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Biomedical subjects

W Ritter

Publications and source records attributed to W Ritter.

At least 91 records · Page 5Linked to original sources
PubMed1992

The effects of an oral thromboxane TP receptor antagonist BAY u 3405, on prostaglandin D2- and histamine-induced bronchoconstriction in asthma, and relationship to plasma drug concentrations.

1. The potent bronchoconstrictors prostaglandin (PG) D2, PG F2 alpha and thromboxane A2 are thought to have a role in the pathogenesis of asthma, mediated via the thromboxane (TP) receptor. 2. BAY u 3405 is a new potent selective competitive TP receptor antagonist. 3. The effect of single oral doses of 20 mg and 50 mg BAY u 3405 was examined against histamine and PG D2 bronchial provocation at 90 min after drug ingestion and, for the 20 mg dose alone, at 60 min after ingestion, in randomised, double-blind placebo controlled crossover studies. A time course study was performed with the 20 mg dose. 4. BAY u 3405 protected against PG D2 bronchial provocation. The 20 mg dose increased the amount of PG D2 required to produce a fall of 20% in the forced expiratory volume in 1 s by 6-fold and 16-fold at 60 min and 90 min after ingestion respectively, and the 50 mg dose by 14-fold at 90 min after ingestion. 5. The specificity of the drug was confirmed in vivo in that there was no significant protection against histamine bronchial provocation at either dose or at either time point. 6. The time course study showed significant protection against PG D2 bronchial provocation at 1 h and at 3 h after a single 20 mg oral dose. 7. There was no correlation between subjects in plasma BAY u 3405 concentration and drug effect. Within the subjects performing the time course study there was a strong correlation in time between drug effect and plasma BAY u 3405 concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Mismatch detection and the latency of temporal judgements.

Event-related potentials were recorded in two auditory tasks involving the discrimination of pitch or duration of binaurally presented tones. Frequently-presented nontarget tones, when compared to the same tones in a simple reaction time task, elicited two negative peaks, NA1 and NA2, followed by a positive peak, nontarget positivity. Infrequently-presented target tones, when compared to the nontargets, elicited mismatch negativity (MMN), followed by N2 and P3b. The peak latencies of NA1 and NA2 did not differ between the pitch and duration tasks, but the duration of NA1 and the peak latencies of mismatch negativity, N2, and P3b, as well as reaction time, increased in parallel for the duration task. It is proposed that the NA1-nontarget positivity sequence reflects the initiation, maintenance, and termination of an attention-modulated process, which is required for the performance of an auditory discrimination task, and that the MMN-N2-P3b sequence reflects a process elicited by infrequently-presented targets, which is the main determinant of reaction time under these testing conditions.

Adult↗
PubMed1992

The chronometry of attention-modulated processing and automatic mismatch detection.

Event-related potentials were recorded from normal subjects in an auditory selective attention task. Targets were rare longer (170-ms) tones of a designated pitch, embedded in a sequence of 100-ms standard tones. The effects of attention-modulated processing were evident in the event-related potentials elicited by the standards. Those to relevant standards were similar for easy (1000 Hz vs. 2000 Hz) and hard (1000 Hz vs. 1030 Hz) pitch separations, and were more negative frontocentrally than those to irrelevant standards. Difference waveforms (attended minus unattended standards) revealed Nd, a negative deflection that was earlier in latency for the easy task (onset, 120 ms; peak, 250 ms) than for the hard task (onset, 250 ms; peak, 350 ms). The speed of detection of the deviant longer tones was insensitive to the attention-modulated processes indexed by Nd. Median reaction time did not differ between tasks, although there were more misses and false alarms in the hard task (and nearly all of the latter were to the irrelevant longer tones). Neither direction of attention nor task difficulty affected the latency of mismatch negativity, N2, or P3 (as identified in difference waveforms: attended or unattended longer tones minus their respective standards). The data suggest that performance was guided by two independent but converging processes, automatic mismatch detection of the longer tone and attention-modulated processing of pitch, followed by selection of response.

