Kamran Barin

Dizziness in the Elderly

Vertigo, unsteadiness, and other balance-related symptoms are common among older adults. These complaints should be taken seriously because they can lead to falls, injuries, loss of independence, and even death. This article provides a review of the underlying causes for the increased prevalence of dizziness with age, and discusses how specific test procedures may need to be modified for older individuals. Issues related to the management of these symptoms in the aging population are also considered.

Effects of vestibular rehabilitation and social reinforcement on recovery following ablative vestibular surgery

This study investigated the relative effects of vestibular rehabilitation (VR) and social reinforcement (SR) on recovery following ablative vestibular surgery. Twenty‐four subjects were randomly assigned to three treatment groups of either VR with SR, VR without SR, or general range of motion (ROM) exercises with SR. Outcome measures included equilibrium scores in dynamic posturography, asymmetry index in rotation testing, motion sensitivity quotient (MSQ), and dizziness handicap inventory (DHI). A multiple comparison of the overall outcome measures showed no significant differences in group performance over an 8‐week period. When individual outcome measures were compared, MSQ and DHI results at the end of the 8‐week treatment period revealed less motion sensitivity and dizziness handicap in groups who received VR, with or without SR, as compared with the group who received ROM exercises. These results suggest that after a vestibular injury most patients can effectively utilize central compensation mechanisms to recover from such an injury, regardless of the type of therapeutic intervention used. On the other hand, the reduction in motion sensitivity and dizziness handicap for patients who received VR could indicate a more rapid and complete recovery for these patients. This investigation is continuing as a long‐term follow‐up study to determine whether there are any long‐term benefits in participating in a VR program.

Effect of head orientation on the diagnostic sensitivity of posturography in patients with compensated unilateral lesions.

Patients with compensated unilateral vestibular lesions often have no detectable abnormality on conventional posturography. The purpose of this study was to determine whether a change in head orientation could improve the diagnostic sensitivity of the test for these patients. Twenty-four patients with known unilateral vestibulopathy and twenty-four normal controls were tested on the EqulTest apparatus in four head positions: head centered, head tilted right, head tilted left, and head extended. The sensory organization test was performed for each head position, using a single trial for each sensory condition. The test sequence was randomized to account for simple order effects. The subjects equilibrium was quantified by a performance index and a composite score of all sensory conditions was calculated for each head position. Patients with unilateral vestibulopathy had more postural sway with the head tilted contralateral to the side of lesion. The difference between the mean composite scores for ipsilateral and contralateral head tilts was statistically significant (p < 0.05). When individual trials were compared, equilibrium scores were significantly different only for sensory conditions that required vestibular input. Head extension increased postural sway in both patients and controls. Equilibrium scores were significantly different for all sensory conditions in which the support was sway-referenced. We suggest that the results of head extension in patients are similar to those found in normal individuals. However, equilibrium scores for right-left head flits are sensitive to the side of lesion and can provide additional information for patients with unilateral vestibulopathy.

Dynamic Stability of Spine Using Stability-Based Optimization and Muscle Spindle Reflex

A computational method for simulation of 3-D movement of the trunk under the control of 48 anatomically oriented muscle actions was developed. Neural excitation of muscles was set based on inverse dynamics approach along with the stability-based optimization. The effect of muscle spindle reflex response on the trunk movement stability was evaluated upon the application of a perturbation moment. The method was used to simulate the trunk movement from the upright standing to 60deg of flexion. Incorporation of the stability condition as an additional constraint in the optimization resulted in an increase in antagonistic activities demonstrating that the antagonistic co-activation acts to increase the trunk stability in response to self-induced postural internal perturbation. In presence of a 30 Nm flexion perturbation moment, muscle spindles decreased the induced deviation of the position and velocity profiles from the desired ones. The stability-generated co-activation decreased the reflexive response of muscle spindles to the perturbation demonstrating that the rise in muscle co-activation can ameliorate the corruption of afferent neural sensory system at the expense of higher loading of the spine.

Quantitative Analysis of the Ankle Strategy Under Translational Platform Disturbance

The ankle strategy is one of the postural adjustment maneuvers humans utilize when the support platform is disturbed. This paper presents a quantitative analysis of the ankle strategy. A three-link sagittal biped model is considered. The first link represents the two legs locked together. The second link represents the two thighs locked together. The third link represents the hip, the torso, the upper limbs, the neck, and the head. The dynamics, control, and stability of the three-link biped, under platform translation, are considered. The disturbance of the platform is represented as an input and the effect of the muscular system is reduced to a set of torques applied to the joints and across the joints. Two digital computer simulations are presented to demonstrate the behavior of the biped under backward or forward platform disturbance. The simulations are compared with experimental measurements of humans subjected to postural disturbances. It is shown that the effect of a horizontal disturbance at the ankle appears to be about 40 times that of the effect of the disturbance at the knees and at least a few hundred times larger than the effect of a disturbance at the hip. This means that, under translational platform disturbance, the ankle angle is subjected to the largest excursion. The knee and the hip angle excursions are relatively minor. Consequently, the biped, as a whole, appears to move as a single inverted pendulum. Major postural corrections are initiated by the ankle excursion. Further, when the available ankle torque is limited or nonexistent, the stability requires resorting to the knee or hip strategies

