Relation of anxiety and other psychometric measures, balance deficits, impaired quality of life, and perceived state of health to dizziness handicap inventory scores for patients with dizziness.

BACKGROUND: An important question influencing therapy for dizziness is whether the strengths of the relationships of emotional and functional aspects of dizziness to 1) anxiety and other mental states, 2) perceived state of health (SoH) and quality of life (QoL) are different in patients with and without normal balance control. We attempted to answer this question by examining these dimensions' regression strengths with Dizziness Handicap Inventory (DHI) scores. METHODS: We divided 40 patients receiving group cognitive behavioural therapy (CBT) and vestibular rehabilitation for dizziness, into 2 groups: dizziness only (DO) and normal balance control; dizziness and a quantified balance deficit (QBD). Group-wise, we first performed stepwise multivariate regression analysis relating total DHI scores with Brief Symptom Inventory (BSI) sub-scores obtained pre- and post-therapy. Then, regression analysis was expanded to include SoH, QoL, and balance scores. Finally, we performed regressions with DHI sub-scores. RESULTS: In both groups, the BSI phobic anxiety state score was selected first in the multivariate regression analysis. In the DO group, obsessiveness/compulsiveness was also selected. The correlation coefficient, R, was 0.74 and 0.55 for the DO and QBD groups, respectively. When QoL and SoH scores were included, R values increased to 0.86 and 0.74, explaining in total 74, and 55% of the DHI variance for DO and QBD groups, respectively. Correlations with balance scores were not significant (R ≤ 0.21). The psychometric scores selected showed the strongest correlations with emotional DHI sub-scores, and perceived QoL and SoH scores with functional DHI sub-scores. CONCLUSIONS: Our findings suggest that reducing phobic anxiety and obsessiveness/compulsiveness during CBT may improve emotional aspects of dizziness and targeting perceived SoH and QoL may improve functional aspects of dizziness for those with and without normal balance control.

Vestibulo-spinal and vestibulo-ocular reflexes are modulated when standing with increased postural threat.

We investigated how vestibulo-spinal reflexes (VSRs) and vestibulo-ocular reflexes (VORs) measured through vestibular evoked myogenic potentials (VEMPs) and video head impulse test (vHIT) outcomes, respectively, are modulated during standing under conditions of increased postural threat. Twenty-five healthy young adults stood quietly at low (0.8 m from the ground) and high (3.2 m) surface height conditions in two experiments. For the first experiment (n = 25) VEMPs were recorded with surface EMG from inferior oblique (IO), sternocleidomastoid (SCM), trapezius (TRP), and soleus (SOL) muscles in response to 256 air-conducted short tone bursts (125 dB SPL, 500 Hz, 4 ms) delivered via headphones. A subset of subjects (n = 19) also received horizontal and vertical head thrusts (∼150°/s) at each height in a separate session, comparing eye and head velocities by using a vHIT system for calculating the functional VOR gains. VEMP amplitudes (IO, TRP, SOL) and horizontal and vertical vHIT gains all increased with high surface height conditions (P < 0.05). Changes in IO and SCM VEMP amplitudes as well as horizontal vHIT gains were correlated with changes in electrodermal activity (ρ = 0.44-0.59, P < 0.05). VEMP amplitude for the IO also positively correlated with fear (ρ = 0.43, P = 0.03). Threat-induced anxiety, fear, and arousal have significant effects on VSR and VOR gains that can be observed in both physiological and functional outcome measures. These findings provide support for a potential central modulation of the vestibular nucleus complex through excitatory inputs from neural centers involved in processing fear, anxiety, arousal, and vigilance.

The effect of gait approach velocity on the broken escalator phenomenon.

