Biomedical subjects

W Becker

Publications and source records attributed to W Becker.

At least 37 records · Page 2Linked to original sources

PubMed1991

Human perception of horizontal trunk and head rotation in space during vestibular and neck stimulation.

The vestibular signal of head motion in space must be complemented by a neck signal of the trunk-to-head excursion in order to provide the individual with information on trunk motion in space. This consideration led us to study psychophysically the role of vestibular-neck interaction for human self-motion perception. Subjects (Ss) were presented with passive horizontal rotations of their trunk and/or head (sinusoidal rotations, f = 0.025 - 0.4 Hz) in the dark for vestibular and neck stimulation, as well as for combinations of both. Ss' perception was evaluated in terms of gain (veridical perception of stimulus magnitude, G = 1), phase, and detection threshold. (1) Perception of trunk rotation in space. During vestibular stimulation (whole-body rotation) and neck stimulation (trunk rotation with the head kept stationary) the frequency-transfer characteristics underlying this perception were very similar. The gain fell short; it was only about 0.7 at 0.4 and 0.2 Hz stimulus frequency and was further attenuated with decreasing frequency. In contrast, the phase was close to that of actual trunk position. The gain attenuation was found to be a function of the peak angular velocity of the stimulus, a fact, which we related to a 'velocity threshold' of the order of 1 deg/s. During the various vestibular-neck combinations used, Ss' perception was again erroneous, reflecting essentially the sum of its two non-ideal constituents. However, there was one noticeable exception; during the combination 'head rotation on stationary trunk', Ss veridically perceived their trunk as stationary (compatible with the notion that the sum yielded 'zero'). (2) Perception of head rotation in space. During vestibular stimulation, Ss' estimates showed the same non-ideal gain-vs.-frequency characteristics as described above for the trunk. Neck stimulation induced an illusion as if the head had been rotated in space. This neck contribution was such that, when it was combined with its vestibular counterpart during head rotation on stationary trunk, the perception became almost veridical. On closer inspection, however, this neck contribution was found to reflect the sum of two components; one was the non-ideal neck signal contributing to the perception of 'trunk in space', the other was an almost ideal neck signal of head-on-trunk rotation. (3) The results could be described by a simple model. In this model, the erroneous vestibular signal 'head in space' is primarily used to create an internal representation of 'trunk in space'.(ABSTRACT TRUNCATED AT 400 WORDS)

Head↗

PubMed1991

Sensitivity of external cuneate neurons to neck rotation in three-dimensional space.

A functionally meaningful vestibular-neck interaction, such as it has been demonstrated for postural reflexes and self-motion perception, requires the spatial and temporal response characteristics of vestibular and neck signals to be similar. We investigated the spatial coding in neurons of the external cuneate nucleus (ECN) with natural neck and vestibular stimulations, and compared them to that of neurons in the descending and medial vestibular nuclei (DVN and MVN, respectively) obtained with vestibular stimulation. Neurons were recorded extracellularly in chronically prepared cats held under light barbiturate anesthesia. Neck stimulation was performed by sinusoidally rotating the animals' trunk relative to the earth-fixed head in six different vertical planes and in the horizontal plane. Vestibular stimulation was elicited by whole-body rotations in the corresponding planes. During neck stimulation in the vertical planes, most ECN neurons showed an approximately sinusoidal discharge modulation about resting rate, which became maximal during rotation in a specific plane. Off this plane, the response declined along a cosine function and reached zero in the orthogonal plane. The majority of these ECN neurons also responded to horizontal neck rotation; the resulting "optimal" direction of rotation in three-dimensional space varied considerably among the neurons. Yet, there was a certain preference; the majority of these ECN neurons fired maximally if trunk rotation in the yaw plane stretched the neck on the ipsilateral side, if roll brought the contralateral shoulder closer to the head, and if pitch brought the back closer to the occiput. A minority of ECN neurons showed more complex response patterns which could not be described by a single, optimal direction. About one third of the neck-sensitive ECN neurons tested showed weak responses during whole body rotation, which might stem from a weak vestibular input to this nucleus. In the DVN and MVN, the optimal direction in three-dimensional space with vestibular stimulation typically had a cosine-like spatial tuning. The spatial distribution of these directions clearly differed from that of neck-sensitive neurons in the ECN. We therefore assume that a further processing of the two input signals takes place at later stages in the CNS (e.g., in the vestibulo-cerebellum) in order to yield a functionally useful vestibular-neck interaction.

