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PubMed1991

Dose-related effect of triazolam on postural sway.

Measurement of clinically relevant benzodiazepine drug effects at hypnotic and anxiolytic doses has been difficult because most measures are subjective, difficult to interpret, or relate to anesthetic doses. A potentially useful measure of drug effect is postural sway, which is a manifestation of the corrective mechanisms associated with the maintenance of upright posture. Postural sway was measured over 8 hours, with a biomechanics force platform, in six healthy male volunteers who received triazolam, 0.125, 0.250, or 0.375 mg, or placebo in a randomized double-blind study. Our results show a dose-dependent increase in postural sway measured as the elliptical area or the 95% confidence ellipse for the area covered by the subjects' sway. After triazolam, 0.250 and 0.375 mg, the area under the sway-time curve and peak effect increased significantly compared with placebo (p less than 0.05). The number of losses of balance when subjects stood on one foot also showed a significant increase with increased dose (p less than 0.05). The rate of loss of balance was positively correlated with the extent of postural sway (r = 0.802; p less than 0.001). The extent of sway when the subjects were drug free predicted this increase in a subject's postural sway with triazolam. Thus at hypnotic or anxiolytic doses of triazolam, computer-assisted force platform measures of sway provide a clinically relevant measure of drug effect. Measurement of drug-induced postural sway may be useful in persons at risk for falls, such as the elderly.

Adult↗

PubMed2005

Postural control and detection of slip/fall initiation in the elderly population.

One of the common causes of morbidity and mortality in workplaces is related to slips or falls. Reaction to external disturbances, such as slips or falls, requires a process of perturbation detection and control of motion changes. Postural control is a common mechanism to compensate unexpected displacements of the body. The ability of postural control diminishes with ageing or neuropathy. In this study, two controlled groups, diabetics and non-diabetics in the elderly population, were investigated to compare how different postural control mechanisms would relate to the detection of perturbation and regain of balance. The ultra-low-vibration Sliding Linear Investigative Platform for Analyzing Lower Limb Stability SYSTEM was used to measure the biomechanical changes of posture and perturbation detection. In phase 1 of the analysis, static measures during quiet standing were considered to investigate the relationship between postural stability and perturbation detection capability. In phase 2 of the analysis, dynamic measures during an occurrence of perturbation were analysed. Statistical tests and linear logistic regression models were applied to find differences of postural control mechanisms and to build a predictive model for perturbation detection quantitatively. It is anticipated that the results of this study will contribute to more comprehensive understanding of postural control mechanisms and design of slip/fall prevention programmes.

Acceleration↗

PubMed2002

Postural instability in idiopathic Parkinson's disease: the role of medication and unilateral pallidotomy.

Postural instability (PI) is common in idiopathic Parkinson's disease (IPD). We measured sensory and motor contributions to PI in 50 patients with advanced IPD, off and on medication and in a subset pre- and 3, 6 and 12 months post-unilateral pallidotomy, using computerized dynamic posturography [specifically, the Sensory Organization Test (SOT) and the Unified Parkinson's Disease Rating Scale (UPDRS) subscale PIGD (Postural Instability and Gait Disorder)]. Off medication, all patients had abnormal PIGD scores. The group could be separated into those with normal SOT equilibrium scores (SOTN) and those, the majority, with abnormal postural control when sensory feedback was limited (SOTABN). Medication improved the PIGD scores but worsened the SOT scores in the majority of patients. Increases in spontaneous sway in some patients contributed to the negative effect of medication on SOT scores. However, this could not explain the detrimental effect of medication on SOT scores in at least 40% of patients. On the other hand, pallidotomy improved both PIGD and SOT scores in both groups. A predictor of good outcome from pallidotomy concerning PI was the degree of worsening of the effect that medication had on SOT5 scores. PI in IPD appears to be multifactorial. We propose that the PIGD score reflects sensory and motor aspects of postural control, with normal sensory feedback, while the SOT equilibrium scores measure the sensory organizational process of postural control in the presence of altered sensory inputs. There is a dissociation between the effects of medication and pallidotomy on motor and sensory components of postural control, which may reflect the underlying pathophysiological mechanism responsible for these different components of PI. We suggest that patients with advanced IPD and PI on medication should consider adjuvant surgical treatment for better postural control.