Adult↗
PubMed1992

A developmental event-related potential study of picture matching in children, adolescents, and young adults: a replication and extension.

Event-related potentials were recorded in a developmental study of picture matching using an adaptation of Posner's (1978) letter-matching tasks. Subjects ranging in age from 6-39 were asked to decide whether two line drawings, presented sequentially, were the same or different on the basis of physical (physical identity), nominal (name identity), or categorical (category identity) criteria. The amplitude of a negativity at 400 ms (Neg400) increased as the number of dimensions on which the two line drawings differed increased. This effect held for all age groups, and was interpreted as reflecting the degree of semantic and/or physical relationship between the two pictures. However, one finding for Neg400 did suggest a qualitative difference in processing mode between the younger and older subjects. Both Neg400 and P3b latencies showed highly significant linear age trends, decreasing with increasing age. These age-related changes were interpreted as demonstrating quantitative speed of processing differences among age groups. The latencies of both Neg400 and P3b increased as the matching criteria became more complex. Moreover, P3b latency increased as the number of dimensions on which the two pictures differed increased, and this did not interact with age. Although both Neg400 and P3b showed age-related changes in scalp distribution, the fact that each was related to the experimental variables in similar fashion in all age groups suggested that they were homologous components across the age range studied. Taken as a whole, the data support continuity of information processing during these tasks across a wide age range.

Adolescent↗
PubMed1991

Event-related potentials during arithmetic and mental rotation.

In separate studies of arithmetic and mental rotation, similar posterior negative slow waves have been found. This similarity was surprising given the difference in cognitive processing required by these tasks. Furthermore, delayed responses were employed in these studies, so that it was not possible to determine the extent to which the slow wave activity was too late to be associated with processing that was specific to performance of the tasks. This experiment was intended to clarify the task-specific and non-specific nature of the slow wave activity. Subjects performed either an arithmetic or mental rotation task at two levels of difficulty on a random, trial-to-trial basis and gave an immediate response. There were a number of late posterior negativities, each with a different timing and topography, which were sensitive to type of task and/or task difficulty. Some components were associated with early task processing that was synchronized to the stimulus while others, revealed by response-synchronized averaging, were associated with later stages of task processing. There also was post-task activity that was sensitive to the difficulty level of the prior operations. In both tasks, there was a pre-frontal positive wave that persisted over most of the pre-response epoch, evidently related to a process that was active throughout the task. There also was centro-frontal phasic negativity, with a large peak at 380 msec in mental rotation, and a smaller, longer latency peak in arithmetic, apparently related to the complexity of the stimulus. Thus we conclude that arithmetic and mental rotation each elicit task-specific slow wave activity.

Adult↗
PubMed1991

Plasma pharmacokinetics and tissue penetration of a novel antifungal triazole, Bay R 3783, and its long-lasting active metabolite, Bay U 3625, in rabbits.

The plasma pharmacokinetics and tissue penetration of Bay R 3783 (BR), a new antifungal triazole, and one of its active metabolites, Bay U 3625 (BU), were studied in rabbits. Plasma levels of BR and BU were determined simultaneously in five rabbits for six days after a single oral dose of 20 or 40 mg/kg BR. For BR, the mean Cmax was 1.9 +/- 0.4 mg/l, the Tmax 2.0 +/- 0.7 h, the AUC alpha 7.5 +/- 1.6 mg.h/l, and the terminal plasma T1/2 2.1 +/- 0.1 h. For BU, the mean Cmax was 0.84 +/- 0.09 mg/l, the Tmax 24 +/- 4 h, the AUC alpha 61.9 +/- 6.5 mg.h/l, and the plasma T1/2 was 48 +/- 3 h. In a multi-dose study, the plasma BR clearance during wash-out gradually diminished, suggesting possible metabolite inhibition of BRs biotransformation. No hepatic or renal toxicity was seen after 28 days of dosing with BR 40 mg/kg/d. Both BR and BU penetrated well into tissues, with tissue drug concentrations over three times higher than in plasma at multiple tissue sites. Persistence of BU in plasma, however, resulted in prolonged, higher tissue levels of BU than of BR. We conclude that BR is converted to a long-lasting active metabolite BU, that persistence of BU in tissue is prolonged, and that these properties may permit BU to contribute significantly to the antifungal activity of BR.