Walking onto a stationary surface previously experienced as moving generates an after-effect commonly known as the "broken escalator" after-effect (AE). This AE represents an inappropriate expression of the locomotor adaptation necessary to step onto the moving platform (or escalator). It is characterised by two main biomechanical components, an increased gait approach velocity (GAV) and a forward trunk overshoot on gait termination. We investigated whether the trunk overshoot and other biomechanical measures are the direct inertial consequence of the increased GAV or whether these are the result of an independent adaptive mechanism. Forty-eight healthy young adults walked onto a movable sled. They performed 5 trials with the sled stationary at their preferred walking velocity (BEFORE trials), 5 with the sled moving (MOVING or adaptation trials), and 5 with the sled stationary again (AFTER trials). For the AFTER trials, subjects were divided into four groups. One group was instructed to walk slowly ("slower"), another with cueing at the BEFORE pace ("metronome"). The third group walked without cueing at the BEFORE pace ("normal"), and the fourth, fast ("faster"). We measured trunk pitch angle, trunk linear horizontal displacement, left shank pitch angular velocity and surface EMG from lower leg and trunk muscles. In the AFTER trials, an AE was observed in these biomechanical measures for all gait speeds, but these were not strongly dependent on GAV. An AE was present even when GAV was not different from that of BEFORE trials. Therefore, we conclude that, although contributary, the trunk overshoot is not the direct consequence of the increased GAV. Instead, it appears to be generated by anticipatory motor activity "just in case" the sled moves, herewith termed a "pre-emptive" postural adjustment.

Characteristics of improvements in balance control using vibro-tactile biofeedback of trunk sway for multiple sclerosis patients.

BACKGROUND AND AIMS: Previously, we determined that training with vibrotactile feedback (VTfb) of trunk sway improves MS patients' balance impairment. Here, we posed 5 questions: 1) How many weeks of VTfb training are required to obtain the best short-term carry over effect (CoE) with VTfb? 2) How long does the CoE last once VTfb training terminates? 3) Is the benefit similar for stance and gait? 4) Is position or velocity based VTfb more effective in reducing trunk sway? 5) Do patients' subjective assessments of balance control improve? METHODS: Balance control of 16 MS patients was measured with gyroscopes at the lower trunk. The gyroscopes drove directionally active VTfb in a head-band. Patients trained twice per week with VTfb for 4 weeks to determine when balance control with and without VTfb stopped improving. Thereafter, weekly assessments without VTfb over 4 weeks and at 6 months determined when CoEs ended. RESULTS: A 20% improvement in balance to normal levels occurred with VTfb. Short term CoEs improved from 15 to 20% (p ≤ 0.001). Medium term (1-4 weeks) CoEs were constant at 19% (p ≤ 0.001). At 6 months improvement was not significant, 9%. Most improvement was for lateral sway. Equal improvement occurred when angle position or velocity drove VTfb. Subjectively, balance improvements peaked after 3 weeks of training (32%, p ≤ 0.05). CONCLUSIONS: 3-4 weeks VTfb training yields clinically relevant sway reductions and subjective improvements for MS patients during stance and gait. The CoEs lasted at least 1 month. Velocity-based VTfb was equally effective as position-based VTfb.

The effect of voluntary lateral trunk bending on balance recovery following multi-directional stance perturbations.

Stabilising shifts of the centre of mass (COM) are observed during balance recovery when subjects simultaneously execute voluntary unilateral knee flexion or unilateral arm raising. Here, we examined whether voluntary lateral trunk bending provided more beneficial stabilising effects, and how motor programs of balance corrections are combined with those of the focal voluntary action. The upright balance of 24 healthy young subjects (19-33 years of age) was perturbed using multi-directional rotations of the support-surface. The perturbations consisted of combined pitch and roll rotations (7.5 degrees and 60 degrees/s) presented randomly in six different directions. Three conditions were tested: perturbation of stance only (PO); combined balance perturbation and cued uphill bending of the trunk (CONT); and combined perturbation and cued downhill bending of the trunk (IPS). For comparison, subjects were required to perform trunk bending alone (TO). Outcome measures were biomechanical responses and surface EMG activity of several muscles. Calculated predicted outcomes (PO + TO) were compared with combined measures (CONT or IPS). CONT trunk bending uphill showed two phases of benefit in balance recovery for laterally but, in contrast to voluntary knee bending, not for posterior directed components of the perturbations. IPS trunk bending had negative effects on balance. Early balance correcting muscle responses were marginally greater than PO responses. Prominent secondary balance correcting responses, having a similar timing as voluntary responses observed under TO conditions, were seen under CONT only in trunk muscles. These, and later stabilising, responses had amplitudes as expected from PO + TO conditions being significantly greater than PO responses. The ability with which different muscle synergies for balance corrections and voluntary trunk bending were integrated into one indicates a flexible adjustment of the CNS programs to the demands of both tasks.