Adult↗

PubMed1999

Postural set for balance control is normal in Alzheimer's but not in Parkinson's disease.

BACKGROUND: It has been suggested that patients with dementia of the Alzheimer type have abnormalities in the basal ganglia, and thus, may have similar sensorimotor problems as patients with basal ganglia degeneration from Parkinson's disease. Whether the similarity extends to balance control is unknown. One distinguishing feature of balance disorder in Parkinson's disease is difficulty with changing postural set in terms of adapting the amplitude of leg muscle activity as a function of support condition. We, therefore, tested whether patients with Alzheimer's disease without extrapyramidal signs would show a similar problem in changing postural set as patients with Parkinson's disease. METHODS: The ability to quickly change postural set was measured by comparing leg muscle activity under two conditions of support (free stance, versus grasping a frame, or sitting) during backward surface translations, during toes up surface rotations, and during voluntary rise to toes. Results were compared among 12 healthy adults, 8 nondemented Parkinson's patients on their usual dose of medication, and 11 Alzheimer patients without extrapyramidal signs. RESULTS: Subjects with Alzheimer's, but not Parkinson's, disease performed similarly to the healthy control subjects. They changed postural set immediately, by suppressing leg muscle activity to low levels when supported. Parkinson subjects did not change postural set immediately. They did not suppress the tibialis anterior in voluntary rise to toes when holding, nor the soleus in perturbed sitting as much as the healthy control and Alzheimer subjects in the first trial. Instead, the Parkinson subjects changed set more slowly, over repeated and consecutive trials in both protocols. The onset latencies of soleus responses to backward surface translations and perturbed sitting, as well as tibialis anterior responses to toes up rotations, were the same for all three groups. CONCLUSION: Alzheimer patients without extrapyramidal signs, unlike nondemented Parkinson's disease patients, have no difficulty in quickly changing postural set in response to altered support conditions. Our results, therefore, do not support the hypothesis that Parkinson's and uncomplicated Alzheimer's diseases share common postural set problems that may contribute to disordered balance control.

Adaptation, Physiological↗

PubMed1986

Postural reactions in infants with Down syndrome. Relationship to motor milestone development and age.

I examined the emergence of automatic postural reactions (righting, equilibrium, and protective reactions) in a group of infants with Down syndrome and in a developmentally matched group of nonhandicapped infants. I assessed the relationship of postural reactions to chronological age and to motor milestone development (as measured by the Bayley Scales of Infant Development). The relationship of postural reactions to chronological age was weaker in the infants with Down syndrome; a regression analysis revealed a slower rate of postural reaction development evident at an age of about five months and older in infants with Down syndrome. The association between postural reactions and motor milestone performance was remarkably similar for both infant groups in degree of association and pattern across the span of motor development tested. The results indicated that, even though the rate of development differed, the association between postural reactions and motor milestones was similar in normal and delayed development. These results support the current rationale that promotes intervention efforts focusing on the facilitation of postural reactions to enhance motor milestone development in infants with Down syndrome.

Age Factors↗

PubMed1990

Changes in posture control across the life span--a systems approach.

In this article, a systems approach to the development of posture control across the life span and its integration with voluntary tasks such as walking is described. Research shows a clear cephalocaudal gradient in the development of postural responses. Postural muscle synergies develop appropriate temporal organization through experience in each new level of postural skill development. Sensory inputs contributing to posture control influence postural responses very early in development, with responses being elicited by vision alone, or by somatosensory and vestibular cues in isolation. Studies of older adults indicate small, but significant, increases in onset latencies and disruptions in the temporal organization of postural muscle responses when subjects are given external threats to balance. In addition, older adults, like young children, use antagonist muscles more often in coactivation with agonist muscles. Older adults also have more difficulty balancing when sensory inputs are reduced experimentally or pathologically. Ankle dorsiflexor muscle weakness is also a factor in balance dysfunction in the older adult.

