plasma renin activity (PRA), plasma aldosterone and plasma antidiuretic hormone were investigated in two groups of normal subjects. One group was studied before and after endogenous volume loading produced by 30 min of head-down tilt. The other group was studied before and after an exogenous volume load in the form of 1 litre of isotonic saline infused over 30 min. Measurements made included right atrial area by two-dimensional echocardiography, PRA, plasma aldosterone, plasma antidiuretic hormone and plasma levels of ANF. There was a significant correlation between the increase in atrial area and plasma ANF concentrations after endogenous and exogenous volume loading. Levels of PRA and plasma aldosterone were suppressed significantly after exogenous volume loading but not after endogenous volume loading. The concentration of plasma antidiuretic hormone was not affected by either procedure. Short-term changes in right atrial pressure appear to regulate the plasma levels of ANF in normal people.

Aldosterone↗
PubMed1988

Rate dependent depression of subsidiary ventricular impulse formation--cause of Stokes-Adams attacks in a patient with rate modulated pacing.

Following His bundle ablation and implantation of a rate adaptive pacemaker (Vitatron TX 911) a 52-year-old gentleman experienced several presyncopal attacks while driving a car. On examination pectoralis muscle contraction caused temporary pacemaker inhibition. Incremental overdrive stimulation demonstrated progressive depression idioventricular automaticity and was associated with similar symptoms following overdrive at high pacing rates. Following appropriate pacemaker programming the patient remained symptom free.

Adams-Stokes Syndrome↗
PubMed1988

Evaluating antiarrhythmic strategies: a knowledge-based system for exploring clinical data.

Medical therapy for cardiac arrhythmias is still to a large extent based on empirical methods. Assessing and evaluating different therapeutical strategies constitutes the starting point for inducing decision methods to select the appropriate regimen for an individual patient. We designed a computer-based system that establishes a set of heuristic rules linking attributes in a data base of patients with rhythm disturbances. A feasibility analysis conducted on a small set of 23 patients indicated that constraints on the number of attributes and their clinical relevancy together with a representation scheme for temporal changes have to be incorporated to provide for a useful and efficient algorithm.

Algorithms↗
PubMed1988

Subsidiary pacemaker function in complete heart block after His-bundle ablation.

To investigate the electrophysiological properties of ventricular impulse formation after His-bundle ablation in 11 patients, incremental ventricular overdrive stimulation studies were performed. The studies, which were spread over a follow-up period of up to 601 days, were carried out invasively with temporary leads as well as noninvasively with the implanted pacemakers and chest wall inhibition. The overdrive pacing rate was increased in steps of 10 beats/min, and the pacing duration was 2 minutes at each level. Ten out of 11 patients had a reliable ventricular escape rhythm; in the remaining patient, consistently no subsidiary pacemaker function was observed up to 10 seconds. In 83% of the studies, incremental ventricular overdrive stimulation caused progressive suppression of ventricular impulse formation with exponential increase in ventricular recovery time and progressive postrecovery subsidiary pacemaker depression. In the remaining 17%, ventricular recovery time showed a heterogeneous response to overdrive stimulation--as possible cause alterations in the sympathetic tone and limitations attributable to the method used are discussed. The results of this study demonstrate a rate-dependent overdrive suppression of subsidiary ventricular pacemaker tissue. This can be of clinical importance in patients with complete heart block and rate-adaptive pacemakers because sudden pacemaker failure or temporary pacemaker inhibition at high stimulation rates may cause Stokes-Adams attacks not reproducible at lower pacing rates.

Aged↗