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Biomedical subjects

M Magnusson

Publications and source records attributed to M Magnusson.

At least 127 records · Page 7Linked to original sources
PubMed1991

Optimal coordination and control of posture and locomotion.

This paper presents a theoretical model of stability and coordination of posture and locomotion, together with algorithms for continuous-time quadratic optimization of motion control. Explicit solutions to the Hamilton-Jacobi equation for optimal control of rigid-body motion are obtained by solving an algebraic matrix equation. The stability is investigated with Lyapunov function theory, and it is shown that global asymptotic stability holds. It is also shown how optimal control and adaptive control may act in concert in the case of unknown or uncertain system parameters. The solution describes motion strategies of minimum effort and variance. The proposed optimal control is formulated to be suitable as a posture and stance model for experimental validation and verification. The combination of adaptive and optimal control makes this algorithm a candidate for coordination and control of functional neuromuscular stimulation as well as of prostheses.

Algorithms↗
PubMed1991

Sensitivity to sensitins and tuberculin in Swedish children. III. Sequential versus simultaneous skin testing.

The aim of this study was to determine whether simultaneous and sequential skin testing with tuberculin and sensitins give consistent results. A total of 475 8- or 9-year-old schoolchildren were skin tested sequentially, at an interval of 3 days, with PPD tuberculin and with either Mycobacterium scrofulaceum or M. avium sensitin. The results were compared with those of 470 simultaneously tested children chosen from the same living area. There were no statistically significant differences between the frequencies of the reactions of sequentially and simultaneously tested children. When the sequential testing procedure was employed, 3.1% reacted to tuberculin, 19% to M. avium sensitin and 30% to M. scrofulaceum sensitin, taking a 6 mm cut-off. The corresponding figures for the simultaneously tested children were 4.7, 21 and 36%, respectively. Thus, there was no indication that the simultaneous testing procedure in itself influenced the results, neither was there any sign of a booster effect when testing in sequence with an interval of 3 days in non-BCG-vaccinated children.

Antigens↗
PubMed1991

Sensitivity to sensitins and tuberculin in Swedish children. I. A study of schoolchildren in an urban area.

Non-BCG-vaccinated schoolchildren (8 or 9 years of age) were simultaneously tested on separate arms with 2 IU PPD RT23 and 0.1 microgram Mycobacterium avium sensitin RS10 or 0.1 microgram Mycobacterium scrofulaceum sensitin RS95. None of the 2819 analysed children had any known exposure to tuberculosis. A total of 3.4% reacted with an induration greater than or equal to 6 mm to PPD RT23. Half the number of children were tested with M. avium sensitin and 25.4% reacted while the remaining were tested with M. scrofulaceum sensitin and 32.4% reacted when the cut-off was 6 mm. For about 90% of the children the sensitin reaction was larger than or equal to the tuberculin (PPD RT23) reaction. Correlation analyses showed that moderate and high PPD RT23 values were combined with still higher sensitin values, indicating that the tuberculin reactions were mainly cross-reactions due to the antigenic similarity between tuberculin and sensitins. The presence of birds, dogs and cats in the homes was combined with an increased frequency of children reacting to the sensitins used. The children with reactions to PPD RT23 greater than or equal to 6 mm were examined and chest X-rays were performed. None of them showed any signs or symptoms of mycobacterial disease. In non-BCG-vaccinated Swedish schoolchildren without clinical signs of tuberculosis and without known contact with a contagious tuberculous person, indurations less than 12 to 14 mm on tuberculin testing are probably caused by atypical mycobacteria. In such cases sensitin tests should be performed to verify the suspicion.

Animals↗
PubMed1991

Sensitivity to sensitins and tuberculin in Swedish children. II. A study of preschool children.

Non-BCG-vaccinated preschool children (4 or 5 years of age) were simultaneously tested on separate arms with a 2 IU PPD RT23 and 0.1 microgram Mycobacterium avium sensitin RS10 or 0.1 microgram Mycobacterium scrofulaceum sensitin RS95. None of the 762 children had any known exposure to tuberculosis. A total of 8.8% reacted with an induration (greater than or equal to 3 mm to PPD RT23 while 2% reacted with greater than or equal to 6 mm. Half the children were tested with M. avium sensitin: 18.9 and 7.8% reacted when 3 and 6 mm cut-off points, respectively, were taken. The remaining children were tested with M. scrofulaceum sensitin: 18.4 and 6.3%, respectively, reacted. In a previous study of schoolchildren aged 8 or 9 years, reactions to sensitins were considerably more frequent. Thus, sensitisation by atypical mycobacteria seems to increase from the preschool to the early school age. This finding probably reflects a continuous exposure of the children to atypical mycobacteria from various sources. The preschool children with a reaction to PPD RT23 greater than or equal to 6 mm were examined and chest X-rays were performed. All children were healthy but one child had enlarged lymph nodes in the mediastinum and abdomen. It cannot be excluded that these pathological findings were caused by atypical mycobacteria.

