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Biomedical subjects

M Magnusson

Publications and source records attributed to M Magnusson.

At least 145 records · Page 8Linked to original sources
PubMed1991

Human postural dynamics.

The study of posture dynamics is important not only to understand disorders of impaired equilibrium and protective reactions to unexpected displacements of the human body, but also to the design of prosthesis and functional neuromuscular stimulation as aids to patients with impaired postural stability and locomotion. Coordinated control of the body segments is a complex aspect of motor behavior, owing to the multiple degrees of freedom of the controlled system. Several interacting subsystems are involved in the dynamics of human posture and locomotion, including the skeletal, neuromuscular, and sensory systems. Human posture control is maintained by somatosensory, vestibular, and visual feedback, integrated within the locomotor and central nervous systems. Studies of posture dynamics and stability therefore entail the study of mechanical aspects of the human body, its sensory systems, and the principles governing coordination in motion control. In this paper is reviewed some of the research done in the field of human posture dynamics, including such topics as biomechanics, equilibrium, stability, motion coordination, neural feedback, neural control systems modeling, motion strategies, optimality of motion, and adaptation. We consider experimental approaches and theoretical models, as well as the gap between them. Principles for the experimental investigation of control systems are considered.

Animals↗
PubMed1990

Characterisation of phenolic glycolipids from Mycobacterium marinum.

The phenolic glycolipids from two strains of Mycobacterium marinum have been isolated and characterised. The glycolipids from M. marinum MNC 170 were principally glycosides of diacyl C37, C39 and C41 phenolphthiocerols A, but in M. marinum MNC 842, these lipids were accompanied by glycosides of diacyl phenolphthiodiolones A and novel phthiotriols A with the same overall chain-lengths. The main acyl components of the phenolic glycolipids from M. marinum MNC 170 were C26 dimethyl and C27 and C29 trimethyl-branched fatty acids, but in the lipids of M. marinum MNC 842, the C27 trimethyl acid was the only principal component. The sugar composition of all these glycolipids had been previously shown to correspond to 3-O-methylrhamnose.

Gas Chromatography-Mass Spectrometry↗
PubMed1990

Recognition of novel glycolipid antigens from smooth variants of Mycobacterium tuberculosis.

A major polar and three minor slightly less polar glycolipids were identified in extracts of two smooth (Canetti) strains of Mycobacterium tuberculosis. Immunostaining on thin-layer chromatograms and enzyme-linked immunosorbent assay (ELISA) of purified lipids demonstrated that the major and the two most polar of the minor glycolipids are potent antigens, reacting with homologous antisera and also with that raised against the type strain (H37Rv).

Antigens, Bacterial↗
PubMed1990

Increased intestinal permeability to differently sized polyethylene glycols in uremic rats: effects of low- and high-protein diets.

Intestinal mucosa forms an important barrier towards harmful agents in the intestinal lumen, besides being the site for absorption of nutrients. Little is known about the intestinal permeability properties in chronic uremia. The permeability toward differently sized polyethylene glycols (PEGs; range 326-1,162 Da) was studied in uremic groups compared to the control groups. The urinary recovery was also recovery of PEGs was increased in the uremic groups compared to the control groups. The urinary recovery was also increased in the groups on the high-protein diet compared to the corresponding group on the low-protein diet. This study suggests an increased permeability of PEG molecules in the range of 546-1,162 Da in uremic rats and a decreased intestinal permeability after a low-protein diet in both a uremic and nonuremic state. Thus, in chronic renal failure the intestinal barrier is impaired but returns towards normal with low-protein diets.

Animals↗
PubMed1990

Urinary excretion of differently sized polyethylene glycols after intravenous administration in uremic and control rats: effects of low- and high-protein diets.

