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Biomedical subjects

T Brandt

Publications and source records attributed to T Brandt.

At least 235 records · Page 13Linked to original sources
PubMed1988

Growth response after administration of pharmacological doses of growth hormone in rats.

Increased levels of endogenous growth hormone (GH) during childhood and adolescence result in a significant elevation of final height both in humans and in laboratory animals. We investigated the growth promoting effects of the administration of pharmacological doses of human GH (25 to 100 IU/kg/day) in 7 rats with severe intrauterine growth retardation (IUGR) due to artificially induced embryofetal alcohol syndrome (EFAS). Such doses of GH led to a marked growth spurt during the time of administration (14 days) exceeding the expected daily length and weight gain significantly, compared to placebo-treated EFAS litter and healthy controls (P less than 0.01, resp. P less than 0.05). This growth increment persisted in all treated animals throughout the total period of observation (250 days). Three out of the seven animals even showed incremental growth curves of both length and weight that stayed continuously within the +/- 2 standard deviation range of normally growing animals. Thus, it is shown for the first time that also exogenous GH administered temporarily at doses beyond the physiological level results in a significant elevation of final body size.

Aging↗
PubMed1987

Pathological eye-head coordination in roll: tonic ocular tilt reaction in mesencephalic and medullary lesions.

The fundamental pattern of coordinated eye-head roll motion is based upon utricular/saccular as well as vertical canal input, and mediated by the graviceptive pathways from the labyrinths via pontomedullary vestibular nuclei to the rostral midbrain tegmentum. The tonic bilateral graviceptive input stabilizes the eyes and head in the normal upright position. A unilateral lesion causes imbalance in vestibular tone in the roll plane which results in a tonic ipsiversive ocular tilt reaction (OTR). OTR, the triad of ipsilateral head tilt, skew deviation and ocular torsion, occurred as a tonic response (nonparoxysmal) persisting over months to years and was presumed to be due to upper brainstem lesions in 3 patients. Precise localization was limited because of the nature of the lesions. A reversible tonic OTR was seen with acute infarction of the dorsolateral medulla oblongata in 4 out of 11 patients. It may be explained by an ipsilateral lesion of the posterior canal pathways. Transient OTR seems not to be rare in acute Wallenberg's syndrome and ocular torsion in these patients is dysconjugate with predominant excyclotropia of the ipsilateral hypotropic eye. A deviation of the subjective visual vertical in the direction of the spontaneous head tilt--a previously undescribed feature of OTR--was present in all 7 patients and indicates a pathological shift of the internal representation of the gravitational vector. With respect to perception (subjective vertical) it is proposed that the manifest ipsiversive OTR represents a motor compensation of an apparent eye-head tilt contraversive to the lesioned side. Despite the resulting postural imbalance and the conflicting true vertical of the visual surround, the eyes, head and body are continuously adjusted to what the central nervous system erroneously computes as being vertical.

Adult↗
PubMed1987

Paroxysmal spontaneous nystagmus and vertigo evoked by lateral eye position.

Prolonged lateral eye position to the extreme left for 5 to 20 seconds, without vestibular stimulation, induced intense attacks of nystagmus and rotational vertigo lasting 50-90 seconds in a patient. During the attacks the nystagmus beat to the right and counterclockwise, while the patient could look freely around. Clinical data were suggestive of repeated strokes in the vertebrobasilar territory, mainly affecting the right dorsolateral medulla oblongata including the vestibular nuclei. A paroxysmal attack of nystagmus and vertigo evoked by voluntary lateral eye position is an unusual clinical finding. This is discussed in the light of multisensory integration within the vestibular system, which also includes eye position information.

Brain↗
PubMed1987

Importance of the visual and vestibular cortex for self-motion perception in man (circularvection).

Circularvection (CV), the optokinetically induced perception of self-motion, is based neurophysiologically upon visual-vestibular convergence. It is yet not known which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system in order to make possible the convergence that has been found: the vestibular nuclei, the thalamus and the vestibular cortex. The functional significance of the visual cortex was demonstrated in 12 patients with homonymous hemianopia who neither perceived CV nor exhibited a postural destabilization when exposed to optokinetic pattern motion (yaw or roll) restricted to the scotoma. The functional significance of the vestibular cortex as well as ipsilateral visual-vestibular interaction was demonstrated in 4 (out of 20) patients with tumour lesions involving the vestibular cortex areas. They either failed to perceive CV or showed a significant increase of CV-latencies when monocular optokinetic stimulation was restricted to the ipsilateral visual cortex. Arguments for and against the following hypothesis are discussed: circularvection is induced by visual motion stimulation of the primary visual cortex which then activates vestibular nuclei neurons by descending pathways and which also informs the vestibular cortex that self-motion with a perceptual direction is involved. Determination of the velocity of CV is mediated by direct visual-vestibular cortex interaction, which most probably is also involved in the perceptual interpretation of motion perception: Self-motion versus object-motion.

