What can posturography tell us about vestibular function?

Balance alterations are associated with neck pain and neck muscle endurance in migraine

BACKGROUND

Migraine patients may present with both cervical and balance dysfunctions. The neck plays an important role in balance by providing substantial proprioceptive input, which is integrated in the central nervous system and influences the balance control systems. Whether balance and neck dysfunctions are associated in patients with migraine is still to be explored.

OBJECTIVES

This study aimed to assess the association between the sensory organization test of balance with neck pain features, cervical strength, endurance, and range of motion in patients with migraine.

METHODS

Sixty-five patients with migraine underwent the sensory organization test assessed with the Equitest-Neurocom® device. Maximum voluntary isometric contraction, cervical flexion and extension range of motion, and cervical flexor and extensor endurance were assessed. In addition, the features of migraine and neck pain were collected. Patients were dichotomized according to cut-off scores of balance performance and the association between outcomes were explored.

RESULTS

Patients with reduced balance performance presented a higher frequency of migraine (p = 0.035), a higher frequency of aura (p = 0.002), greater neck pain intensity (p = 0.013), and decreased endurance of cervical flexors (p = 0.010) and extensors (p < 0.0001). The total balance score was correlated with age (r = -0.33; p = 0.007), migraine frequency (r = -0.29; p = 0.021), neck pain intensity (r = -0.26; p = 0.038), and endurance of the cervical flexors (r = 0.39; p = 0.001) and extensors (r = 0.36; p = 0.001). Migraine frequency, neck pain intensity, and endurance of the cervical flexors can predict 21% of the sensory organization test variability.

CONCLUSION

Neck pain features and endurance of the cervical muscles are related to reduced balance performance in patients with migraine. These results shed light to a better understanding of balance alterations in migraine patients.

A modified two-dimensional sensory organization test that assesses both anteroposterior and mediolateral postural control

Background

The Sensory Organization Test (SOT) was designed to measure changes in postural control in response to unreliable visual and/or proprioceptive feedback. However, secondary to the manipulation of sensory cues in only the sagittal plane, the SOT is capable of only describing postural control in a single direction. The present study aimed to characterize postural responses to a modified SOT designed to concurrently challenge both anteroposterior and mediolateral postural control.

Methods

Twenty-one healthy adult volunteers (30.6 ± 10.2 years) completed the standard anteroposterior one-dimensional (1D) SOT, in addition to a modified SOT with the support surface sway-referenced to both anteroposterior and mediolateral postural sway (two-dimensional, 2D). Our primary analysis concerned a comparison of mediolateral, as well as anteroposterior postural sway measured during the standard one-dimensional (i.e., pitch tilt) and the novel two-dimensional (i.e., roll and pitch tilt) sway-referenced paradigms. Here, postural sway was quantified by calculating the root mean square distance (RMSD) of the center of pressure (CoP) during each trial.

Results

Our data showed that the 2D sway-referenced conditions yielded a selective increase in mediolateral postural sway relative to the standard 1D conditions for both wide (η2 = 0.66) and narrow (η2 = 0.78) stance conditions, with anteroposterior postural sway being largely unaffected (η2 = 0.001 to 0.103, respectively). The ratio between mediolateral postural sway in the sway-referenced conditions and postural sway in the corresponding stable support surface conditions was greater for the 2D (2.99 to 6.26 times greater) compared to 1D paradigms (1.25 to 1.84 times greater), consistent with a superior degradation of viable proprioceptive feedback in the 2D paradigm.

Conclusion

A modified 2D version of the SOT was shown to provide a greater challenge to mediolateral postural control relative to the standard 1D SOT protocol, putatively as a result of a superior capacity to degrade proprioceptive feedback in the mediolateral direction. Given these positive findings, future studies should investigate the clinical utility of this modified SOT as a means by which to better characterize sensory contributions to postural control in the presence of various sensorimotor pathologies, including vestibular hypofunction.

Balance control impairments in Fabry disease

Background

Fabry disease (FD) is a rare inherited lysosomal storage disorder caused by the deficiency of the enzyme alpha-galactosidase A. This deficiency leads to an accumulation of glycosphingolipids leading to progressive and multisystemic disease, including renal, cardiac, and neurological damages. FD may also have neuro-otological and visual impairments, which can generate postural control alterations, inner ear, and vision being involved in this function. This study aimed to evaluate the impact of FD on postural control.

Methods

In total, fourteen adult patients (8 men/6 women, mean age = 37.6 ± 11.4 years) and two children (mean age = 11 years) with FD and 19 healthy adults (12 men/7 women, mean age = 36.5 ± 16.9 years) and two healthy children (mean age = 10.5 years) took part in this study. Postural control was evaluated by a sensory organization test combining three visual situations (eyes open, eyes closed, and sway referenced visual surround motion) with two platform situations (stable platform and sway referenced platform motion), aiming to calculate a composite equilibrium score (CES), a high score being representative of good postural control. Somatosensory (R^SOM), visual (R^VIS), and vestibular (R^VEST) contributions to postural control were calculated, a low score reflecting a poor use of the indicated sensory input.

Results

The CES was lower in adult patients with FD compared with the healthy subjects (p < 0.001). R^VIS (p = 0.001) and R^VEST (p = 0.003) were lower in patients with FD compared with the control group, whereas no difference in R^SOM was observed.

Conclusion

Inner ear and visual pathologies associated with the central nervous system impairments are factors of postural control impairments. Physical activities, which can also be rehabilitative, by maintaining or increasing the weight of proprioception, may help diminish dependency on altered sensorial inputs.

Migraine and balance impairment: Influence of subdiagnosis, otoneurological function, falls, and psychosocial factors

OBJECTIVE

To assess the balance sensory organization among patients with migraine, considering the influence of migraine subdiagnosis, otoneurological function, falls, and psychosocial factors.

BACKGROUND

Migraine has been associated with vestibular symptoms and balance dysfunction; however, neither comprehensive balance assessment nor associated factors for greater impairment have been addressed thus far.

METHODS

Patients from a tertiary headache clinic with a diagnosis of episodic migraine with aura (MWA), without aura (MWoA), and chronic migraine (CM) were included for this cross-sectional study (30 patients per group). Thirty headache-free controls (CG) were recruited. Participants underwent a comprehensive evaluation protocol, including the Sensory Organization Test (SOT) and otoneurological examination. Questionnaires about fear of falls, dizziness disability, and kinesiophobia were administered.