Animals↗
PubMed1991

Experimental examinations concerning the problem of deformed emerging bees after infestation with Varroa jacobsoni.

The deformations of bees occurring in connection with varroatosis was examined both in case of natural and artificial infestation. Under both conditions, the number of bees showing wing deformations increased with the degree of mite infestation. Shortened abdomina, however, only appeared in the case of natural infestation. Inadequate brood care in colonies severely infested by Varroa mites is supposed to be responsible. Wing deformations could be produced by experimental haemolymph extraction.

Animals↗
PubMed1991

The relationship between N2 and N400: scalp distribution, stimulus probability, and task relevance.

The N2 and N400 components of the event-related brain potential were compared along several dimensions. In one task, subjects discriminated on the basis of size, and in another task, subjects discriminated on the basis of semantic category. In one set of conditions stimuli deviated infrequently along one stimulus dimension (either in size or semantic category) and in another set of conditions stimuli deviated infrequently along two stimulus dimensions (both size and semantic category). When subjects discriminated on the basis of size, infrequent deviation in the size of the stimuli was associated with a negativity that peaked around 320 ms (N2). When subjects discriminated on the basis of semantic category, infrequent deviation in the semantic category of the stimuli was associated with a negativity that peaked around 400 ms (N400). N2 and N400 were found to be generally alike in scalp distribution, hemispheric asymmetry, and sensitivity to stimulus probability. N2 was not elicited when size changes were task irrelevant and N400 was not elicited when changes in semantic category were task irrelevant.

Adult↗
PubMed1991

[Radiologic diagnosis of erectile dysfunction].

Possibilities of radiological cooperation in diagnostics and therapy of erectile dysfunction are demonstrated. Besides SKAT-testing and pharmaco-duplex-sonography, pharmaco-cavernosometry and cavernosography procure the decisive confirmation of venous leakage. The veins which are not compressable during erection can eventually be obliterated under radiological control with the help of mini-coils. Pelvic and penile arteriography are mandatory for the localization of arterial obliterations which can be treated either surgically or by angioplasty. The value of interventional radiological measures in the arterial region can be clearly substantiated in common iliac and internal iliac stenoses. However, the results obtained in the venous region by occluding interventional measures have yet to be evidenced by systematic examinations, as the surgical treatment has not shown much success up to now.

Angiography↗
PubMed1990

[Development of infestation with Varroa jacobsoni O. in bee colonies in Tunisia].

The mite Varroa jacobsoni, an ectoparasite of the honey bee, was imported to Tunisia probably in 1976. Afterwards, this parasitosis caused severe losses of colonies for several years. The continued examination of the level of infestation in colonies of a "GTZ" project stated a steady number of mites since 1980. Only in a few colonies, the infestation was above the limit of damage. Though the colonies in North West Tunisia did not receive any treatment since 1986 there was no increase of infestation. In order to investigate the reason for this the mites' ability of reproduction was examined during two following years. The portion of infertile female mites in the worker brood in most of the colonies was with 50% considerably higher than in Europe. In Brazil, the adaptation between host and mite produced similar low reproduction rates. As, however, in Tunisia the portion of infertile females in the drone brood of the individual colonies corresponded to the one in the worker brood climatic conditions are supposed to be responsible.

Animals↗
PubMed1990

Short-term memory storage and retention: an event-related brain potential study.

