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Biomedical subjects

R Jürgens

Publications and source records attributed to R Jürgens.

At least 19 recordsLinked to original sources
PubMed1991

A comparison of normal and tangential magnetic field component measurements in biomagnetic investigations.

Because of the way most available hardware gradiometers are designed and in view of the prediction, by theory, that the normal magnetic field component provides all available information on the intrinsic current source, MEG and MCG measurements generally consider only the field vector normal to the head or truck surface. However, when looking for single events, the information contained in the normal component often cannot be fully sampled, because the sensor array has limited dimensions and therefore covers only a fraction of the field's spatial extension. Simulation of a current dipole in a sphere using realistic parameters shows that there is a considerable area where the amplitude of the tangential field components is larger than that of the normal one. Measurements using a 28-channel magnetometer system with normal and tangential pick-up coils and a current dipole in a phantom model confirm this prediction; depending on dipole orientation, the signal-to-noise ratio (SNR) could improve by a factor of up to 20 if the total field was considered instead of only the normal component. MCG recordings with the same instrument demonstrated a broad area above the heart where the tangential SNR was clearly better than the normal one. Preliminary measurements indicate that tangential components can also be recorded in the MEG; it is suggested that they may help source localisation.

Brain↗
PubMed1990

Human oblique saccades: quantitative analysis of the relation between horizontal and vertical components.

Are the horizontal and vertical components of oblique saccades produced by two separate pulse generators or by a single, vectorial pulse generator? To investigate this question, purely horizontal and vertical ("cardinal") saccades as well as oblique saccades with a meridional direction of +/- 45 deg (horizontal and vertical components of equal size) were recorded in 10 human subjects using a magnetic search coil. The components of oblique saccades were slower than cardinal saccades of comparable size, yet the oblique vector velocity was slightly larger than the velocity along cardinal directions. The onset of the two components was always synchronized, but their times to peak velocity and their durations, although approximately equal on average, frequently were different in individual trials; the component velocities were weakly correlated only. Correspondingly, the trajectory of oblique saccades exhibited various types of curvature which often changed from trial to trial. There was no correlation between curvature and aiming accuracy. These results are discussed in terms of various models of saccade generation. It is suggested that each of the two components is generated by its own local feedback pulse generator; the two components would be coordinated by crosscoupling the two local feedback circuits at the level of their error signals. By contrast, the extraretinal feedback that prepares corrective saccades is apparently not evaluated componentwise but may use a vector representation, since the latency of oblique corrective saccades was a function of the vectorial error magnitude.

Data Collection↗
PubMed1989

Cerebral glucose metabolism in the course of subacute sclerosing panencephalitis.

Regional cerebral glucose metabolism was studied in a 15-year-old boy with subacute sclerosing panencephalitis before and after therapy with human interferon beta, using positron emission tomography of fluorine 18-2-fluoro-2-deoxyglucose. At first examination, metabolism was symmetrically decreased in the thalamus, cerebellum, and all cortical areas except prerolandic motor cortex, but increased in lentiform nucleus. A computed tomographic scan was normal. Six months later, bilateral focal necrosis centered in the previously hypermetabolic putamen was demonstrated by computed tomography and magnetic resonance imaging. The caudate nucleus and the superoposterior part of the putamen were spared, still showing increased metabolism. Corresponding with some clinical improvement, cortical glucose consumption rates had returned to a normal level.

Adolescent↗
PubMed1989

Interaction between cervico-ocular and vestibulo-ocular reflexes in normal adults.

The interaction of the cervico-ocular reflex (COR) and the vestibulo-ocular reflex (VOR) was studied in 20 human Subjects (Ss) during application of synergistic and antagonistic combinations of neck and vestibular stimuli, and during two different psychophysical tasks related to the Ss' self-motion sensation. Slow and quick eye movement responses were analyzed separately. Neck stimulation produced by horizontal rotation of the trunk about the stationary head elicited slow COR eye movements of very low gain; COR direction was anticompensatory, unlike the compensatory one of the VOR. During either a synergistic combination of neck and labyrinthine stimuli (head rotation on stationary trunk) or an antagonistic combination (head-to-trunk rotation counter to head-in-space rotation), the resulting slow eye movements were slightly larger than those during labyrinthine stimulation alone (whole body rotation). This weak neck contribution could be described by a directionally non-specific enhancement of VOR gain and a linear summation of VOR and COR slow phases. These effects were essentially independent of whether the Ss estimated the magnitude of their head turning or trunk turning in space. If Ss were estimating their trunk turning, neck stimulation also evoked quick eye movements, but these were small and hardly affected the VOR quick phases during the combined stimulations. In contrast, if Ss estimated their head turning, neck stimulation evoked large quick phases, which interfered with the quick phases of the VOR; during the synergistic combination of head and neck stimuli. COR quick phases added to those of the VOR, thereby shifting the gaze in the direction of head rotation (reorientation of gaze). With the antagonistic combination they subtracted, so that the VOR slow phase could compensate the head rotation in space (stabilization of gaze). These findings suggest that (1) the slow phase of the COR has no functional significance in intact humans and (2) the quick phase of the COR plays a role for both stabilization and reorientation of gaze depending on the behavioural context.