The intestine constitutes a barrier towards potentially harmful agents in the intestinal lumen. Different-sized polyethylene glycols (PEGs; range 326-1,1162 Da) have been used to study the intestinal permeability properties in 5/6-nephrectomized rats on either a high- (22%) or low-protein (8%) diet. PEGs were administered intravenously, and the urinary recovery was measured. The 24-hour urinary recovery of PEGs was significantly reduced in the uremic groups. The ratios between different sizes of PEGs, indicating a size-selective escape of molecules from blood, were decreased in the uremic groups. The urinary recovery was in general increased in the control group on the high-protein diet compared to the control group on the low-protein diet. The results provide evidence for an increased permeability of larger PEGs (range 634-1,162 Da) in uremic rats and that the protein content of the diet might affect the permeability properties.

Animals↗
PubMed1990

[A new method to study behavioral categories and systems of interaction of young children. Initial data].

In the first part of this paper we report on a new method we have developed for the study of the genesis and regulations of the behavior of infants in interactive situations. Detailed information is given on the following aspects: 1. The technical characteristics of the device that allows the infants to be seated in an upright position; 2. The different periods of the experimental procedure; 3. The method used for analyzing the behavioral data. As infants were video-taped without any interruption (real-time record), the behavioral data were analysed in two different ways: A. Macroscopic analyses were carried out using 84 items and 12 categories of behavior. These analyses allowed us to measure the temporal evolution of a limited set of easily recognized behaviors from one experimental period to the next and one experimental session to the next at one-week time intervals; B. Microscopic analyses were carried out with a special software program (THEME) using 222 items divided among 14 categories of behavior. This program was created by Magnusson. It allows the worker to search for significant patterns in sequential events which are recorded in real time, i.e. intra-individual behavioral structure as well as interindividual relationship (interaction). Information is given on the theoretical model and the pattern identification method. The first data can be thus summarized: 1. Four month old infants show a high level competence in their visual attention span in relation to each other; 2. They appear to have varied and complex behavior and interaction processes; 3. Each child has his or her own behavior dynamics throughout each experimental session and from one period to the next; 4. There are some special relationships between infant-infant interactions and the modalities of interaction between each infant and its mother; 5. Periodical behavioral "outbursts" are observed, which might in themselves constitute organizers of behavior; 6. It also makes clear the existence and structure of significant intra- and inter-individual behavioral patterns some of which are particularly complex (patterns are defined as significant connections between two items at least, within a critical time interval, calculated by THEME); 7. It reveals the function of these patterns in mutual adjustment processes between both infants throughout the experimental session.

Attention↗
PubMed1990

The loads on the lumbar spine during work at an assembly line. The risks for fatigue injuries of vertebral bodies.

This study was performed in an attempt to determine the total spinal compressive load during assembly line work to find a possible association with the many complaints of back pain. A flexion analyzer was used to register trunk movements, and analysis of postures and lifted weights was done from video recordings. The load on the spine at the L3 level was calculated through a biomechanical model, meant for analysis of static, sagittally symmetric postures and lifting tasks. Maximum lift tests were performed before and after a full work day. The peak load on the L3-L4 level when lifting corresponded to an average 22% of the load at the lift test. The mean load during a work cycle was 818 N. It was concluded that the many complaints of back pain could not be attributed to high peak loads, repetitivity of the lifts, or large load doses. Monotony, stress, and low job satisfaction are more likely factors of greater importance.

Adult↗
PubMed1989

Does hyperkinetic circulation constitute a pre-hypertensive stage? A 5-year follow-up of haemodynamics in young men with mild blood pressure elevation.

