Destabilization of human balance control by static and dynamic head tilts

Temporal adaptation of the postural control following a prolonged fin swimming

PURPOSE

Postural control deteriorates following a transition between two environments, highlighting a sensory conflict when returning to natural conditions. Aquatic immersion offers new perspectives for studying postural control adaptation in transitional situations. Our aim is to study immediate and post-task static postural control adaptation on land after a prolonged fin swimming exercise in total immersion.

METHODS

Standing static postural control was assessed in 14 professional or recreational SCUBA divers (11 men, 3 women; 33.21 ± 10.70 years), with eyes open and closed, before, immediately after, and in the following 20 min following a fully-immersed 45-min fin swimming exercise. Centre-of-pressure metrics (COP) including average position, amplitude, velocity, length and 95% ellipse were evaluated in medial-lateral (x-axis) and anterior-posterior (y-axis) directions with a force platform. The Romberg ratio was also assessed for each metric.

RESULTS

A two-way repeated measures analysis of variance revealed a significant effect of the measurement period on COPx vel (p = 0.01), COPy vel (p < 0.01) and Length (p < 0.01), and of the visual condition on COPy vel (p < 0.01) and Length (p < 0.01). Eyes closed measures were systematically higher than eyes open measures despite there being no significant difference in the Romberg ratio in all periods. Post-immersion, the velocity and total trajectory of the centre of pressure remained systematically lower than baseline values in both visual conditions.

CONCLUSION

Post-immersion, COP velocity and length significantly decreased, suggesting a sensory reweighting strategy potentially associated with ankle stiffening.

Head movement and its relation to hearing

Head position at any point in time plays a fundamental role in shaping the auditory information that reaches a listener, information that continuously changes as the head moves and reorients to different listening situations. The connection between hearing science and the kinesthetics of head movement has gained interest due to technological advances that have increased the feasibility of providing behavioral and biological feedback to assistive listening devices that can interpret movement patterns that reflect listening intent. Increasing evidence also shows that the negative impact of hearing deficits on mobility, gait, and balance may be mitigated by prosthetic hearing device intervention. Better understanding of the relationships between head movement, full body kinetics, and hearing health, should lead to improved signal processing strategies across a range of assistive and augmented hearing devices. The purpose of this review is to introduce the wider hearing community to the kinesiology of head movement and to place it in the context of hearing and communication with the goal of expanding the field of ecologically-specific listener behavior.

Investigation of Head Shake Sensory Organization Test (HS-SOT) in three planes: Test-retest reliability and age-related differences

BACKGROUND

In recent years, it has been determined that SOT sensitivity is insufficient in patients who develop vestibular compensation and therefore the Head Shake Sensory Organization Test (HS-SOT) has been developed.

RESEARCH QUESTION

How differs the balance performance of healthy adults that is tested with HS-SOT according to age and test planes? What is the test-retest reliability level of the HS-SOT in three planes?

METHODS

Our prospective study, which has a methodological research design, included 80 participants divided into three groups by age range (Group 1: 20-39 years (n = 30); Group 2: 40-49 years (n = 30) and Group 3: 50-64 years (n = 20)). SOT and HSSOT ( yaw, pitch, roll) were performed to all participants. To investigate the testretest reliability of the HS-SOT, a total of 27 participants were re-evaluated one week later. The HS-SOT performance of the participants was compared between age groups and test planes. Intra-class correlation coefficient and minimum detectable change values (MDC) was calculated to test-retest reliability of HS-SOT.

RESULTS

HS-SOT scores (HS-2 and HS-5) did not differ significantly between age groups. The balance performance of individuals for the pitch plane was lower than other planes. Only the HS-5 score showed a significant difference between the sessions. HS-5 scores were higher in the re-test; for the first group in the pitch plane and for the third group in the yaw plane. The test-retest reliability level of these conditions was "moderate-good" for both groups. The corresponding MDC value was highest (14.01) for the HS-5 (yaw) score of the elderly group.

SIGNIFICANCE

The findings from this study demonstrated that the test plane influences the HS-SOT, a learning/practice effect may occur because of repeated HS-SOT evaluation, and this effect is more explicit in the elderly. This study provides a perspective for the evaluation and follow-up processes of patients with balance problems.

The Effects of Different Kinds of Smooth Pursuit Exercises on Center of Pressure and Muscle Activities during One Leg Standing

This study examined the effects of gaze fixation and different kinds of smooth-pursuit eye movements on the trunk and lower extremity muscle activities and center of pressure.

METHODS

Twenty-four subjects were selected for the study. The activity of trunk and lower limb muscles (tibialis anterior, lateral gastrocnemius, medial gastrocnemius, vastus midialis obliques, vastus lateralis, biceps femoris, rectus abdominis, and erector spinae) and the COP (center of pressure) (surface area ellipse, length, and average speed) were measured to observe the effects of gaze fixation and different kinds of smooth-pursuit eye movements on the center of pressure and muscle activities during one leg standing. Before the experiment, a Gaze point GP3 HD Eye Tracker (Gazept, Vancouver, BC, Canada) was used to train eye movement so that the subjects would be familiar with smooth eye movement. Repeated each exercise 3 times at random. In order to avoid the sequence deviation caused by fatigue, the movement sequence is randomly selected.

RESULT

The center of pressure and muscle activities were increased significantly when the smooth-pursuit eye movement with one leg standing compared with gaze fixation with one leg standing. In smooth-pursuit eye movements, the changes in the center of pressure and muscle activities were increased significantly with eye and head movement. When the head and eyes moved in opposite directions, the center of pressure and muscle activities were increased more than with any other exercises.

CONCLUSION

Smooth-pursuit eye movement with one leg movement affects balance. In particular, in the smooth-pursuit eye movement with one leg standing, there were higher requirements for balance when the eyes and head move in the opposite direction. Therefore, this movement can be recommended to people who need to enhance their balance ability.

The effect of COVID-19 pandemic and wearing face masks on ophthalmology practice: What is known so far? A narrative review

Face masks, along with other preventive measures, can help slow the spread of COVID-19. Despite the positive effect of the mask in combating the virus, it has some negative effects on the human body that must be followed up on and reduced. In this study, we discuss the impact of wearing face masks on the eye and the common issues associated with using them. The literature search was conducted using electronic databases such as PubMed and Google Scholar. Only articles published in English were included. A total of 39 relevant articles were deemed eligible. After the duplicate articles were removed, the titles and abstracts of 20 papers underwent full-text screening. The review comprised both prospective and retrospective investigations, case reports, and a series of reporting ocular symptoms following the use of face masks. The COVID-19 pandemic affected ophthalmology practices in managing patients. New factors must be considered, especially when dealing with anti-VEGF injections, such as the risk of endophthalmitis, tests and symptoms of patients with glaucoma, and the emerging symptoms associated with the COVID-19 vaccination. The use of face masks and breathing aids seemed to influence the tear film.

Individual Cofactors and Multisensory Contributions to the Postural Sway of Adults with Diabetes

To assess the interactions between individual cofactors and multisensory inputs on the postural sway of adults with type 2 diabetes and healthy subjects, 69 adults accepted to participate in the study (48 with/ 21 without diabetes). Assessments included neuro-otology (sinusoidal-rotation and unilateral-centrifugation), ophthalmology and physiatry evaluations, body mass index (BMI), physical activity, quadriceps strength, the ankle/brachial index and polypharmacy. Postural sway was recorded on hard/soft surface, either with eyes open/closed, or without/with 30° neck extension. The proportional differences from the baseline of each condition were analyzed using Multivariate and Multivariable analyses. Patients with polyneuropathy and no retinopathy showed visual dependence, while those with polyneuropathy and retinopathy showed adaptation. Across sensory challenges, the vestibulo-ocular gain at 1.28 Hz and the BMI were mainly related to changes in sway area, while the dynamic visual vertical was mainly related to changes in sway length. The ankle/brachial index was related to the effect of neck extension, with contributions from quadriceps strength/physical activity, polyneuropathy and polypharmacy. Across conditions, men showed less sway than women did. In conclusion, in adults with diabetes, sensory inputs and individual cofactors differently contribute to postural stability according to context. Rehabilitation programs for adults with diabetes may require an individualized approach.