Postural instability in cerebellar ataxia: correlations of knee, arm and trunk movements to center of mass velocity.

The aim of this study was to investigate the correlations between body segment movements and center of mass (COM) velocity during pathological balance corrections of spinocerebellar ataxia (SCA) patients compared with controls, and to relate correlations indicating instability to EMG activity differences. Eighteen SCA patients and 21 age-matched controls were tested. Upright standing was perturbed using rotations of the support surface. We recorded body motion and surface EMG. For lateral perturbations peaks in COM lateral velocity were larger in SCA patients than controls. These peaks were correlated with increased ("hypermetric") trunk roll downhill and reduced uphill knee flexion velocity. Subsequent arm abduction partially corrected the lateral instability. Early balance correcting responses in knee and paraspinal muscles showed reduced amplitudes compared with normal responses. Later responses were consistent with compensation mechanisms for the lateral instability created by the stiffened knee and pelvis. We conclude that truncal hypermetria coupled with insufficient uphill knee flexion is the primary cause of lateral instability in SCA patients. Holding the knees and pelvis more rigid possibly permits a reduction in the controlled degrees of freedom and concentration on arm abduction to improve lateral instability. For backwards perturbations excessive posterior COM velocity coincided with marked trunk hypermetric flexion forwards. We concluded that this flexion and the ensuing backwards shift of the pelvis result from rigidity which jeopardizes posterior stability. Timing considerations and the lack of confirmatory changes in amplitudes of EMG activity suggest that lateral and posterior instability in SCA is primarily a biomechanical response to pelvis and knee rigidity resulting from increased muscle background activity rather than changed evoked responses.

Trunk sway analysis to quantify the warm-up phenomenon in myotonia congenita patients.

OBJECTIVE: Patients with autosomal recessive myotonia congenita display myotonia and transient paresis that diminish with repetitive muscle contractions (warm-up phenomenon). A new approach is presented to quantify this warm-up phenomenon under clinically relevant gait and balance tasks. METHODS: Ten patients with DNA proven autosomal recessive myotonia congenita and 14 age-matched controls participated. Subjects performed six everyday gait and balance tasks. Balance control during these tasks was monitored using two angular velocity transducers that measured trunk movements in anterior-posterior (pitch) and medio-lateral (roll) directions at the level of the lumbar vertebral column. Tasks were performed under two conditions in randomised order: after a 10-minute seated rest period ("rested") and after having consecutively repeated the task five times ("warm-up"). Controls were also tested twice. RESULTS: "Rested" patients showed the greatest abnormalities (increased sway in pitch and roll) for tandem walking and walking stairs. Balance impairment was also evident for all other tasks. After "warm-up," balance was markedly improved in patients, as reflected by decreased trunk sway (especially during tandem walking) and reduced task duration for all tasks. These results were not only evident at the group level but also clearly present in individual patients. CONCLUSION: The results show that trunk sway analysis detects postural instability in myotonia congenita patients during everyday gait and balance tasks. Moreover, this technique provides a useful tool to quantify the warm-up phenomenon, suggesting a potential use as clinical endpoint in future clinical trials.

Epidemiology and pathophysiology of falls in facioscapulohumeral disease.