Adult↗
PubMed1988

Human immune response to group A streptococcal carbohydrate (A-CHO). III. Comparison of the efficiencies of anti-idiotopic antibody and of nominal antigen in the induction of IgM anti-A-CHO-producing B cells.

In this study the efficiencies of a monoclonal anti-idiotopic (Id) antibody (anti-Id498) and of various preparations of nominal antigen in the induction of an antigen-specific human B cell response in vitro were compared. Anti-Id498 recognizes a recurrent, binding site-related Id present on IgM antibodies with specificity for N-acetyl-D-glucosamine, the immunodominant group of streptococcal group A carbohydrate (A-CHO). We have previously shown that anti-Id498 induces IgM anti-A-CHO secretion from B cells of donors that possess Id-498+ antibodies in their serum. A-CHO was presented to B cells either in soluble or insoluble form, i.e. coupled to beads or as intact bacteria. Purified blood B cell populations from three Id+ healthy donors with high numbers of circulating anti-A-CHO B cells were used and antibody-producing B cells are enumerated in a single-cell assay (spot ELISA). The data show that anti-Id498 was superior in the induction of IgM anti-A-CHO-secreting B cells in two donors (factor 4.6 and 13.5 as compared to the most efficient antigenic stimulation). In the third donor antigen stimulation was slightly more efficient than anti-Id but only with Sepharose-bound A-CHO and not with soluble A-CHO or intact bacteria. The increase of specific B cells induced after stimulation with anti-Id498 could be abolished after addition of autologous T cells in two donors. On the contrary, an enhancement of the specific response was observed after addition of autologous T cells in antigen-stimulated cultures. Neither suppression nor enhancement were induced by addition of irradiated T cells.

Antibodies, Anti-Idiotypic↗
PubMed1988

Early involvement of the nervous system by human immune deficiency virus (HIV). A study of 79 patients.

We report on 79 patients of different stages of human immune deficiency virus (HIV) infection according to the Walter-Reed staging classification (WR). Comparing the HIV antibody content per weight IgG in serum and cerebrospinal fluid (CSF), 54 patients (68%) showed higher antibody activity in CSF than in serum, indicating intrathecal antibody production and thus a local challenge with the virus. The percentage of patients with these antibodies in CSF increased from stage WR 1 (33%) to WR 5 (90%). It decreased again in WR 6 (68%). Twenty-one patients with intrathecally produced antibodies but without evidence for opportunistic or preexistent neuropsychiatric diseases were further analyzed. Even in stages WR 1 and 2 these patients showed distinct clinical signs. These consisted mostly in apathic personality change (n = 13), peripheral neuropathy (n = 8) or mild hemisyndrome (n = 9). Progression to severe dementia solely caused by HIV encephalitis seems to be possible. More often acceleration of the mental disorder indicates a synergistic action of other pathogens. Our study gives further evidence for very frequent, early and clinically active involvement of the nervous system by the HIV infection.

Acquired Immunodeficiency Syndrome↗
PubMed1987

[The supinator syndrome. Study of the course in 20 patients and therapeutic recommendations].

Between 1972 and 1984, 20 cases of the supinator syndrome were examined with clinical and electrophysiological methods in our clinic. In 12 cases we found an idiopathic supinator syndrome in the strict sense and in 8 cases a traumatic lesion of the r. profundus of the radial nerve. We carried out follow-up studies in most of the patients. From these findings we attempt to derive guidelines for treatment. An absolute indication for operative revision in our opinion is present only in the case of complete transsection by trauma. Otherwise, the spontaneous course can be observed. The operative results in idiopathic cases are poor; it seems to be purposeless to operate patients who have a paresis for a long time. Therefore, the decision for or against an operative intervention has to be made soon after the diagnosis is secured.