Postural control in Chiari I malformation: protocol for a paediatric prospective, observational cohort - potential role of posturography for surgical indication

INTRODUCTION

Chiari I malformation (CM1) is an anatomical abnormality characterised by the cerebellar tonsils descending at least 5 mm below the foramen magnum. CM1 causes obstruction of cerebrospinal fluid (CSF) circulation as well as direct compression on the brainstem, thus causing typical consequences (syringomyelia), and typical clinical features (characteristic headaches and neurological impairment). Surgery is the only available treatment, indicated when symptomatology is present. However, sometimes patients have atypical complaints, which are often suggestive of otolaryngological (ears, nose and throat, ENT) involvement. This may be difficult for a neurosurgeon to explain. Our study aims to investigate the relationship between one of these atypical symptoms, for example, postural instability, in a paediatric population using a Computerised Dynamic Posturography (Equitest, NeuroCom, Clackamas, OR). To our knowledge, there are no previously published studies carried out on children with CM1, using dynamic posturography.

METHODS AND ANALYSIS

Forty-five children aged 6-18 years old presenting with radiologically confirmed CM1 and presenting ENT clinical complaints will be included in the study for a duration of 3 years. As primary endpoint, posturographic results will be described in the population study. Second, posturographic results will be compared between patients with and without indication for surgery. Finally, preoperative and postoperative posturographic results, as well as CSF circulation quality at foramen magnum level, syringomyelia, sleep apnoea syndrome, scoliosis and behaviour will be compared in the operated patient group.

ETHICS AND DISSEMINATION

This protocol received ethical approval from the Clinical Research Delegation of Nancy University Hospital, in accordance with the National Commission on Informatics and Liberties (Commission Nationale de l'Informatique et des Libertés) (protocol number 2019PI256-107). Our data treatment was in accordance with the Methodology of reference Methodology Reference-004 specification for data policy. The study findings will be disseminated via peer-reviewed publications and conference presentations, especially to the Neurosphynx's rare disease healthcare network.

TRIAL REGISTRATION NUMBER

NCT04679792; Pre-results.

Sex differences in the association of postural control with indirect measures of body representations

Besides anthropometric variables, high-order body representations have been hypothesised to influence postural control. However, this has not been directly tested before. Moreover, some studies indicate that sex moderates the relationship of anthropometry and postural control. Therefore, as a proof of concept we investigated the association of body representations with postural control as well as the influence of participants’ sex/gender. Body image measures were assessed with a figural drawing task. Body schema was tested by a covert and an overt task. Body sway was measured during normal bipedal quiet standing with eyes closed (with/without neck extended). Statistical analysis consisted of hierarchical multiple linear regressions with the following regression steps: (1) sensory condition, (2) sex/gender, (3) age, (4) anthropometry, (5) body schema, (6) body image, (7) sex/gender-interactions. Across 36 subjects (19 females), body schema was significantly associated with body sway variability and open-loop control, in addition to commonly known influencing factors, such as sensory condition, gender, age and anthropometry. While in females, also body image dissatisfaction substantially was associated with postural control, this was not the case in males. Sex differences and possible causes why high-order body representations may influence concurrent sensorimotor control of body sway are discussed.

Immediate Effects of Vibrotactile Biofeedback Instructions on Human Postural Control

Vibrotactile biofeedback can improve balance and consequently be helpful in fall prevention. However, it remains unclear how different types of stimulus presentations affect not only trunk tilt, but also Center of Pressure (CoP) displacements, and whether an instruction on how to move contributes to a better understanding of vibrotactile feedback.Based on lower back tilt angles (L5), we applied individualized multi-directional vibrotactile feedback to the upper torso by a haptic vest in 30 healthy young adults. Subjects were equally distributed to three instruction groups (attractive - move in the direction of feedback, repulsive - move in the opposite direction of feedback & no instruction - with attractive stimuli). We conducted four conditions with eyes closed (feedback on/off, Narrow Stance with head extended, Semi-Tandem stance), with seven trials of 45s each. For CoP and L5, we computed Root Mean Square (RMS) of position/angle and standard deviation (SD) of velocity, and for L5 additionally, the percentage in time above threshold. The analysis consisted of mixed model ANOVAs and t-tests (α-level: 0.05).In the attractive and repulsive groups feedback significantly decreased the percentage above threshold (p<0.05). Feedback decreased RMS of L5, whereas RMS of CoP and SD of velocity in L5 and COP increased (p<0.05). Finally, an instruction on how to move contributed to a better understanding of the vibrotactile biofeedback.

Stationary auditory white noise improves postural control in healthy adults: A novel study on head-shaking

BACKGROUND

Auditory cues might play a role in postural control.

OBJECTIVE

The primary aim of this study was to investigate the association between white noise and head-shake (HS) related changes in postural sway.

METHODS

Fifty healthy adults underwent Synapsys Posturography System (SPS) evaluation. The posturography (PG) evaluation consisted of two protocols: sensory organization test (SOT) and SOT with head-shake (HS) (HS-SOT). The standard SOT protocol of SPS involves a battery of six postural conditions. In the current study, participants underwent only four SOT conditions. The participants were asked to stand barefoot on the SPS platform (static platform and foam). The SOT standing conditions were as follow: (1) firm surface (force platform only) with eyes open (SOT1); (2) firm surface with eyes closed (SOT2); (3) foam surface (which was positioned on the force platform) with eyes open (SOT4); and (4) foam surface with eyes closed (SOT5). For the HS-SOT protocol, we asked the participants to move their heads left and right (i.e., yaw head rotation) in the mentioned SOT conditions. Each postural condition was 10 seconds long. Both SOT and HS-SOT postural conditions were conducted across the two hearing modes of silence and noise. To achieve our aims, comparison of sway parameters between SOT and HS-SOT, and between hearing modes were considered.

RESULTS

White noise was associated with a reduction in postural sway. The reduction observed in sway area, sway amplitude, and sway frequency. Moreover, HS significantly increased postural sway in all HS-SOT conditions compared to their SOT equivalents (i.e., HS-SOT1 compared to SOT1, etc.). The presence of white noise was associated with a decrease in the HS-related increase in postural sway.

CONCLUSIONS

Considering the results, this study adds to the body of literature suggesting that white noise contributes to postural control, and the implications of this for rehabilitation need to be further investigated.

Effect of vision loss on plasticity of the head and neck proprioception

AIM

To investigate whether head and neck proprioception and motor control could be compensatory enhanced by long-term vision loss or impairment.

METHODS

Individuals who were blind, low vision or sighted were included in the study, which would undergo the head repositioning test (HRT). The constant error (CE), absolute error (AE), variable error (VE) and root mean square error (RMSE) of each subject were statistically analyzed. Data were analyzed using the SAS 9.4. Tukey-Kramer for one-way ANOVA was used for comparison of blind, low vision, and sighted subjects, as well as to compare subjects with balanced vision, strong vision in the left eye and strong vision in the right eye. Independent sample t-test was used to compare subjects with congenital blindness and acquired blindness, as well as left and right hand dominance subjects.

RESULTS

A total of 90 individuals (25 blind subjects, 31 low vision subjects, and 34 sighted subjects) were included in the study. Among the blind subjects, 14 cases had congenital blindness and 11 cases had acquired blindness. Among the blind and low vision subjects, 21 cases had balanced binocular vision, 17 cases had strong vision in the left eye and 18 cases had strong vision in the right eye. Among all subjects, 11 cases were left hand dominance, and 79 cases were right hand dominance. There were significant differences in AE, VE, and RMSE in head rotation between blind, low vision, and sighted subjects (P<0.01), in AE, VE, and RMSE between blind and sighted (P<0.01), and in VE and RMSE between low vision and sighted (P<0.05). No significant difference between blind and low vision (P>0.05). Significant differences in CE and AE of head right rotation and CE of general head rotation between congenital and acquired (P<0.05). No significant differences between left and right hand dominance and in balance or not of binocular vision (P>0.05).

