Journal of Vestibular Research

The aim of the studies reported here was to quantify changes in balance control for stance and gait tasks with age and to pinpoint possible advantages and difficulties in using these tasks and measures derived from them to identify pathological balance control in patients. Some 470 normal subjects in the age range 6 to 82 were examined for a battery of 14 stance and gait tasks. During the tasks, angular velocity transducers mounted at lumbar 1–3 measured pitch and roll angular velocities of the body. A combination of outcome measures from several tasks was used to create an overall balance control index. Three types of sensory analyses on pitch angle and velocity amplitudes for stance trials were used to quantify possible changes in the contributions of visual, somatosensory and vestibular inputs to balance control with age for 2-legged stance tasks. Correlation analysis on task variables was used to determine the relationship of subjects' age and height on outcome measures.

Outcome measures showed a characteristic "L" or "U" shaped profile with a rapid decrease in values between 7 and 25 years of age, a plateau until 55 then a gradual increase with age after 55 years of age for most stance and gait tasks. The sensory analysis technique using differences between stance tests indicated that visual contributions to balance control continuously increased with age between the ages of 15 and 80, and vestibular and lower leg somatosensory contributions remain relatively constant with age. Sensory analysis calculated as commonly-used quotients of outcome measures revealed large variance across all ages, asymmetric distributions, and no clear trends in sensory contributions to stance with age. A third technique based on a discriminant function analysis using measures from model patient populations indicated that proprioceptive but not vestibular contributions first increased with age and then decreased after 55 years of age. Correlations of outcome measures with age and height indicated that both contributed equally to changes in outcome measures between the ages of 7 and 25, otherwise height had no effect. We conclude that both stance and gait tasks should be selected for identifying changes in balance control from that of healthy persons with a preference for gait tasks as these show less variation with age. Because of the large increases in variance in the elderly and those younger than 20 years, appropriate age-matched reference values should be employed to ascertain if trunk sway is out of normal ranges.

Imbalance is a common clinical problem in elderly persons. Subsequently falls and fractures may occur. Age-related balance problems constitute an underestimated but prominent public health problem and a socioeconomic burden. At the histological level the peripheral vestibular system in animals and humans exhibits a variety of age-related changes. The number of otoconia in the utricule and the saccule is reduced with increasing age. Degenerated otoconia caused by aging showed distinct changes of the shape. Moreover age-related decreasing hair cell counts, lipofuscin inclusions and deformation of cilia are observed in human vestibular sensory and supporting cells. Results of vestibular function testing of age-related balance disorders still remain controversially. Regular balance training and vestibular rehabilitation results in less more falls and imbalance.

A tone-burst stimulation of 500 Hz seems to be clinically most appropriate to elicit vestibular evoked myogenic potentials (VEMPs) because those VEMPs can be recorded at the lowest stimulus intensity possible. However, little is known about gender and age-related changes of the amplitude in tone-burst (500 Hz) evoked VEMPs. The aim of the present paper was therefore to investigate the influence of gender and age on VEMP amplitude in relation to the tonic muscle activity.

VEMPs of 64 healthy subjects were recorded ipsilaterally during air- or bone-conducted tone burst stimulation. The EMG of the tonically activated sternocleidomastoid muscle was recorded ipsilaterally with surface electrodes. Averages were taken for P1/N1 amplitudes of male and female volunteers within 3 different age groups.

Although the amplitude decreased with increasing age the tonic activity was not significant different between the age groups. Consequently the relation between VEMP amplitude and tonic muscle activity decreased with increasing age. The normative values of the age-dependent relation between VEMP amplitude and tonic muscle activity were described by the 90% confidence interval of the individual values. Normative thresholds were calculated. Normal saccular receptor function could be diagnosed if the VEMP amplitude is above (or equal to) the normative value at a given tonic muscle activity and age.

Normative data as described above are required to diagnose isolated saccular defects, which are indicative of a vestibular disorder.

Transitions to and from microgravity, as experienced during a spaceflight mission, radically alter the demands on sensorimotor coordination. In this contribution, attention is directed to the vestibulo-oculomotor response to active head roll-tilt, generally referred to as ocular counterroll (OCR). Results are presented from a single-case longitudinal study over a 435-day spaceflight and from three further subjects over a 30-day period in microgravity.

1. Under one-g test conditions, with the head initially in the comfortable-upright position, active head-to-trunk roll tilt elicits a combined canal- and otolith-mediated oculomotor response, which manifests as a volley of torsional nystagmus beats combined with a tonic OCR. In microgravity it appears that only the transitory canal-mediated torsional nystagmus response remains. In both conditions the initial nystagmus response commences with an anticompensatory torsional fast phase.

2. Under zero-g conditions the head movements were comparable to those under one-g conditions but a consistent reduction in head velocity was observed. Despite this, eye velocity and eye-head velocity gain for the torsional component were found to be enhanced by up to 50% over the first thirty days in prolonged microgravity.