This experiment was concerned with event-related brain potential (ERP) activity related to short-term storage and retention of information in working memory. Our approach was to record the ERPs elicited by a stimulus that had to be memorized while varying the number of items (1, 3 or 6) in the task stimulus. In order to distinguish between ERP effects associated with perceptual complexity and retention of information, there was a second condition in which subjects were required to search the task stimulus for a match with a previously presented item. Thus, in the search condition subjects only had to remember one item (match or mismatch). ERP activity was recorded for 2450 msec after task stimulus offset. Two long-duration components varied as a function of task and memory load: a posterior positive wave and a frontal negative wave. Posterior positive wave amplitude was directly related to information load in the memory task but was negligible in the search task. Following the posterior positive wave was a frontal negative wave which occurred at the highest load level in the memory task but was totally absent in the search task. A P3b was elicited in both tasks. P3b was sensitive to information acquisition processes, but it did not distinguish between memory retention and visual search processes. While P3b amplitude did not vary with task or load, its latency increased with load in both tasks.

Adult↗
PubMed1990

Differentiation of negative event-related potentials in an auditory discrimination task.

Several different negative potentials elicited in auditory perceptual tasks make spatially and temporally overlapping contributions to the scalp-recorded event-related potential. Frequent non-target tones in a 2-stimulus oddball pitch discrimination task, when compared with the same stimuli in ignore or simple reaction time conditions, elicit a negative deflection with two peaks (NA1 and NA2) differing in their latency and topography from the exogenous N92-P156 deflections. Oddball tones, when compared with the frequent ones, elicit mismatch negativity (MMN) in both ignore and discrimination conditions; MMN displays a frontocentral-posterolateral polarity inversion. In the discrimination condition, MMN is followed by N2 and P3b; the former has a more central amplitude maximum than MMN, and no posterolateral polarity inversion. When the pitch discrimination task was made more difficult, there was no effect on NA1 or NA2, but the latency of MMN, N2, P3b, and reaction time all increased in parallel. It is hypothesized that MMN reflects the outcome of an automatic mismatch detection process, and that the subsequent processing of targets is related to the event of mismatch detection.

Acoustic Stimulation↗
PubMed1990

The pharmacokinetics of BAY R3783 and its efficacy in the treatment of experimental cryptococcal meningitis.

We studied the pharmacokinetics and efficacy of BAY R3783, a new antifungal azole compound, in rabbits and compared it with fluconazole and itraconazole. BAY R3783 has at least two active metabolites, BAY U3624 and BAY U3625. We measured serum concentrations of all three compounds; the peak serum level for the parent compound was approximately two hours post dose. BAY R3783 and its metabolites also crossed the blood-CSF barrier; the mean CSF level of BAY R3783 was 30.5% of simultaneous serum levels. The in-vivo activity of the azoles was compared in a model of cryptococcal meningitis in immunosuppressed rabbits. BAY R3783, fluconazole and itraconazole all reduced yeast counts in the CSF with equal efficacy over ten days of therapy at 100 mg/day. In this model, BAY R3783 was effective in the treatment of cryptococcal meningitis.

Animals↗
PubMed1990

Multiple sources of P3b associated with different types of information.

This experiment investigated how the P3a, P3b, and Slow Wave components of the event-related brain potential (ERP) respond to manipulations of the nature, timing, and extent of information delivery. There were two experiments in which the total amount of task information was distributed between pairs of successive stimuli (S1 and S2) within each trail. The task was to predict the relation between S1 and S2. In Experiment 1, the S1 could resolve no, partial, or all uncertainty with respect to the prediction outcome (correct or incorrect). Each S1 delivered three types of information: 1) outcome information--which resolved the subjects' uncertainty about the correctness of their prediction; 2) procedural information--which resolved uncertainty about how much outcome information would be delivered by S1; and 3) memory information--the identity of S1, which had to be stored for subsequent comparison with S2. In Experiment 2, the activity of these components was contrasted in two conditions in which the S1 delivered either memory information alone or both memory and procedural information. P3a and Slow Wave were sensitive only to outcome information. P3b was sensitive to all three types of information, and its scalp topography varied as a function of the type of information. The topographic variations indicate that P3b is not a unitary phenomenon but rather is a composite of activity arising from multiple intracranial sources of bioelectric activity.

