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Biomedical subjects

D Lehmann

Publications and source records attributed to D Lehmann.

At least 163 records · Page 9Linked to original sources
PubMed1986

Pneumococcal vaccine prevents death from acute lower-respiratory-tract infections in Papua New Guinean children.

In three double-blind placebo-controlled trials of pneumococcal capsular polysaccharide vaccines against death from acute lower-respiratory-tract infections (ALRI), children were vaccinated at 6 months to 5 years of age. The efficacy of the vaccines against ALRI as the sole cause of death was estimated at 59% in children vaccinated when younger than 5 years (p = 0.008) and 50% in children vaccinated when younger than 2 years (p = 0.043). Mortality from all causes was 19% less in the vaccinated group.

Acute Disease↗
PubMed1986

Averaging of spectral power and phase via vector diagram best fits without reference electrode or reference channel.

A method is proposed to average results of Fourier analysis over epochs without assigning zero amplitude values to any electrode or zero phase values to any channel. The Fourier sine and cosine values of each electrode define its entry location into a vector diagram for the frequency component. The entry constellations thus formed are translated so that the mean of all entries (the virtual average reference which is the location of best fit) is at the centre of each constellation, and then they are rotated around the means into angles of best fit so that the sum of the squared distances between corresponding entries is minimal. The method leads to non-ambiguous mean results, with variance information for all recording points. Approaches for the assessment of the constellations, their transformation into field maps, and the problems with conventional phase measurements vs. real electrodes are discussed. The virtual average reference (spatial high pass filter) is proposed for assessing the time sequence (phase differences) between entry points, thus describing the internal structure of the constellations without bias and without reference to a zero phase point. Comparison of voltage and current density result constellations and consideration of reference-independent descriptors of the scalp field potential maps support the validity of the average reference for the approach.

Electroencephalography↗
PubMed1986

Event-related potentials of the brain and cognitive processes: approaches and applications.

Event-related potentials (ERPs) are recordings of the electric field which the brain produces in fixed time-relation to an event. ERPs open a time and space window onto covert steps of brain information processing which need not be accompanied by overt behavior or private experiences. ERPs are the only noninvasive method which resolves the dynamic pattern of events in the human brain down to the millisecond range. Early ERP components are valuable tools in clinical testing of the afferent sensory systems in the absence of anamnestic or clinical pathology. Later components (e.g. the 'P300') index intermediate, covert steps of information processing and have clarified the time course and the contingencies of processes in attention, decisions and language. ERP waveshapes show electric potential differences between two recording points. Conventional analysis often ignores the fact that there is no unique voltage amplitude or signal latency for a single point, and interprets ambiguous results. Although important insights have emerged with such strategies, full utilization of ERP data requires unambiguous ERP assessment and converging evidence from neuropsychological and cognitive experimentation. Sequences of field distribution maps offer an unbiased display of ERP data. Spatial analysis yields unambiguous values for further comprehensive assessment, and should precede analysis over time. Examples of spatial analysis have shown that different ERP field configurations follow the presentation of noun and verb meaning of homophone words; that the ERP effects to subjective contours resemble those to attention in time course and topography; that the 'cognitive' P300 component reflects the specific stimulus location; and that subliminal information influences the configuration of late ERP fields.

Attention↗
PubMed1985

Blot-immunobinding test for the detection of anti-sperm antibodies.

A blot-immunobinding test was used to detect anti-sperm antibodies in human sera and to identify the corresponding auto- or iso-antigens on human sperm. A high proportion of sera at a 1:100 dilution from fertile persons, as well as infertile patients, contains antibodies reactive with sperm. This phenomenon might be physiological. At 1:2,000 dilution, a higher binding capacity was detected in the sera from infertile groups, but a few fertile persons were also positive. Antibodies to a single antigenic determinant with Mr of approximately 14,000 were found in a significantly higher proportion among males with unexplained infertility.

Antibodies↗
PubMed1985

Automatic classification of visual evoked responses.

An automatic method performing selective averaging of visual evoked potentials depending on the state of the EEG background activity is described. The method is based on adaptive segmentation of the EEG signal and on fuzzy clustering. A simulation example, extracting two different square pulses from the background activity, is given, as well as an example averaging two types of visual evoked potentials from the background EEG signal.

Adult↗
PubMed1985

Effect of benzodiazepine hypnotics on all-night sleep EEG spectra.