Aging↗

PubMed1997

Postural perturbations: new insights for treatment of balance disorders.

This article reviews the neural control of posture as understood through studies of automatic responses to mechanical perturbations. Recent studies of responses to postural perturbations have provided a new view of how postural stability is controlled, and this view has profound implications for physical therapy practice. We discuss the implications for rehabilitation of balance disorders and demonstrate how an understanding of the specific systems underlying postural control can help to focus and enrich our therapeutic approaches. By understanding the basic systems underlying control of balance, such as strategy selection, rapid latencies, coordinated temporal spatial patterns, force control, and context-specific adaptations, therapists can focus their treatment on each patient's specific impairments. Research on postural responses to surface translations has shown that balance is not based on a fixed set of equilibrium reflexes but on a flexible, functional motor skill that can adapt with training and experience. More research is needed to determine the extent to which quantification of automatic postural responses has practical implications for predicting falls in patients with constraints in their postural control system.

Biomechanical Phenomena↗

PubMed1988

Response preparation and posture control. Neuromuscular changes in the older adult.

Experiments comparing the characteristics of neuromuscular responses underlying balance control in young and old adults have shown a number of differences between the two populations. Postural muscle response latencies of the ankle musculature activated by external threats to balance are slightly, but significantly, longer in the latter population. In addition, some aging subjects show a temporal reversal of proximal and distal muscle response onset in some trials. There is also a breakdown of the correlation of the amplitude of the muscle responses within a synergy in some of the older subjects tested. Older adults also exhibited cocontraction of agonist and antagonist muscles within a response synergy to a greater extent than young adults. This stiffening of the joints by antagonist cocontraction could be a compensation for the lack of the ability to fine-tune the postural responses to the same degree as the young adults. Analysis of sensory integration abilities showed an impairment in balance control under conditions of reduced or conflicting sensory information. When they were given inappropriate visual and somatosensory inputs, half of the older adults lost balance on the first trial. In most instances, however, the older adults were able to maintain balance during a second trial consisting of the same sensory stimuli. When visual cues were reduced by restricting the visual field to either central or peripheral visual cues, we found no difference in postural muscle response latencies. However, the aging adult group showed more losses of balance than the younger group with peripheral vision removed or with eyes closed. In addition, there was a strong correlation between the subjects that showed stronger deficits on an initial neurological exam and the number of times that balance was lost. Studies on changes in the linkage between postural and voluntary muscle interactions during voluntary arm movements in older adults indicate an increase in the latency of feed-forward activation of postural muscles. However, voluntary muscle response onset latencies show greater increases in the old compared to the young. This suggests that deterioration of the speed of activation of the postural control system is not the only factor that limits the speed of voluntary movement onset. Measurements have not yet been made on the amplitude regulation of feed-forward responses of postural muscles during a voluntary task. It may be that the regulation of the speed of activation of the two systems is less important than the fine tuning of the correlation of appropriate response amplitudes between the two systems.(ABSTRACT TRUNCATED AT 400 WORDS)

Aged↗

PubMed1992

Recovery of postural equilibrium control following spaceflight.

Decreased postural stability is observed in most astronauts immediately following spaceflight. Because ataxia may present postflight operational hazards, it is important to determine the incidence of postural instability immediately following landing and the dynamics of recovery of normal postural equilibrium control. It is postulated that postflight postural instability results from in-flight adaptive changes in central nervous system (CNS) processing of sensory information from the visual, vestibular, and proprioceptive systems. The purpose of the present investigation was to determine the magnitude and time course of postflight recovery of postural equilibrium control and, hence, readaptation of CNS processing of sensory information. Thirteen crew members from six spaceflight missions were studied pre- and postflight using a modified commercial posturography system. Postural equilibrium control was found to be seriously disrupted immediately following spaceflight in all subjects. Readaptation to the terrestrial environment began immediately upon landing, proceeded rapidly for the first 10-12 hours, and then proceeded much more slowly for the subsequent 2-4 days until preflight stability levels were reachieved. It is concluded that the overall postflight recovery of postural stability follows a predictable time course.