Adult↗
PubMed1989

Channel probability and Nd: an event-related potential sign of attention strategies.

Event-related potentials were recorded in a two-channel selective attention paradigm designed to assess the effects of channel probability on processing negativity. For channel probabilities of 70% or greater, the subtraction Nd for standard tones was greatly reduced or absent. This change was due to apparent processing negativity in the waveform of the irrelevant standards at high channel probabilities. Deviant long tones showed similar early Nds to standard tones, and also developed late attention-related negativity commencing at about 500 ms from stimulus onset. It was concluded that there was no evidence that processing negativity to the relevant tones, defined as a negative component associated with selective attention, is affected by channel probability. Changes in Nd amplitude as the channel probabilities became more unequal were attributed to changes in strategies used by subjects, which primarily altered ERPs associated with the irrelevant tones.

Adult↗
PubMed1989

The value of angiography in cerebrovascular disease.

The expanding availability of digital subtraction angiography has essentially contributed in lowering the risks in the use of angiography of the cerebral arteries. The best results in imaging the cerebral artery are achieved by conventional subtraction angiography after selective catheterisation. This is, however, only important for diagnosis in intracerebral pathological changes distal of the Circulus Willisi or in connection with preoperative interventional radiological treatment. Pre-clinical diagnosis of patients with cerebrovascular occlusive disease as well as clinical diagnosis with Doppler and B-scan US sonography can be optimally complemented by DSA using 4-5 French catheters entered in the thoracic ascending aorta. Using this technique, the sensitivity and specificity with an image-matrix of 512 is diagnostically adequate and includes an only limited examination risk. Complication with lasting neurological defects will be least observed after intravenous pre-atrial application of contrast media and most after selective angiography of the carotid artery. Here the extent of the multiple arteriosclerotic obliteration is of essential importance. The quality of interpretation of the diagnostic findings essentially depends on indications not only about the grade of obliteration but also on the morphological details. At present DSA with application of contrast media into the thoracic ascending aorta in combination with the duplex-scan method represent the optimum for the diagnosis of cerebrovascular disease. In spite of lower specificity intravenous application of contrast media has to be preferred for post-operative controls and controls of progressing disease with "screening".

Carotid Arteries↗
PubMed1989

[Results of percutaneous transluminal angioplasty].

Percutaneous transluminal angioplasty (PTA) can be subdivided into three epochs: 1. from its inception by Dotter and Judkins up to the first coronary artery stenosis dilatation with the Grüntzig balloon catheter system; 2. from the introduction of coronary stenosis dilatation by Grüntzig up to its unequivocal acceptance; 3. the period of influence of low-risk coronary dilatation on peripheral angioplasty and the search for techniques to compliment or obviate the need for balloon dilatation. The Grüntzig double-lumen balloon catheter system contributed to the lower rate of complications and higher success rate. The clinical acceptance appeared greater for the coronary arteries since, in contrast to the peripheral vascular system, the indication for treatment is established by the physician performing the dilatation. PTA implies percutaneous puncture of a vessel with Seldinger technique and introduction of devices such as guidewires, Dotter or Grüntzig catheters among others, catheters with fiberglass for laser conduction and instruments for fractionating, drilling and cutting. The goal of PTA is to completely or partially eliminate, without surgery, intraluminal vascular narrowing in the presence of peripheral arterial disease in stage II, III or IV. Prerequisite to the use of PTA are: 1. adequate fluoroscopic and angiographic facilities; 2. adequate instrumentation; 3. experience with at least 200 procedures; 4. knowledge of the pathophysiology and adjunctive treatment; 5. knowledge of the treatment of complications; 6. cooperation with a vascular surgery service. A number of factors may influence the results of treatment. Adjunctive medical treatment: the use of platelet aggregation inhibitors and heparin influences the rate of early rethrombosis.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