BACKGROUND AND AIMS: Muscle weakness is a potentially important, yet poorly studied, risk factor for falls. Detailed studies of patients with specific myopathies may shed new light on the relation between muscle weakness and falls. Here falls in patients with facioscapulohumeral disease (FSHD) who suffered from lower limb muscle weakness were examined. This study provides insights into the prevalence, relevance and pathophysiology of falls in FSHD. METHODS: A validated questionnaire was used as well as a prospective 3 month follow-up to examine the prevalence, circumstances and consequences of falls in 73 patients with FSHD and 49 matched healthy controls. In a subgroup of 28 subjects, muscle strength was also examined and balance was assessed electrophysiologically using body worn gyroscopes. RESULTS: In the questionnaire, 30% of the patients reported falling at least once a month whereas none of the controls did. Injuries occurred in almost 70% of the patients. The prospective study showed that patients fell mostly at home, mainly due to intrinsic (patient related) causes, and usually in a forward direction. Fallers were unstable while climbing stairs, rising from a chair and standing with eyes closed whereas non-fallers had normal balance control. Frequent fallers had greater muscle weakness than infrequent fallers. CONCLUSION: These findings demonstrate the high prevalence and clinical relevance of falls in FSHD. The relation between muscle weakness and instability among fallers is also highlighted. Because patients fell mainly at home, fall prevention strategies should focus on home adaptations. As mainly intrinsic causes underlie falls, the impact of adopting balance strategies or balance training should be explored in this patient group.

Control of roll and pitch motion during multi-directional balance perturbations.

Does the central nervous system (CNS) independently control roll and pitch movements of the human body during balance corrections? To help provide an answer to this question, we perturbed the balance of 16 young healthy subjects using multi-directional rotations of the support surface. All rotations had pitch and roll components, for which either the roll (DR) or the pitch (DP) component were delayed by 150 ms or not at all (ND). The outcome measures were the biomechanical responses of the body and surface EMG activity of several muscles. Across all perturbation directions, DR caused equally delayed shifts (150 ms) in peak lateral centre of mass (COM) velocity. Across directions, DP did not cause equally delayed shifts in anterior-posterior COM velocity. After 300 ms however, the vector direction of COM velocity was similar to the ND directions. Trunk, arm and knee joint rotations followed this roll compared to pitch pattern, but were different from ND rotation synergies after 300 ms, suggesting an intersegmental compensation for the delay effects. Balance correcting responses of muscles demonstrated both roll and pitch directed components regardless of axial alignment. We categorised muscles into three groups: pitch oriented, roll oriented and mixed based on their responses to DR and DP. Lower leg muscles were pitch oriented, trunk muscles were roll oriented, and knee and arm muscles were mixed. The results of this study suggest that roll, but not pitch components, of balance correcting movement strategies and muscle synergies are separately programmed by the CNS. Reliance on differentially activated arm and knee muscles to correct roll perturbations reveals a dependence of the pitch response on that of roll, possibly due to biomechanical constraints, and accounts for the failure of DP to be transmitted equally in time across all limbs segments. Thus it appears the CNS preferentially programs the roll response of the body and then adjusts the pitch response accordingly.

Effect of subthalamic nucleus deep brain stimulation on axial motor control and protective arm responses in Parkinson's disease.

