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Biomedical subjects

G Horstmann

Publications and source records attributed to G Horstmann.

18 recordsLinked to original sources
PubMed1994

Vestibular and somatosensory contributions to responses to head and body displacements in stance.

The relative contribution of vestibular and somatosensory information to triggering postural responses to external body displacements may depend on the task and on the availability of sensory information in each system. To separate the contribution of vestibular and neck mechanisms to the stabilization of upright stance from that of lower body somatosensory mechanisms, responses to displacements of the head alone were compared with responses to displacements of the head and body, in both healthy subjects and in patients with profound bilateral vestibular loss. Head displacements were induced by translating two 1-kg weights suspended on either side of the head at the level of the mastoid bone, and body displacements were induced translating the support surface. Head displacements resulted in maximum forward and backward head accelerations similar to those resulting from body displacements, but were not accompanied by significant center of body mass, ankle, knee, or hip motions. We tested the effect of disrupting somatosensory information from the legs on postural responses to head or body displacements by sway-referencing the support surface. The subjects' eyes were closed during all testing to eliminate the effects of vision. Results showed that head displacements alone can trigger medium latency (48-84 ms) responses in the same leg and trunk muscles as body displacements. Nevertheless, it is unlikely that vestibular signals alone normally trigger directionally specific postural responses to support surface translations in standing humans because: (1) initial head accelerations resulting from body and head displacements were in opposite directions, but were associated with activation of the same leg and trunk postural muscles; (2) muscle responses to displacements of the head alone were only one third of the amplitude of responses to body displacements with equivalent maximum head accelerations; and (3) patients with profound bilateral vestibular loss showed patterns and latencies of leg and trunk muscle responses to body displacements similar to those of healthy subjects. Altering somatosensory information, by sway-referencing the support surface, increased the amplitude of ankle muscle activation to head displacements and reduced the amplitude of ankle muscle activation to body displacements, suggesting context-specific reweighting of vestibular and somatosensory inputs for posture. In contrast to responses to body displacements, responses to direct head displacements appear to depend upon a vestibulospinal trigger, since trunk and leg muscle responses to head displacements were absent in patients who had lost vestibular function as adults.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1991

[A comparative study between bone marrow scintigraphy and magnetic resonance tomography in oncologic patients].

In 35 patients with malignant bone or bone marrow disease, comparative BMS and MRT were performed. Both methods are useful for the early recognition of malignant changes in the skeleton, frequently at a stage when radiographs and bone scans are still negative. BMS provides a global picture of the marrow and can demonstrate focal or diffuse defects within malignant infiltration. Portions of the skeleton which do not contain erythropoietic marrow, or those obscured by high liver or spleen activity, cannot be evaluated. MRT shows the highest sensitivity. The lesions are usually characterised by circumscribed low signal (T1) or high signal (T2) areas. The size and extent were accurately demonstrated. Definite information regarding malignancy was not possible by MRT alone. The method is limited because it is slow, expensive and not easily available. MRT should therefore be reserved for specific problems and is not suitable for examination of the entire bone marrow as, for instance, for staging.

Adult↗
PubMed1990

Chronic intravenous toxicity of the new antibiotic cefpirome in monkeys.

Chronic intravenous toxicity studies in monkeys were carried out with 3-[(2,3-cyclopenteno-1-pyridinium)-methyl]-7-[2-syn-methoximino - 2-(2-aminothiazol-4-yl)-acetamido]-ceph-3-em-4-carboxylate (cefpirome, HR 810; CAS 84957-29-9) a new cephalosporin derivative. In a 90-day study in rhesus monkeys (4 males/4 females per group) dosages of 0, 50, 160 and 500 mg/kg/day were administered. In a 6-month study 5 groups of 6 male and 6 female cynomolgus monkeys received NaCl-solution (0.9%), the vehicle, and 50, 200 or 800/400 mg/kg/d (the highest dosage had to be lowered after the first week due to acute drug intolerance). For clarification of the dose relationship to the findings in the 800/400 mg/kg group, a supplementary 6-month study with 500 mg/kg cefpirome including a vehicle control was also performed. 50 mg cefpirome/kg/d was well tolerated; so too were 160 and 200 mg/kg apart from a slight beta 2-microglobulinuria and/or enzymuria. Almost exclusively at the high dosages retching and vomiting, and exclusively at the high dosages diarrhea, inappetence and physical weakness were sporadically seen in the first phase of the studies. 500 and 400 mg/kg led to increasing signs of discrete renal tubular changes (enzymuria, beta 2-microglobulinuria, cylindruria and minimal histological changes in 2 animals of the 400 mg/kg group). In one rhesus monkey (500 mg/kg) and two cynomolgus monkeys (800 mg/kg) severe kidney damage had developed within the first week. In all dosage groups of the 90-day study special histological methods revealed a dose-dependent increase and enlargement of lysosomes in the epithelia of the proximal renal tubules. Increased cytolysis was, however, not observed. In all the studies there was a dose-dependent increase in the kidney weights of the intermediate and highest dosage groups. The females of the 400 mg/kg group showed slight anemia accompanied by a slight increase in the reticulocyte count. One animal of this group died prematurely probably due to pulmonary embolism. The signs of slight renal impairment including lysosome enlargement, and the slight anemia proved to be reversible.