Adult↗

PubMed2003

Postural stability in the elderly during sensory perturbations and dual tasking: the influence of refractive blur.

PURPOSE: To determine the influence of refractive blur on postural stability during somatosensory and vestibular system perturbation and dual tasking. METHODS: Fifteen healthy, elderly subjects (mean age, 71 +/- 5 years), who had no history of falls and had normal vision, were recruited. Postural stability during standing was assessed using a force platform, and was determined as the root mean square (RMS) of the center of pressure (COP) signal in the anterior-posterior (A-P) and medial-lateral directions collected over a 30-second period. Data were collected under normal standing conditions and with somatosensory and vestibular system perturbations. Measurements were repeated with an additional physical and/or cognitive task. Postural stability was measured under conditions of binocular refractive blur of 0, 1, 2, 4, and 8 D and with eyes closed. The data were analyzed with a population-averaged linear model. RESULTS: The greatest increases in postural instability were due to disruptions of the somatosensory and vestibular systems. Increasing refractive blur caused increasing postural instability, and its effect was greater when the input from the other sensory systems was disrupted. Performing an additional cognitive and physical task increased A-P RMS COP further. All these detrimental effects on postural stability were cumulative. CONCLUSIONS: The findings highlight the multifactorial nature of postural stability and indicate why the elderly, many of whom have poor vision and musculoskeletal and central nervous system degeneration, are at greater risk of falling. The findings also highlight that standing instability in both normal and perturbed conditions was significantly increased with refractive blur. Correcting visual impairment caused by uncorrected refractive error could be a useful intervention strategy to help prevent falls and fall-related injuries in the elderly.

Aged↗

PubMed1989

Age related decline in postural control mechanisms.

In order to study voluntary and reflexive mechanisms of postural control, young and elderly persons were given large-fast and small-slow ankle-rotation postural disturbances while standing on a movable platform capable of measuring ground reaction forces. Large-fast rotations were employed to activate long-loop reflexes, and small-slow rotations were employed to tap the higher level sensory integration aspects of postural control. Overall, the elderly persons exhibited more perturbation induced sway and showed a slowing in voluntary, as opposed to reflexive mechanisms of correcting postural disturbance. For both age groups, reflexive mechanisms were found to be relatively intact. When small perturbations were given, the elderly persons swayed more than young participants and produced sporadic reflexive activity. Moreover, elderly persons did not adapt to the small perturbations and exhibited increased postural sway to repetitive presentation of the perturbation, whereas young participants substantially decreased their postural sway. These data demonstrate that elderly persons are at some disadvantage when posture is under the control of slower, higher level sensory integrative mechanisms.

Adult↗

PubMed2000

Study of anticipatory postural adjustments in an air pistol-shooting task.

A segmental teleokinetic movement performed from an upright standing position is usually preceded by a sequence of postural movements having the goal of counteracting the imbalance which will be caused by the forthcoming movement. This study had two aims, (1) to verify whether the postural component was programmed in the same way as that of the teleokinetic component and (2) to verify whether the postural component was specific to the direction and speed of the movement. 12 participants performed a pistol-shooting task involving a rapid arm-raising movement. Three directions, two time deadlines, and three types of cue were manipulated. This study showed that the postural component was sensitive to the cue effects, the characteristics of anticipatory postural adjustments were specific to the direction of the movement, and the characteristics of the postural muscle EMG burst were the same whether the participants programmed or deprogrammed and reprogrammed their movements for a given direction. The speed parameter did not seem to have any significant influence on the characteristics of the anticipatory postural adjustments.