RESULTS

All migraine groups presented lower composite SOT scores than controls (CG: 82.4 [95% confidence interval (CI): 79.5-85.3], MWoA: 76.5 [95% CI: 73.6-79.3], MWA: 66.5 [95% CI: 63.6-69.3], CM: 69.1 [95% CI: 66.3-72.0]; p < 0.0001). Compared to controls and to MWoA, MWA and CM groups exhibited greater vestibular (CG: 75.9 [95% CI: 71.3-80.4], MWoA: 67.3 [95% CI: 62.7-71.8], MWA: 55.7 [95% CI: 51.2-60.3], CM: 58.4 [95% CI: 53.8-63.0]; p < 0.0001) and visual functional impairment (CG: 89.6 [95% CI: 84.2-94.9], MWoA: 83.2 [95% CI: 77.9-88.6], MWA: 68.6 [95% CI: 63.3-74.0], CM: 71.9 [95% CI: 66.5-77.2], p < 0.0001). Fall events during the assessment were documented more often among patients with migraine (CG: 0.0, interquartile range [IQR], 0.0, 0.0); MWoA: 1.0 [IQR: 1.0, 1.0], MWA: 2.0 [IQR: 1.8, 4.3], CM: 1.0 [IQR: 1.0, 2.0]; p = 0.001). The SOT scores correlated with fear of falls (r = -0.44), dizziness disability (r = -0.37), kinesiophobia (r = -0.38), and migraine frequency (r = -0.38). There was no significant influence of the vestibular migraine diagnosis in the study outcomes when used as a covariate in the analysis (composite score [F = 3.33, p = 0.070], visual score [F = 2.11, p = 0.149], vestibular score [F = 1.88, p = 0.172], somatosensory score [F = 0.00, p = 0.993]).

CONCLUSIONS

Aura and greater migraine frequency were related to falls and balance impairment with sensory input manipulation, although no otoneurological alterations were detected. The diagnosis of vestibular migraine does not influence the balance performance. The vestibular/visual systems should be considered in the clinical examination and treatment of patients with migraine.

The effect of latin dance on dynamic balance

BACKGROUND

Figures and movements in Latin dance are effectively used to provide posture stabilization and balance control. A Computerized Dynamic Posturography can be used to complete a functional evaluation of postural control and stability in static and dynamic conditions, mediated by the interaction between the visual, vestibular, and somatosensory systems.

RESEARCH QUESTION

According to the results of Computerized Dynamic Posturography, do dancers have better postural control and stability when compared to non-dancers, and can dance activity be recommended for vestibular rehabilitation?

MATERIAL AND METHODS

Our study included 26 professional Latin dancers and 26 non-dancers as a control group whoboth had no problems with their hearing or balance. Pure-tone audiometry and Computerized Dynamic Posturography tests were applied to the participants. The test results for the professional dancers and the control group were compared and evaluated. In statistical analysis, the Mann-Whitney U and Independent Samples T tests were used. A value of p < 0.05 was accepted for significance.

RESULTS

According to the results of the Computerized Dynamic Posturography, the dancers generally performed better than the control group. While statistically significant and better performances were observed in dancers in terms of the composite balance, visual and vestibular scores within the scope of the Sensory Organization Test (p < 0.05), no statistically significant difference was found for somatosensory and preference scores (p > 0.05). Also, significant differences were obtained between the two groups in some subtests of Adaptation, Unilateral Stance and Limits of Stability assessment (p < 0.05). No significant difference was observed in Rhythmic Weight Shift results (p > 0.05).

IMPORTANCE

The results of thisresearch demonstrate that balance and posture improve through dance. Therefore, adding appropriate dance activities to vestibular rehabilitation programmes might be helpful.

Effect of Smartphone Use on Static and Dynamic Postural Balance in Healthy Young Adults

Purpose The purpose of this study was to investigate the possible effects of smartphone usage in the biomechanical balance system. Method Twenty-five healthy young adults (10 men, 15 women) between the ages of 18 and 25 years without balance problems were included in the study. Sensory organization, adaptation, rhythmic weight shift, and functional limitation tests (unilateral stance, sit to stand, walk across, tandem walk, step quick turn, step up down, forward lunge) have been applied. Results Significant results were obtained in parameters of sensory organization, tandem walk, walk across, and unilateral stance tests (p < .05). Conclusion The effects of using smartphones on postural control and balance in different circumstances, such as standing and walking, must be comprehensively determined to prevent accident.

A Novel Head Mounted Display Based Methodology for Balance Evaluation and Rehabilitation

In this paper, we present a new augmented reality (AR) head mounted display (HMD)-based balance rehabilitation method. This method assesses the individual’s postural stability quantitatively by measuring head movement via the inertial measurement unit sensor integrated in the AR HMD. In addition, it provides visual feedback to train through holographic objects, which interacts with the head position in real-time. We implemented applications for Microsoft HoloLens and conducted experiments with eight participants to verify the method we proposed. Participants performed each of three postural tasks three times depending on the presence or absence of augmented reality, the center of pressure (COP) displacement was measured through the Wii Balance Board, and the head displacement was measured through the HoloLens. There are significant correlations (p < 0.05) between COP and head displacement and significant differences (p < 0.05) between with/without AR feedback, although most of them were not statistically significant likely due to the small sample. Despite the results, we confirmed the applicability and potential of the AR HMD-based balance rehabilitation method we proposed. We expect the proposed method could be used as a convenient and effective rehabilitation tool for both patients and therapists in the future.

Head Down Tilt Bed Rest Plus Elevated CO2 as a Spaceflight Analog: Effects on Cognitive and Sensorimotor Performance

Long duration head down tilt bed rest (HDBR) has been widely used as a spaceflight analog environment to understand the effects of microgravity on human physiology and performance. Reports have indicated that crewmembers onboard the International Space Station (ISS) experience symptoms of elevated CO₂ such as headaches at lower levels of CO₂ than levels at which symptoms begin to appear on Earth. This suggests there may be combinatorial effects of elevated CO₂ and the other physiological effects of microgravity including headward fluid shifts and body unloading. The purpose of the current study was to investigate these effects by evaluating the impact of 30 days of 6° HDBR and 0.5% CO₂ (HDBR + CO₂) on mission relevant cognitive and sensorimotor performance. We found a facilitation of processing speed and a decrement in functional mobility for subjects undergoing HDBR + CO₂ relative to our previous study of HDBR in ambient air. In addition, nearly half of the participants in this study developed signs of Spaceflight Associated Neuro-ocular Syndrome (SANS), a constellation of ocular structural and functional changes seen in approximately one third of long duration astronauts. This allowed us the unique opportunity to compare the two subgroups. We found that participants who exhibited signs of SANS became more visually dependent and shifted their speed-accuracy tradeoff, such that they were slower but more accurate than those that did not incur ocular changes. These small subgroup findings suggest that SANS may have an impact on mission relevant performance inflight via sensory reweighting.

Wireless inertial measurement unit (IMU)-based posturography

BACKGROUND

Classical posturography techniques have been recently enhanced by the use of different motion tracking devices, but for technical reasons they are not used to track directly the body spatial position of a subject.

OBJECTIVE

To describe and clinically evaluate a wireless inertial measurement unit-based mobile system to track body position changes.

METHODS

The developed system used a calculus transformation method using the acceleration data corrected by Kalman and Butterworth filters to output position data. A prospective non-randomized clinical study involving 15 healthy subjects was performed to evaluate the agreement between the confidence ellipse areas synchronously measured by the new developed system and a classical posturography system while performing a modified clinical test of sensory interaction in balance.

RESULTS

The overall intra-class correlation index was 0.93 (CI 0.89, 0.96). Grouped by conditions, under conditions 1-4, Pearson's correlation was 0.604, 0.78, 0.882, and 0.81, respectively.

CONCLUSION

The developed wireless inertial measurement unit-based posturography system was valid for tracking the sway variances in normal subjects under habitual clinical testing conditions. Further studies are needed to validate this system on patients and also under other posture conditions.