CONCLUSION

Long-term vision loss or impairment does not lead to compensatory enhancement of head and neck proprioception and motor control. Acquired experience contributes to HRT performance in the blind and has long-lasting effects on plasticity in the development of proprioception and sensorimotor control.

Age-Related Changes in Standing Balance in Preschoolers Using Traditional and Nonlinear Methods

Considerable disagreement exists on the linearity of the development of standing balance in children. This study aimed to use different traditional and nonlinear methods to investigate age-related changes in standing balance in preschoolers. A sample of 118 preschoolers took part in this study. A force platform was used to record the center of pressure during standing balance over 15 s in three conditions: eyes open, eyes closed, and/or head extended backward. Detrended fluctuation analysis (DFA), recurrence quantification analysis (RQA), and traditional measures were used to evaluate standing balance. The main results are as follows: (1) Higher range and SD in the anterior-posterior (AP) direction were observed for 5-year-old than for 4-year-old children, while higher DFA coefficient (at shorter time scales) and higher determinism and laminarity in the AP direction were found for 5-year-old children compared to 3- and 4-year-old children; and (2) as sensory conditions became more challenging, all traditional measures increased and DFA coefficients (at shorter and longer time scales) decreased in the AP and mediolateral directions, while determinism and laminarity significantly declined in the AP direction. In conclusion, although increased postural sway, 5-year-old preschool children's balance performance improved, and their control strategy changed significantly compared with the younger preschoolers. Sensory perturbation (eye closure and/or head extension) changed preschoolers' balance performance and control strategy. Moreover, both traditional and nonlinear methods provided complementary information on the control of standing balance in preschoolers.

The Effects of Texting, Sitting Surface Stability, and Balance Training on Simulated Driving Performance and Perceived Workload in Young and Older Drivers

It has been shown that texting degrades driving performance, but the extent to which this is mediated by the driver’s age and postural stability has not been addressed. Hence, the present study examined the effects of texting, sitting surface stability, and balance training in young and older adults’ driving performance. Fifteen young (mean age = 24.3 years) and 13 older (mean age = 62.8 years) participants were tested in a driving simulator with and without texting on a smartphone and while sitting on a stable or unstable surface (i.e., a plastic wobble board), before and after a 30-min sitting balance training. Analyses of variance showed that texting deteriorated driving performance but irrespective of sitting surface stability. Balance training decreased the negative effects of texting on driving, especially in older adults. Perceived workload increased when drivers were texting, and balance training reduced perceived workload. Perceived workload was higher while sitting on the unstable surface, but less so after balance training. Path analyses showed that the effects on driving performance and perceived workload were (indirectly) associated with changes in postural stability (i.e., postural sway). The study confirms that texting threatens safe driving performance by challenging postural stability, especially in older adults. The study also suggests that it is important to further investigate the role balance training can play in reducing these negative effects of texting.

A Postural Assessment Utilizing Machine Learning Prospectively Identifies Older Adults at a High Risk of Falling

Introduction: Falls are the leading cause of accidental death in older adults. Each year, 28.7% of US adults over 65 years experience a fall resulting in over 300,000 hip fractures and $50 billion in medical costs. Annual fall risk assessments have become part of the standard care plan for older adults. However, the effectiveness of these assessments in identifying at-risk individuals remains limited. This study characterizes the performance of a commercially available, automated method, for assessing fall risk using machine learning.

Methods: Participants (N = 209) were recruited from eight senior living facilities and from adults living in the community (five local community centers in Houston, TX) to participate in a 12-month retrospective and a 12-month prospective cohort study. Upon enrollment, each participant stood for 60 s, with eyes open, on a commercial balance measurement platform which uses force-plate technology to capture center-of-pressure (60 Hz frequency). Linear and non-linear components of the center-of-pressure were analyzed using a machine-learning algorithm resulting in a postural stability (PS) score (range 1–10). A higher PS score indicated greater stability. Participants were contacted monthly for a year to track fall events and determine fall circumstances. Reliability among repeated trials, past and future fall prediction, as well as survival analyses, were assessed.

Results: Measurement reliability was found to be high (ICC(2,1) [95% CI]=0.78 [0.76–0.81]). Individuals in the high-risk range (1-3) were three times more likely to fall within a year than those in low-risk (7–10). They were also an order of magnitude more likely (12/104 vs. 1/105) to suffer a spontaneous fall i.e., a fall where no cause was self-reported. Survival analyses suggests a fall event within 9 months (median) for high risk individuals.

Conclusions: We demonstrate that an easy-to-use, automated method for assessing fall risk can reliably predict falls a year in advance. Objective identification of at-risk patients will aid clinicians in providing individualized fall prevention care.

Head stabilization during standing in people with persisting symptoms after mild traumatic brain injury

Increased postural sway is often observed in people with mild traumatic brain injury (mTBI), but our understanding of how individuals with mTBI control their head during stance is limited. The purpose of this study was to determine if people with mTBI exhibit increased sway at the head compared with healthy controls. People with persisting symptoms after mTBI (n = 59, 41 women) and control participants (n = 63, 38 women) stood quietly for one minute in four conditions: eyes open on a firm surface (EO-firm), eyes closed on a firm surface (EC-firm), eyes open on a foam pad (EO-foam), and eyes closed on foam (EC-foam). Inertial sensors at the head, sternum, and lumbar region collected tri-axial accelerations. Root-mean-square (RMS) accelerations in anteroposterior (AP) and mediolateral (ML) directions and sway ratios between the head and sternum, head and lumbar, and sternum and lumbar region were compared between groups. Temporal coupling of anti-phase motion between the upper and lower body angular accelerations was assessed with magnitude squared coherence and cross-spectral phase angles. People with mTBI demonstrated greater sway than controls across conditions and directions. During foam-surface conditions, the control group, but not the mTBI group, reduced ML sway at their head and trunk relative to their lumbar by increasing the expression of an anti-phase hip strategy within the frontal plane. These results are consistent with suggestions of inflexible or inappropriate postural control in people with mTBI.

Constraints of Load and Posture on Coordination Variability and Marksmanship Performance

The purpose of this study was to assess the establishment of dynamic marksmanship performance under different load and postural configurations. Participants quickly established two postures (forward and high targets) under head, trunk, and extremity loads during marksmanship performance. With the dynamic establishment of posture, load disrupted coordinative dynamics, resulting in reduced speed and accuracy on target. Specifically, torso loads increased segmental variability while establishing posture, and smaller head and upper extremity loads extended quieting time before firing. Increased head extension at the high target further destabilized posture, with reduced accuracy across all loads. Large torso loads reduced the adaptability to modulate postural fluctuations at the foot center of pressure while establishing postures for marksmanship, as evidenced by reductions in center of pressure variability. This study expands traditional static marksmanship research, providing insight into relations between task performance, coordinative variability, and postural control while dynamically establishing precision postures.

Challenges to the central nervous system during human spaceflight missions to Mars

Space travel presents a number of environmental challenges to the central nervous system, including changes in gravitational acceleration that alter the terrestrial synergies between perception and action, galactic cosmic radiation that can damage sensitive neurons and structures, and multiple factors (isolation, confinement, altered atmosphere, and mission parameters, including distance from Earth) that can affect cognition and behavior. Travelers to Mars will be exposed to these environmental challenges for up to 3 years, and space-faring nations continue to direct vigorous research investments to help elucidate and mitigate the consequences of these long-duration exposures. This article reviews the findings of more than 50 years of space-related neuroscience research on humans and animals exposed to spaceflight or analogs of spaceflight environments, and projects the implications and the forward work necessary to ensure successful Mars missions. It also reviews fundamental neurophysiology responses that will help us understand and maintain human health and performance on Earth.

