Postural Disequilibrium Research Articles

P22-F Quantitative balance assessment in SCA1 patients – longitudinal study

Background Spinocerebellar ataxia type 1 (SCA1) belongs to polyglutamine CAG repeat neurodegenerative disorders involving principally the cerebellum, brainstem and spinocerebellar tracts. One of the dominating symptoms is a postural disequilibrium. As there is need of biomarkers to follow the natural course of SCA we aimed to assess the progression of balance impairments by static posturography. Methods The subjects were: 26 symptomatic SCA1 patients (aged 39.2 ± 12.4 years, CAG 50.7 ± 6.3) with mean disease duration 5.5 ± 5.1 and 38 age- and gender- matched healthy controls (HC). They underwent static posturography during 5 years of observation. The movements of the center of feet pressure (COP) during quiet standing with eyes open (EO) and closed (EC) were evaluated by calculation of: mean radius, developed surface area and COP movement velocity. Severity of ataxia was evaluated with Scale for Assessment and Rating of Ataxia (SARA). Results All the COP sway measures have differed statistically significant from HC (p Conclusions Our study confirmed that quantitative posturography reflects objectively progression of postural disequilibrium in patients with ataxia. It might be a useful biomarker in the future therapeutic trials.

Lower regulatory frequency for postural control in patients with fibromyalgia and chronic fatigue syndrome.

As many similar symptoms are reported in fibromyalgia (FM) and chronic fatigue syndrome (CFS), underlying defcits may potentially also be similar. Postural disequilibrium reported in both conditions may thus be explained by similar deviations in postural control strategies. 75 females (25/group FM, CFS and control, age 19–49 years) performed 60 s of quiet standing on a force platform in each of three conditions: 1) firm surface with vision, 2) firm surface without vision and, 3) compliant surface with vision. Migration of center of pressure was decomposed into a slow and a fast component denoting postural sway and lateral forces controlling postural sway, analyzed in the time and frequency domains. Main effects of group for the antero-posterior (AP) and medio-lateral (ML) directions showed that patients displayed larger amplitudes (AP, p = 0.002; ML, p = 0.021) and lower frequencies (AP, p < 0.001; ML, p < 0.001) for the slow component, as well as for the fast component (amplitudes: AP, p = 0.010; ML, p = 0.001 and frequencies: AP, p = 0.001; ML, p = 0.029) compared to controls. Post hoc analyses showed no significant differences between patient groups. In conclusion, both the CFS- and the FM-group differed from the control group. Larger postural sway and insufficient control was found in patients compared to controls, with no significant differences between the two patient groups.

Postural Stabilization Strategies to Motor Contagion Induced by Action Observation Are Impaired in Parkinson's Disease.

Postural reactions can be influenced by concomitant tasks or different contexts and are modulated by a higher order motor control. Recent studies investigated postural changes determined by motor contagion induced by action observation (chameleon effect) showing that observing a model in postural disequilibrium induces an increase in healthy subjects’ body sway. Parkinson’s disease (PD) is associated with postural instability and impairments in cognitively controlled balance tasks. However, no studies investigated if viewing postural imbalance might influence postural stability in PD and if patients are able to inhibit a visual postural perturbation. In this study, an action observation paradigm for assessing postural reaction to motor contagion in PD subjects and healthy older adults was used. Postural stability changes were measured during the observation of a static stimulus (control condition) and during a point-light display of a gymnast balancing on a rope (biological stimulus). Our results showed that, during the observation of the biological stimulus, sway area and antero-posterior and medio-lateral displacements of center of pressure significantly increased only in PD participants, whereas correct stabilization reactions were present in elderly subjects. These results demonstrate that PD leads to a decreased capacity to control automatic imitative tendencies induced by motor contagion. This behavior could be the consequence either of an inability to inhibit automatic imitative tendencies or of the cognitive load requested by the task. Whatever the case, the issue about the ability to inhibit automatic imitative tendencies could be crucial for PD patients since it might increase falls risk and injuries.