Adolescent↗
PubMed1986

Locally synthesized antibodies in cerebrospinal fluid of patients with AIDS.

Twelve patients with AIDS were examined by enzyme-linked immunosorbent assay for antibody activity of IgG in serum and CSF. Two patients were only anti-HTLV III antibody carriers (stage I), two had lymphadenopathy syndrome (stage II) and eight had manifest AIDS (stage III). Eight of the 12 patients had 2- to 8-fold higher antibody titres in CSF than in serum, indicating that anti-HTLV III antibodies were produced in the nervous system. One of these patients with obviously locally synthesized anti-HTLV III antibodies in CSF belonged to stage I, two to stage II and five to stage III. Only four of these eight patients also showed locally synthesized IgG in CSF as measured by laser-nephelometry. In contrast, 61 controls with normal CSF (12), impaired blood-CSF barrier (12) multiple sclerosis (12) and various infections of the CNS other than HTLV III (25), the last two groups with locally synthesized IgG in CSF, all revealed negative results. It appears possible that locally synthesized anti-HTLV III antibodies in CSF are a sensitive and early indicator of an HTLV III infection of the nervous system.

Acquired Immunodeficiency Syndrome↗
PubMed1986

[Brain involvement in acquired immunodeficiency syndrome (AIDS): computed tomography (CT) and magnetic resonance tomography (MR)].

Involvement of the central nervous system in acquired immune deficiency syndrome (AIDS) is usually due to opportunistic infections; these frequently offer a difficult differential diagnostic problem. Imaging methods play an important part in the elucidation of symptoms. CT and MR findings were analysed in 13 patients with AIDS and neurological symptoms. Some infections of the central nervous system (encephalitis of unknown aetiology, cytomegalic encephalitis, meningitis) may show cerebral atrophy or even no morphological changes. Toxoplasmosis and PML are the most common opportunistic infections typical changes on CT and MR may lead to diagnosis. MR offers advantages compared with CT in its higher sensitivity for the demonstration even of small lesions.

Acquired Immunodeficiency Syndrome↗
PubMed1982

Disturbed smooth pursuit and saccadic eye movements in schizophrenia.

Smooth pursuit and saccadic eye movements of schizophrenic patients were examined. In a pendulum (0.5 Hz) tracking task schizophrenic inpatients had a slightly lower smooth pursuit gain than outpatients and controls, who showed no significant differences. The number of saccades, counter-saccades and velocity arrests occurring in a 20 s tracking epoque was the same in patients and controls, but patients made larger saccades. When tracking a stepping target by saccadic eye movements, schizophrenic inpatients, and to a lesser extent outpatients, exhibited longer reaction times than controls and had a higher incidence of "non-fixation" (saccades away from the target while the target is stationary). Schizophrenic patients also showed a significantly larger proportion of dysmetric saccades (undershooting the target). While similar changes of reaction time and non-fixation score were observed in manic-depressives and alcoholics, dysmetria was more often found in schizophrenics and possibly constitutes the expression of a specific impairment of attention.

Adolescent↗
PubMed1977

Pragmatic-semantic and syntactic factors influencing ear differences in dichotic listening.

In a three-factorial experiment sequences of 3 words were presented dichotically. The sequences consisted of two uninflected nouns denoting a person or a group of persons and 1 verb denoting an interaction. The three factors were Ear, Syntactic Structuredness vs. Unstructuredness and Semantic-Pragmatic Structuredness vs. Unstructuredness. The sequences in the syntactic unstructuredness condition are spoken in staccato form without sentence intonation and the order of the 2 nouns and the verb was at random; in the syntactic structuredness condition the sequences were spoken fluently and with sentence intonation and the order was always N-V-N. Semantic-pragmatic structuredness of the sequences means that one of the two potential actor-object-relations between the two nouns of a sequence was more probable than the other. The results show that it is only the left hemisphere that is responsive to syntactic structuredness, while the two hemispheres seems to be equally responsive to semantic-pragmatic structuredness. But it is possible that the two hemispheres differ in the manner in which they make use of semantic structures: the left hemisphere in a selective manner, appropriate for the solution of a specific task, and the right hemisphere in a more diffuse and global manner.

Adolescent↗