Adult↗
PubMed1987

Importance of the visual cortex for postural stabilization: inferences from pigeon and frog data.

Optokinetically induced self-motion with its consequences for postural balance is based upon visual-vestibular convergence. It is a matter for speculation which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system. The functional significance of the visual cortex was tested by a behavioral approach in two animals, selected for their different evolutionary stage: frog (midbrain visual center); pigeon (primitive neocortical center). Lateral postural sway during optokinetic stimulation in roll served as a measurement for induced rollvection and apparent body tilt. Roll motion elicits a tonic 'compensatory' postural adjustment towards the direction of pattern motion in pigeon as in man but not in frog. From the lack of this reaction we infer that the frog does not perceive rollvection because it has no visual cortex. This agrees with the absence of visual-vestibular convergence in the frogs vestibular nuclei neurons as well as the absence of a nystagmus velocity storage in the brainstem. The animal experiments fit human data in hemianopic patients who also only experience rollvection when stimulated in the unaffected hemifield.

Animals↗
PubMed1987

Object-motion detection affected by concurrent self-motion perception: applied aspects for vehicle guidance.

Thresholds and response times for object-motion detection are significantly raised during concurrent real or visually induced self-motion perception. This was demonstrated by standardized laboratory experiments in which subjects had to react to a suprathreshold visual stimulus (1 degree-light spot moving with 5 degrees/s speed) under different stimulus conditions of simultaneously perceived self-motion. Elevated response times (mean elevation factor: 3.27) were also obtained for the detection of changes in inter-vehicle distance (headway) under real road conditions with the simultaneous involvement of self- and object-motion perception compared to a corresponding (object-motion perception) simulation in the laboratory without any self-motion. With regard to vehicle guidance, existing concepts of safe stopping distances, which depend upon adequate detection of a collision course and the corresponding reaction times, have to be recalculated.

Adult↗
PubMed1986

European vestibular experiments on the Spacelab-1 mission: 5. Contribution of the otoliths to the vertical vestibulo-ocular reflex.

The gain of the vestibulo-ocular reflex in the sagittal plane may be due to a cooperation between otoliths and the vertical semi-circular canals. The present space experiment was aimed at studying the influence of the absence of gravity stimulation on the otoliths, by comparing VOR gain and phase in space and on ground. Measurements were taken the 5th and the 7th day of flight, the subject being asked to perform, eyes closed, active head oscillations in pitch while fixating an imaginary target in front of him. No significant decrease of the VOR gain was found in space, but a change in phase was noted. A significant increase of the VOR gain was found 14 h after landing. Control experiments have been done on ground on several subjects. They indicate that pitch VOR gain during active head movements is about one, with eyes open in darkness at 1 Hz.

Adaptation, Physiological↗
PubMed1986

Object-motion detection affected by concurrent self-motion perception: psychophysics of a new phenomenon.

Thresholds for object-motion detection are significantly raised when concurrent self-motion perception is induced by either vestibular, or visual, or cervico-somatosensory stimulation. Active sinusoidal horizontal head oscillations with compensatory vestibulo-ocular reflex (VOR) and foveal or eccentrical target presentation; 'passive' head movements with fixation suppression of the VOR; pure body oscillations with the head fixed in space (cervical stimulation); optokinetically induced apparent self-motion (circularvection). This new visual phenomenon of a physiological 'inhibitory interaction' between object- and self-motion perception seems to have a somatosensory motor analogue. It may reflect the disadventageous side effect due to unspecificness of an otherwise beneficial space constancy mechanism, which provides us with the image of a stable world during locomotion.

Adolescent↗
PubMed1985

Mild central pontine myelinolysis: a frequently undetected syndrome.

Over a period of 1 year we diagnosed central pontine myelinolysis (CPM) in five patients all of whom survived, two of them with complete functional recovery despite extensive lesions on cranial computerized tomography and magnetic resonance imaging. Diagnosis was based upon the combination of an acute brainstem dysfunction with typical neuroradiological features; a history of chronic alcoholism or a preceding hyponatremia may serve as a diagnostic hint. The spectrum of symptoms ranged from severe tetraplegia and cranial nerve palsies to latent signs of pyramidal tract lesions and discrete ocular motor abnormalities. In two patients pontine and extrapontine manifestations of demyelination were confirmed neuroradiologically; in one patient a solely extrapontine manifestation was present. Thus it is reasonable that: (1) the incidence of comparatively mild forms of CPM as well as extrapontine manifestations are more frequent than hitherto assumed, (2) the clinical outcome of the syndrome is better than expected from earlier fatal case reports and is quite independent of the extent of the lesion as it appears with brain imaging methods.

Adult↗
PubMed1985

Is obligatory bed rest after lumbar puncture obsolete?

