Effects of microvascular decompression surgery on posture control: A case report in an elderly patient.

AIMS OF THE STUDY: We report the case of an 84-year-old woman with neurovascular conflict of the left cochleovestibular nerve. Prior to surgery, the patient complained of positional vertigo and dizziness for the past two years, and marked instability. Hearing loss and tinnitus were reported on the left side. The aim of this study was to investigate the effects of microvascular decompression of the cochleovestibular nerve on posture control. MATERIALS AND METHODS: Evaluation of cochleovestibular function and posture control was performed before and after surgery. Postural performance was analyzed in static and dynamic conditions, with and without vision, and with optokinetic stimulation. Perception of the static visual vertical (SVV) was recorded in darkness. RESULTS: Positional vertigo and tinnitus disappeared immediately after the decompression. The SVV remained unchanged one week after the surgery. Speech intelligibility of the left ear was improved (30 dB), and the vestibular deficit on this side was also significantly reduced (54% versus 18%). However, the more spectacular result was the effect on postural control. This elderly patient improved her postural balance in both static and dynamic conditions, and became able to maintain her equilibrium in the more challenging dynamic conditions, with and without vision, as early as one week after the surgery, a postural performance that she had been unable to do preoperatively. CONCLUSION: This work is the first to show that the postural deficits resulting from neurovascular conflict of the cochleovestibular nerve are strongly improved after microvascular decompression.

Effects of haptic supplementation on postural stability in unilateral vestibular loss patients.

The effects of haptic supplementation on postural stability during upright standing with vision were investigated in 11 unilateral vestibular loss (UVL) patients and compared to 12 age-marched controls. All the participants were instructed to grip a fixed or mobile stick. In the mobile conditions, the lower extremity of the stick was in contact with a slippery or a rough surface. Postural stability was assessed by the root mean square (RMS) and the velocity of the center of foot pressure (CoP) displacements in both antero-posterior (AP) and medio-lateral (ML) directions. Results showed that RMS was larger in UVL patients than in aged-matched participants in AP direction. However, in the mobile stick conditions, only the rough surface improved postural stability. In addition, RMS was more sensitive to haptic supplementation than CoP velocity. The present study confirms the importance of haptic information in the multi-sensory (re) weighting process underlying postural control in UVL patients.

Vestibular compensation and vestibular rehabilitation. Current concepts and new trends.

The aim of this review is to present the current knowledge of the mechanisms underlying the vestibular compensation and demonstrating how the vestibular rehabilitation is conducted to help the recovery of balance function. Vestibular rehabilitation is based on improving the natural phenomenon called vestibular compensation that occurs after acute vestibular disturbance or chronic and gradual misbalance. Central compensation implies three main mechanisms namely adaptation, substitution and habituation. The compensation, aided by the rehabilitation aimed to compensate and/or to correct the underused or misused of the visual, proprioceptive and vestibular inputs involved in the postural control. As the strategy of equilibration is not corrected, the patient is incompletely cured and remains with inappropriate balance control with its significance on the risk of fall and impact on quality of life. The vestibular rehabilitation helps to correct inappropriate strategy of equilibrium or to accelerate a good but slow compensation phenomenon. Nowadays, new tools are more and more employed for the diagnosis of vestibular deficit (that may include various sources of impairment), the assessment of postural deficit, the control of the appropriate strategy as well to facilitate the efficiency of the rehabilitation especially in elderly people.

Age-related changes in posture control are differentially affected by postural and cognitive task complexity.

The simple postural task of quiet standing, which requires minimal attentional resources, is generally paired with cognitive activity. Competition for attentional resources is a consequence of simultaneously performing balance tasks and cognitive tasks, and impairment of attentional resource allocation with aging leads to increased risks of fall. We investigated age-related changes in posture control during dual task performance, using a paradigm that crossed a static (quiet standing) and a dynamic (keeping balance on a translational force plate) postural task and cognitive tasks of low demand (mental arithmetic) and high demand (spatial memory). Postural performance was analyzed through center-of-pressure displacements using both statistical (body sway area/sway velocity) and nonlinear (wavelet transform) methods in three age groups (younger, middle-aged, and older healthy participants). Results showed that 1) the nonlinear analysis method was more sensitive than the traditional approach in distinguishing performance between age groups, a result that explains discrepancies in the dual-task literature; 2) dual-tasking costs were dependent on both postural task difficulty and cognitive task complexity, corroborating previous investigations; 3) younger adults improved their postural performance during dual-tasking, but older adults lowered their performance; 4) balance recovery strategies in the dynamic postural task appeared to differ in younger versus older adults. Together, our findings on dual-tasking can be interpreted within the conceptual frame of task prioritization: shifting attention away from postural task automates posture control in the younger adults, whereas prioritization of postural task and selection of compensatory strategy are the main characteristics of posture control in the older population.

Posture control, aging, and attention resources: models and posture-analysis methods.

This paper reviews the literature on balance and cognitive function in normal aging. The first part provides a general background of dual tasking (postural performance under a concurrent cognitive activity) and summarizes the main relevant models capable of explaining the poorer postural performance of older-healthy adults compared to younger-healthy adults: the cross-domain competition model, the nonlinear interaction model, and the task-prioritization model. In the second part, we discuss the main limitations of the traditional-posturographic analyses used in most of the dual-task investigations and explain how these can account for some discrepancies found in the literature. New methods based on the stabilogram-diffusion analysis and the wavelet transform are proposed as better approaches to understand posture control. The advantages of these new methods are illustrated in young adults and elderly people performing a simple postural task (quiet standing) simultaneously with a mental or a spatial task.

Recalibration of somesthetic plantar information in the control of undisturbed upright stance maintenance.

To assess the effects of changes in somesthetic plantar information on upright quiet stance, a rotary plantar massage was applied under the feet of healthy subjects for ten minutes. The controlling variable, the centre of pressure (CP) displacements, were recorded, before and after massage, through a force platform and decomposed into two elementary motions: the vertical projection of the centre of gravity (CG(v)) and the difference between the latter and the CP (CP-CG(v)) along medio-lateral ML and antero-posterior AP directions. These motions were processed through frequency analysis and modelled as fractional Brownian motion. For CP-CG(v) motions, the frequency analysis shows that massage under the plantar soles induces a decrease of the amplitudes along the ML direction suggesting reduced overall muscular activity (abductor-adductor muscles of the hip according to Winter et al.). A general trend is that the CG(v) amplitudes are also diminished after massage especially in the ML direction, indicating a better distribution of the body weight on the two supports. On the other hand, the effects tend to vanish after about 8 minutes. Conversely, when the massage was given under the toes, no particular effect on any elementary motion was observed, suggesting that the plantar mechanoreceptors under the toes necessitate stronger stimulation to respond significantly and/or that the greater sensitivity obtained was not used by the CNS. Overall, this data emphasises the fact that a recalibration of somesthetic cues may occur when enhanced afferent information is fed to the postural system.