Accelerometry (ACC) shows promise as an easily implemented clinical measure of balance. The purpose of the study was to estimate test–retest reliability of ACC measures and determine the relationship between ACC measured at the pelvis and underfoot center of pressure (COP) measures during sensory organization test (SOT) conditions. Eighty-one subjects were recruited from the community with no known orthopedic or vestibular deficits (19–85 years). Subjects completed three consecutive, ninety second trials for each of the six SOT conditions, while wearing the accelerometer. ACC and COP time series were described by calculating the normalized path length, root mean square (RMS), and peak-to-peak values. The test–retest reliability of the three measures within each SOT condition was estimated over three trials using the intraclass correlation coefficient. ACC and COP test–retest reliability were similar, ranging from 0.63 to 0.80 using ACC and 0.42 to 0.81 using COP for the measure of normalized path length. Linear regression between ACC and COP measures showed significant correlation under almost every SOT condition using both single and average measures across trials. The degree of association between COP and ACC was equivalent when using the first trial or the 3-trial average, suggesting that one trial may be sufficient. The use of accelerometry may have value in estimating balance function and minimizing clinical evaluation time.

Objective: Development of an easy to administer, low-cost test of vestibular function.Methods: Members of the NIH Toolbox Sensory Domain Vestibular, Vision, and Motor subdomain teams collaborated to identify 2 tests: 1) Dynamic Visual Acuity (DVA), and 2) the Balance Accelerometry Measure (BAM). Extensive work was completed to identify and develop appropriate software and hardware. More than 300 subjects between the ages of 3 and 85 years, with and without vestibular dysfunction, were recruited and tested. Currently accepted gold standard measures of static visual acuity, vestibular function, dynamic visual acuity, and balance were performed to determine validity. Repeat testing was performed to examine reliability. Results:The DVA and BAM tests are affordable and appropriate for use for individuals 3 through 85 years of age. The DVA had fair to good reliability (0.41-0.94) and sensitivity and specificity (50%-73%), depending on age and optotype chosen. The BAM test was moderately correlated with center of pressure (r 5 0.42-0.48) and dynamic posturography (r 5 20.48), depending on age and test condition. Both tests differentiated those with and without vestibular impairment and the young from the old. Each test was reliable. Conclusion:The newly created DVA test provides a valid measure of visual acuity with the head still and moving quickly. The novel BAM is a valid measure of balance. Both tests are sensitive to age-related changes and are able to screen for impairment of the vestibular system. Neurology â 2013;80 (Suppl 3):S25-S31 GLOSSARY BAM 5 Balance Accelerometry Measure; COP 5 center of pressure; DS 5 double-limb feet together stance; DVA 5 dynamic visual acuity; ETDRS 5 Early Treatment Diabetic Retinopathy Study; ICC 5 intraclass correlation coefficient; logMAR 5 logarithm of the minimum angle of resolution; NPL 5 normalized path length; SOT 5 sensory organization testing; SVA 5 static visual acuity; TS 5 tandem stance; VH 5 vestibular hypofunction; VOR 5 vestibulo-ocular reflex; VSP 5 vestibulospinal outputs.The vestibular system is an integral component of our sensory experience and sensory-motor function. Healthy peripheral and central vestibular anatomy is essential for functionally relevant gaze stability during head motion and postural control. 1 However, gaze stabilization and balance are enabled by multiple sensory inputs (e.g., visual, somatosensory, and vestibular), integration and interpretation of these redundant sources of orientation, and motor output, each of which may be affected by age or damage. [1][2][3][4] Patients with vestibular pathology often report oscillopsia (due to gaze instability), imbalance, and/or vertigo. The redundancy of the sensory information confounds distinction of the causal mechanisms of oscillopsia and/or imbalance. However, the unique contributions of the vestibulo-ocular reflex (VOR) and vestibulospinal outputs (VSP) to gaze stability and balance, respectively, can direct the identification of tests to screen for pathology of the vestibular system. Th...

Railroad workers are exposed to a unique work setting of irregular walking surfaces. Research and injury statistics suggest a possible causal relationship between irregular walking surfaces and postural instability. The purpose of this study was to examine the impact of extended duration of exposure to ballast on postural stability. Sixteen healthy adult males walked on a 7.62m x 4.57m (25ft x 15ft) walking surface of No Ballast (NB) or covered with Ballast (B). Participants were assessed on six NeuroCom® Equitest postural stability testing conditions prior to ballast surface and again every 30 minutes for 4 hours. Following at least 72 hours, participants repeated the protocol for a flat (NB) surface. Dependent variables were mediallateral (M/L) and anterior-posterior (A/P) sway velocity and root mean square (RMS) sway components. Repeated measures ANOVA revealed significant differences between surface conditions and exposure time. Overall, the ballast surface condition induced greater sway parameters in each of the six-postural stability testing conditions for time interval and surface conditions. Walking on ballast for extended durations has a deleterious effect on postural stability compared to walking on a flat (NB) surface. The findings provide preliminary information for improve existing work practices for injury prevention.

Most adaptive optical systems are based on a least-squares fit algorithm to optimize performance, and generally do not adequately address stability or uncertainty in the system. This paper describes the implementation of an H-infinity controller for an adaptive optical system, in order to optimize the closed-loop stability of the system.

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