Towards computerized diagnosis of neurological stance disorders: data mining and machine learning of posturography and sway

We perform classification, ranking and mapping of body sway parameters from static posturography data of patients using recent machine-learning and data-mining techniques. Body sway is measured in 293 individuals with the clinical diagnoses of acute unilateral vestibulopathy (AVS, n = 49), distal sensory polyneuropathy (PNP, n = 12), anterior lobe cerebellar atrophy (CA, n = 48), downbeat nystagmus syndrome (DN, n = 16), primary orthostatic tremor (OT, n = 25), Parkinson's disease (PD, n = 27), phobic postural vertigo (PPV n = 59) and healthy controls (HC, n = 57). We classify disorders and rank sway features using supervised machine learning. We compute a continuous, human-interpretable 2D map of stance disorders using t-stochastic neighborhood embedding (t-SNE). Classification of eight diagnoses yielded 82.7% accuracy [95% CI (80.9%, 84.5%)]. Five (CA, PPV, AVS, HC, OT) were classified with a mean sensitivity and specificity of 88.4% and 97.1%, while three (PD, PNP, and DN) achieved a mean sensitivity of 53.7%. The most discriminative stance condition was ranked as "standing on foam-rubber, eyes closed". Mapping of sway path features into 2D space revealed clear clusters among CA, PPV, AVS, HC and OT subjects. We confirm previous claims that machine learning can aid in classification of clinical sway patterns measured with static posturography. Given a standardized, long-term acquisition of quantitative patient databases, modern machine learning and data analysis techniques help in visualizing, understanding and utilizing high-dimensional sensor data from clinical routine.

A quantitative analysis of postural control in elderly patients with vestibular disorders using visual stimulation by virtual reality

Introduction

Postural instability is one the most common disabling features in vestibular disorders.

Objective

This study aimed to analyze the limit of stability and the influence of manipulation of visual, somatosensorial and visual–vestibular information on postural control in older adults with vestibular disorder, with and without a history of falls.

Methods

Cross-sectional study. Participants – 76 elderly patients with vestibular disorder (G1, without falls; G2, with falls) and 41 healthy elderly subjects (control group; CG). Using posturography, analyzed were limit of stability area, body center of pressure, and velocity of oscillation in the standing position in 10 conditions, including open/closed eyes, unstable surface with eyes closed, saccadic and optokinetic stimuli, and visual–vestibular interaction.

Results

Limit of stability area in CG was better compared with G1-2, and center of pressure values were worse in G1 than in CG. Center of pressure area in all conditions and velocity of oscillation in the following conditions: open/closed eyes, optokinetic stimulation, and visual–vestibular interaction showed worse values in G2 than in CG. Center of pressure area in the following conditions: open/closed eyes, saccadic and optokinetic stimuli, visual–vestibular interaction, and unstable surface with eyes closed showed worse values in G2 than in G1.

Conclusion

Older adults with vestibular disorder presented reduced limit of stability and increased postural sway in the following conditions: conflict between visual and somatosensory information and visual–vestibular interaction. Deterioration in postural control was significantly associated with history of falls.

Inhibition and decision-processing speed are associated with performance on dynamic posturography in older adults

Changes in cognition due to age have been associated with falls and reduced standing postural control. Sensory integration is one component of postural control that may be influenced by certain aspects of cognitive functioning. This study investigated associations between measures of cognitive function and sensory integration capabilities for healthy young and older adults. Dynamic posturography was performed using the Equitest Sensory Organization Test (SOT) protocol to evaluate sensory integration during standing using sway-referencing of the platform and/or visual scene to alter somatosensory and visual inputs. The Equilibrium Score was used as a measure of sway. Cognitive testing examined aspects of cognitive function that have been associated with falls in older adults. A correlational analysis investigated associations between the cognitive measures and postural sway during the altered sensory conditions of the SOT. For older subjects only, slower decision-processing speed was associated with increased sway during SOT conditions whenever somatosensation was altered. Reduced perceptual inhibition was associated with increased sway whenever somatosensation was intact, and particularly when vision was altered in the presence of somatosensation. Visuospatial construct ability was associated with sway only when the eyes were closed during altered somatosensation. Task-switching was associated with sway only when vision and somatosensation were intact. With increased age, deficits in decision speed and inhibition appear associated with the sensory integration crucial for balance maintenance. Associations are modulated by the availability of somatosensation and vision. These associations define situations and individual differences in aspects of cognition that may relate to situational loss of balance in older adults.

Balance in multiple sclerosis: relationship to central brain regions

Dizziness, postural instability, and ataxia are among the most debilitating symptoms of multiple sclerosis (MS), reflecting, in large part, dysfunctional integration of visual, somatosensory, and vestibular sensory cues. However, the role of MS-related supratentorial lesions in producing such symptoms is poorly understood. In this study, motor control test (MCT) and dynamic sensory organization test (SOT) scores of 58 MS patients were compared to those of 72 healthy controls; correlations were determined between the MS scores of 49 patients and lesion volumes within 26 brain regions. Depending upon platform excursion direction and magnitude, MCT latencies, which were longer in MS patients than controls (p < 0.0001), were correlated with lesion volumes in the cortex, medial frontal lobes, temporal lobes, and parietal opercula (r's ranging from 0.20 to 0.39). SOT test scores were also impacted by MS and correlated with lesions in these same brain regions as well as within the superior frontal lobe (r's ranging from - 0.28 to - 0.40). The strongest and most consistent correlations occurred for the most challenging tasks in which incongruent visual and proprioceptive feedback were given. This study demonstrates that supratentorial lesion volumes are associated with quantitative balance measures in MS, in accord with the concept that balance relies upon highly convergent and multimodal neural pathways involving the skin, muscles, joints, eyes, and vestibular system.

Update on the Clinical, Radiographic, and Neurobehavioral Manifestations in FXTAS and FMR1 Premutation Carriers

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder caused by a repeat expansion in the fragile X mental retardation 1 (FMR1) gene. The disorder is characterized by kinetic tremor and cerebellar ataxia, shows age-dependent penetrance, and occurs more frequently in men. This paper summarizes the key emerging issues in FXTAS as presented at the Second International Conference on the FMR1 Premutation: Basic Mechanisms & Clinical Involvement in 2015. The topics discussed include phenotype-genotype relationships, neurobehavioral function, and updates on FXTAS genetics and imaging.

The Effect of Spinal Tap Test on Different Sensory Modalities of Postural Stability in Idiopathic Normal Pressure Hydrocephalus

BACKGROUND/AIMS

Postural instability in patients with normal pressure hydrocephalus (NPH) is a most crucial symptom leading to falls with secondary complications. The aim of the current study was to evaluate the therapeutic effect of spinal tap on postural stability in these patients.

METHODS

Seventeen patients with clinical symptoms of NPH were examined using gait scale, computerized dynamic posturography (CDP), and neuropsychological assessment. Examinations were done before and after spinal tap test.

RESULTS

The gait score showed a significant improvement 24 h after spinal tap test in all subtests and in the sum score (p < 0.003), while neuropsychological assessment did not reveal significant differences 72 h after spinal tap test. CDP showed significant improvements after spinal tap test in the Sensory Organization Tests 2 (p = 0.017), 4 (p = 0.001), and 5 (p = 0.009) and the composite score (p = 0.01). Patients showed best performance in somatosensory and worst performance in vestibular dominated tests. Vestibular dominated tests did not improve significantly after spinal tap test, while somatosensory and visual dominated tests did.