Screening for Vestibular Disorders Using the Modified Clinical Test of Sensory Interaction and Balance and Tandem Walking With Eyes Closed

OBJECTIVES

Determine accurate cut-points and optimal combinations of screening tests of balance to detect patients with vestibular disorders.

STUDY DESIGN

Case-control study.

SETTING

Out-patient tertiary care.

SUBJECTS AND METHODS

Community-dwelling adults, without known neurological deficits or significant musculoskeletal disorders, including patients with vestibular disorders and healthy controls without vestibular disorders were tested while standing on medium density compliant foam with feet together and eyes closed under three head movement conditions, head stationary, and head moving in yaw and pitch at 0.33 Hz, for up to 30 seconds per trial. Dependent measures were trial duration, number of head movements during head movement trials, trunk kinematic measures, and number of correct tandem steps during tandem walking trials.

RESULTS

Receiver operator characteristics (ROC), sensitivity and specificity, and specific cut-points were calculated. Individual tests had moderate ROC values, from 0.67 to 0.84. ROC values were higher in the head moving trials than the head stationary trial and best for subjects aged 40 to 79. Using combined analyses of two or more tests, including published data on tandem walking, ROC values were higher, 0.80 to 0.90. Age- and sex-related performance differences were found.

CONCLUSION

Balance skills in standing and walking differ, so testing both skills is optimal and increases the likelihood of finding a deficit. Patients should be compared to age-appropriate norms. Kinematics and number of head movements were not very useful. This combined set of rapid, low-tech balance tests is useful in an initial approach to screening patients who may have vestibular disorders.

Effects of head motion on postural stability in healthy young adults with chronic motion sensitivity

Background

Motion sensitivity, or motion sickness, is common in modern vehicular and visually stimulating environments. Several studies have shown a relationship between motion sensitivity and decreased postural stability. We aimed to evaluate the effects of head motion (horizontal and vertical) on postural stability in healthy adults with and without chronic motion sensitivity (CMS).

Methods

Sixty healthy adult men and women (age, 20–40 years) with CMS (CMS group, n = 30) and without CMS (non-CMS group, n = 30) participated in the study. Postural stability was assessed during three conditions (static, horizontal head motion, and vertical head motion) using computerized dynamic posturography. Group and condition-related differences in equilibrium scores were evaluated.

Results

There was no significant group x condition interaction (F_2,114 = 0.9, partial ƞ² = 0.04, p = 0.35). However, significant condition-related differences in equilibrium scores were observed (F_2,114 = 26.4, partial ƞ² = 0.31, p < 0.001). Equilibrium scores were significantly worse in the horizontal and vertical head motion conditions compared to those in the static condition (p < 0.001), but were comparable in vertical and horizontal head motion conditions (p = 0.27).

Conclusions

Postural stability was lower in the horizontal and vertical conditions compared to the static condition. However, horizontal and vertical head motions had comparable effects on postural stability in both CMS and non-CMS groups, contrary to our expectations.

Head and neck extension more than 30° may disturb standing balance in healthy older adults

Although there is clinical evidence of postural instability at extreme angles of head extension, the effects of lower angles on balance have been not investigated. This study aimed to investigate the effects of different head and neck extension angles on standing balance in older adults, and to determine the critical angle of instability. Twenty-eight healthy older adults were tested at 0°, 20°, 30° and 40° head and neck extension. The center of pressure (COP) parameters were recorded with a force plate. Significant differences were observed between 30° and 40° compared to 0° in anteroposterior and mediolateral COP displacement and total COP velocity, and between 40° and 0° in mediolateral COP velocity. Head and neck extension at 30° was the critical angle associated with the appearance of instability, and this value should be considered in the ergonomic design of work and living spaces, exercise programming and daily activities in older adults.

POSTURAL STABILITY STRATEGIES IN TRANSTIBIAL AMPUTEES DURING QUIET STANDING IN ALTERED SENSORY CONDITIONS WEARING THREE TYPES OF PROSTHETIC FEET

Individuals with transtibial amputation exhibit altered movement strategy to sustain stability during quiet standing due to reduced proprioception on the amputated limb. The aim of this study is to determine the movement strategies in anterior–posterior and medial–lateral directions in predicting the overall postural stability. In this crossover study, postural stability of ten transtibial amputees was assessed using computed posturography while wearing different prosthetic foot types: solid ankle cushion heel (SACH), single axis (SA) and energy storage and return (ESAR). Three stability indices were measured during four conditions: standing with eyes opened and closed, standing on compliant surface and standing with tilted head. From the standard multiple regression analysis, 63% to 99% of the OSI score in all sensory conditions were explained from the MLSI score, while 11% to 56% from the APSI score. The Pearson’s [Formula: see text] indicated significant strong positive relationship between OSI and MLSI [Formula: see text]–[Formula: see text] during all sensory conditions. The APSI score was significantly lower than OSI during eyes-closed and head extended conditions for all prosthetic feet [Formula: see text]. Adjustments in postural stability strategies in transtibial amputees mostly occurred in medial–lateral direction regardless of prosthetic feet types and altered sensory conditions.

Clinical significance of head shake movement in three planes in individuals with dizziness

PURPOSE

This study aims to evaluate the efficacy of head shake movement on three head movement planes (yaw, pitch and, roll) in patients with dizziness despite normal vestibular test results.

MATERIALS AND METHODS

Twenty individuals aged between 20 and 51 years with complaints of dizziness were included in the study, and their results were compared with the results from twenty age- and gender-matched controls. Participants were assessed using the Sensory Organization Test, Head Shake-Sensory Organization Test which is based on the modification of the Sensory Organization Test on the yaw, pitch, and roll planes, videonystagmography, caloric test, and Dizziness Handicap Inventory.

RESULTS

Significant differences were found in the yaw (p = 0.007), pitch (p < 0.001), and roll (p = 0.002) planes between the study and control groups of the Head Shake-Sensory Organization Test-5 scores. There were no statistically significant differences between the two groups of the Head Shake-Sensory Organization Test-2 scores in the yaw (p = 0.448), pitch (p = 0.213), and roll (p = 0.531) planes. When the sensitivity and specificity of Head Shake-Sensory Organization Test-5 conditions were examined, the highest specificity was observed in the pitch plane (100%), followed by the yaw (95%) and roll plane (95%).

CONCLUSION

Dynamic head movements are an important parameter for the evaluation of balance performance. The head shake modification could be used effectively in three-movement planes in individuals with dizziness.

Sensorimotor impairment from a new analog of spaceflight-altered neurovestibular cues

Exposure to microgravity during spaceflight causes central reinterpretations of orientation sensory cues in astronauts, leading to sensorimotor impairment upon return to Earth. Currently there is no ground-based analog for the neurovestibular system relevant to spaceflight. We propose such an analog, which we term the "wheelchair head-immobilization paradigm" (WHIP). Subjects lie on their side on a bed fixed to a modified electric wheelchair, with their head restrained by a custom facemask. WHIP prevents any head tilt relative to gravity, which normally produces coupled stimulation to the otoliths and semicircular canals, but does not occur in microgravity. Decoupled stimulation is produced through translation and rotation on the wheelchair by the subject using a joystick. Following 12 h of WHIP exposure, subjects systematically felt illusory sensations of self-motion when making head tilts and had significant decrements in balance and locomotion function using tasks similar to those assessed in astronauts postspaceflight. These effects were not observed in our control groups without head restraint, suggesting the altered neurovestibular stimulation patterns experienced in WHIP lead to relevant central reinterpretations. We conclude by discussing the findings in light of postspaceflight sensorimotor impairment, WHIP's uses beyond a spaceflight analog, limitations, and future work.NEW & NOTEWORTHY We propose, implement, and demonstrate the feasibility of a new analog for spaceflight-altered neurovestibular stimulation. Following extended exposure to the analog, we found subjects reported illusory self-motion perception. Furthermore, they demonstrated decrements in balance and locomotion, using tasks similar to those used to assess astronaut sensorimotor performance postspaceflight.

Physiological and Functional Alterations after Spaceflight and Bed Rest

Supplemental digital content is available in the text.