In a previous haemodynamic examination, 44 young men (18-22 years) with blood pressure elevation above the 98th percentile, mean arterial blood pressure (MAP) greater than or equal to 95 +/- 6 mm Hg, showed an increased cardiac index (dye-dilution) and an enhanced resistance at maximal vasodilation of the hand (venous occlusion plethysmography during hyperaemia). This latter finding suggested arteriolar wall hypertrophy. However, the subgroup with the highest cardiac index (greater than or equal to 3.86 1 min-1 x m2) (n = 18) displayed normal vascular resistance at maximal dilation in comparison with the normotensive control group (n = 29). Consequently, functional signs of arteriolar hypertrophy were restricted to individuals with normal or low cardiac index. At the re-investigation 5 years later, a significant reduction in blood pressure was observed in the normotensive control group (MAP: from 88 +/- 7 to 85 +/- 7 mm Hg, P less than 0.05). There was no change in individuals with initially elevated blood pressure. Furthermore, cardiac index fell significantly with time in this latter group. Thus, the blood pressure elevation in the hypertensive group, previously mainly dependent on high blood flow was, 5 years later, more related to an increased total peripheral resistance, (delta total peripheral resistance = 8%). However, no definite evidence indicating development of hypertrophy of the resistance vessels of the hand was observed during the follow-up period. Since the hyperkinetic subgroup did not display a concomitant fall in blood pressure with cardiac output, our results do not support the theory that the hyperkinetic form of borderline hypertension is a temporary phenomenon, explained by the inclusion of anxious individuals afraid of the experimental situation. Hyperkinetic hypertension may be the initial phase of sustained hypertension in a subgroup of the future hypertensive population.

Adult↗
PubMed1989

Effects of intravenous diazepam and thiopental on the vestibulo-ocular reflex in man.

The effects of i.v. injection of diazepam 0.3 mg/kg and thiopental 6.0 mg/kg on vestibulo-ocular reflex (VOR) were studied in 9 healthy volunteers. One hour after injection of both diazepam and thiopental VOR gain was reduced and time constant shortened. Four hours after intravenous injection of diazepam the VOR gain was still significantly reduced and had not yet returned to control 8 h after injection. Although both drugs were detected in blood still 8 h after the injection, there were no longer significant effects on VOR. Moreover, individual values of VOR gain and time constant did not correlate with the blood concentrations of the drugs. Decrease of VOR gain and shortening of time constant after i.v. given diazepam and thiopental in man are interpreted as resulting from both specific effects on VOR and non-specific reduction of alertness.

Adult↗
PubMed1989

Determination of characteristic parameters of human postural dynamics.

Posture control performance was quantified in three variables (swiftness, stiffness, damping). Subjects were tested with a force platform recording body sway induced by vibrators attached to the calf muscles. Parameter estimation was made with identification of a transfer function representing the stabilized inverted pendulum. It is conjectured that the state feedback parameters identified are suitable for use in assessing ability to maintain posture.

Adult↗
PubMed1989

Dynamic performance of vibration induced anterior-posterior sway during upright posture in normal subjects.

Human postural control works as a dynamic feedback control system. The dynamic performance of postural control for anterior-posterior movements during upright posture are defined by three parameters. These parameters reflect the stiffness, the damping and the swiftness of a response to an induced perturbation. In the present study 23 normal subjects were investigated. Both with open and closed eyes, there was a negative correlation between swiftness and stiffness. With open eyes there was also a weak correlation between swiftness and damping. When the subjects were tested with open eyes there was a prominent and highly significant increase of stiffness and a reduction of swiftness of the responses. It was found that proprioceptive information from the calf muscles contributes in postural control of movements up to 1 Hz and visual information is important for movements up to 0.05 Hz. The present findings suggest that postural control changes dynamic strategies depending on the available sensory feedback.

Adolescent↗
PubMed1989

Reduction of the time constant in the VOR as a protective mechanism in acute vestibular lesions.

Fourteen patients with vestibular neuritis were examined at onset of symptoms and after one year. Postrotatory time constant and gain in the vestibulo-ocular reflex (VOR) were measured after rotation with a velocity step of 150 deg/s. There was no significant difference in gain towards the healthy side at onset of the disease compared to recordings after one year. The time constant towards the healthy side was significantly shorter at onset compared to measurements after one year. The results reflect the loss of unilateral vestibular function on the velocity storage mechanism, both in the acute situation and after compensation. The findings indicate that reduction of the time constant in the VOR is not only due to unilaterally vestibular impairment but it is also an effect of the generally reduced activity in the vestibular system after a lesion and may act as protective mechanism in acute vertigo.