Stereotactic surgical interventions for Parkinson's disease (PD) can considerably improve appendicular motor signs, but their effect on axial motor signs--especially balance control under optimal drug therapy--remains unclear. Here, we investigated the effect of bilateral subthalamic nucleus (STN) stimulation on levodopa-resistant axial and appendicular postural impairment in PD. Fourteen patients (11 with young-onset PD) and 18 age-matched controls were included. Patients were tested after intake of a suprathreshold levodopa dose, ensuring optimal response to drug therapy, and with stimulators both turned on and off. Balance control was assessed using multidirectional dynamic posturography. Outcome measures included full body kinematics and surface electromyography of paraspinal and deltoid muscles. Patients with stimulators turned off showed early decreased trunk roll with a loss of directional dependency, followed by increased and abnormally directed--i.e. destabilizing--trunk roll. Pelvis pitch motion showed decreased directional dependency in these patients. The abnormal trunk motion was not corrected by STN stimulation, but directional dependency of both trunk and pelvis motion partially improved, along with a general decrease in muscle activity. Even with stimulators off, protective arm movements were similar in the optimally treated patients and controls, indicating that these appendicular signs respond better to dopaminergic treatment than axial motor control. Our findings indicate that instability in PD results from a reduced flexibility of the trunk and pelvis that is largely resistant to STN stimulation combined with optimal drug treatment. These postural abnormalities are therefore likely associated with non-dopaminergic pathology. In contrast, protective arm movements did appear to be levodopa-responsive. Future studies should focus on identifying subgroups of optimal responders, particularly patients with levodopa-induced dyskinesias.

Identifying deficits in balance control following vestibular or proprioceptive loss using posturographic analysis of stance tasks.

OBJECTIVE: To distinguish between normal and deficient balance control due to vestibular loss (VL) or proprioceptive loss (PL) using pelvis and shoulder sway measures. METHODS: Body-worn gyroscopes measured pelvis and shoulder sway in pitch (anterior-posterior) and roll (side-to-side) directions in 6 VL, 6 PL and 26 control subjects during 4 stance tasks. Sway amplitudes were compared between groups, and were used to select optimal measures that could distinguish between these groups. RESULTS: VL and PL patients had greater sway amplitudes than controls when standing on foam with eyes closed. PL patients also swayed more when standing with eyes closed on firm support and eyes open on foam. Standard sensory analysis techniques only differentiated VL patients from controls. Stepwise discriminate analysis showed that differentiation required pitch measures for VL patients, roll measures for PL patients, and both measures for all three groups. Pelvis measures yielded better discrimination than shoulder measures. CONCLUSIONS: Distinguishing between normal and deficient balance control due to VL or PL required pitch and roll pelvis sway measures. SIGNIFICANCE: Accurate identification of balance deficits due to VL or PL may be useful in clinical practice as a functional diagnostic tool or to monitor balance improvements in VL or PL patients.

The influence of knee rigidity on balance corrections: a comparison with responses of cerebellar ataxia patients.

Knee rigidity due to aging or disease is associated with falls. A causal relationship between instability and knee rigidity has not been established. Here, we examined whether insufficient knee movement due to knee rigidity could underlie poor balance control in patients. We addressed this by examining the effect of artificially "locking" the knees on balance control in 18 healthy subjects, tested with and without individually fitted knee casts on both legs. Subjects were exposed to sudden rotations of a support surface in six different directions. The primary outcome measure was body centre of mass (COM) movement, and secondary outcome measures included biomechanical responses of the legs, pelvis and trunk. Knee casts caused increased backward COM movement for backward perturbations and decreased vertical COM movement for forward perturbations, and caused little change in lateral COM movement. At the ankles, dorsiflexion was reduced for backward perturbations. With knee casts, there was less uphill hip flexion and more downhill hip flexion. A major difference with knee casts was a reversed pelvis pitch movement and an increased forward trunk motion. These alterations in pitch movement strategies and COM displacements were similar to those we have observed previously in patients with knee rigidity, specifically those with spinocerebellar ataxia (SCA). Pelvis roll and uphill arm abduction were also increased with the casts. This roll movement strategy and minor changes in lateral COM movement were not similar to observations in patients. We conclude that artificial knee rigidity increases instability, as reflected by greater posterior COM displacement following support surface tilts. Healthy controls with knee casts used a pitch movement strategy similar to that of SCA patients to offset their lack of knee movement in regaining balance following multidirectional perturbations. This similarity suggests that reduced knee movements due to knee rigidity may contribute to sagittal plane postural instability in SCA patients and possibly in other patient groups. However in the roll plane, healthy controls rapidly compensate by adjusting arm movements and hip flexion to offset the effects of knee rigidity.