Acetylglucosamine↗
PubMed1988

Involvement of different receptors in the regulation of human posture.

Compensatory electromyographic (EMG) responses and several biomechanical parameters were studied following impulsive disturbance of the lower limbs during stance on a treadmill. Treadmill acceleration impulses were backwards or forwards directed, or their direction was inverted after 30 ms. Backwards directed impulses were followed by gastrocnemius and forwards directed ones by tibialis anterior EMG responses (latency 65-75 ms) whose duration depended on impulse duration. When the direction of the impulse was inverted, the respective antagonistic leg muscles were activated, with a delay of 68 to 75 ms after onset of stretch of these muscles. The behaviour of the EMG responses could best be correlated to the displacement at the ankle joint and may be described in terms of a stretch reflex response. The function of this stretch reflex mechanism is suggested to be connected with the control of the body's centre of gravity in order to prevent falling. Head movements induced by the impulses showed little correlation with the appearance of the EMG responses, suggesting that the vestibular system is unlikely to be significantly involved in the generation of these responses.

Biomechanical Phenomena↗
PubMed1985

Mucopolysaccharidosis-like alterations in cardiac valves of rats treated with tilorone.

The purpose of this study was to examine whether the aortic and mitral valves of rats are involved in the mucopolysaccharidosis-like disorder induced by tilorone. Rats were treated with large doses of the drug for periods of 1-21 weeks. After chronic drug treatment the leaflets of both heart valves were thickened and opaque. In all treated animals the spongiosa layer of the stroma was crowded with vacuolated cells; the fibrosa layer was altered only after prolonged treatment. Ultrastructurally, the vacuolated cells of the spongiosa could be identified as histiocytes and fibroblasts, the former being the most susceptible cell type. The fibroblasts of the fibrosa represented the least sensitive cell type. The histochemical results showed that the clear cytoplasmic vacuoles in the spongiosa cells were due to lysosomal storage of polyanionic material with staining characteristics similar to cartilage matrix. After discontinuation of drug treatment the alterations persisted for several weeks. The present study shows that heart valves are involved in the mucopolysaccharidosis-like disorder induced by tilorone. The molecular pathomechanism of the disorder and the exact identification of the storage material must await further analysis.

Animals↗
PubMed1984

Tension development and muscle activation in the leg during gait in spastic hemiparesis: independence of muscle hypertonia and exaggerated stretch reflexes.

In 15 patients with spastic hemiparesis the development of tension of calf muscles in relation to their electrical activation and their stretching period was studied on both sides during locomotion. Only in the spastic leg did isolated small biphasic potentials appear in the gastrocnemius E.M.G. with monosynaptic latency at the beginning of the stance phase, while the remaining gastrocnemius activation was reduced compared to the unaffected side. Perturbations of gait were followed in the spastic leg by a large monosynaptic response, while the polysynaptic reflex response was reduced. In the unaffected leg only a strong polysynaptic response appeared, which suggests a reciprocal modulation of monosynaptic and polysynaptic reflex responses. Tension development paralleled the gastrocnemius E.M.G. in the unaffected leg, while in the spastic leg tension was more closely correlated to muscle stretch. It is concluded that in spasticity the exaggerated monosynaptic reflexes represent only a small part of leg extensor activation during gait and that the tension development does not depend on these reflexes.