Introduction

Exposure to microgravity causes alterations in multiple physiological systems, potentially impacting the ability of astronauts to perform critical mission tasks. The goal of this study was to determine the effects of spaceflight on functional task performance and to identify the key physiological factors contributing to their deficits.

Methods

A test battery comprised of seven functional tests and 15 physiological measures was used to investigate the sensorimotor, cardiovascular, and neuromuscular adaptations to spaceflight. Astronauts were tested before and after 6-month spaceflights. Subjects were also tested before and after 70 d of 6° head-down bed rest, a spaceflight analog, to examine the role of axial body unloading on the spaceflight results. These subjects included control and exercise groups to examine the effects of exercise during bed rest.

Results

Spaceflight subjects showed the greatest decrement in performance during functional tasks that required the greatest demand for dynamic control of postural equilibrium which was paralleled by similar decrements in sensorimotor tests that assessed postural and dynamic gait control. Other changes included reduced lower limb muscle performance and increased HR to maintain blood pressure. Exercise performed during bed rest prevented detrimental change in neuromuscular and cardiovascular function; however, both bed rest groups experienced functional and balance deficits similar to spaceflight subjects.

Conclusion

Bed rest data indicate that body support unloading experienced during spaceflight contributes to postflight postural control dysfunction. Further, the bed rest results in the exercise group of subjects confirm that resistance and aerobic exercises performed during spaceflight can play an integral role in maintaining neuromuscular and cardiovascular functions, which can help in reducing decrements in functional performance. These results indicate that a countermeasure to mitigate postflight postural control dysfunction is required to maintain functional performance.

Differences in postural stability and dynamic visual acuity among healthy young adults in relation to sports activity: a cross sectional study

[Purpose] Sports activity has been shown to improve postural stability and vestibular function in healthy older adults. The hypothesis was that healthy young adults undertaking sports activity will also have better postural stability and vestibular function compared with healthy young adults who do not undertake sports activity. The purpose of this study was to investigate the differences in postural stability and vestibular function between healthy young adults who undertake sports activity and those who do not undertake such activity. [Participants and Methods] Thirty-nine healthy young adults were recruited and divided into sports and non-sports groups on the basis of their response to a questionnaire concerning regular participation in sports activities over the past 12 months. In both groups, postural stability was measured during quiet standing and standing during head rotation, and dynamic visual acuity was assessed during head rotation. [Results] The results showed significant differences in postural stability during head rotation and dynamic visual acuity between the two groups, whereas no significant differences were found in postural stability during quiet standing. [Conclusion] The results suggest that healthy young adults who undertake sports activity have better postural stability during head rotation and better dynamic visual acuity. The causal effect of these differences is not clear and further investigation is warranted.

Critical Role of Somatosensation in Postural Control Following Spaceflight: Vestibularly Deficient Astronauts Are Not Able to Maintain Upright Stance During Compromised Somatosensation

The free-fall of orbital spaceflight effectively removes the gravitational vector used as a primary spatial orientation reference on Earth. Sustained absence of this reference drives adaptive changes in the internal perception-action models of the central nervous system (CNS), most notably in the processing of the vestibular otolith inputs. Upon landing, the return of the gravitational signal triggers a re-adaptation that restores terrestrial performance; however, during this period, the individual suffers from a functional vestibular deficiency. Here we provide evidence of a transient increase of the weighting of somatosensory inputs in postural control while the CNS resolves these vestibular deficiencies. Postural control performance was measured before and after spaceflight in 11 Shuttle astronauts and 11 matched controls and nine elderly who did not experience spaceflight. A quiet-stance paradigm was used that eliminated vision, modulated the lower extremity somatosensory cues by subtly modulating the orientation of the support surface beneath feet of subjects in all groups. Additionally, in astronauts and matched controls, we challenged the vestibular system with dynamic head tilts. Postural stability on the landing day (R+0) was substantially decreased for trials with absent visual and altered somatosensory cues, especially those also requiring dynamic head tilts ( ± 5° @ 0.33 Hz) during which 20/22 trials ended prematurely with a fall. In contrast, none of the astronauts fell during eyes-closed, dynamic head tilt trials with unaltered somatosensory cues, and only 3/22 trials resulted in falls with eyes-closed and altered somatosensory cues, but static upright head orientation. Furthermore, postural control performance of astronauts was either statistically not different or worse than that of healthy elderly subjects during the most challenging vestibular conditions on R+0. Overall, our results demonstrate a transient reweighting of sensory cues associated with microgravity-induced vestibular deficiencies, with a significant increase in reliance on somatosensory cues, which can provide an effective reference even without vision and with dynamic vestibular challenges. The translation of these results to aging population suggests that elderly individuals with visual and vestibular deficits may benefit from therapeutic interventions enhancing sensorimotor-integration to improve balance and reduce the risk of falling.

Devices and tasks involved in the objective assessment of standing dynamic balancing - A systematic literature review

BACKGROUND

Static balancing assessment is often complemented with dynamic balancing tasks. Numerous dynamic balancing assessment methods have been developed in recent decades with their corresponding balancing devices and tasks.

OBJECTIVE

The aim of this systematic literature review is to identify and categorize existing objective methods of standing dynamic balancing ability assessment with an emphasis on the balancing devices and tasks being used.

DATA SOURCES

Three major scientific literature databases (Science Direct, Web of Science, PLoS ONE) and additional sources were used.

STUDY SELECTION

Studies had to use a dynamic balancing device and a task described in detail. Evaluation had to be based on objectively measureable parameters. Functional tests without instrumentation evaluated exclusively by a clinician were excluded. A total of 63 articles were included.

DATA EXTRACTION

The data extracted during full-text assessment were: author and date; the balancing device with the balancing task and the measured parameters; the health conditions, size, age and sex of participant groups; and follow-up measurements.

DATA SYNTHESIS

A variety of dynamic balancing assessment devices were identified and categorized as 1) Solid ground, 2) Balance board, 3) Rotating platform, 4) Horizontal translational platform, 5) Treadmill, 6) Computerized Dynamic Posturography, and 7) Other devices. The group discrimination ability of the methods was explored and the conclusions of the studies were briefly summarized.

LIMITATIONS

Due to the wide scope of this search, it provides an overview of balancing devices and do not represent the state-of-the-art of any single method.

CONCLUSIONS

The identified dynamic balancing assessment methods are offered as a catalogue of candidate methods to complement static assessments used in studies involving postural control.

Balance, Proprioception, and Gross Motor Development of Chinese Children Aged 3 to 6 Years

The authors' aim was to find the features of balance, proprioception, and gross motor development of Chinese children 3-6 years old and their correlations, provide theoretical support for promoting children's motor development, and enrich the world theoretical system of motor development. This study used a Tekscan foot pressure measurement instrument (Tekscan, Inc., Boston, MA), walking on a balance beam, Xsens 3-dimensional positional measuring system (Xsens Technologies, Enschede, the Netherlands), and Test of Gross Motor Development-2 to assess static balance, dynamic balance, knee proprioception, and levels of gross motor development (GMD) of 3- to 6-year-old children (n = 60) in Beijing. The results are as follows: children had significant age differences in static balance, dynamic balance, proprioception, and levels of GMD; children had significant gender differences in static balance, proprioception, and levels of GMD; children's static balance, dynamic balance, and proprioception had a very significant positive correlation with GMD (p < .01), but no significant correlation with body mass index.