The effect of a single, oral bedtime dose of the benzodiazepine hypnotics flunitrazepam (FR; 2 mg), flurazepam (FR; 30 mg), and triazolam (TR; 0.5 mg) on the sleep stages and the sleep EEG was investigated in eight healthy, young subjects. In comparison to the placebo night, all drugs reduced the percentage of stage 1 and REM sleep, increased stage 2, and decreased the number of stage shifts. For FN and FR, some of these changes persisted in the postdrug night. All-night spectral analysis of the EEG showed a reduction of low-frequency activity (0.25-10.0 Hz) in stages 2, 3 + 4 and REM sleep, changes that persisted for all three drugs in the post-drug night. In the drug nights, activity in the spindle frequency range (11-14 Hz) was enhanced particularly in stage 2 and 3 + 4, activity in the high frequency range (17-25 Hz) particularly in REM sleep and stage 1. In the first third of the drug night, the depression of low-frequency activity in stage 2 was either absent (FR) or less prominent (FN, TR) than in the following part of the night. The results demonstrate that benzodiazepine hypnotics induce specific changes in the EEG spectra which reflect the immediate and residual drug effects more sensitively than conventional sleep scores.

Adult↗
PubMed1984

Evoked potential correlates of figure and ground.

Brain potentials averaged during the viewing of an alternating, positive and negative "hidden man" puzzle picture were averaged from 8 subjects before and after they learned to recognize the figure. After figure recognition in comparison to before recognition, there was significantly more evoked positivity at 64/96 ms latency, and more negativity at 224/256 ms and at 352-480 ms latency over parietal areas during the viewing of the positive picture (recognizable as face) referred to the values obtained during viewing of the negative picture (not recognizable as face). It is hypothesized that separate physiological changes might reflect learned meaningfulness of the figure (which entails increased attention) and figure extraction from ground.

Attention↗
PubMed1984

EEG assessment of brain activity: spatial aspects, segmentation and imaging.

High temporal resolution and sensitivity to index different functional brain states makes the EEG a powerful tool in psychophysiology. Its full potential can now be utilized since recording technology and computational power for the large data masses has become affordable. However, basic traditional strategies in EEG need reviewing. Conventional, spontaneous or evoked EEG traces which are used for various complex analyses give ambiguous information on EEG power (amplitude) and phase for a given point on the scalp. Principally, analysis should first be done over space, then over time, to avoid ambiguities or pre-selections. First or second spatial derivative computations can provide "reference-free" data for analyses over time. We propose to use direct, spatial approaches for the analysis of the scalp EEG field distributions when simultaneous recordings in several EEG channels can be examined. The ambiguity of the conventional EEG waveshapes results in different, equally "correct" scalp maps of EEG power of the same multichannel data for different reference electrodes. An exception are scalp maps of EEG power computed against the common, average reference, as they are related to the reference-free spatial distribution (maps) of the maximal and minimal (extreme) field values over time, and thus are directly interpretable in terms of net orientation of the generator process. A proposed, reference-free EEG segmentation into epochs of periodically stationary spatial distributions of the mapped scalp EEG fields uses the locations of maximal and minimal (extreme) field values at each moment in time as classifiers, and thus avoids the priviledging of two arbitrarily chosen recording points in the field.

Brain↗
PubMed1984

Spatial analysis of evoked potentials in man--a review.

Steps in brain information processing are reflected on the scalp as changes of the electric potential which is evoked by the stimulus. However, for a given recording point on the scalp, there is no absolute amplitude or phase information of the electric brain potential. This means that the shape of an evoked potential waveform which is recorded from a given scalp location crucially depends on the location of the chosen reference. Only unbiased results of evoked potential data evaluation can be hoped to elucidate or map successfully into information processing models established by other methods, e.g. behavior measurements. Conventional recordings vs a common reference contain only one of many possible sets of waveshapes. In order to avoid ambiguities or bias of results, the entire evoked potential data set firstly must be analysed over space, and reference-independent parameters must be extracted. For each time point, the spatial distribution of the potentials is viewed as field map. The parameter extraction in a direct approach at each time point includes, e.g. locations of field peaks and troughs, voltage and gradient between them, and global electrical field power; or, parameters via the first or second spatial derivative of the electric field. In the second step, changes of these reference-independent field measurements are analysed over time. At component latency which is defined by maximal, global field power or by voltage range, mapped field distributions can be compared using maximal/minimal field value locations or complete maps. Significantly different field configurations establish the activity of non-identical neural generators. Classification of the field configurations (examination of orbits of field extrema over time) leads to the segmentation of series of field maps (multichannel EP data) into short epochs of stationary spatial configurations (i.e. spatially characterized components) with equal consideration of all recording points, and without the amplitude criterion. The application of these principles to the following problems is discussed: comparison of evoked potentials between different analysis times, in particular pre-stimulus and post-stimulus electric brain states; zero baseline for measurement; reference electrode; identification of evoked components in time and space. Illustrations of these problems include functional differences of input-analysing sub-systems, and the topography of cognition- and speech-related electric brain activity.