Animals↗

PubMed1991

Octreotide scintigraphy localizes somatostatin receptor-positive islet cell carcinomas.

Tyr-3-Octreotide is a synthetic derivative of somatostatin and a somatostatin-receptor analogue. The iodine-123-labelled compound localizes somatostatin-receptor-positive tumours. In this paper two patients are reported in whom somatostatin receptors were demonstrated in vitro. In a 60-year-old female with an islet cell carcinoma of the pancreas, multiple liver metastases and previously unrecognized bone metastases in the right acetabulum could be diagnosed as the reason for a persistent hypoglycaemia. In a 60-year-old male an islet cell carcinoma of the pancreas was localized with 123I-Tyr-3-octreotide. The somatostatin receptors were demonstrated in vitro and the tumour was successfully treated with somatostatin. These studies demonstrate that 123I-Tyr-3-octreotide offers the possibility of localizing somatostatin-receptor-positive tumours and their metastases. Moreover the method makes it possible to determine the receptor status of a tumour in vivo.

Adenoma, Islet Cell↗

PubMed1991

Mode of action of the molluscicide bromoacetamide.

1. Uptake of bromoacetamide was found to be upgraded with exposure time (6, 12, 24 hr) and drug concentration (0.1, 0.5, 1.0 ppm). 2. Bromoacetamide was also absorbed by carp and mice, but drug concentration was markedly lower than in snails. Drug clearance from carp as well as from mice is more rapid than that of snails. 3. The ultrastructure of hepatopancreas cells are markedly influenced by bromoacetamide, including swelling of mitochondria and splitting of cristae. This finding is correlative in a decrease in action of enzymes located in mitochondria (ornithine carbamyl-transferase, citric acid synthase). 4. Oxygen uptake and glucose uptake, as well as urea excretion, are reduced and glycogen reserve are decreased.

Acetamides↗

PubMed1991

Contents of essential and toxic mineral elements in Swedish market-basket diets in 1987.

Market baskets containing sixty food items included in the average Swedish diet were purchased from three shops in four major Swedish cities during autumn 1987. Food items were selected on the basis of food-balance-sheet data. Freeze-dried homogenates representative of each city were analysed for twelve essential or toxic mineral elements. The energy content of the market baskets (11.5 MJ) corresponded to the reference value for male adults. At this energy level the contents of calcium (1180 mg), magnesium (300 mg), iron (16 mg), zinc (12 mg) and selenium (44 micrograms) were above or close to the Swedish recommended daily intakes. The contents of manganese (3.7 mg) and molybdenum (150 micrograms) were within and that of copper (1.2 mg) was below the safe and adequate intake values given in the US recommended dietary allowance (Food and Nutrition Board, National Research Council, 1989). The content of nickel was 82 micrograms. The contents of lead (17 micrograms), cadmium (12 micrograms) and mercury (1.8 micrograms) in the daily diet were low compared with the provisional tolerable intakes set by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (World Health Organization, 1972, 1989). The market-basket contents of Ca, Mg, Fe and Zn calculated from values in the Swedish food composition tables were close to the analysed values, indicating that the Swedish food tables provide relevant information for the estimation of the dietary supply of these elements.

Cadmium↗

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↗

PubMed1991

Serial scintigraphic imaging for visualization of passive transport processes in the human fallopian tube.