CONCLUSION

Postural stability in NPH is predominantly affected by deficient vestibular functions, which did not improve after spinal tap test. Conditions which improved best were mainly independent from visual control and are based on proprioceptive functions.

Characterization and Early Detection of Balance Deficits in Fragile X Premutation Carriers With and Without Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS)

Fragile X-associated tremor/ataxia syndrome (FXTAS) results from a "premutation" size 55-200 CGG repeat expansion in the fragile X mental retardation 1 (FMR1) gene. Core motor features include cerebellar gait ataxia and kinetic tremor, resulting in progressive mobility disability. There are no published studies characterizing balance deficits in FMR1 premutation carriers with and without FXTAS using a battery of quantitative measures to test the sensory integration underlying postural control, automatic postural reflexes, and dynamic postural stability limits. Computerized dynamic posturography (CDP) and two performance-based balance measures were administered in 44 premutation carriers, 21 with FXTAS and 23 without FXTAS, and 42 healthy controls to compare balance and functional mobility between these groups. Relationships between FMR1 molecular variables, age, and sex and CDP scores were explored. FXTAS subjects demonstrated significantly lower scores on the sensory organization test (with greatest reductions in the vestibular control of balance), longer response latencies to balance perturbations, and reduced stability limits compared to controls. Premutation carriers without FXTAS also demonstrated significantly delayed response latencies and disrupted sensory weighting for balance control. Advancing age, male sex, increased CGG repeat size, and reduced X activation of the normal allele in premutation carrier women predicted balance dysfunction. These postural control deficits in carriers with and without FXTAS implicate dysfunctional cerebellar neural networks and may provide valuable outcome markers for tailored rehabilitative interventions. Our findings suggest that CDP may provide sensitive measures for early detection of postural control impairments in at-risk carriers and better characterize balance dysfunction and progression in FXTAS.

The effect of various degrees of foot posture on standing balance in a healthy adult population

PURPOSE

Foot biomechanics plays a significant role in the quality of standing and walking. It has been believed that even minor biomechanical alterations in the foot support surface may influence strategies to maintain body standing balance. Hence, the aim of this study was to investigate the role of various degrees of foot posture on static and dynamic standing balance components in a healthy adult population.

SUBJECTS AND METHODS

A convenience sample of 41 healthy adult subjects with a mean age of 24.3 ± 6.4 years and a body mass index (BMI) of 29 kg/m(2) participated in this study. On the basis of foot posture index (FPI), the participants were allocated into either group A or B. Group A included 16 subjects with an FPI range of 6-11 whereas group B included 25 subjects with an FPI range of 0-5. Standing balance components were analyzed using computerized dynamic posturography (CDP) by the Modified Clinical Test of Sensory Interaction on Balance (mCTSIB) and the limit of stability (LOS).

RESULTS

Spearman's correlation coefficient showed a significant correlation between the standing dynamic balance and FPI in group B but not in group A. Moreover, it also showed no significant correlation between the standing static balance component and FPI in either group A or B.

CONCLUSION

This study concluded that higher degrees of FPI might have an effect on standing dynamic balance in healthy subjects. These components may require extra attention during the preventive aspects of rehabilitation.

Elderly Use Proprioception Rather than Visual and Vestibular Cues for Postural Motor Control

Multiple factors have been proposed to contribute to the deficits of postural control in the elderly. They were summarized as sensory, motor, and higher-level adaptation deficits. Using a model-based approach, we aimed to identify which of these deficits mainly determine age-related changes in postural control. We analyzed postural control of 20 healthy elderly people with a mean age of 74 years. The findings were compared to data from 19 healthy young volunteers (mean age 28 years) and 16 healthy middle-aged volunteers (mean age 48 years). Postural control was characterized by spontaneous sway measures and measures of perturbed stance. Perturbations were induced by pseudorandom anterior-posterior tilts of the body support surface. We found that spontaneous sway amplitude and velocity were significantly larger, and sway frequencies were higher in elderly compared to young people. Body excursions as a function of tilt stimuli were clearly different in elderly compared to young people. Based on simple feedback model simulations, we found that elderly favor proprioceptive over visual and vestibular cues, other than younger subjects do. Moreover, we identified an increase in overall time delay challenging the feedback systems stability, and a decline in the amplitude of the motor feedback, probably representing weakness of the motor system. In general, these parameter differences between young and old may result from both deficits and compensation strategies in the elderly. Our model-based findings correlate well with deficits measured with clinical balance scores, which are widely used in clinical practice.

Clinical efficacy of the Romberg test using a foam pad to identify balance problems: a comparative study with the sensory organization test

The modified Romberg test using a foam pad ("MRuFP") as a bedside examination has been used to assess the function of the complex sensory input needed for upright stance. The objective of this study was to assess its clinical value detecting vestibular falls in comparison with the sensory organization test (SOT), the gold standard. In total, 80 patients who had undergone the MRuFP, SOT, and bithermal caloric tests were included in this study. The MRuFPs were performed on two (height 12 cm, MRu2FP) or three (18 cm, MRu3FP) layers of foam pads. The odds ratios of falling on SOT were calculated. Iterative algorithms were used for linear curve fitting between the balance time on the MRuFP and SOT equilibrium score (ES). The diagnostic performance of MRuFP under different conditions was poor, with low sensitivity (0.07-0.63), when the results of SOT were used as the gold standard. However, the odds ratios of failing SOT condition 5 were 6.78 (95% CI = 1.26-36.50) for patients with abnormal findings on eyes closed (EC)-MRu2FP and 10.91 (95% CI = 2.58-46.11) for those on the EC-MRu3FP in patients without caloric weakness. In patients with caloric weakness, the odds ratio of failing SOT condition 5 for patients with abnormal findings on EC-MRu2FP was 7.0 (95% CI = 0.69-70.74, p > 0.05), and 32.0 for those on EC-MRu3FP (95% CI = 2.81-364.7). A linear equation was presented as the model fit (adjusted R(2) = 0.355) predicting the SOT condition 5 ES according to the balance time on EC-MRu3FP. In conclusion, the EC-MRu3FP, as a bedside examination, correlated well with SOT condition 5 as an objective measure.

Vestibular deficits leading to disequilibrium and falls in ambulatory amyotrophic lateral sclerosis

OBJECTIVE

To assess vestibular deficits in response to disequilibrium in ambulatory individuals with amyotrophic lateral sclerosis (ambALS).

DESIGN

All participants completed standard protocols for the Sensory Organization Test (SOT) by computerized dynamic posturography.

SETTING

Multidisciplinary amyotrophic lateral sclerosis clinic at an academic medical center.

PARTICIPANTS

Study participants (N=34) consisted of ambALS (n=19) and healthy controls (HC) (n=15).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Equilibrium scores (ESs) obtained from averaged sway amplitude in condition 5 (ES5) and condition 6 (ES6) of the SOT.

RESULTS

In conditions of altered somatosensory information with vision absent or vision sway-referenced, the mean ± SD scores for ambALS (ES5=51.4±22.5; ES6=50.8±22.1) were lower than those for HC (ES5=65.4±11.7, P≤.03; ES6=58.9±12.5, P>.05). Seven ambALS (37%) experienced a total of 19 falls during the sway-referenced support test conditions. There were no falls in the HC.