After lumbar puncture (LP) an epidural CSF leakage caused by delayed closure of a dural defect leads to a decrease in CSF pressure. The resultant venous dilatation as well as downward shift of the brain with traction on pain-sensitive blood vessels and nerves frequently evokes post-lumbar puncture headache (PLPH), when the patient assumes the upright position. In previous studies differing opinions have been expressed about the prophylactic value of the posture taken by the patient after LP. The present study was designed to evaluate the benefit of the decrease of hydrostatic CSF pressure on the dural rent, when the patient lies down in a prone position with the head tilted down at an angle of 10 degrees for 30 min immediately after LP: is it possible to accelerate the closure of the dural defect in this way and prevent PLPH? One group of patients (n = 78) lay in a prone position with the head tilted down at an angle of 10 degrees for 30 min, the other group (n = 82) rose immediately after LP. PLPH was found to be independent of the posture in both groups and affected 44% and 41% of the patients, respectively, so that there is no longer any justification for requiring patients to remain in bed after LP.

Adolescent↗
PubMed1985

[Therapy of orbital and retroorbital space occupying processes with optic nerve compression].

Space occupying lesions involving the optic nerve require individual management. Graves' disease is first treated with cortisone: failures of treatment require radiation and operative decompression. Good results have been achieved with cytostatic drugs and, in acute progressive loss of vision, with plasmapheresis. Idiopathic pseudo-tumor orbitae disappears with cortisone, failures of treatment indicate malignant development of a lymphoma, which requires management with cytostatic drugs or radiation. Granulomatous infiltration of the optic nerve in sarcoidosis should be treated first of all with steroids before proceeding to operative treatment. Primary optic nerve tumors such as gliomas and meningeomas should be removed operatively if they are located in front of the chiasm and continue to grow. If the chiasm is involved, radiation is preferable. Doubtful cases of clinically almost indistinguishable pinealomas which are very radiosensitive require primary radiation therapy. Sinus cavernosus fistulas should be treated by selective angiographic occlusion of the fistula. If this is impossible, the internal carotid artery may be occluded by introducing a ballon catheter. Loss of vision after blunt head trauma should be treated with megadoses of steroids, operative treatment is only promising in cases with progressive loss of vision.

Arteriovenous Malformations↗
PubMed1984

Interaction between perceived self-motion and object-motion impairs vehicle guidance.

When one is riding in a vehicle, perceptual thresholds for motion of objects are significantly elevated above those determined under corresponding but simulated conditions in the laboratory without concurrent self-motion perception. Authorities on road traffic accidents should thus consider an additional perceptual time of at least 300 milliseconds for detecting critical changes in headway beyond the usual reaction time. Detection times thus corrected consequently lead to an alteration of our conception of safe intervehicle distances in a convoy. This elevation of thresholds for object-motion during self-motion, with its consequences for visual control of vehicle guidance, can be seen as a disadvantageous side effect of an otherwise beneficial space-constancy mechanism, which provides us with a stable world during locomotion.

Automobile Driving↗
PubMed1984

Effects of rectilinear acceleration and optokinetic and caloric stimulations in space.

During the flight of Spacelab 1 the crew performed a number of experiments to explore changes in vestibular function and visual-vestibular interactions on exposure to microgravity. Measurements were made on the threshold for detection of linear oscillation, vestibulo-ocular reflexes elicited by angular and linear movements, oculomotor and posture responses to optokinetic stimulations, and responses to caloric stimulation. Tests were also conducted on the ground, during the 4 months before and on days 1 to 6 after flight. The most significant result was that caloric mystagmus of the same direction as on the earth could also be evoked in the weightless environment.

Acceleration↗
PubMed1984

Visual stabilization of posture. Physiological stimulus characteristics and clinical aspects.

Visual stabilization of posture is critically dependent on stimulus characteristics as well as on the performance of the visual system. The purpose of the present investigation was to obtain quantitative data in man by means of posturography of fore-aft and lateral body sway in relation to different visual stimulus characteristics. Visual acuity, when decreased logarithmically, causes a linearly increasing postural instability, twice as prominent for fore-aft than for lateral sway. Any measurable visual contribution for fore-aft sway ceases with an acuity lower than 0.03 and for lateral sway with an acuity lower than 0.01. The central area of the visual field as compared with the peripheral retina dominates postural control. The foveal region exhibits a powerful contribution, in particular for lateral sway. A partial but significant visual stabilization is preserved with a visual input rate between 1 to 4 Hz flicker frequency. As soon as continuous motion perception becomes involved with frequencies higher than 4 Hz, visual stabilization gradually improves with a saturation at frequencies higher than 16 Hz. Lateral body sway activity and eye-object distance are linearly related: body sway decreases with increasing distance corresponding to the linear decrease of net retinal displacement with increasing eye-object distance. Aspects of 'afferent' and 'efferent' visual motion perception, which involve fore-aft and lateral body sway differently, are evaluated. The clinical relevance is demonstrated in patients with oculomotor disturbances. The results are discussed with respect to the variety of related clinical disorders, which involve reduction in visual acuity, field defects, accommodation disturbances and ocular oscillations.

Accommodation, Ocular↗