Age Factors↗
PubMed1991

Impaired intestinal barrier function measured by differently sized polyethylene glycols in patients with chronic renal failure.

The intestinal mucosa plays a fundamental role as the site for absorption of nutrients, and as an important barrier from potentially harmful agents in the intestinal lumen. Little is known of the permeability properties of the intestinal mucosa in uraemic patients. The intestinal permeability to differently sized polyethylene glycols (PEGs; range 326-1254 daltons) was studied in nine patients with chronic renal failure (24 hour endogeneous creatinine clearance 5-24 ml/minute). The maximum 24 hour urinary recovery of PEGs was decreased in the uraemic patients but relatively more of the larger than the smaller PEGs were found in these patients. The results suggest a reduced urinary recovery of PEGs caused by renal dysfunction but also a relatively increased intestinal permeability to larger PEGs in the uraemic patients.

Adult↗
PubMed1991

Small intestinal peptidases and disaccharidases in rats with acute uremia.

Acute uremia was induced in rats with temporary clamping of the left renal pedicle and contralateral nephrectomy. Jejunal peptidase activities (aminopeptidase N, dipeptidyl peptidase IV and aminopeptidase A), disaccharidase activities (maltase, sucrase, lactase and trehalase) and morphology were studied. A significant (p less than 0.05) increase in aminopeptidase N activity and a positive correlation between aminopeptidase N activity and serum urea was found in the uremic rats. The other peptidase activities showed a slight increase in the uremic rats. A shortening of the microvilli of the small intestinal epithelial cells in the uremic rats was seen by electron microscopy. The disaccharidase activities was unaltered. This study shows the presence of functional alterations in the small intestine in rats with acute uremia. The observations are also compatible with different regulation mechanisms for the brush border peptidases and disaccharidases.

Acute Disease↗
PubMed1991

Postural compensation in children with congenital or early acquired bilateral vestibular loss.

The relative roles of different receptor systems in compensating for vestibular loss were studied in 18 children (12 to 16 years of age) with congenital or early acquired bilateral vestibular loss (BVL) and impaired hearing, and compared to that in 33 normal children (9 to 16 years of age). Postural stability was studied with posturography evaluating the velocity of anterior-posterior body sway. With closed eyes the increase of sway velocity did not differ between the groups, either with or without simultaneous proprioceptive disturbances when the subjects were standing on a bare surface. Body sway velocities were found to increase more in subjects with a BVL than in normal children when subjects were standing on foam rubber. When proprioceptive cues were disturbed, body sway velocities increased in both groups, but significantly more in children with BVL when subjects stood on foam rubber. This occurred both with and without open eyes.

Adolescent↗
PubMed1991

Intervertebral motion during vibration.

Vibration exposure is widely recognized as a risk factor for low back pain. An experimental protocol was designed to quantify the intervertebral motion response in human subjects to sinusoidal vertical vibration at 5 and 8 Hz, and at a variety of acceleration levels. Intervertebral motion in the mid-sagittal plane was measured using a transducer linkage system attached to pins placed directly into the spinous processes of adjacent vertebrae. The postures of the subjects were carefully controlled. The effects of forward flexion, arm support, gravitational load, and sitting on a cushion were evaluated. The rigid body motion of the superior vertebra with respect to the inferior vertebra was expressed in terms of relative sagittal plane rotation, axial translation, and anterior-posterior shear translation. It was found that the lumbar motion segments exhibited coupled periodic behaviour in response to sinusoidal vertical vibration, with up to 1 mm peak-to-peak displacement in the axial direction. The greatest intervertebral motion occurred when the subject was exposed to 5 Hz vibration as compared to 8 Hz. For a constant frequency of 5 Hz excitation, the peak-to-peak amplitudes of the computed motions tended to increase as the acceleration level increased. In the flexed posture, with no arm support, the active trunk musculature helped reduce the intervertebral motion. Additional gravitational load on the shoulders caused increased relative axial displacement. A polyethylene foam cushion placed on the seat reduced vibration transmission at 5 Hz excitation and consequently decreased the intervertebral motion.

Adult↗
PubMed1991

Delayed onset of ototoxic effects of gentamicin in patients with Meniére's disease.