CONCLUSIONS

Nearly 37% of ambALS with normal clinical balance testing have decreased ability to use the vestibular input and required increased reliance on visual input for postural orientation to sustain equilibrium. The mechanism of this alteration in sensory preference is not completely clear. Extrapyramidal involvement early in ALS may be indicated.

Study of audiovestibular dysfunction in children with systemic lupus erythematosus

OBJECTIVE

Inner ear dysfunction in systemic lupus erythematosis patients has been reported but audiovestibular involvement is not well documented especially in pediatrics. This study was designed to evaluate silent audiovestibular dysfunction among SLE children.

METHODS

Case control study examined in allergy and immunology clinic; pediatrics hospital and audiovestibular clinic; Ain Shams University from January 2009 to December 2010. Thirty-five systemic lupus erythematosus children (diagnosed according to American College of Rheumatology); age group 8-16 years, were randomly selected. Five of them were excluded due to one or more exclusion criteria (previous otitis media, stroke, lupus cerebritis, meningitis or encephalitis, audiovestibular symptom). Ten of them refused enrollment or could not complete full battery. Seventeen females and three males, mean age 12.9 ± 2.6 years, completed the study. Control group included 20 normal subjects, age and sex matched. Full clinical assessment, basic audiological evaluation and vestibular testing (videonystagmography VNG and computerized dynamic posturography CDP) were conducted for children included in the study.

RESULTS

Five systemic lupus erythematosus patients had sensorineural hearing loss strongly associated with +ve antiphospholipid antibody and two had conductive hearing loss. Two children in control group had conductive hearing loss (p=0.05). Abnormal VNG findings was significantly higher among systemic lupus erythematosus children (40%) compared to controls (0%) and associated with +ve antiphospholipid antibodies (χ(2)=10, p=0.002, Fisher exact test=0.003). Twenty-five percentage of systemic lupus erythematosus children had abnormal CDP findings reflecting impaired balance function associated with positive antiphospholipid antibodies showing significant statistical difference compared to controls (0% affection) (χ(2)=5.7, p=0.017, Fisher exact test=0.047).

CONCLUSION

Silent audiovestibular dysfunction is prevalent among systemic lupus erythematosus children especially those positive for antiphospholipid antibodies necessitating routine regular evaluation.

Computerized dynamic posturography analysis of balance in individuals with a shoulder stabilization sling

INTRODUCTION

Sling immobilization of the upper limb may affect balance. Computerized dynamic posturography (CDP) provides a validated, objective assessment of balance control and postural stability under dynamic test conditions. We tested the balance of individuals with a shoulder stabilization sling (SSS) using an EquiTest machine to objectively assess imbalance while wearing a sling.

METHODS

Forty-two right hand dominant (RHD) adults (16 females, 26 males; average age 22 years; range 20-35 years) were included in the study, comprising six controls and two SSS groups with 18 dominant hands (DH) and 18 non dominant hands (NDH). CDP assessed balance by the Sensory Organization Test (SOT), Motor Control Test (MCT), and Adaptation Test (ADT).

RESULTS

The composite equilibrium scores (CES) were as follows: controls 80.8 %, sling DH 71.1 versus sling NDH 69.6 %. Sling use has lower CES compared to controls (p = 0.025). The use of a sling caused 31 % of subjects to have decreased CES. 22.9 % of sling users had imbalances. Among sling users, the DH group had 19.1 % imbalances compared to 26.8 % for the NDH group (p = 0.044). There were six absolute falls in the DH group versus 12 in the NDH group.

CONCLUSIONS

Wearing a sling causes balance decompensation in almost one-third of healthy volunteers, and this is greater when worn in the non dominant hand, with double the number of falls. This has significant implications for patients having prolonged use of a sling. Consideration should be given to operative procedures or conservative management of shoulder pathology where sling use is required and promotion of the early discontinuation of sling use can be considered.

Getting Your Sea Legs

Sea travel mandates changes in the control of the body. The process by which we adapt bodily control to life at sea is known as getting one's sea legs. We conducted the first experimental study of bodily control as maritime novices adapted to motion of a ship at sea. We evaluated postural activity (stance width, stance angle, and the kinematics of body sway) before and during a sea voyage. In addition, we evaluated the role of the visible horizon in the control of body sway. Finally, we related data on postural activity to two subjective experiences that are associated with sea travel; seasickness, and mal de debarquement. Our results revealed rapid changes in postural activity among novices at sea. Before the beginning of the voyage, the temporal dynamics of body sway differed among participants as a function of their (subsequent) severity of seasickness. Body sway measured at sea differed among participants as a function of their (subsequent) experience of mal de debarquement. We discuss implications of these results for general theories of the perception and control of bodily orientation, for the etiology of motion sickness, and for general phenomena of perceptual-motor adaptation and learning.

Normative data for the balance error scoring system in adults

Background. The balance error scoring system (BESS) is a brief, easily administered test of static balance. The purpose of this study is to develop normative data for this test. Study Design. Cross-sectional, descriptive, and cohort design. Methods. The sample was drawn from a population of clients taking part in a comprehensive preventive health screen at a multidisciplinary healthcare center. Community-dwelling adults aged 20–69 (N = 1, 236) were administered the BESS within the context of a fitness evaluation. They did not have significant medical, neurological, or lower extremity problems that might have an adverse effect on balance. Results. There was a significant positive correlation between BESS scores and age (r = .34). BESS performance was similar for participants between the ages of 20 and 49 and significantly declined between ages 50 and 69. Men performed slightly better than women on the BESS. Women who were overweight performed significantly more poorly on the test compared to women who were not overweight (P < .0001; Cohen's d = .62). The BESS normative data are stratified by age and sex. Conclusions. These normative data provide a frame of reference for interpreting BESS performance in adults who sustain traumatic brain injuries and adults with diverse neurological or vestibular problems.

Postural function in idiopathic normal pressure hydrocephalus before and after shunt surgery: a controlled study using computerized dynamic posturography (EquiTest)

INTRODUCTION

Postural dysfunction is one of the major features of idiopathic normal pressure hydrocephalus (iNPH). With computerized dynamic posturography (CDP) balance can be assessed objectively. The primary aim of this study was to describe the postural function in iNPH patients pre- and post-operatively in comparison with healthy individuals (HI) using CDP.

SUBJECTS AND METHODS

Thirty-five patients (16 M, 19 F) with a mean age of 73 (range 49-81) with iNPH, and sixteen HI (7 M, 9 F) aged 73 (62-89) were included. iNPH patients were operated on with a ventriculo-peritoneal shunt. Patients and HI were tested regarding motor function, balance and cognition. CDP, EquiTest (NeuroCom International, Clackamas, OR), was performed before and three months after shunt surgery and twice in HI, with a three-month interval.

RESULTS

Pre-operatively, the 35 patients had poorer balance measured with the Sensory Organizing Test (SOT) score in every condition (p=0.01 in SOT 1 and p<0.001 in SOT 2-6) compared to the HI. The greatest difference was in test conditions measuring mainly vestibular function, where loss of balance (LOB) was frequent. Twenty patients were evaluated three months after shunt surgery and 18/20 (90%) of them were considered shunt responders, with a mean improvement of motor score of 26% (range 5-67%). There was an improvement post-operatively in the weighted composite SOT score (p<0.05) but no significant change in any of the SOT conditions. LOB was not significantly reduced in any of the test conditions.