Adolescent↗

PubMed1989

A control systems framework for understanding normal and abnormal posture.

This paper presents a brief overview of a control systems framework for understanding normal and abnormal posture, with a special emphasis on postural control during arm movements. The need for meaningful and valid definitions of postural output is discussed. A distinction is drawn between the joint posture and balance outputs of the system. The roles of commands and perturbing inputs in controlling and disturbing joint posture and balance are described. The effects of initial conditions on command inputs and postural outputs are considered. Mechanisms for correcting postural errors are described, with a major focus on active closed-loop and open-loop control processes. The method of objectively describing system behavior by the gains, time delays, and thresholds of input-output functions is presented. All concepts are developed in relation to their clinical implications.

Arm↗

PubMed1999

Postural compensation after intratympanic gentamicin treatment of Menière's disease.

We have treated 93 patients with severe Menière's disease with gentamicin (GM) applied with 1 to 4 or intratympanic injections in a prospective study. The patients were tested at frequent intervals and followed up for two years. Postural stability was evaluated on posturography. Unsteadiness and gait between attacks, working capacity and vertigo were scored. Before commencing the treatment 47 of the patients complained from moderate to severe postural instability. After treatment moderate to severe postural instability was met in 19 patients. Initially the sway velocity was 27 mm/s on average being significantly worse than in referents. Two weeks after treatment the sway velocity increased to 33 mm/s. Thereafter the sway velocity slowly started to decline to 31 mm/s after two years. Patients with severe attacks of rotatory vertigo had a good postural outcome with GM treatment. In logistic regression analysis the most significant risk factor for poor recovery after GM treatment was severely reduced gait before commencing the treatment with odds ratio of 2.0. Subjectively, after two years, the patients rated their postural stability significantly improved when compared to pretreatment values. The good subjective rating of postural stability is related to postural training program where in the absence of attacks, the patients have learned to cope with daily tasks.

Adult↗

PubMed1999

[Postural balance following stroke: towards a disadvantage of the right brain-damaged hemisphere].

In the light of studies published in the last ten years, we have suspected a differential influence of the sides of hemispheric cerebral lesions on posture and balance. A study was aimed at verifying this hypothesis, the method of which being original because many possible confounding factors such as age, sex as well as topography and size of the brain lesion have been taken into account in the statistical analysis. Inclusion criteria were: right-handed patients, first stroke, no previous disease which might have affected balance. Their postural abilities (ranging from 0 to 36) were assessed 90 +/- 3 days after stroke onset on a clinical scale. This clinical assessment was used here because it could be easily performed in all patients, irrespective of the severity of their impairment. Lesion locations were determined using the Atlas by Talairach and Tournoux and the number of cerebral areas altered gave an estimation of the lesion size. The first fifty patients consecutively admitted to rehabilitation and responding to the inclusion criteria were thus examined (25 with a right and 25 with a left hemispheric lesion; 14 women and 36 men; mean age 57.2 = yrs). The main result was lower postural performances in right brain-damaged patients than in left brain damaged patients (21.5 vs 29.4; p = 0.01). Postural abilities were also inversely related to age (r = -0.28; p = 0.04), lesion size (r = -0.41; p = 0.003) and were lower in women than in men (22.1 vs 28.8; p = 0.02). This study therefore confirms the existence of a right hemispheric dominance for postural control. The existence of inverse correlation between postural abilities and the number of omitted targets in cancellation task on one hand (r = -0.63, p < 0.001), the ipsilesional bias in line bissection on the other hand (r = -0.36; p = 0.01), argued for a relationship between the main result of this study and the well known cerebral organization of spatial information processing, based on a right hemisphere dominance for spatial attention and/or representation. The 'postural neglect' concept is discussed.

Aged↗

PubMed1999

The role of vision on postural strategy evaluated in patients affected by congenital nystagmus as an experimental model.