Brain↗
PubMed1984

[Temporal dynamics of spectral EEG parameters during nocturnal sleep in healthy adults].

We recorded all-night sleep EEG's of six healthy male volunteers (age 23 to 29 years) from F3, F4, P3, P4, 01, 02, T3, T4 to Cz as reference electrode. Power and coherence spectra were calculated for ten frequency bands from 0-30 cps. We examined their changes through the different cycles of all sleep stages. In general there was a decrease in power as well as in coherence from the 1st to the 4th cycle of the different sleep stages with some variations depending on frequency and derivation. The highest power was most often in the 1st cycle in stages REM, 2, 3 and 4, whereas in stage 1 it was most often in the 2nd cycle. The trends in power from the 1st to the 4th cycle were similar for stages REM and 2 with a power decrease from the 1st to the 2nd cycle. In stage 1 there was most often a power increase between these two cycles. Coherence maxima were for stages REM, 1, 2 and 3 most often in the 1st cycle, for stage 4 most often in the 2nd cycle. The coherence trends were similar for stages 1 and 2 with a decrease most often from the 1st to the 2nd cycle. In stage REM the decline was more constantly found from the 2nd to the 3rd cycle. The power trends were more consistent than the coherence trends. We found more often similar power changes from the 1st to the 4th cycle of a specific sleep stage than similar coherence changes.

Adult↗
PubMed1984

Oral rehydration therapy: combining anthropological and epidemiological approaches in the evaluation of a Papua New Guinea programme.

The impact of an oral rehydration therapy (ORT) programme for diarrhoeal disease was evaluated by means of continuing surveillance of this Papua New Guinea population. Mortality from diarrhoeal disease in the under-fives fell from 3.3/1000/annum before the ORT programme to 1.3/1000/annum after the programme had become established. However there is evidence that the attendance rate for diarrhoea treatment has begun to fall from its previously high level. These trends are explicable in terms of the target population's expectations of Western treatments. The implications of these findings for the design and evaluation of similar health programmes are discussed.

Attitude to Health↗
PubMed1983

A single dose of benzodiazepine hypnotics alters the sleep EEG in the subsequent drug-free night.

All-night spectral analysis of the sleep EEG was used to study the effect and after-effect of a single bedtime dose of flunitrazepam (2 mg), flurazepam (30 mg) or triazolam (0.5 mg) in healthy young males. In the night of drug treatment all 3 hypnotics reduced the EEG slow waves and enhanced the activity in the frequency range of sleep spindles. In the subsequent drug-free night, the latter changes were no longer present after triazolam, whereas the reduction of slow wave activity persisted after all compounds.

Adult↗
PubMed1983

Monocular and binocular evoked average potential field topography: upper and lower hemiretinal stimuli.

Scalp potentials evoked by monocular and binocular 2/s checkerboard reversals with checks of 56 or 14 min were recorded from four midline electrodes between inion and 7.5 cm above inion vs a common anterior reference in 31 normals. The electrode location and latency of the evoked maximal occipitally positive potential difference between any 2 of the 5 electrodes, between 80 and 140 ms latency was determined in each run. Mean maximum locations over subjects for upper hemiretinal, binocular stimuli were more anterior than for monocular stimuli; for lower hemiretinal stimuli, inverted location differences were found. Binocular responses also had shorter latencies than monocular responses. Since area 18 is more anterior to 17 for upper, more posterior to 17 for lower hemiretinal projection to cortex, the results suggest that neurons which respond only if both eyes are simultaneously stimulated are more frequent in higher than lower order visual areas.

Biophysical Phenomena↗