CONCLUSION

CDP showed that the patients had a poorer balance than the HI. The greatest difference was in SOT 5-6, indicating that the postural disturbance is of primarily central vestibular origin. There was a slight improvement of balance post-operatively.

Continuous equilibrium scores: factoring in the time before a fall

The equilibrium (EQ) score commonly used in computerized dynamic posturography is normalized between 0 and 100, with falls assigned a score of 0. The resulting mixed discrete-continuous distribution limits certain statistical analyses and treats all trials with falls equally. We propose a simple modification of the formula in which peak-to-peak sway data from trials with falls is scaled according the percent of the trial completed to derive a continuous equilibrium (cEQ) score. The cEQ scores for trials without falls remain unchanged from the original methodology. The cEQ factors in the time before a fall and results in a continuous variable retaining the central tendencies of the original EQ distribution. A random set of 5315 Sensory Organization Test trials were pooled that included 81 falls. A comparison of the original and cEQ distributions and their rank ordering demonstrated that trials with falls continue to constitute the lower range of scores with the cEQ methodology. The area under the receiver operating characteristic curve (0.997) demonstrates that the cEQ retained near-perfect discrimination between trials with and without falls. We conclude that the cEQ score provides the ability to discriminate between ballistic falls from falls that occur later in the trial. This approach of incorporating time and sway magnitude can be easily extended to enhance other balance tests that include fall data or incomplete trials.

Limbic encephalopathy and central vestibulopathy caused by mefloquine: a case report

Mefloquine is a 4-methanolquinoline anti-malarial that in recent years has fallen out of favor for use as chemoprophylaxis against infection with chloroquine-resistant Plasmodium falciparum malaria owing in part to growing concerns of side effects and potential neurotoxicity. Despite over 20 years of licensed use, the pathophysiological mechanisms underlying mefloquine's neuropsychiatric and physical side effects and the clinical significance of the drug's neurotoxicity have remained poorly understood. In this report, an adverse reaction to mefloquine chemoprophylaxis is described characterized by prodromal symptoms of anxiety with subsequent development of psychosis, short-term memory impairment, confusion and personality change accompanied by complaints of disequilibrium and vertigo, with objective findings of central vestibulopathy. It is posited that these effects represent an idiosyncratic neurotoxic syndrome of progressive limbic encephalopathy and multifocal brainstem injury caused by the drug. This case provides insights into the clinical significance of mefloquine neuronal gap junction blockade and neurotoxicity demonstrated in animal models, points to recommendations for the management of affected patients including diagnostic considerations and appropriate referrals, and highlights critical implications for the continued safe use of the medication.

Altered postural control strategies and sensory organization in children with developmental coordination disorder

The postural control of children with and without developmental coordination disorder (DCD) was compared under conditions of reduced or conflicting sensory input. Twenty-two children with DCD (16 males, 6 females; mean age 7 years 6 months, SD 1 year 5 months) and 19 children with normal motor development were tested (13 males, 6 females; mean age 6 years 11 months, SD 1 year 1 month). Standing balance, sensory organization and motor control strategy were evaluated using the sensory organization test (SOT). The results revealed that children with DCD had lower composite equilibrium scores (p<.001), visual ratios (p=.005) and vestibular ratios (p=.002) than normal children in the control group. No significant between-group difference in their average somatosensory ratio was observed. Additionally, children with DCD had lower motor strategy scores (swayed more on their hips) than the normal children when forced to depend on vestibular cues alone to balance (p<.05). We conclude that children with DCD had deficits in standing balance control in conditions that included reduced or conflicting sensory signals. The visual and vestibular systems tended to be more involved in contributing to the balance deficits than the somatosensory system. Moreover, children with DCD tended to use hip strategy excessively when forced to rely primarily on vestibular signals to maintain postural stability.

Identifying factors associated with falls in postmenopausal breast cancer survivors: a multi-disciplinary approach

OBJECTIVE

To identify neuromuscular, balance, and vision factors that contribute to falls in recently treated breast cancer survivors (BCS) and explore links between fall risk factors and cancer treatment.

DESIGN

Case-control plus prospective observation.

SETTING

Comprehensive cancer center.

PARTICIPANTS

BCS (N=59; mean age, 58y) within 2 years of chemotherapy completion and/or on adjuvant endocrine therapy.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Objective measures of postural control, vision, and neuromuscular function included: (1) a sensory organization test (SOT), (2) a visual assessment battery, (3) muscle mass by dual energy x-ray absorptiometry, and (4) neuromuscular function with strength by repetition maximum, power by timed stair climb, and gait speed by 4m walk. Falls were self-reported for the past year (retrospective) and monthly for 6 months (prospective).

RESULTS

Fifty eight percent of BCS reported falls in the past year. BCS with a history of falls had lower SOT scores with a vestibular deficit pattern in postural control (P<.01) and took longer to read letters on the contrast sensitivity chart (P<.05). Vestibular score on the SOT mediated the relationship between treatment and falls among BCS who received chemotherapy only, but not adjuvant endocrine therapy.

CONCLUSIONS

Results of this project suggest that balance disturbances of vestibular origin and delays in detecting low contrast visual stimuli are associated with falls in BCS. Future studies that track falls and fall risk factors in BCS from diagnosis through treatment are warranted, as are studies that can identify treatment-related vestibular dysfunction and altered visual processing.

Abnormal sensory integration affects balance control in hemiparetic patients within the first year after stroke

OBJECTIVE

Impairments in balance can be a consequence of changes in the motor, sensory, and integrative aspects of motor control. Abnormal sensory reweighting, i.e., the ability to select the most appropriate sensory information to achieve postural stability, may contribute to balance impairment. The Sensory Organization Test is a component of Computerized Dynamic Posturography that evaluates the impact of visual, vestibular, and somatosensory inputs, as well as sensory reweighting, under conditions of sensory conflict. The aim of this study is to compare balance control in hemiparetic patients during the first year post-stroke and in age-matched neurologically normal subjects using the Berg Balance Scale and Computerized Dynamic Posturography.

METHODS

We compared the Berg Balance Scale and Sensory Organization Test scores in 21 patients with hemiparesis after first-ever ischemic stroke and in 21 age-matched, neurologically normal subjects. An equilibrium score was defined for each Sensory Organization Test condition.

RESULTS

Berg Balance Scale scores were significantly lower in the patients than in the neurologically normal subjects. Equilibrium scores were significantly lower in the patients than in the neurologically normal subjects for those Sensory Organization Test conditions that did not provide appropriate somatosensory information and under conditions of sensory conflict. A history of falls was more frequent in patients with lower equilibrium scores.

CONCLUSION

During the first year after a stroke, defective sensory reweighting significantly impacts balance control in hemiparetic patients. These results are important for the planning of effective rehabilitation interventions.