Assessing Somatosensory Utilization during Unipedal Postural Control

Multisensory-visual, vestibular and somatosensory information is integrated for appropriate postural control. The primary goal of this study was to assess somatosensory utilization during a functional motor task of unipedal postural control, in normal healthy adults. Assessing individual bias in the utilization of individual sensory contributions during postural control may help customization of rehabilitation protocols. In this study, a test paradigm of unipedal stance control in supine orientation with and without vision was assessed. Postural control in this test paradigm was hypothesized to utilize predominantly contributions of somatosensory information from the feet and ankle joint, with minimal vestibular input. Fourteen healthy subjects "stood" supine on their dominant leg while strapped to a backpack frame that was freely moving on air-bearings, to remove available otolith tilt cues with respect to gravity that influences postural control when standing upright. The backpack was attached through a cable to a pneumatic cylinder that provided a gravity-like load. Subjects performed three trials each with Eyes-open (EO) and Eyes-closed (EC) while loaded with 60% body weight. There was no difference in unipedal stance time (UST) across the two conditions with EC condition challenging the postural control system greater than the EO condition. Stabilogram-diffusion analysis (SDA) indicated that the critical mean square displacement was significantly different between the two conditions. Vestibular cues, both in terms of magnitude and the duration for which relevant information was available for postural control in this test paradigm, were minimized. These results support our hypothesis that maintaining unipedal stance in supine orientation without vision, minimizes vestibular contribution and thus predominantly utilizes somatosensory information for postural control.

Change in the natural head-neck orientation momentarily altered sensorimotor control during sensory transition

Achilles tendon vibration generates proprioceptive information that is incongruent with the actual body position; it alters the perception of body orientation leading to a vibration-induced postural response. When a person is standing freely, vibration of the Achilles tendon shifts the internal representation of the verticality backward thus the vibration-induced postural response realigned the whole body orientation with the shifted subjective vertical. Because utricular otoliths information participates in the creation of the internal representation of the verticality, changing the natural orientation of the head-neck system during Achilles tendon vibration could alter the internal representation of the earth vertical to a greater extent. Consequently, it was hypothesized that compared to neutral head-neck orientation, alteration in the head-neck orientation should impair balance control immediately after Achilles tendon vibration onset or offset (i.e., sensory transition) as accurate perception of the earth vertical is required. Results revealed that balance control impairment was observed only immediately following Achilles tendon vibration offset; both groups with the head-neck either extended or flexed showed larger body sway (i.e., larger root mean square scalar distance between the center of pressure and center of gravity) compared to the group with the neutral head-neck orientation. The fact that balance control was uninfluenced by head-neck orientation immediately following vibration onset suggests the error signal needs to accumulate to a certain threshold before the internal representation of the earth vertical becomes incorrect.

Postural Ataxia in Cerebellar Downbeat Nystagmus: Its Relation to Visual, Proprioceptive and Vestibular Signals and Cerebellar Atrophy

Background

The cerebellum integrates proprioceptive, vestibular and visual signals for postural control. Cerebellar patients with downbeat nystagmus (DBN) complain of unsteadiness of stance and gait as well as blurred vision and oscillopsia.

Objectives

The aim of this study was to elucidate the differential role of visual input, gaze eccentricity, vestibular and proprioceptive input on the postural stability in a large cohort of cerebellar patients with DBN, in comparison to healthy age-matched control subjects.

Methods

Oculomotor (nystagmus, smooth pursuit eye movements) and postural (postural sway speed) parameters were recorded and related to each other and volumetric changes of the cerebellum (voxel-based morphometry, SPM).

Results

Twenty-seven patients showed larger postural instability in all experimental conditions. Postural sway increased with nystagmus in the eyes closed condition but not with the eyes open. Romberg’s ratio remained stable and was not different from healthy controls. Postural sway did not change with gaze position or graviceptive input. It increased with attenuated proprioceptive input and on tandem stance in both groups but Romberg’s ratio also did not differ. Cerebellar atrophy (vermal lobule VI, VIII) correlated with the severity of impaired smooth pursuit eye movements of DBN patients.

Conclusions

Postural ataxia of cerebellar patients with DBN cannot be explained by impaired visual feedback. Despite oscillopsia visual feedback control on cerebellar postural control seems to be preserved as postural sway was strongest on visual deprivation. The increase in postural ataxia is neither related to modulations of single components characterizing nystagmus nor to deprivation of single sensory (visual, proprioceptive) inputs usually stabilizing stance. Re-weighting of multisensory signals and/or inappropriate cerebellar motor commands might account for this postural ataxia.

The Neurovestibular Challenges of Astronauts and Balance Patients: Some Past Countermeasures and Two Alternative Approaches to Elicitation, Assessment and Mitigation

Astronauts and vestibular patients face analogous challenges to orientation function due to adaptive exogenous (weightlessness-induced) or endogenous (pathology-induced) alterations in the processing of acceleration stimuli. Given some neurovestibular similarities between these challenges, both affected groups may benefit from shared research approaches and adaptation measurement/improvement strategies. This article reviews various past strategies and introduces two plausible ground-based approaches, the first of which is a method for eliciting and assessing vestibular adaptation-induced imbalance. Second, we review a strategy for mitigating imbalance associated with vestibular pathology and fostering readaptation. In discussing the first strategy (for imbalance assessment), we review a pilot study wherein imbalance was elicited (among healthy subjects) via an adaptive challenge that caused a temporary/reversible disruption. The surrogate vestibular deficit was caused by a brief period of movement-induced adaptation to an altered (rotating) gravitoinertial frame of reference. This elicited adaptation and caused imbalance when head movements were made after reentry into the normal (non-rotating) frame of reference. We also review a strategy for fall mitigation, viz., a prototype tactile sway feedback device for aiding balance/recovery after disruptions caused by vestibular pathology. We introduce the device and review a preliminary exploration of its effectiveness in aiding clinical balance rehabilitation (discussing the implications for healthy astronauts). Both strategies reviewed in this article represent cross-disciplinary research spin-offs: the ground-based vestibular challenge and tactile cueing display were derived from aeromedical research to benefit military aviators suffering from flight simulator-relevant aftereffects or inflight spatial disorientation, respectively. These strategies merit further evaluation using clinical and astronaut populations.

Stabilisation times after transitions to standing from different working postures

Transitioning to standing after maintaining working postures may result in imbalance and could elicit a fall. The objective of this study was to quantify the magnitude of imbalance using a stabilisation time metric. Forty-five male participants completed three replications of conditions created by one of four working postures (bent at waist, squat, forward kneel, reclined kneel) and three durations within posture. Participants transitioned to quiet standing at a self-selected pace. Stabilisation time, based on changes in centre of pressure velocity, was used to indicate the initiation of steady state while standing. Stabilisation time was significantly affected by static postures but not duration within posture. The largest stabilisation times resulted from transitions initiated from a bent at waist posture. The smallest were associated with the kneeling postures, which were not significantly different from each other. Findings may lead to recommendations for redesign of tasks, particularly in high-risk environments such as construction. Statement of Relevance: Task performance on the jobsite often requires individuals to maintain non-erect postures. This study suggests that working posture affects stabilisation during transition to a standing position. Bending at the waist and squatting resulted in longer stabilisation times, whereas both kneeling postures evaluated resulted in greater imbalance but for a shorter duration.

Modified head shake sensory organization test: Sensitivity and specificity

The Sensory Organization Test (SOT) of Computerized Dynamic Posturography (EquiTest™ equipment) is a valuable tool for investigating how an individual uses balance system sensory input (vestibular, vision, proprioception/somatosensory) to maintain quiet stance; however, it is limited as a screening tool for identifying peripheral vestibular system dysfunction. Previous research has shown that adding horizontal head-shake to portions of the standard SOT battery improved the identification of peripheral vestibular system asymmetry; however, flaws in the methods were noted. The objective of this work was to evaluate the sensitivity and specificity of the modified head-shake SOT (HS-SOT) protocol for identification of peripheral vestibular system lesion. Fifteen patients with chief complaint of instability, vertigo, and/or lightheadedness, with and without a caloric unilateral weakness (UW) and fifteen age-matched healthy controls were included in the final analysis. Ten of the 15 patients demonstrated a caloric UW≥25%. Participants completed standard conditions 2 and 5 of SOT with head still and during four horizontal head-shaking tasks (i.e., HS-SOT2-60°/s, HS-SOT2-120°/s, HS-SOT5-15°/s, and HS-SOT5-60°/s). Average equilibrium scores decreased as condition difficulty increased (SOT2, HS-SOT2-60°/s, HS-SOT2-120°/s, SOT 5, HS-SOT5-15°/s, and HS-SOT5-60°/s) for each group; as expected, a lower decline was noted for controls (slope=-6.59) compared to patients (slope=-11.69). The HS-SOT5-15°/s condition was superior for identifying peripheral vestibular asymmetry (AUC=0.90 sensitivity=70%, specificity=100%), with the strongest correlation to caloric UW% (rs=-0.743, p=0.000006). HS-SOT5-15°/s appears to be a promising screening measure for peripheral vestibular asymmetry.