Adult↗
PubMed1978

Tracheobronchial clearance in health and disease: with special reference to interciliary fluid.

Rats were exposed to influenza B virus for 2 hours. Mucociliary function in the isolated airway preparation of these animals was studied from the first day after exposure and at regular intervals for up to 190 days. Transmission electron microscopy (TEM) studies were done at times corresponding to the mucociliary function studies. TEM studies confirmed the results of the mucociliary function studies: pathological changes were first apparent three days after exposure and began in the distal bronchioles. The morphological studies further demonstrated that the infection progressed proximally to include the entire tracheobronchial tree by the 18th day. The alterations observed included an increase in the number of goblet cells, a decrease in the number of microvilli and a reduction in the amount of interciliary fluid. The last two changes were closely correlated with the severity of the infection. The abnormalities found in mucociliary function included hypersecretion of mucus, inactive and hypoactive zones, synchronization of cilia beating, and a sticking together of the cilia tips.

Animals↗
PubMed1978

N-Acetylcysteine and mucociliary activity in mammalian airways.

The effect of N-acetylcysteine on mucus trasnport velocity (MV), ciliary beat frequency (CBF), mucus production (MP), mucus lysis and on the micro-morphology of the secretory cells was studied in mammalian airways. The results showed that: 1. MV increased in healthy rats and rabbits, as well as in bronchitic rats, after concentrations as low as 10(-14) g/ml. Depression of MV occurred first at 10(-6) and 10(-5) g/ml in healthy and bronchitic animals, respectively. 2. CBF was stimulated at concentrations between 10(-12) and 10(-10) g/ml and decreased at concentrations above 10(-8) g/ml. 3. MP increased by approximately 100% over control values. 4. Lysis of stagnant mucus was evident first at a concentration of 10(-11) g/ml after 15 min incubation. 5. TEM confirmed the increased activity of the mucus secreting cells and showed that no pathological changes occurred within the cell following incubation at 10(-7) g/ml for up to 150 min. The importance of these findings on the overall mucociliary function is discussed.

Acetylcysteine↗
PubMed1976

Adrenergic compounds and the respiratory tract. A physiological and electron-microscopical study.

Studies were undertaken to determine the effect of several adrenergic compounds on ciliary activity and on the micromorphology of the goblet cells and mucous glands. All the substances tested, L-adrenaline, d-L-ephedrine, N-isopropyl-noradrenaline and 1-(4-amino-3, 5-dichlorphenyl)-2-tert-butyl-aminoethanol-HCl increased ciliary activity, but have markedly different effects on goblet cells, mucous glands and on the quality of the produced mucus.

Animals↗
PubMedDate not supplied

Influence of temperature and decreased water content of inspired air on the ciliated bronchial epithelium. A physiological and electron microscopical study.

Experiments have been carried out on the bronchi and intrapulmonary airways of rats in vitro, to determine the physiological effects of air with water content (WC) of: 2.19 mg/1 (5% RH (relative humidity) 37 degrees C), 8.77 mg/1 (20% RH, 37 degrees C), 24.13 mg/1 (50% RH, 37 degrees C) and 30.71 mg/1 (70% RH, 37 degrees C) on ciliary beat frequency; and also, the morphological effect of air at temperatures of 30, 40 and 48 degrees at a constant WC of 28.0 mg/l on the ciliated epithelium. The results showed that (i) ciliary beat frequency decreased with decreasing WC and irreversible ciliostasis was reached sooner, the lower the WC value; (ii) ciliary beat frequency was not significantly affected above 24 mg/l; (iii) 45 min and 90 min exposure at 30 degrees C caused an enormous increase in the depth of the mucus film. The cilia and the epithelial cells did not differ from the controls at 40 degrees C; (iv) in airways exposed for 45 min at 48 degrees C, the cilia appeared to be in total disarray. Some were clustered together in whirling arrangements, while others were detached from their bases. The substructure and the cytoplasm of the cells on the surface and in the deeper layers, appeared to have been destroyed; (v) after 90 min at 48 degrees C, the damage to all structures had progressed. Only isolated tissue or cytoplasmic elements were perceptible.

Air↗