Moment measurement accuracy of a parallel spherical robot for dynamic posturography

This paper characterizes the moment measurement accuracy for a novel parallel spherical robot (SR) for dynamic posturography, controllable by position or impedance. The SR consists of three linear motors placed on a support base, a moving base, and three passive arms equipped with uniaxial load cells permitting impedance controlled perturbations. To evaluate the accuracy, a subject stood still on the SR, set in position control mode, while selected sinusoidal trajectories were applied. The moments computed by the load cells were compared to the value measured by a six-component force platform, placed on top of the rotating base. For the intended application of the SR, the errors were negligible with the worse case of only 4 Nm in a total of 15 trials (five conditions, three repetitions). The observed moment error was related mainly to the intrinsic accuracy of the sensors, equal to about 7 N. To demonstrate clinical applicability, the platform was set to impedance control mode and a protocol was tested with a 12-year-old girl with brain injury and a group of four healthy subjects. In total, 24 trials (eight conditions, three repetitions) were recorded for each subject. The results of this pilot study identified distinctive postural behaviors and therefore showed that the SR can be considered as an effective tool for dynamic posturography.

Electrotactile feedback of sway position improves postural performance during galvanic vestibular stimulation

The purpose of this study was to assess the influence of electrotactile feedback on postural control performance during binaural galvanic vestibular stimulation (GVS). Postural equilibrium was measured with a computerized hydraulic platform in 10 healthy adults (6M, 4F, 24-65 y). Feedback of anterior-posterior (AP) and mediallateral (ML) body sway was derived from a 2-axis linear accelerometer mounted on a torso belt and displayed on a 144-point electrotactile array held against the anterior dorsal tongue. Subjects were trained to use the tongue electrotactile feedback (TEF) by voluntarily swaying to draw figures on their tongue, both with and without GVS. Subjects performed 24 randomized trials (20-s duration with eyes closed, 2 trials per condition), including 4 support surface conditions (fixed, rotational sway-referenced, translating the support surface proportional to AP sway, and combined rotational-translational support-platform sway referencing), and 3 feedback conditions (baseline, GVS, and GVS with TEF). Postural performance was assessed using deviations from upright (peak-to-peak and root-mean-square sway) and convergence toward stability limits (time and distance to limit of support boundaries). Postural stability was impaired (with respect to baseline) during GVS in all platform conditions, with larger decrements in performance during trials with rotation sway-referencing. Electrotactile feedback improved performance with GVS toward non-GVS levels, especially during trials with rotation sway-referencing. These results demonstrate the effectiveness of TEF in providing sensory substitution to maintain postural stability during vestibular disturbances.

Space and motion discomfort and abnormal balance control in patients with anxiety disorders

OBJECTIVE

Previous research suggested that panic disorder with agoraphobia is associated with abnormalities on vestibular and balance function tests. The purpose of this study was to further examine psychiatric correlates of vestibular/balance dysfunction in patients with anxiety disorders and the specific nature of the correlated vestibular abnormalities. The psychiatric variables considered included anxiety disorder versus normal control status, panic disorder versus non-panic anxiety disorder diagnosis, presence or absence of comorbid fear of heights, and degree of space and motion discomfort (SMD). The role of anxiety responses to vestibular testing was also re-examined.

METHODS

104 subjects were recruited: 29 psychiatrically normal individuals and 75 psychiatric patients with anxiety disorders. Anxiety patients were assigned to four subgroups depending on whether or not they had panic disorder and comorbid fear of heights. SMD and anxiety responses were measured by questionnaires. Subjects were examined for abnormal unilateral vestibular hypofunction on caloric testing indicative of peripheral vestibular dysfunction, asymmetric responses on rotational testing as an indicator of an ongoing vestibular imbalance and balance function using Equitest dynamic posturography as an indicator of balance control. Logistic regression was used to establish the association between the psychiatric variables and vestibular or balance test abnormalities.

RESULTS

Rotational test results were not significantly related to any of the psychiatric variables. The presence of either panic attacks or fear of heights increased the probability of having caloric hypofunction in a non-additive fashion. SMD and anxiety responses were independently associated with abnormal balance. Among specific posturography conditions, the association with SMD was significant for a condition that involved the balance platform tilting codirectionally with body sway, suggesting an abnormal dependence on somatosensory cues in the control of balance.

CONCLUSION

In patients with anxiety disorders, higher SMD is indicative of somatosensory dependence in the control of balance. The absence of both panic and fear of heights reduces the probability of having peripheral vestibular dysfunction. Future research should examine if vestibular rehabilitation can be of value for patients with anxiety disorders complicated by SMD.

Changing control strategies during standard assessment using computerized dynamic posturography with older women

The goal of this investigation was to explore the use of spectral analysis to examine the data obtained during computerized dynamic posturography (CDP). In particular, we examined whether spectral analysis would provide more detailed information about underlying postural control strategies and potential learning across conditions and trials of the sensory organization test (SOT). Twenty older women between the ages of 60 and 72 (mean=65.2) were assessed using standard testing protocol. Participants showed significant improvements from the first to the second trials in their equilibrium scores in the more difficult conditions. This finding was reflected in the spectral analysis data by a shift in the frequency distribution towards greater power in the lower frequency range. This frequency change likely reflects a change in the ankle strategy used to maintain balance during the more difficult conditions.

Modeling locomotor dysfunction following spaceflight with Galvanic vestibular stimulation

In this study locomotor and gaze dysfunction commonly observed in astronauts following spaceflight were modeled using two Galvanic vestibular stimulation (GVS) paradigms: (1) pseudorandom, and (2) head-coupled (proportional to the summed vertical linear acceleration and yaw angular velocity obtained from a head-mounted Inertial Measurement Unit). Locomotor and gaze function during GVS were assessed by tests previously used to evaluate post-flight astronaut performance; dynamic visual acuity (DVA) during treadmill locomotion at 80 m/min, and navigation of an obstacle course. During treadmill locomotion with pseudorandom GVS there was a 12% decrease in coherence between head pitch and vertical translation at the step frequency relative to the no GVS condition, which was not significantly different to the 15% decrease in coherence observed in astronauts following shuttle missions. This disruption in head stabilization likely resulted in a decrease in DVA equivalent to the reduction in acuity observed in astronauts 6 days after return from extended missions aboard the International Space Station (ISS). There were significant increases in time-to-completion of the obstacle course during both pseudorandom (21%) and head-coupled (14%) GVS, equivalent to an ISS astronaut 5 days post-landing. An attempt to suppress head movement was evident during both pseudorandom and head-coupled GVS while negotiating the obstacle course, with a 20 and 16%, decrease in head pitch and yaw velocity, respectively. The results of this study demonstrate that pseudorandom GVS generates many of the salient features of post-flight locomotor dysfunction observed in astronauts following short and long duration missions. An ambulatory GVS system may prove a useful adjunct to the current pre-flight astronaut training regimen.

Biomechanic Modeling of Sit-to-Stand to Upright Posture for Mobility Assessment of Persons With Chronic Stroke

OBJECTIVE

To test the suitability of using biomechanic measures associated with a minimum measured input model (MMIM) approach to assess mobility of people with chronic stroke during the execution of a sit-to-stand (STS) to upright posture motor task.

DESIGN

Single group, observational.

SETTING

Institutional settings in the United States and Italy.