Effects of a program of cognitive-behavioural group therapy, vestibular rehabilitation, and psychoeducational explanations on patients with dizziness and no quantified balance deficit, compared to patients with dizziness and a quantified balance deficit.

BACKGROUND: We examined whether a program combining cognitive-behavioural therapy (CBT), vestibular rehabilitation (VR) and psychoeducation is equally effective in improving psychometric measures in patients with dizziness independent of a balance deficit. Measures of patients with dizziness only (DO) were compared to those of patients also having a quantified balance deficit (QBD). METHODS: 32 patients (23 female, 9 male) with persistent dizziness were analysed as 2 groups based on stance and gait balance control: those with QBD (pathological balance) or DO (normal balance). Dizziness Handicap Inventory (DHI) and Brief Symptom Inventory (BSI) questionnaires were used pre- and post-therapy to assess psychometric measures. Patients then received the same combination therapy in a group setting. RESULTS: The QBD group mean age was 60.6, SD 8.3, and DO group mean age 44.8, SD 12.1, years. Pre-therapy, questionnaire scores were pathological but not different between groups. Balance improved significantly for the QBD group (p=0.003) but not for the DO group. DHI and BSI scores improved significantly in the DO group (0.001

Threat effects on human oculo-motor function.

Neuro-anatomical evidence supports the potential for threat-related factors, such as fear, anxiety and vigilance, to influence brainstem motor nuclei controlling eye movements, as well as the vestibular nuclei. However, little is known about how threat influences human ocular responses, such as eye saccades (ES), smooth pursuit eye tracking (SP), and optokinetic nystagmus (OKN), and whether these responses can be facilitated above normal baseline levels with a natural source of threat. This study was designed to examine the effects of height-induced postural threat on the gain of ES, SP and OKN responses in humans. Twenty participants stood at two different surface heights while performing ES (ranging from 8° to 45° from center), SP (15, 20, 30°/s) and OKN (15, 30, 60°/s) responses in the horizontal plane. Height did not significantly increase the slope of the relationship between ES peak velocity and initial amplitude, or the gain of ES amplitude. In contrast height significantly increased SP and OKN gain. Significant correlations were found between changes in physiological arousal and OKN gain. Observations of changes with height in OKN and SP support neuro-anatomical evidence of threat-related mechanisms influencing both oculo-motor nuclei and vestibular reflex pathways. Although further study is warranted, the findings suggest that potential influences of fear, anxiety and arousal/alertness should be accounted for, or controlled, during clinical vestibular and oculo-motor testing.

Mental body transformation deficits in patients with chronic balance disorders.

BACKGROUND: Movements may be generated consistent with imagining one's own body transformed or "disembodied" to a new position. Based on this concept we hypothesized that patients with objective balance deficits (obj-BD) would have altered neural transformation processes executing own body transformation (OBT) with functional consequences on balance control. Also we examined whether feeling unstable due to dizziness only (DO), without an obj-BD, also lead to an impaired OBT. METHODS: 32 patients with chronic dizziness were tested: 16 patients with obj-BD as determined by balance control during a sequence of stance and gait tasks, 16 patients with dizziness only (DO). Patients and 9 healthy controls (HCs) were asked to replicate roll trunk movements of an instructor in a life size video: first, with spontaneously copied (SPO) or "embodied" egocentric movements (lean when the instructor leans); second, with "disembodied" or "transformed" movements (OBT) with exact replication - lean left when the instructor leans left. Onset latency of trunk roll, rise time to peak roll angle (interval), roll velocity, and amplitude were measured. RESULTS: SPO movements were always mirror-imaged. OBT task latencies were significantly longer and intervals shorter than for SPO tasks (p < 0.03) for all groups. Obj-BD but not DO patients had more errors for the OBT task and, compared to HCs, had longer onset latencies (p < 0.05) and smaller velocities (p < 0.003) and amplitudes (p < 0.001) in both the SPO and OBT tasks. Measures of DO patients were not significantly different from those of HCs. CONCLUSIONS: Mental transformation (OBT) and SPO copying abilities are impaired in subjects with obj-BD and dizziness, but not with dizziness only. We conclude that processing the neuropsychological representation of the human body (body schema) slows when balance control is deficient.