In treatment of Meniére's disease, installations of gentamicin are continued until there are signs of disturbance of vestibular or cochlear function. However, since it has been demonstrated that gentamicin is eliminated slowly from the inner ear, a continuing ototoxic effect may be suspected. The present study aimed to investigate the delay of onset of symptoms of ototoxic effects. Five patients with Meniére's disease and disabling vertigo were treated with intratympanic installation of gentamicin. The patients received two installations at two consecutive days, after which the treatment was abated, although no patient showed any symptoms of affection of the vestibular or cochlear end organs. All patients, however, developed vertigo and nystagmus beating toward the not treated ear within 3 to 5 days after the last installation. At 3 months and 1 year later, the treated ear showed no reaction on bithermal caloric stimulation and all patients had a complete relief of attacks of vertigo but hearing levels were about the same compared to before treatment. The present findings demonstrate a delayed onset of ototoxic effects and it is suggested that gentamicin treatment should not be carried on until symptoms develop. Furthermore, extremely low dose treatment may produce loss of vestibular function with the desired relief of vertigo and with less hazards of affecting the hearing level.

Adult↗
PubMed1991

Postural control in blinds and in Usher's syndrome.

The postural control mechanisms were evaluated in 10 blinds and in 10 subjects with Usher's syndrome. The results were compared with 27 age matched healthy volunteers. In visual conditions the subjects with Usher's syndrome performed worse, but in nonvisual condition they performed equally well as the controls. The results were the same irrespective of whether the tests were performed on a rigid surface or foam rubber covered surface. The blinds and controls performed equally well on the bare surface, but the blinds performed significantly better on the foam rubber covered surface. The results indicate that in subjects with Usher's syndrome the vestibulo-cochlear degeneration is well compensated but the postural stability aggravated due to retinal degeneration. Blind subjects have a better postural control than their seeing referents, but the difference is only evident in situations in which the postural control is hampered by surface perturbation.

Adolescent↗
PubMed1991

Effect of proprioceptor stimulation on postural stability in patients with peripheral or central vestibular lesion.

Body sway in upright stance at rest and after inducing proprioceptor stimulation, elicited by vibration applied to the calf or neck muscles, was studied in 11 patients with peripheral lesion and in 17 patients with central vestibular lesion. The responses were compared with those of 20 normal subjects. Vibratory stimulus was applied at five different frequencies, ranging from 32 to 150 Hz, and at a constant amplitude of 2.1 mm. Postural stability was measured with a force platform in terms of average deviation of body position (ADBP) analyzed in relation to the individual maximum support distance in the anterio-posterior direction. In patients with peripheral vestibular lesion ADBP was moderately increased, compared to normal subjects, when the calf muscles were exposed to vibration under eyes closed conditions (i.e. no visual information available); stimulation of neck muscles both under eyes open and eyes closed conditions and stimulation of calf muscles with open eyes produced an ADBP of the same magnitude as in controls. In patients with central vestibular lesion, proprioceptor stimulation of calf and neck muscles caused increased ADBP whether with eyes open or closed. The ADBP induced by stimulation of neck muscles was significantly greater in patients with a central lesion than in those with a peripheral vestibular lesion. The results indicate that patients with peripheral lesion differ from those with central vestibular lesion in their reaction to proprioceptor stimulus; and that in patients with central vestibular lesion proprioceptor stimulation of the neck muscles produces disproportionately powerful cervico-collic reflexes.

Brain Stem↗
PubMed1991

Effects of restrained cervical mobility on voluntary eye movements and postural control.

The effects of restrained cervical mobility on pursuit eye movements (PEMS), voluntary saccades and postural control, as measured by posturography, were studied in 11 healthy subjects whose cervical spine movement had been restrained for 5 days by means of a rigid neck-collar. At day 5 mean peak velocity of voluntary saccades at amplitudes of 40 degrees and 60 degrees was significantly reduced, as was mean peak gain of PEMs at a stimulus velocity of 50 degrees/s; the variance of body position in vibration-induced body sway was significantly increased, but there was no difference in variance of galvanically-induced body sway or in velocity of vibration-induced body sway. The results suggest that restriction of cervical movements per se affects voluntary eye movements, a conclusion also consistent with findings in patients with tension headache. Restriction of cervical movement only marginally affects postural control.

Adult↗
PubMed1991

Delayed onset of ototoxic effects of gentamicin in treatment of Menière's disease. Rationale for extremely low dose therapy.

Five patients with Menière's disease and disabling vertigo were treated with two intratympanic instillations of gentamicin given at an interval of about 12 h. Although no further gentamicin treatment was given despite the absence of any discernible effects on the vestibular endorgan at that time, all patients developed vertigo and nystagmus beating toward the untreated ear within 3 to 5 days after the last instillation. Neither at the 3 month follow-up nor 1 year later did the treated ear show any reaction to bithermal caloric stimulation despite the fact that the hearing levels were almost the same as before treatment. All 5 patients obtained complete relief from attacks of vertigo, but had persisting tinnitus. As gentamicin has been shown to be slowly eliminated from the inner ear, and may thus exert persistent ototoxic effect, it is suggested that gentamicin treatment should not be continued until symptoms of ototoxic effects on the inner ear can be discerned. Extremely low-dose treatment may produce sufficient loss of vestibular function to provide relief from vertigo, and with less risk of affecting the hearing level.

Adult↗