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At least 235 records · Page 13Linked to original sources
PubMed2005

Sway patterns in orthostatic tremor: impairment of postural control mechanisms.

Sway parameters in orthostatic tremor (OT) patients were compared with age-matched controls. The effects of vision (eyes open or closed), stance width (feet apart or together), and external support (with or without) on sway and 14-18 Hz energy were measured. Sway in OT patients decreased in the presence of each of the stabilizing factors but the extent of benefit obtained by OT patients was significantly less than controls for support for the sagittal plane (22% vs. 42% decrease; P < 0.01) and feet apart in the mediolateral plane (38% vs. 65% decrease; P < 0.01). Three patients with proprioceptive loss also had a reduced response to these factors. Energy in the 14-18 Hz range did not always change in parallel with sway levels. Vision suppresses activity at the OT frequency in patients. Postural control mechanisms in OT remain responsive to postural conditions, but patients differ significantly from normals in the degree of their responsiveness. OT appears to have disruption of the normal generation or processing of proprioceptive signals as one of its important components.

Aged↗
PubMed2007

Acute effects of a lateral postural assist on voluntary step initiation in patients with Parkinson's disease.

Anticipatory postural adjustments (APAs) for lateral weight transfer and stability precede and accompany voluntary stepping. Patients with Parkinson's disease (PD) show delays in step initiation with altered APA characteristics that may reflect impaired interactions between posture and locomotion. The purpose of this study was to examine the influence of a lateral postural assist on step initiation in patients with early stage PD while off medication and healthy controls. Subjects performed self-paced rapid forward steps. In one condition (ASSIST), the APA was assisted at onset with a lateral pull applied to the pelvis by a motor-driven robotic system. Ground reaction forces and whole body kinematics were recorded to characterize the APA and step characteristics. Overall, PD subjects had a longer APA duration (P < 0.01) and longer first step duration (P < 0.027) than Control subjects. With the ASSIST, the APA duration for both groups was shorter (P < 0.001), the step onset time was earlier (P < 0.001), and the speed of the first step became faster for PD subjects. Postural assistance affecting the interaction between posture and locomotion may have therapeutic potential for improving movement function in patients with PD.

Aged↗
PubMed1987

Stability of the head: studies in normal subjects and in patients with labyrinthine disease, head tremor, and dystonia.

The dynamics of postural control of the head were investigated in normal human subjects and patients with neurological disease. The technique adopted was to measure the head movements provoked by passive, unpredictable oscillations of the trunk in the frequency range 0-6-7 Hz when subjects were required (a) to try to stabilise their head "in space" and (b) to try to make their heads move "en bloc" with the trunk. Head movement responses were characterised by the gain and phase with respect to trunk movement (transfer function) and degree of linear relationship between head and trunk (coherence). The normal transfer function approximated a cascade of two second-order, underdamped, systems representing the passive inertial, viscous, and elastic properties of the muscle and joints of the head and neck. Stabilisation of the head "in space" produced about 40% reduction in transmission of body movement, was only evident at frequencies less than 1 Hz and was affected partly by voluntary movements. An alabyrinthine patient could also achieve some spatial stabilisation. The findings indicate a weak role for vestibular-collic reflexes and emphasise that the primary control of head posture during unpredictable movement is through the tonic visco-elastic properties of neck muscles that work to stabilise the head on the shoulders. In patients with dystonia of the neck and essential and cerebellar head tremor, the head showed a tendency to unstable oscillation (resonance). The instability and dystonia could be measured in terms of visco-elastic constants and damping ratios. The head movements of some tremor patients did not linearly follow the trunk movement, showing that the motion stimulus provoked abnormal phasic muscle activity at frequencies other than those of the tremor. The technique quantifies head control in movement disorders and is sensitive to abnormal function.

Adolescent↗
PubMed1992

The coordination of posture and voluntary movement in patients with cerebellar dysfunction.