Does focal mechanical stimulation of the lower limb muscles improve postural control and sit to stand movement in elderly?

Imbalance in elderly is a common problem strictly related to fall. This study investigates the possibility that a new protocol based on the focal mechanical muscle vibration may improve balance and stability in elderly. Pre-post non-randomized clinical trial has been used. Patients referring postural disequilibrium with negative vestibular bed-side examinations have been treated with focal muscle vibration applied to quadriceps muscles and evaluated before and immediately after therapy and after 1week and after 1month with postural stabilometric examination and with an inertial measurement units during the time up and go test. Stabilometric analysis showed statistically significant differences in both the area (p = 0.01) and sway (p < 0.01) of the center of pressure during the close eyes tests. Moreover, the global time of the time up and go test was reduced (p < 0.05) and the rotation velocity was increased (p < 0.01). The findings confirm the beneficial role of focal muscle vibration in elderly patients improve postural stability and mobility.

Contribution of Head Position, Standing Surface, and Vision to Postural Control in Community-Dwelling Older Adults

Postural control requires the integration of sensorimotor information to maintain balance and to properly position and orient the body in response to external stimuli. Age-related declines in peripheral and central sensory and motor function contribute to postural instability and falls. This study investigated the contribution of head position, standing surface, and vision on postural sway in 26 community-dwelling older adults. Participants were asked to maintain a stable posture under conditions that varied standing surface, head position, and the availability of visual information. Significant main and interaction effects were found for all three factors. Findings from this study suggest that postural sway responses require the integration of available sources of sensory information. These results have important implications for fall risks in older adults and suggest that when standing with the head extended and eyes closed, older adults may place themselves at risk for postural disequilibrium and loss of balance.

Selective skin sensitivity changes and sensory reweighting following short-duration space flight

Skin sensory input from the foot soles is coupled with vestibular input to facilitate body orientation in a gravitational environment. Anecdotal observations suggest that foot sole skin becomes hypersensitive following space flight. The veritable level of skin sensitivity and its impact on postural disequilibrium observed post space flight have not been documented. Skin sensitivity of astronauts (n = 11) was measured as vibration perception at the great toe, fifth metatarsal and heel. Frequencies targeted four classes of receptors: 3 and 25 Hz for slow-adapting (SA) receptors and 60 and 250 Hz for fast-adapting (FA) receptors. Data were collected pre- and post-space flight. We hypothesized that skin sensitivity would increase post-space flight and correlate to balance measures. Decreased skin sensitivity was found on landing day at 3 and 25 Hz on the great toe. Hypersensitivity was found for a subset of astronauts (n = 6) with significantly increased sensitivity to 250 Hz at the heel. This subset displayed a greater reduction in computerized dynamic posturography (CDP) equilibrium (EQ) scores (-54%) on landing vs. non-hypersensitive participants (-11%). Observed hyposensitivity of SA (pressure) receptors may indicate a strategy to reduce pressure input during periods of unloading. Hypersensitivity of FAs coupled with reduced EQ scores may reflect targeted sensory reweighting. Altered gravito-inertial environments reduce vestibular function in balance control which may trigger increased weighting of FAs (that signal foot contact, slips). Understanding modulations to skin sensitivity has translational implications for mitigating postural disequilibrium following space flight and for on-Earth preventative strategies for imbalance in older adults.

Do equilibrium constraints modulate postural reaction when viewing imbalance?

Action observation and action execution are tightly coupled on a neurophysiological and a behavioral level, such that visually perceiving an action can contaminate simultaneous and subsequent action execution. More specifically, observing a model in postural disequilibrium was shown to induce an increase in observers’ body sway. Here we reciprocally questioned the role of observers’ motor system in the contagion process by comparing participants’ body sway when watching displays of antero-posterior vs. lateral imbalance. Indeed, during upright standing, biomechanical constraints differ along the antero-posterior (A-P) and medio-lateral (M-L) axes; hence an impact of observers’ postural constraints on the contagion response would result in different reactions to both types of stimuli. In response to the displays, we recorded greater area of center of pressure (CoP) displacement when watching forward/backward compared to left/right imbalance. In addition, after normalizing A-P and M-L CoP displacements by a control condition (fixation cross), A-P CoP path length when viewing forward imbalance tended to be higher than M-L CoP path length when viewing imbalance to the left or right. These results indicate that postural contagion is promoted when the display is compatible with observers’ motor stabilization strategy which is mainly oriented along the A-P axis. In terms of clinical application, this study brings new indications for adaptation of observational training devices in rehabilitation programs.