Spontaneous migration of a radionuclide tracer from the vagina to the peritoneum may be visualized by scintigraphic imaging (hysterosalpingoscintigraphy, HSS). A prospective study was designed to evaluate diagnostic criteria for normal tubal passage of a control group (n = 7) and to establish the predictive value of the HSS technique in defining functional deficiency in anatomically patent tubes. In 56 patients with tubal and unexplained infertility, a comparison between the results of the tracer migration study and of contrast hysterosalpingography and laparoscopy was made. The overall correlation was 65%. Clearly discrepant results (i.e. an abnormal migration pattern in anatomically patent tubes) were recorded in 18% and were positively, yet not significantly associated with tubal adhesive disease and with a history of tubal microsurgery. Interpretation of scans was equivocal in another 18% of patients due to undetectable ascension of the tracer to the uterus. It is suggested that the radionuclide is moved forward by the same passive transport processes which are concerned with support of the migration of spermatozoa to the ovum, and that failure of tubal migration of the tracer may render patients eligible for in-vitro fertilization/embryo transfer treatment.

Adult↗

PubMed1991

Clinical relevance of activity parameters in Crohn's disease estimated by the faecal excretion of 111In-labeled granulocytes.

The fecal excretion of 111In-oxine-labeled autologous granulocytes was determined in 58 patients with Crohn's disease. A representative analysis of the total amount of excreted cells requires a 4-day stool sampling at least in those patients suffering from Crohn's ileitis or ileocolitis. Various laboratory tests (Orosomucoid, alpha 1-antitrypsin, C-reactive protein, erythrocyte sedimentation rate, leukocytes, thrombocytes, albumin, Fe, alpha 1-globulin and alpha 2-globulin) and the van Hees index significantly correlated with this specific estimate of intestinal inflammation, indicating that it is of little importance which one is clinically used for the assessment of inflammatory activity in Crohn's disease.

Adult↗

PubMed1991

HLA-A2, or a closely linked gene, confers susceptibility to early-onset sporadic Alzheimer's disease in men.

There is a weak association between Alzheimer's disease (AD) and the histocompatibility antigen HLA-A2, suggesting that A2 has either a minor role in AD or a major role in a subtype of it. To test these alternatives, we studied 54 consecutively ascertained AD patients diagnosed by NINCDS-ADRDA criteria. Patients had a higher frequency of A2 than control subjects, primarily due to the elevated frequency of this antigen in men with early onset of dementia (less than or equal to 60 years): 92% of early-onset men had A2 as compared with 44% of controls. This finding suggests that A2, or a closely linked gene, confers susceptibility to early-onset AD in men. Furthermore, A2 appears to be primarily associated with sporadic AD, rather than with the familial subtype.

Age Factors↗

PubMed1991

Guided tissue regeneration for implants placed into extraction sockets: a study in dogs.

Twelve 10 mm implants were placed into immediate extraction sockets in dogs. Six implants were isolated with PTFE membranes and 6 sites served as controls. Standardized clinical measurements were taken at test and control sites. At 18 weeks the dogs were anesthetized and flaps were laid for the purpose of obtaining clinical measurements. The average gain of bone around augmented implants was 2.6 mm, while control sites had an average bone gain of 1.0 mm. Ridge width adjacent to augmented sites increased by 1.2 mm and control sites had an increased width of 0.6 mm. Histologic evaluation of test and control specimens showed greater bone formation around augmented implants. Implants augmented with PTFE membranes had clinically significant amounts of bone regeneration when compared with controls.

Alveolar Process↗

PubMed1991

Regeneration procedures: grafting materials, guided tissue regeneration, and growth factors.

Flap debridement, bone grafting, and guided tissue regeneration have the capacity of regenerating bone, periodontal ligament, and cementum. Alloplastic materials are used to fill periodontal defects, and healing occurs by repair. While varying amounts of new bone may form with allografts, a long junctional epithelium is usually the mode of attachment. Flap debridement has been reported to successfully treat multiple walled intrabony defects. Healing results in bone regeneration. However, there is probably a long junctional epithelium adjacent to the root. Defects treated by guided tissue regeneration have been demonstrated to heal with new cementum, periodontal ligament, and bone. Recently, growth factors have been discussed as a possible means of enhancing wound healing.

Bone Transplantation↗

PubMed1991