Shoulder elevation affects joint position sense and muscle activation differently in upright and supine body orientations

OBJECTIVE

Investigate the effects of shoulder elevation on repositioning errors in upright and supine body orientations, and examine these effects on anterior and posterior deltoid muscle activation. We hypothesized decreased errors, and altered anterior and posterior deltoid activation with increasing elevation, in both orientations.

DESIGN

Crossover trial.

SETTING

University laboratory.

PARTICIPANTS

Thirty-five college-aged participants.

INTERVENTION

Subjects attempted to replicate target positions of various elevation angles in upright and supine body orientations. Also, anterior and posterior deltoid activation was recorded in each shoulder position and body orientation.

MAIN OUTCOME MEASURES

Vector and variable repositioning errors, anterior and posterior deltoid percentage of maximal contraction.

RESULTS

Vector error was greater in supine compared to upright at 90° and 110°, but not at 70°. Variable error was larger in supine than upright, but was unaffected by elevation. Anterior deltoid activation increased with elevation in the upright posture only. Posterior deltoid activation increased with elevation across postures.

CONCLUSIONS

Muscle activation, external torque, and cutaneous sensations may combine to provide afferent feedback, and be used with centrally-generated signals to interpret the state of the limb during movement. Clinicians may prescribe open kinetic chain exercises in the upright posture with the shoulder elevated approximately 90-100°.

Short-term differential training decreases postural sway

Differential training has been shown to enhance motor learning in sports skills. In the present study differential training was applied to the minimization of postural sway. A differential training group performed 15 one minute practice trials, each with different postural movement instructions. A repetitive practice group performed 15 trials standing as still as possible for one minute. Pre- and post-tests were performed standing as still as possible in 1 and 2-leg stance. Accelerometry data were collected approximately at the level of the center of mass (COM) and at the head. The root mean square jerk (RMSJ) of movement at the COM and head was estimated for the anteroposterior and mediolateral axes of motion. A significant Group × Test interaction revealed that the differential training led to lower anteroposterior RMSJ on the post-test than on the Pre-test in both the 1 and 2-leg stance tasks. A significant Group × Effector × Test interaction revealed that the decrease in anteroposterior RMSJ with differential training occurred in the RMSJ of the head but not the COM. The repetitive practice did not lead to a significant change in anteroposterior RMSJ at either the COM or the head. Neither form of training led to a significant change in mediolateral RMSJ. The results indicated that differential training can enhance motor learning not only in complex sports skills but in relatively simple motor tasks such as maintaining quiet stance.

Vestibular functioning and migraine: pilot study comparing those with and without vertigo

Background:

The current study compared a migrainous vertigo group with a migraine without vertigo group. It was hypothesised that those with migrainous vertigo would have more abnormal test results during a non-migrainous period than those who suffer from migraine without vertigo.

Methods:

Both groups, comprising 10 participants each, were tested using: the gaze stabilisation test, dynamic visual acuity test, sensory organisation test, head shake sensory organisation test and functional gait assessment.

Results:

Eighteen females and 2 males aged 18–53 years participated. There were no significant differences between the two groups for the dynamic visual acuity test, sensory organisation test or head shake sensory organisation test. However, mean dynamic visual acuity loss was greater in both groups than in a normal population, and the head shake sensory organisation (sway) test was well below the normal mean. The functional gait assessment showed a significant difference (p = 0.0025) between the two groups.

Conclusion:

Both groups showed abnormalities in vestibular functioning compared with norms, suggesting that both had some degree of vestibular dysfunction. However, vestibular dysfunction was greater in the migrainous vertigo group than in the migraine without vertigo group, as evidenced by differences in functional gait assessment.

Defining soldier equipment trade space: load effects on combat marksmanship and perception-action coupling

Soldier equipment compromises task performance as temporal constraints during critical situations and load increase inertial and interactive forces during movement. Methods are necessary to optimise equipment that relate task performance to underlying coordination and perception-action coupling. Employing ecological task analysis and methods from dynamical systems theory, equipment load and coordination was examined during two sub-tasks embedded in combat performance, threat discrimination and dynamic marksmanship. Perception-action coupling was degraded with load during threat discrimination, leading to delays in functional reaction time. Reduced speed and accuracy during dynamic marksmanship under load was related to disrupted segmental coordination and adaptability during postural transitions between targets. These results show how reduced performance under load relates to coordination changes and perception-action coupling. These changes in functional capability are directly related to soldier survivability in combat. The methods employed may aid equipment design towards more optimised performance by modifying equipment or its distribution on humans.

New analyses of the sensory organization test compared to the clinical test of sensory integration and balance in patients with benign paroxysmal positional vertigo

OBJECTIVES/HYPOTHESIS

To determine whether the Sensory Organization Test (SOT) of the computerized dynamic posturography battery or the Clinical Test of Sensory Integration and Balance (CTSIB) is more likely to indicate balance disorders in people with benign paroxysmal positional vertigo (BPPV).

STUDY DESIGN

Normal controls were compared to patients with unilateral BPPV of the posterior semicircular canal.

METHODS

Subjects performed tests with eyes open or closed on stable and unstable surfaces, with head still or with head moving at 0.33 Hz in pitch or yaw. Dependent variables were the percent time of the standard duration each subject could perform the task, the number of head motions made, and kinematic variables measured with head- and torso-mounted inertial motion units.

RESULTS

Because equilibrium scores of control subjects improved significantly over repeated trials on SOT, patients were given only one trial per condition. For percent time between-group differences were found on CTSIB with eyes closed, on foam, head moving in yaw showing significantly reduced performance by BPPV subjects compared to controls. Compared to controls, patients made significantly fewer head movements on CTSIB, eyes closed, on foam, head still, in pitch and yaw. Kinematic data also differed between the groups on tests with eyes closed and unstable surfaces with different head movement combinations, indicating increased instability in BPPV patients.

CONCLUSIONS

For screening, CTSIB with head movements is more likely than SOT to indicate balance deficits, especially when dependent measures include percent time as well as head movement counts and kinematic measures.

Significance of adequate postural control in the appearance of habitual upright bipedal locomotion

Analysis of qualitative indicators of stability of the body during different types of locomotion in primates suggests that bipedal locomotion is not variation of some other type of locomotion. Transition from quadrupedal to bipedal locomotion is accompanied by a qualitative difference in body stability. Because of assuming an upright bipedal posture, the center of mass is lifted, the surface of the base of support is reduced, and the body structure does not provide passive stability in relation to inertial moments of the body around Y-axis. Additional head movements, trunk rotations, forelimb manipulations with objects and surveying the surroundings are necessary for survival, but they increase the degree of freedom of movement and further complicate the task of maintaining balance in the case of a postural change from erect quadrupedal to erect bipedal. This article presents a hypothesis that the transition from quadrupedal to habitual upright bipedal locomotion was caused by qualitative changes in the nervous system that allowed controlling the more demanding type of locomotion. The ability to control a more demanding posture increases possibilities of interactions between the organism and the complex environment and consequently increases the survival rate, breeding possibilities, and chances for occupying a new environmental niche. Existing data show that ability to execute the more demanding type of locomotion was made possible because of changes in the frontal lobe and pyramidal system. Only after the more demanding posture was enabled by changes in the nervous system, could advantages of bipedal over quadrupedal locomotion be utilized, including better scanning of the environment, carrying food and infants, simultaneous upper extremity movements and observation of the environment, limitless manipulation of objects with upper extremities above the individual, and less space for rotating around the Z-axis. The aforementioned advantages of habitual bipedal over quadrupedal locomotion are present in physically complex environments, such as the forest, which is associated with the appearance of habitual bipedal locomotion.