Postural adjustments associated with the task of rising on tiptoes were investigated in a reaction time paradigm in 10 normal subjects and 18 patients with cerebellar disorders. Cerebellar dysfunction was due to either degenerative cerebellar disease, tumor, or ischemia. Displacements of the center of foot pressure (CFP) were recorded. The task, accomplished by the triceps surae muscle (executional activity, mean latency of 411 ms), is mechanically effective only if the center of gravity has been shifted forward in advance. To this effect, a phasic burst of preparatory EMG activity in the tibialis anterior normally occurs at a mean latency of 163 ms, shifting the center of gravity forward. Shortly thereafter, activity of the quadriceps femoris (175 ms) extends the knee and aids the forward shift of the center of gravity. Different aspects of this motor sequence were disturbed in individual patients: Latencies of preparatory and executional activity were uncorrelated in 15 of the 18 patients. Executional (n = 16) or preparatory (n = 13) EMG activity was tonic instead of phasic. Latencies of either preparatory or executional EMG activities or both were prolonged (n = 10). The time interval between motor preparation and execution was increased (n = 9). The trial-to-trial variability of biomechanical parameters and EMG latency was increased. Preparatory EMG activity in the quadriceps was entirely missing (n = 9), resulting in knee bending at the unsuccessful attempt to rise on tiptoes. Patients who were most severely affected had no preparatory activity at all (n = 2), and therefore were unable to perform the task.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Quantification of postural sway patterns in tardive dyskinesia.

An assessment was made of the orientation and variability in postural center of pressure patterns in individuals with tardive dyskinesia (TD) and/or developmental disability during quiet standing. Postural patterns were compared and contrasted between four groups of individuals: those with (a) TD and developmentally disabled (severely and profoundly retarded); (b) developmental disability only; (c) TD but of normal intelligence; and (d) a healthy control group. The center of pressure displacements were derived from the lateral, vertical, and anterior-posterior force and moment components of force platform measurements. Analyses demonstrated that individuals with TD in combination with developmental disability had a different center of pressure orientation and variability compared to healthy individuals and individuals suffering only from developmental disability or TD. The center of pressure pattern in the developmentally disabled TD group was characterized by a more prominent lateral orientation, whereas in the other three groups, it had a more predominant anterior-posterior orientation. In addition, the variability in these orientation components was much smaller in the developmentally disabled TD group, indicating a more regular pattern of sway in the center of pressure during quiet standing in these individuals. These findings show that assessments of postural center of pressure profile orientation and variability may be useful indicators for investigating TD, especially in distinguishing between developmental disability and TD.

Adult↗
PubMed1997

Step initiation in Parkinson's disease: influence of levodopa and external sensory triggers.

We studied anticipatory postural adjustments contributing to gait initiation deficits in patients with Parkinson's disease (PD) to determine if these deficits could be improved by administration of levodopa or by external stimuli. Ground reaction forces and body kinematics were recorded for self-generated and cutaneous cue-triggered step initiation in normal subjects and in PD subjects when OFF and when ON. The effects of assisting anticipatory postural sway with a surface translation coupled with a cutaneous cue were also examined. Decreased force production, decreased velocity of movement, and slowed execution of the anticipatory postural adjustments for self-generated step characterized step initiation in PD subjects when OFF. These impairments were significantly less evident when the PD subjects were ON. Both PD and normal subjects increased force and velocity of movement when a cutaneous cue was used as a go signal. When subjects voluntarily initiated a step in response to the surface translation, both PD and normal subjects executed the anticipatory postural adjustments for step more rapidly, but the PD subjects, both ON and OFF, failed to increase force to execute push-off more rapidly. In conclusion, dopaminergic therapy and an external stimulus similarly improve the deficient force production for the anticipatory postural adjustments associated with step initiation in PD. The findings also suggest that force production during the postural adjustment phase of self-generated, but not externally triggered, step initiation is influenced by dopaminergic pathways.

Aged↗
PubMed1998

Effective treatment of orthostatic tremor with gabapentin.

We report seven patients with orthostatic tremor (OT) who were successfully treated with the anticonvulsant gabapentin. Five of the patients had been previously tried on clonazepam, the most commonly used drug for OT, four without any benefit. The degree of improvement perceived by the patients with gabapentin varied from 60-80% (mean 73%). The effective dose of gabapentin ranged from 300-1800 mg/day (mean 1030 mg/day). The side effects were generally mild, transient, and dose-related. Duration of response has so far ranged from 2-22 months (mean 11 months) with all patients still currently benefiting from gabapentin. We conclude that gabapentin may be an effective treatment for OT. Further trials are indicated.

Acetates↗
PubMed1988

Changes in center of gravity in boys with Duchenne muscular dystrophy.

A study was undertaken, using methods of stabilometry to compare stability of stance in normal children (n = 37) and those with Duchenne muscular dystrophy (n = 61). The purpose of this study was to monitor changes in the locus of the center of gravity and the range and frequency of sway and to evaluate the effect of orthotic application in an attempt to obtain information that would assist further development of orthoses. In group 1, boys with Duchenne muscular dystrophy who were still walking without assistance (mean age 7.2 +/- 1.76 years), the analysis of sway showed that, between 5 and 6 years of age, the boys already had ranges of anteroposterior (A/P) and lateral (Lat) sway that were significantly greater than those found in normal children (A/P P less than 0.05, Lat P less than 0.01). In group 2, boys with Duchenne muscular dystrophy when orthoses had been introduced (n = 23, mean age 10.4 +/- 1.47 years), the center of gravity was returned to a more normal position. There was a reduction of the anteroposterior range of sway, but the lateral range of sway remained significantly greater (P less than 0.01) as did the frequency of sway in both the anteroposterior and lateral directions (A/P P less than 0.001, Lat P less than 0.001).