3. The results obtained from the 435-day mission indicate that the initially enhanced response decreases – over the course of several months – to preflight baseline level.

The findings indicate that otolith- and canal-ocular responses are not simply added linearly, but rather that the afferent otolith signal also plays an inhibitory, or stabilising role on the canal-mediated response. Further, presuming a re-weighting of otolithic afferent information during prolonged microgravity, it is proposed that a corollary inverse re-weighting of corollary neck-proprioceptive afferences provides an effective substitute.

In contrast to the idea that the torsional VOR is an evolutionary relic, it is postulated from the above findings that the anticompensatory saccade and the inherent low gain of OCR result as a compromise between intended reorientation to a tilted visual field and VOR compensation.

Caloric testing in prone/supine position and constant velocity off-vertical axis rotation (OVAR) in yaw axis (rotate-then-tilt paradigm) can evaluate labyrinth function and vestibular-ocular reflex (VOR) behaviour before and after endolymphatic shunt surgery (ESS). Preoperative and postoperative otolith dysfunction can be documented by constant velocity OVAR, before the VOR is modulated by the vestibular compensation. Vestibulo-ocular responses in prone/supine position and linear VOR (lVOR) OVAR responses were observed in 10 patients before and after ESS. Ipsilateral caloric reaction in prone/supine position was reduced after ESS. Otolith-ocular function and canal-otolith-interaction were improved postoperatively. Meniere's patients with bias component opposite to normal when rotating towards the lesioned ear showed relief of symptoms postoperatively. The bias component returning to normal can help to identify the relief of Meniere's attacks after ESS. The canal-otolith interaction can be observed pre- and postoperatively by means of caloric reaction in prone/supine position as part of the clinical routine.

Vestibular dysfunction of either central or peripheral origin can significantly affect balance, posture, and gait. We conducted a pilot study to test the effectiveness of training with the BrainPort® balance device in subjects with a balance dysfunction due to peripheral or central vestibular loss. The BrainPort® balance device transmits information about the patient's head position via electrotactile stimulation of the tongue. Head position data is sensed by an accelerometer and displayed on the tongue as a pattern of stimulation. This pattern of stimulation moves forward, backward, and laterally on the tongue in direct response to head movements. Users of the device were trained to use this stimulation to adjust their position in order to maintain their balance.

Twenty-eight subjects with peripheral or central vestibular loss were trained with the BrainPort balance device and tested using the following standardized quantitative measurements of the treatment effects: Computerized Dynamic Posturography (CDP) using the Sensory Organization Test (SOT), Dynamic Gait Index (DGI), Activities-specific Balance Confidence Scale (ABC), and Dizziness Handicap Inventory (DHI). All subjects had chronic balance problems and all but one had previously participated in vestibular rehabilitation therapy. The scores on the clinical tests upon entry into the study were compared to their scores following training with the BrainPort balance device. Our results exhibit consistent positive and statistically significant improvements in balance, posture and gait. These results exceed what could normally be achieved in three to five days of traditional balance training alone. Since this was not a controlled study, we are unable to distinguish the degree to which these improvements are attributable to training with the BrainPort balance device versus the balance exercises performed by all subjects as a part of the BrainPort training sessions. Nonetheless, after training with the BrainPort balance device, all subjects demonstrated significant improvements in performance beyond what might be expected from conventional vestibular rehabilitation therapy.

Balance is accomplished by the congruent integration of visual, vestibular and somatosensory input and the execution of adequate control movements. With increasing age, nonlinear dynamics of central control systems become more regular. In unilateral vestibular dysfunction, sensory input to central systems is similarly less complex, because of one sided reduction of information influx. This study aimed to increase postural stability in patients with vestibular asymmetry and resulting disequilibrium by implementing a computerized visual training method relying on the principles of stochastic resonance. 24 subjects (average age 64a, 31–78a, 15 women, 9 men), with minimum 3 months of persisting disequilibrium due to vestibular dysfunction, were either treated with computerized optokinetic therapy (COKT), or solely observed. Treated patients were requested to read texts, stochastically moving in a previously defined matrix, during 10 sessions over three weeks. The Sensory Organization Test (SOT) was used for comparative posturographic measurements. COKT patients showed significant improvement in conditions 4, 6 and composite score. A significant post-therapeutic difference was seen between therapy and control groups in conditions 1, 6 and composite score. The results show a clinical benefit and we conclude COKT to be an effective rehabilitation method in patients with chronic disequilibrium.

In a prospective, non-randomized pilot study, two groups of patients with dizziness for more than one year due to posttraumatic otolith disorders had been investigated. They were treated by a one-day vestibular rehabilitation training with/without auditory feedback. It could be shown that auditory feedback training for a limited period of time can reduce significantly trunk sway compared to those patients who did vestibular exercises alone without auditory feedback. This audiofeedback-based therapy seems to be a promising tool in the vestibular rehabilitation and in treating patients with otolith disorders in particular. Long-term effects cannot yet be assessed with the present data of our series.