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.

A head shake sensory organization test to improve the sensitivity of the sensory organization test in the elderly

OBJECTIVE

The head shake sensory organization test (HS-SOT) is an expansion of the sensory organization test (SOT), which evaluates impairment of the patient's ability to apply vestibular input while actively moving the head. HS-SOTs has been proposed to increase the sensitivity of SOTs. The purpose of this study was to investigate the value of HS-SOTs in a healthy population with respect to age and compare the sensitivity of HS-SOTs with that of SOTs in the elderly population.

METHODS

One hundred two (n = 102) healthy subjects were divided into 3 age groups: the young adult group (between 20 and 39 yr), the adult group (between 40 and 59 yr), and the elderly group (between 60 and 79 yr). The subjects underwent SOTs and HS-SOTs.

RESULTS

The equilibrium scores of HS-SOTs underwent more significant change than those of SOTs in the elderly group. The equilibrium score ratio SOT2/HS-SOT2 (HS-SOT during SOT condition 2) decreased by 4% more in the elderly group compared with that of the young adult group. The ratio of SOT5/HS-SOT5 decreased by 54% more in the elderly group compared with that of the young adult group.

CONCLUSION

In the elderly, equilibrium scores of HS-SOTs changed more than those of SOTs. In addition, SOT5/HS-SOT5 demonstrated more sensitive changes in the elderly than SOT2/HS-SOT2 did.

A longitudinal study of balance in migraineurs

CONCLUSION

Balance in migraineurs, even in those without vestibular symptoms, deteriorates slightly over 1 year in the most challenging test conditions, when measured with posturography.

OBJECTIVE

To discover by a longitudinal study of a group of migraineurs and their controls, whether the well-known, mild imbalance found on posturography in migraineurs is static or progressive.

METHODS

Posturographic measures of sway under incrementally more challenging conditions (up to eyes closed standing on a foam surface with the head extended) using the modified clinical test of sensory interaction on balance, limits of stability test, and tandem gait tests in a group of 19 migraineurs and 19 age- and gender-matched controls, all of whom who had been tested over 1 year before.

RESULTS

After 1 year migraineurs showed a slight but statistically significant deterioration: in postural sway especially, when measured with eyes closed standing on a foam surface with the head extended backwards; in reaction time; and in maximal excursion on the limits of the stability test; and perhaps in walk speed and step width on the tandem walk test.

Is head-on-trunk extension a proprioceptive mediator of postural control and sit-to-stand movement characteristics?

During stance, head extension increases postural sway, possibly due to interference with sensory feedback. The sit-to-stand movement is potentially destabilizing due to the development of momentum as the trunk flexes forward and the body transitions to a smaller base of support. It is unclear what role head orientation plays in the postural and movement characteristics of the sit-to-stand transition. The authors assessed how moving from sitting to standing with head-on-trunk extension compared with moving with the head neutral or flexed, or with moving with the head facing forward in space (which would involve head-on-trunk extension, but not head-in-space extension) in healthy, young participants. Head-on-trunk extension increased center of pressure variability, but decreased movement velocities, movement duration, and trunk flexion compared with flexed and neutral head-on-trunk orientations. Similarities in movement characteristics between head-on-trunk extension and the forward head-in-space orientation suggest that stabilizing the head in space does not fully counteract the postural and movement changes due to head-on-trunk extension. Findings suggest that proprioceptive feedback from the neck muscles contributes to the regulation of posture and movement, and therefore should not be overlooked in research on the role of sensory feedback in postural control.

Changes in Listing plane thickness caused by vestibular schwannoma: a parameter for evaluating the accuracy of the gravity-oriented internal model

OBJECTIVE

Three-dimensional analysis of video-oculograms can be used to calculate Listing plane for patients and experimental subjects. Listing plane reflects the head's orientation with respect to gravity, which suggests that the plane is derived from otolithic vestibular input, itself, or from a gravity-oriented internal model constructed through integration of visual, vestibular, and proprioceptive sensory inputs. The goal of this study was to determine whether the Listing plane can serve as a parameter for evaluating static (peripheral or central) vestibular function.

STUDY DESIGN

Prospective study.

SETTING

Tertiary referral center.

PATIENTS

Healthy subjects and patients with unilateral vestibular schwannoma without any previous treatment.

INTERVENTION

Diagnostic.

MAIN OUTCOME MEASURES

Video-oculograms were recorded from healthy subjects (aged 36.8 ± 6.3 yr) and from patients (aged 60.3 ± 7.5 yr) during voluntary gaze with the head in an upright or each-side-down orientation, and the thicknesses of the calculated Listing planes were then compared.

RESULTS

Results revealed thickening of the Listing plane in patients only when the head was in an impaired-side-down orientation (1.250 ± 0.795 and 1.074 ± 0.759 degrees in the right- and left-side-down head orientations in healthy subjects versus 2.222 ± 1.237 degrees in the impaired-side-down orientation in patients), and this thickening correlated with caloric weakness. By contrast, neither the sensation of postural instability nor postural disturbance in force platform recordings contributed to the thickness of Listing plane.

CONCLUSION

The thickness of the Listing plane could be a novel parameter for quantitatively evaluating static vestibular (otolithic) function, although central compensation might exist.

Effects of common working postures on balance control during the stabilisation phase of transitioning to standing

Standing after maintaining working postures may result in imbalance and could elicit a fall. The objective of this study was to assess the magnitude of this imbalance. Forty-five male participants completed three replications of conditions created by four static postures and three durations within posture. Participants transitioned to quiet standing at a self-selected pace. Body segment location and displacement of the centre of pressure (COP) were recorded using a motion capture system and two forceplates, respectively. Balance control measures were calculated during the stabilisation phase. All balance control measures were significantly affected by static posture but not duration within posture. Bending over at waist generally caused the smallest changes in balance control measures, whereas the reclined kneeling posture resulted in the largest. Findings may lead to recommendations for redesign of tasks to reduce the use of certain working postures, particularly in high-risk environments such as construction. STATEMENT OF RELEVANCE: Task performance on the jobsite often requires individuals to maintain non-erect postures. This study suggests that the working posture chosen affects stabilisation during a transition to a standing position. Bending at the waist or squatting seems to have less of an affect on balance control measures, whereas both types of kneeling postures evaluated resulted in greater imbalance.

Influência dos sistemas sensoriais na manutenção do equilíbrio em gestantes

INTRODUÇÃO: Existe um grande número de fatores interferindo na atuação do equilíbrio, porém a importância dada a cada um dos sistemas sensoriais durante a gestação ainda é desconhecida. O objetivo deste estudo foi investigar a influência dos sistemas visual, somatossensorial e vestibular no equilíbrio em diferentes fases da gestação. MÉTODO: Para a realização deste estudo foram avaliados dois grupos: grupo de gestantes (GG), e grupo de mulheres não gestantes (GC). O equilíbrio corporal foi mensurado por meio das seis condições do Teste de Organização Sensorial (TOS), utilizando-se uma plataforma de força AMTI®. As variáveis relacionadas com a manutenção da estabilidade corporal foram a amplitude do deslocamento do centro de força nas direções ântero-posterior (COPap) e médio-lateral (COPml). Para comparação entre os grupos e entre os testes sensoriais, utilizou-se Anova One-Way, e para a identificação das diferenças utilizou-se o teste post hoc HSD de Tukey. O nível de significância adotado para todos os testes foi de 5%. RESULTADOS: As diferenças nas oscilações corporais são mais evidentes a partir do segundo trimestre de gestação, e a manipulação sensorial se mostra como fator agravante sobre essas oscilações. CONCLUSÃO: O processo de gestação influencia o equilíbrio em ambas as direções avaliadas (COPap e COPml) e as oscilações corporais aumentam com a dificuldade da tarefa (manipulação sensorial) e com o avançar da gestação.