PARTICIPANTS

Twenty-nine subjects with chronic unilateral lower-limb impairments and resultant mobility limitations secondary to stroke.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Manual measurement of lower-limb strength; performance-based tests including repeated chair standing, walking speed, and standing balance; and ground reactions measured with a force platform during STS and upright posture. The ground reactions were fed to a telescopic inverted pendulum model of the musculoskeletal system. Parameters representing the model outputs were compared with performance-based and strength measures to assess, respectively, motor ability and impairment-related changes in subjects' motor strategies.

RESULTS

The parameters derived from the model effectively differentiated between motor strategies associated with different performance-based scores, and allowed the identification of relevant difficulties encountered in STS execution. These difficulties could be associated with different strength scores. This was also true for subjects scoring the maximum in both performance-based and strength tests.

CONCLUSIONS

The MMIM is a relatively inexpensive and noninvasive approach that enhances mobility assessment of hemiparetic subjects with different motor ability levels. It provides information that correlates well with performance-based and strength scores and, in addition, it allows for subject-specific motor strategy identification.

Modeling postural instability with Galvanic vestibular stimulation

In this study the effect of a pseudorandom binaural bipolar Galvanic stimulus generated by a sum of nonharmonically related sine waves on postural control was functionally assessed using computerized dynamic posturography (CDP), and the results compared to vestibulopathic patient populations and astronauts exposed to microgravity. The standardized CDP test battery comprised six sensory organization tests (SOTs) that combined three visual conditions (eyes open, eyes closed, and sway-referenced vision) with two proprioceptive conditions (fixed and sway-referenced support surfaces). Subjects (12) performed 18 randomized trials (three trials of each of the six SOTs) as a baseline, repeated the 18 trials with Galvanic vestibular stimulation (GVS), and then performed a post-GVS baseline. A 10 min rest period was inserted between each test battery. Anterioposterior postural sway increased significantly and was in the abnormal range (fifth percentile) during GVS for SOTs where visual input was compromised (sway-referenced surround) or absent. Postural stability returned to baseline when GVS was removed. An analysis of sensory input scores (somatosensory, visual, and vestibular) demonstrated the specificity of GVS in distorting vestibular input to postural control. The SOT scores observed in astronauts on landing day did not differ significantly to that generated by GVS in our normal subjects. GVS also induced a similar pattern of instability on CDP as profound bilateral vestibular loss, although not as severe. The results suggest that unpredictably varying GVS quantitatively and qualitatively models postural instability of vestibular origin.

Interobserver reliability in evaluating postural stability between clinicians and posturography

OBJECTIVES

To assess the interobserver reliability in assessing postural stability and to compare with results obtained by computerized posturography.

DESIGN

Cross-sectional study.

SETTING

Balance clinic, teaching hospital.

PARTICIPANTS

81 patients attending with a primary complaint of imbalance.

MAIN OUTCOME MEASURES

Inter-rater reliability between two clinicians and the modified Clinical Test for the Sensory Interaction on Balance (mCTSIB) as assessed by the Neurocom VSR Balance Master platform.

RESULTS

Inter-rater reliability scores were high (0.53-0.81) for all conditions of the mCTSIB except for the easiest, i.e. firm surface eyes open, where concordance levels were poor to fair.

CONCLUSIONS

Overall there was good agreement between observers and the computerized mCTSIB.

Contribution of muscle strength and integration of afferent input to postural instability in persons with stroke

OBJECTIVE

To determine the relationship of muscle strength to postural sway in persons with stroke under standing conditions in which vision and ankle proprioception were manipulated.

METHODS

Forty persons with stroke and 40 healthy older adult controls were recruited from the community and underwent balance testing consisting of 6 conditions that manipulate vision and somatosensory information while standing. Postural sway was measured during each condition. In addition, lower extremity joint torques and cutaneous sensation from the plantar surface of the foot were assessed.

RESULTS

Postural sway was increased with more challenging standing conditions (i.e., when multiple sensory systems were manipulated) to a greater extent with the group with stroke compared to controls. Muscle strength was only correlated to sway during the most challenging conditions. Furthermore, a greater number of persons with stroke fell during the balance testing compared to controls.

CONCLUSIONS

Impairments in re-weighting/integrating afferent information, in addition to muscle weakness, appear to contribute to postural instability and falls in persons with stroke. These findings can be used by clinicians to design effective interventions for improving postural control following stroke.

General vestibular testing

A dysfunction of the vestibular system is commonly characterized by a combination of phenomena involving perceptual, ocular motor, postural, and autonomic manifestations: vertigo/dizziness, nystagmus, ataxia, and nausea. These 4 manifestations correlate with different aspects of vestibular function and emanate from different sites within the central nervous system. The diagnosis of vestibular syndromes always requires interdisciplinary thinking. A detailed history allows early differentiation into 9 categories that serve as a practical guide for differential diagnosis: (1) dizziness and lightheadedness; (2) single or recurrent attacks of vertigo; (3) sustained vertigo; (4) positional/positioning vertigo; (5) oscillopsia; (6) vertigo associated with auditory dysfunction; (7) vertigo associated with brainstem or cerebellar symptoms; (8) vertigo associated with headache; and (9) dizziness or to-and-fro vertigo with postural imbalance. A careful and systematic neuro-ophthalmological and neuro-otological examination is also mandatory, especially to differentiate between central and peripheral vestibular disorders. Important signs are nystagmus, ocular tilt reaction, other central or peripheral ocular motor dysfunctions, or a unilateral or bilateral peripheral vestibular deficit. This deficit can be easily detected by the head-impulse test, the most relevant bedside test for the vestibulo-ocular reflex. Laboratory examinations are used to measure eye movements, to test semicircular canal, otolith, and spatial perceptional function and to determine postural control. It must, however, be kept in mind that all signs and ocular motor and vestibular findings have to be interpreted within the context of the patient's history and a complete neurological examination.

Mal de Debarquement and Posture: Reduced Reliance on Vestibular and Visual Cues

OBJECTIVE

The neural mismatch theory assumes that the intersensory conflicts leading to motion sickness are resolved by changes in the relative weighting of the various senses that contribute to orientation. If this sensory rearrangement persists after disembarkment, it might result in mal de debarquement (MD): ataxia and a rocking sensation sometimes felt after landing. The objective of the present study was to examine possible changes in sensory organization in naval crew members with differing susceptibility to MD with computerized dynamic posturography (CDP).

STUDY DESIGN

Cross-sectional parallel-group design.

METHODS

Seventeen subjects susceptible to MD (SMD) and 17 subjects nonsusceptible to MD (NSMD) (healthy male volunteers aged 18-22) participated in the study. CDP was performed twice with each subject, before and immediately after sailing, using the EquiTest system (NeuroCom, Inc., Clackamas, OR).

RESULTS

The SMD group showed a significant reduction in their scores on sensory organization tests 3, 4, and 5 after sailing. Sensory pattern analysis revealed reduced use of inputs from the vestibular and visual systems to maintain balance. Prolonged latencies of the motor responses to unexpected pitch perturbations were also recorded in the postsailing CDP of the SMD group. Reduced performance on the presailing CDP task, which presents the greatest challenge to the vestibular system, was found to control for the presence of MD postsailing.

CONCLUSIONS

The results show that MD is associated with postural instability, slower motor reflexes, and larger sways in response to abrupt changes in the body's center of gravity. These findings may be explained by under reliance on vestibular and visual inputs and increased dependence on the somatosensory system for the maintenance of balance.