The Halpern Syndrome of Monocular Visual Vertigo: A Rare Cause of Monocular Eye Closure

Background: Halpern syndrome is a vestibular disorder characterized by vertigo, a tendency to tilt to one side, and spontaneous closure of the ipsilateral eye. Symptoms are exacerbated during monocular viewing with the ipsilateral eye and alleviated during monocular viewing with the contralateral eye. It has long been attributed to a mismatch between visual and vestibular input.Methods: Reexamination of Halpern syndrome in light of new concepts of visuo-vestibular disease.Results: The visually dependent postural disequilibrium in Halpern syndrome recapitulates the dorsal light reflex in fish, in which unequal luminance input to the two eyes evokes a tilt of the body toward the brighter side.Conclusion: Patients with Halpern syndrome close one eye to restore vertical postural orientation. Halpern syndrome may result from reactivation the dorsal light reflex in the setting of central vestibular disease.

Ketamine Improves the Management of Exaggerated Postoperative Pain Observed in Perioperative Fentanyl-treated Rats

Although opioids are unsurpassed analgesics, experimental and clinical studies suggest that opioids activate N-methyl-d-aspartate pronociceptive systems leading to pain hypersensitivity and short-term tolerance. Because it is difficult in humans to differentiate pain from hyperalgesia during the postoperative period, the authors performed experimental studies with fentanyl using the rat incisional pain model for evaluating relations between hyperalgesia and short-term tolerance. Because N-methyl-d-aspartate receptor antagonists oppose both pain hypersensitivity and tolerance induced by opioids, the authors examined the capability of ketamine for improving exaggerated postoperative pain management. During halothane anesthesia, a hind paw plantar incision was performed in rats receiving four fentanyl subcutaneous injections (100 microg/kg per injection, every 15 min). In some groups, three subcutaneous ketamine injections (10 mg/kg per injection, every 5 h) were performed in saline- or fentanyl-treated rats. One day after surgery, the analgesic effect of morphine (2 mg/kg subcutaneous) was tested. Analgesia, mechanical hyperalgesia, tactile allodynia, and pain score were assessed for several days using the paw pressure vocalization test, the von Frey application test, and the postural disequilibrium test. Fentanyl induced analgesia but also produced exaggerated postoperative pain as indicated by the enhancement of hyperalgesia, allodynia, and weight-bearing decrease after hind paw plantar incision. Ketamine pretreatment prevented such a fentanyl-induced enhancement of postoperative pain and improved its management by morphine. By opposing postoperative pain hypersensitivity and subsequent short-term tolerance induced by perioperative opioid use, ketamine not only improves exaggerated postoperative pain management but also provides better postoperative rehabilitation.

Postural instability induced by virtual reality exposure: development of a certification protocol.

Exposure to virtual environments often causes users to experience symptoms of motion sickness. An accessory manifestation of motion sickness symptoms is postural disequilibrium. If the postural disequilibrium that occurs persists beyond the time an individual is within the confines of the laboratory or system site, user safety could be compromised and products liability issues could be forthcoming. In this study, a portable, automated postural assessment system is developed that can be employed before and after exposure to a virtual reality (VR) system in order to certify that a user's balance on exiting the system is at least demonstrably as good as it was on entering. It is argued that if the "coming out" balance performance is sufficiently poorer than the "going in" balance, then the user should be retained until the pretest balance performance is regained. The results from a set of normative and validation experiments on postural equilibrium identified several reliable measures of stance that could serve as a basis for certification. Furthermore, a new automated video-based measure using only head movement showed that performance over sessions is stable and reliable. The head movement changes that occur with stimuli, such as alcohol and simulator exposure, are well behaved, predictable, and significant even with small samples. The implication is that the proposed objective measure of postural stability, in conjunction with procedures for obtaining self-reports of symptoms, can afford some measure of certification that exposure to a given VR system is without harm.