Childhood Imbalance and Chronic Otitis Media With Effusion: Effect of Tympanostomy Tube Insertion on Standardized Tests of Balance and Locomotion

The goal of this study was to investigate the role of chronic otitis media with effusion as a cause of childhood imbalance. Nineteen 4‐ to 6‐year‐old children with chronic otitis media with effusion and 14 matched control children underwent a series of laboratory tests, including two standardized tests of balance and locomotion: the Peabody Developmental Motor Scales (PDMS) and the Bruininks‐Oseretsky Test of Motor Proficiency (BOTMP). The children in the chronic otitis media with effusion group underwent tympanostomy tube insertion. Both groups underwent the same battery of tests within 6 to 8 weeks of initial testing. Analysis of variance for the PDMS and BOTMP demonstrated significantly lower performance in the balance subscales for the otitis group before (P < .01). Both otitis and control groups improved when retested. The improvement was greater and approaching significance in the otitis group on the PDMS and BOTMP (P = .056 and .097, respectively). It is concluded that chronic otitis media with effusion significantly affects balance and coordination skills in 4‐ to 6‐year‐old children. These skills improve after tympanostomy tube insertion at a rate greater than that of the control group.

A Recursive Free-Body Approach to Computer Simulation of Human Postural Dynamics

A recursive, free-body approach to the estimation of joint torques associated with observed motion in linkage mechanisms has recently been shown to be computationally more efficient than any other known approach to this problem. This paper applies this method to the analysis of human postural dynamics and shows how it can also be used to compute accelerations for specified joint torques. The latter calculation, referred to here as the direct dynamics problem, has until now involved symbolic complexity to such an extent as to generally limit computer simulation studies of postural control to very simple models. The model presented in this paper is both straightforward and general, and removes this obstacle to the investigation of possible neural control mechanisms by means of computer simulation. A computationally oriented linearization procedure for the direct dynamics problem is also included in the paper. Finally, example simulation results and corresponding measured body motions for human subjects are presented to validate the method.

Feature extraction and quantification of the variability of dynamic performance profiles due to the different sagittal lift characteristics

Investigation of manual material handling (MMH) tasks, such as lifting, requires the quantification of the various kinematic and kinetic parameters of performance for assessment of the functional capacity and/or task demand profiles. Traditional statistical descriptive analyses usually involve computing the summary statistics (maximum, minimum, mean, and/or range) of the resulting performance parameters over the cycle duration (i.e., lifting/lowering cycle). Consequently, the significant information content of the time-varying signals is diminished, limiting the sensitivity of subsequent hypothesis testing procedures. The present study developed a methodology for representing and quantifying performance data variability of the kinematic and kinetic motion profiles due to the different lift characteristics (load, mode, and speed) during MMH tasks while capturing the temporal characteristics. Using a database of motion profiles from a manual lifting experiment, the Karhunen-Loeve Expansion (KLE) feature extraction technique was shown to be quite effective for representing the various motion profiles. The number of basis vectors (eigenvectors) and corresponding coefficients needed for accurate representation were substantially smaller than the original data set, resulting in data compression. Moreover, the effects of lift characteristics were investigated using analysis of variance techniques that recognize the vectorial constitution of the waveforms. The application of these techniques will enable the quantification of highly phasic profiles and enhance the ability to document the effect of intervening measures such as educational or physical training/exercise on the kinematic and kinetic patterns of performance. Additionally, the differential influence of lift characteristics on the variability of performance during different phases of lifting and lowering provides added resolution in the analysis of MMH tasks.

Dynamics, Stability, and Control of Stepping

The dynamics, stability, and control of stepping are considered. The role of internal models is elaborated. The main objective of the paper is to provide a better understanding of the machinery and processing in the central nervous system (CNS) that relates to stepping. The role of the vestibular system in balance and balance recovery is described. Balance and balance recovery are essential in stepping, and guarantee the stability of the system before, during, and after stepping. In sagittal standing, humans use two distinct sets of control strategies to maintain their postural stability in response to external disturbance. In one set of strategies, the configuration of the base of support, namely, the position of the feet, remains unchanged. The ankle and hip strategies are examples of postural adjustments where the feet do not move. When the disturbances are large, and move the center of mass or pressure outside the support boundaries, stepping strategies are required. A simple control strategy is proposed for illustrative purposes. Its effectiveness is verified by computer simulation of a seven-link two-dimensional sagittal biped. The applications of the model in assessing trauma and injury are discussed.

A low-cost, portable system for the assessment of the postural response of wheelchair users to perturbations

Maintaining seated postural stability presents a serious challenge to wheelchair users in vehicles, even during normal driving conditions. The purpose of this research was to develop a system for the study of seated postural control in response to perturbations similar to those that might be experienced during vehicle turning and braking. A servo-controlled tilt platform was constructed to provide a low-cost, small, and easily transportable device for generating precise and repeatable perturbations. Tilt platform operation was examined for accuracy and reproducibility of a desired perturbation. Repeatability was high with a mean signal-to-noise ratio (SNR) of 45.4 for a given perturbation measured across 11 subjects. An initial comparison of stability results obtained on the tilt platform and in a vehicle showed a correspondence, although differences were apparent. The tilt platform has been used successfully to assess balance in spinal cord-injured subjects and to test wheelchair securement systems.