Acute Disease↗
PubMed1989

Comparative studies of antigenic glycolipids of mycobacteria related to the leprosy bacillus.

The leprosy bacillus, Mycobacterium leprae, is a member of a small group of mycobacteria comprising the species Mycobacterium bovis, Mycobacterium marinum, Mycobacterium kansasii, Mycobacterium tuberculosis, Mycobacterium ulcerans and related taxa. This relationship is based on the similarity of the characteristic lipid types in the cell envelope. Mycobacterium leprae produces a phenolic glycolipid antigen which is species specific. This communication reports a comparison of the specificity of the lipid antigens of other members of this group of mycobacteria. Mycobacterium kansasii, in accordance with previous studies, produces phenolic glycolipid and trehalose-based lipooligosaccharide antigens which do not cross react with antisera raised against other mycobacteria. The phenolic glycolipid and an uncharacterised polar glycolipid, with the properties of a lipooligosaccharide, from Mycobacterium marinum are also shown to be specific antigens. An acylated trehalose glycolipid antigen from Mycobacterium tuberculosis H37Rv reacts strongly with antisera raised against the same strain and sera from eight out of ten tuberculosis patients. The phenolic glycolipid antigen, isolated only from Mycobacterium tuberculosis "Canetti" variants, did not react with antisera raised against the type strain, Mycobacterium tuberculosis H37Rv, although it had been shown previously to react with sera from tuberculosis patients. It is apparent that there are populations of the tubercle bacillus which differ in the lipid antigens expressed on their cell surface.

Antigens, Bacterial↗
PubMed1989

Evaluation of smooth pursuit and voluntary saccades in nitrous oxide-induced narcosis.

The effect of inhaling nitrous oxide on pursuit eye movements (PEM) and voluntary saccades was studied in nine healthy subjects. Eye movements were recorded before, during, and 10 min after exposure for 15 min to normoxic mixtures of 14%, 21%, and 28% nitrous oxide. At all concentrations, there was a significant decrease in gain of PEM at a target velocity of 60 degrees/s, the decrease being of comparable magnitude at concentrations of 14% and 21%. By 10 min after exposure to nitrous oxide, the gain of PEM had recovered to pre-test values. There was also a highly significant decrease in the peak velocity of voluntary saccades at all concentrations of nitrous oxide; the decrease was more pronounced at the higher concentrations, and the existence of a dose-dependent relationship is suspected. Exposure to 21% nitrous oxide for only 2 min was enough to induce significant reduction in peak velocity of voluntary saccades. By 10 min after exposure to nitrous oxide, the peak velocity of voluntary saccades had recovered but had not reached pre-test values. The findings suggest that both PEM and voluntary saccades decrease with reduced alertness in mild narcosis. Moreover, as the effects of nitrous oxide are considered typical of inert gases in general, our findings suggest that voluntary eye movements may also be a suitable variable for use in assessing the effects of inert gas narcosis.

Adult↗
PubMed1988

TSH response to TRH and haloperidol response latency in psychoses.

Thyroid-stimulating hormone (TSH) response to thyrotropin-releasing hormone (TRH) was measured in 19 acutely psychotic (DSM-III schizophrenia, 7; schizophreniform, 2; schizoaffective, 3; affective, mood-incongruent psychosis, 5; manic, mood-congruent psychosis, 2) drug-free patients prior to systematic trials of lithium and/or haloperidol. TSH response was not associated with sex, age, baseline T4, or baseline TSH. A reduced TSH response was associated with affective diagnosis and was a significant predictor of a positive, rapid response to neuroleptic treatment.

Adult↗
PubMed1988

Drug response patterns as a basis of nosology for the mood-incongruent psychoses (the schizophrenias).

Interaction of therapeutic drugs with a series of different biopathological substrates of psychosis might be expected to generate a series of different response patterns. Herein the authors suggest that multi-modal response patterns following lithium and neuroleptic treatment of psychotic patients may aid in resolving the heterogeneity of psychotic disorders and lead to a new nosology of the psychoses.

Haloperidol↗