Postural Disequilibrium following Adaptation to Virtual Environments: Concerns for Post Simulator Activity

Postural Disequilibrium following Adaptation to Virtual Environments: Concerns for Post Simulator Activity

Limitations of postural equilibrium tests for examining simulator sickness : K.M. Hamilton, L. Kantor and L.E. Magee 1989 Aviation, Space and Environmental Medicine60(3), 246–251

The psychometric properties of four ataxia tests and their sensitivities to disorientation were examined to assess their potential for measuring balance disturbances frequently reported with simulator sickness. The study was conducted in two parts. In the first, subjects practiced for 10 sessions to examine learning effects and to stabilize performance. In the second, the sensitivities of the four tests were examined by comparing performance before and after exposure to sensory conflict produced using a disorientation training flight simulator. Subjective measures of disorientation, including reports of postural disequilibrium, were also collected. The results indicated initial learning on all four ataxia measures. Two of the tests, the Stand on One Leg Eyes Closed and the Sharpened Romberg, exhibited acceptable levels of reliability. However, only the latter showed sufficient sensitivity to corroborate subjective reports of postural disequilibrium.

Postural Disequilibrium following Training Flights

The use of flight simulators for training military aircrew and commercial pilots has been increasing dramatically since World War II. However, the advantages of simulator training, such as cost-effectiveness and variety of missions which can be safely flown, may be offset by the occurrence of ataxia and other symptoms associated with simulator training. The present paper reports on postural disequilibrium following training in eight Navy flight simulators. Tests of standing steadiness were administered to 726 Naval and Marine Corps aviators prior to and then just following their regular flight training. Statistically significant ataxic effects were found following simulator exposure. The implications of these data for safety are discussed.

Postural equilibrium in adolescent idiopathic scoliosis.

Postural equilibrium has been quantified by stabilometry in 57 patients with adolescent idiopathic scoliosis aged 10-16 years. Treatment was required in 39 cases whereof 18 were placed under observation only. The control group comprised 32 healthy children of the same age. An experimental design was made to vary the degree of difficulty of upright standing in four different test situations. The postural sway was analysed in the sagittal and lateral direction as well as in the area of total sway. The scoliotic patients had a significantly poorer postural control compared with the healthy children in all the tests. The difference was most pronounced in tests in which the proprioceptive functions were most important for maintaining the postural equilibrium. The left convex patients had quantitatively more pronounced reactions than the right convex patients. Patients with small curvatures, i.e., patients placed under observation only, had significantly increased postural sway compared with patients with more severe deformity. This fact, together with findings in patients with double primary curvatures, and the results of the study of brace effects, indirectly indicate the possibility of a postural disequilibrium as a contributory causative factor in adolescent idiopathic scoliosis.

THE EFFECT OF EXPERIMENTALLY-INDUCED STRESS ON PENTYLENETETRAZOL SEIZURE THRESHOLD IN MICE.

The effect of 20 min of intermittent foot shock on spontaneous activity and overt behavior was studied in mice. In addition, the effect of a pain-induced conditioned emotional response, and of total body immobilization and postural disequilibrium on the pentylenetetrazol seizure threshold was determined. Foot shock decreased spontaneous motor activity, and induced responses characterized by immobility, crouching, and increased defecation. The pain-induced conditioned emotional response, total body immobilization, and postural disequilibrium all lowered seizure threshold. Data are presented which indicate that there is a direct relation between the reduction in seizure threshold and the intensity of the disturbed emotional state. In addition, it is suggested that the observed increase in brain excitability caused by apprehension and anxiety may result from the effect of endogenouslyreleased catecholamines on the central nervous system. Reference is made to the relation between these findings and the effect of emotional disturbances on seizure frequency in human epileptics.