Child↗
PubMed1999

Lateral reach: a clinical measure of medio-lateral postural stability.

BACKGROUND AND PURPOSE: Medio-lateral postural instability has recently been identified as a risk factor for falls in the elderly community-dwelling population. However, few clinical tests involve challenges to stability limits in the medio-lateral direction. A lateral reach test was thus developed. Preliminary evaluation of the symmetry, accuracy, test-retest repeatability, and construct validity of the lateral reach test was undertaken to ensure its validity and repeatability prior to clinical application. METHOD: Sixty healthy older female subjects (aged 72.5 +/- 5 years) participated in this study which involved two tasks. The first was the clinical test: a maximal lateral reach to the right and left, recorded by a clinical measure (observation of hand excursion) and a laboratory measure (3D analysis of hand marker excursion). The second was the recording of centre of pressure (COP) stability limits in the lateral direction by use of a dual force platform system. Eighteen subjects returned for repeatability testing. RESULTS: No significant differences in the measures were found between the sides. Lateral reach as measured by the clinical measure was significantly (p < 0.05) correlated with both the laboratory measure of reach (r = 0.650) and with COP stability limits (r = 0.331). The clinical measure of reach was not significantly different (p > 0.01) from the laboratory measure. High test-retest repeatability (r > 0.94) was found for all measures. CONCLUSIONS: The clinical lateral reach test was found to be an accurate measure of lateral reach ability. As it was significantly correlated with COP excursion it was deemed a valid indicator of lateral stability limits. In addition, the lateral reach test had high test-retest repeatability and was symmetrical between the sides. These promising results support both it's use where a clinical indicator of medio-lateral postural stability is desired and further investigation of the lateral reach test in clinical populations.

Aged↗
PubMed2000

Visual judgements of steadiness in one-legged stance: reliability and validity.

BACKGROUND AND PURPOSE: There is a paucity of information about the validity and reliability of clinicians' visual judgements of steadiness in one-legged stance. Such judgements are used frequently in clinical practice to support decisions about treatment in the fields of neurology, sports medicine, paediatrics and orthopaedics. The aim of the present study was to address the validity and reliability of visual judgements of steadiness in one-legged stance in a group of physiotherapists. METHOD: A videotape of 20 five-second performances was shown to 14 physiotherapists with median clinical experience of 6.75 years. Validity of visual judgement was established by correlating scores obtained from an 11-point rating scale with criterion scores obtained from a force platform. In addition, partial correlations were used to control for the potential influence of body weight on the relationship between the visual judgements and criterion scores. Inter-observer reliability was quantified between the physiotherapists; intra-observer reliability was quantified between two tests four weeks apart. RESULTS: Mean criterion-related validity was high, regardless of whether body weight was controlled for statistically (Pearson's r = 0.84, 0.83, respectively). The standard error of estimating the criterion score was 3.3 newtons. Inter-observer reliability was high (ICC (2,1) = 0.81 at Test 1 and 0.82 at Test 2). Intra-observer reliability was high (on average ICC (2,1) = 0.88; Pearson's r = 0.90). The standard error of measurement for the 11-point scale was one unit. CONCLUSIONS: The finding of higher accuracy of making visual judgements than previously reported may be due to several aspects of design: use of a criterion score derived from the variability of the force signal which is more discriminating than variability of centre of pressure; use of a discriminating visual rating scale; specificity and clear definition of the phenomenon to be rated.

Adult↗
PubMed2001

Assessment of sensorimotor and cognitive deficits induced by a moderate traumatic injury in the right parietal cortex of the rat.

The purpose of this study was to set-up a battery of behavioral tests to assess sensorimotor and cognitive deficits following a moderate traumatic brain injury (TBI) in rats. Coordinated walking ability was evaluated in an accelerated rotarod test. Vestibulomotor function and fine motor coordination were assessed by using a beam-walking task. Rotarod and beam-walking performances were both altered in injured rats compared to sham-operated and control rats. A more pronounced and longer-lasting deficit was measured in the beam-walking test. Cognitive function was studied by using the Lashley maze paradigm. A spatial localization deficit was significant for 4 weeks posttrauma in TBI rats. The beam-walking task and the Lashley maze are robust and sensitive methods in detecting sensorimotor and cognitive impairment after TBI in rats, respectively. These tests are proposed for evaluating the ability of new pharmacological agents to improve the functional recovery after a TBI in rats.