The role of vision in postural control is crucial and is strictly related to the characteristics of the visual stimulus and to the performance of the visual system. The purpose of this investigation was to evaluate the effects of chronically reduced visual cues upon postural control in patients affected by Congenital Nystagmus (CN). These patients have developed since birth a postural strategy mainly based on vestibular and somatosensorial cues. Fifteen patients affected by CN and 15 normal controls (NC) were enrolled in the study and evaluated by means of dynamic posturography. The overall postural control in CN patients was impaired as demonstrated by the equilibrium score and by the changes of the postural strategy. This impairment was even more enhanced in CN than in NC group when somatosensorial cues were experimentally reduced. An aspecific pattern of visual impairment and a pathological composite score were also present. Our data outline that in patients affected by CN an impairment of the postural balance is present especially when the postural control relies mainly on visual cues. Moreover, a decrease in accuracy of the somatosensory cues has a proportionally greater effect on balance than it has on normal subjects.

Adult↗

PubMed2000

[Posture and aging. Current fundamental studies and management concepts].

FUNDAMENTAL IMPORTANCE OF POSTURE: In the elderly subject, preservation of posture is fundamental to maintaining functional independence. In recent years, there has been much progress in our understanding of the mechanisms underlying strategies used to control equilibrium in the upright position. Physiological aging, associated with diverse disease states, dangerously alters the postural function, particularly anticipated adjustments which allow an adaptation of posture to movement. CLINICAL ASSESSMENT OF POSTURE: Several tests have been developed to assess posture in the elderly subject, particularly the time it takes to start walking. We selected certain tests which can be used in everyday practice to predict falls: the stance test, the improved Romberg test, the "timed get up and go test", measurement of walking cadence, assessment of balance reactions, sitting-standing and standing-sitting movements and capacity to get up off the floor. PATIENT CARE: Elderly patients with equilibrium disorders can benefit from specific personalized rehabilitation protocols. Different techniques have been developed for multiple afferential stimulation, reprogramming postural strategies, and correcting for deficient motor automatisms.

Accidental Falls↗

PubMed2002

Postural control and venous gas bubble formation during hypobaric exposure.

BACKGROUND: Earlier studies have shown that acute hypoxia at simulated altitudes up to 18,000 ft affects postural control. The main objective of this study was to investigate whether this is caused by hypoxia or by other effects of reduced barometric pressure. Doppler monitoring was included to rule out venous gas emboli (VGE) as a possible cause of disturbed postural control. A secondary objective was to evaluate two conventional altitude chamber training profiles regarding release of VGE. HYPOTHESIS: Chamber flights up to 18,000 ft affect postural control due to acute hypoxia or other effects of reduced barometric pressure such as bubble formation. VGE probably will not be formed at the altitude chamber flight profiles and procedures selected for this study. METHODS: Repeated registrations of postural control and Doppler monitoring for detection of possible VGE were performed on 12 subjects before, during, and after exposure to two different altitude chamber flight profiles. In chamber flight profile 1 the subjects were first preoxygenated for 45 min and then exposed to a normoxic environment at altitudes of 25,000, 18,000, 14,000, and 8000 ft. Chamber flight profile 2 consisted of an 80 min exposure to 14,000 ft without preoxygenation or supplemental oxygen for the first 60 min. RESULTS: In chamber flight profile 1, where normoxic conditions were achieved during all balance testing, no significant changes in postural control were found. No VGE were observed and no subjective dizziness was reported during this exposure. In chamber flight profile 2, a significant influence on postural control was reported for the eyes-open condition, when breathing air at 14,000 ft. These changes normalized when reaching ground level. VGE were observed in one of the 12 subjects after 75 min at 14,000 ft. Another subject complained of severe dizziness during the initial part of the decompression to 14,000 ft, and was excluded from further experiments. CONCLUSIONS: Changes in postural control at altitudes up to 18,000 ft is probably due to acute hypoxia. VGE may form during acute altitude exposure to 14,000 ft.

Adult↗