The effect of vibrotactile biofeedback of trunk sway on balance control in multiple sclerosis.

BACKGROUND: Patients with multiple sclerosis (MS) suffer from diminished balance control due to slowed sensory conduction and possibly delayed central processing. Vibrotactile biofeedback of trunk sway has been shown to improve balance control in patients with peripheral and central vestibular disorders. Here, the effects of vibrotactile feedback training on trunk sway and a possible carry-over effect was measured in MS patients during stance and gait. METHODS: Ten MS patients (mean age 46.8±7.7 years, 40% male) participated in a crossover study in which 7 different stance and gait tasks were trained with and without angle feedback for stance and angular velocity feedback for gait. An assessment sequence of 12 tasks was performed once before and twice after the training sequence. Trunk sway was measured with body-worn gyroscopes. Head mounted vibrotactile biofeedback of trunk sway was provided during one crossover training arm and the following second assessment sequence. RESULTS: Biofeedback generally leads to a decrease in sway but an increase in sway angular velocities during some stance tasks compared to training without biofeedback. Biofeedback while walking eyes open resulted in a decreased sway angular velocity. The greatest changes were found in the pitch direction of trunk sway. Effects diminished after biofeedback was removed. CONCLUSIONS: This study showed that vibrotactile biofeedback of trunk sway beneficially effects stance and provides significant improvement in gait compared to training without biofeedback in MS patients.

Effect of bilateral subthalamic nucleus stimulation on balance and finger control in Parkinson's disease.

We aimed to quantify the effects of bilateral subthalamic nucleus (STN) stimulation in Parkinson's disease (PD) on stance and gait ("axial"motor control), and related this to effects on finger movements ("appendicular" motor control). Fourteen PD patients and 20 matched controls participated. Subjects completed several balance and gait tasks (standing with eyes open or closed, on a normal or foam surface; retropulsion test; walking with eyes closed; walking up and down stairs; Get Up and Go test). Postural control was quantified using trunk sway measurements (angle and angular velocity) in the roll and pitch directions. Subjects further performed a pinch grip reaction time task, where we measured isometric grip forces, as well as movement and reaction times. Patients were examined with STN stimulators switched on or off (order randomised across patients), always after a supramaximal levodopa dosage. STN stimulation improved postural control, as reflected by a reduced trunk sway tremor during stance, a reduced duration for all gait tasks, an increased trunk pitch velocity while rising from a chair, and improved roll stability. STN stimulation also improved finger control, as reflected by a reduced time to reach maximum grip force, without altering reaction times and maximum force levels. Improvements in finger control timing did not correlate with reduced task durations during gait. We conclude that STN stimulation affords improvement of postural control in PD, over and above optimal drug treatment. STN stimulation also provides a simultaneous effect on distal and axial motor control. Because improvements in distal and axial motor control were not correlated, we assume that these effects are mediated by stimulation of different structures within the STN.

Trunk sway measurements during stance and gait tasks in Parkinson's disease.

To achieve a unified assessment of postural instability in Parkinson's disease (PD) over a range of clinical stance and gait tasks, which may provide an insight into a tendency to fall, we measured trunk sway in the anterior-posterior and medial-lateral directions in freely moving PD patients and age-matched controls. We also measured task duration as time to complete the task or time to loss of balance. Patients had larger amplitudes of trunk sway velocities for stance tasks (e.g. mean pitch velocity when standing on two-legs eyes closed equalled 19.1 +/- 6.4 for PD patients on medication versus 4.8 +/- 0.3 degrees/s for controls, p = 0.0003) and for an expected (following prior warning) retropulsion test (mean roll angle equalled 4.3 +/- 0.5 degrees for PD patients versus 2.2 +/- 0.6 degrees for controls, p = 0.0003) than controls. Patients were more likely to fall earlier for stance tasks, and took longer to complete gait tasks (e.g. walking 3 m eyes closed, mean time 6.8 +/- 0.6 sees versus 4.9 +/- 0.1 sees, p = 0.0001). These differences between patients and controls were, in most cases, independent of medication. Based on these results we defined a simple test battery of stance and gait tasks that could discriminate between PD patients who had recent falls and controls. These results indicate that trunk sway measures recorded during stance and gait tasks provide useful information on balance deficits leading to falls in PD patients.