Animals↗
PubMed2002

Vestibulospinal control of posture.

To better understand the role of the vestibular system in postural coordination, we compared the ability of subjects with complete, bilateral loss of vestibular function and age-matched control subjects to maintain equilibrium and postural orientation during sinusoidal displacements of the support surface at a variety of frequencies. We also examined the ability of visual or somatosensory-light touch information to substitute for missing vestibular information in dynamic postural coordination. The results suggest that vestibular information is used as a gravitational reference frame to prevent slow drift of the trunk in space during complex postural tasks. Furthermore, visual information or somatosensory information from light touch of a finger on a stable reference can significantly substitute for loss of vestibular function.

Gravitation↗
PubMed1980

Chronic self-stimulation of the dentate nucleus for the relief of spasticity.

It has been assumed but not yet proved that cerebellar cortical stimulation activates the Purkinje cells, with subsequent inhibition of the deep cerebellar nuclei. However, the relatively crude, widespread excitation induced by several surface electrode arrays and the parameters of stimulation currently used, may produce other effects than selective activation of only one specific cellular type which, furthermore, seems to be rarely present in these particular patients, as demonstrated by biopsy studies prior to electrode placement. The dentate nucleus was chronically implanted with a stimulating system in a patient with spasticity due to cerebral palsy. Chronic self-stimulation induced a significant improvement in motor function, with relief of spasticity and improvement in speech, posture, balance and gait. Electrophysiological studies demonstrated a decrease in the amplitude of V1 and V2 responses and in the H/M and T/M ratios, an increase in the silent period, and marked effects in the H reflex recovery curve, as well as diminished contralateral cortical somato-sensory evoked potentials. This result seems to indicate that the clinical effects of cerebellar cortical stimulation are not due to prosthetically induced inhibition of the dentate nucleus.

Adult↗
PubMed1991

New posture equilibrometer for the diagnosis of vestibular disease.

The vestibulospinal level of vestibular function is commonly neglected in the evaluation of vertiginous patients. We have now developed a new posture equilibrometer. A transducer is placed on the head of the subject being tested. With this meter we can record body swaying, X (left-right) and Y (fore-aft) components of angular displacement, angular velocity, and angular acceleration. A detailed analysis of the data can be made by having patients keep their eyes either open or closed during the Romberg test. The head is turned left or right in this test, while the eyes are opened and closed in the Mann test. The posture equilibrometer has enabled us to evaluate more precisely vestibulospinal function and sensory interactions.

Adolescent↗
PubMed1981

Alcohol and postural imbalance. A force plate study.

A total of 16 normal, medium sized persons were given 20 g of alcohol every hour for 4-5 h. This yielded blood alcohol concentrations between 0.1 mg/ml and 1.7 mg/ml (0.1-1.7%) during the 4-5 h of testing. By use of a computer-assisted force plate system, objective measurements of postural imbalance were performed each hour. An increasing postural imbalance was found at blood alcohol concentrations above 0.6 mg/ml (0.6%). The results illustrate the risk of intake of alcohol by people highly dependent on a safe standing position.

Adult↗
PubMed1994

Characteristics of posture alterations associated with a stepping movement in cats.

The relationship between changes in posture and the performance of a forelimb movement required for a transition between two stance positions was analysed in cats. The task consisted of an operantly conditioned, forelimb stepping movement from one support platform to another located more anterior. The reward was given only after a specific vertical force was applied to the second platform. This ensured that the cat performed a clear transition from its initial stance posture to another requiring a different weight distribution. The strategy adopted by an animal during the conditioned movement was studied by analysing the distribution of the vertical forces as a function of time. Specific quantitative functions were used to describe the weight distribution in the anterior-posterior, right-left and diagonal directions as the task was performed. The temporal parameters characterising this behaviour were not significantly different between animals, except for reaction times. In contrast, spatial parameters reflected in the distribution of vertical forces generated during the performance of the task were characteristic for each animal. As a consequence, a variety of strategies were employed. Nevertheless some general features were found, including the persistence of a diagonal support pattern during the phasic part of the movement, and an initial movement to the side of the forepaw performing the movement. The findings support the view that each animal exhibits a specific strategy for performing this well-learned task, and that the strategy is consistently employed over consecutive trials of the movement.

Animals↗