Improvements in balance after total hip replacement.

We have investigated whether control of balance is improved during stance and gait and sit-to-stand tasks after unilateral total hip replacement undertaken for osteoarthritis of the hip. We examined 25 patients with a mean age of 67 years (sd 6.2) before and at four and 12 months after surgery and compared the findings with those of 50 healthy age-matched control subjects. For all tasks, balance was quantified using angular measurements of movement of the trunk. Before surgery, control of balance during gait and sit-to-stand tasks was abnormal in patients with severe osteoarthritis of the hip, while balance during stance was similar to that of the healthy control group. After total hip replacement, there was a progressive improvement at four and 12 months for most gait and sit-to-stand tasks and in the time needed to complete them. By 12 months, the values approached those of the control group. However, trunk pitch (forwards-backwards) and roll (side-to-side) velocities were less stable (greater than the control) when walking over barriers as was roll for the sit-to-stand task, indicative of a residual deficit of balance. Our data suggest that patients with symptomatic osteoarthritis of the hip have marked deficits of balance in gait tasks, which may explain the increased risk of falling which has been reported in some epidemiological studies. However, total hip replacement may help these patients to regain almost normal control of balance for some gait tasks, as we found in this study. Despite the improvement in most components of balance, however, the deficit in the control of trunk velocity during gait suggests that a cautious follow-up is required after total hip replacement regarding the risk of a fall, especially in the elderly.

The balance control of bilateral peripheral vestibular loss subjects and its improvement with auditory prosthetic feedback.

OBJECTIVES: We investigated whether long-term bilateral vestibular loss subjects could combine auditory biofeedback of trunk sway with their remaining natural sensory inputs on balance to provide an improved control of trunk sway. A successful integration of natural and artificial signals would provide a basis for a balance prosthesis. METHODS: Trunk sway of 6 bilateral peripheral vestibular loss subjects (BVL) was recorded using either angular position- or velocity-based auditory feedback or no feedback during stance and gait tasks. Roll and pitch trunk movements were recorded with angular velocity transducers mounted just above the waist and feedback without a delay to 4 loudspeakers placed at the left, right, front and rear borders of the 5 m long by 4 m wide test environment. The two types of auditory feedback or no feedback were provided to the subjects in random order. In the feedback modes, sway greater than a preset angle (ca. 0.5 deg) or velocity (ca. 3 deg/s) thresholds caused a tone to be emitted from the speaker towards which the subject moved. The tone volume increased with increasing angle or angular velocity amplitude. RESULTS: For all stance tasks BVL subjects without auditory feedback had a significantly different balance control with respect to that of normal controls. BVL sway values eyes open on a normal surface were reduced with auditory feedback with the greatest reductions in the roll plane. Specifically for the task of standing on 1 leg eyes open with position-auditory- feedback, amplitudes of pitch and roll angles and angular velocities were indistinguishable from those of normal controls. Sway during stance tasks on foam with eyes closed showed no improvement with feedback, remaining greater than normal. For some gait tasks there was a decrease in trunk sway with velocity feedback. CONCLUSION: These initial results indicate that subjects with vestibular loss could incorporate the auditory prosthetic sensory information into their balance commands, particularly in the roll plane if the balance task is performed with eyes open. Position information appears more useful than velocity information in reducing trunk sway during stance tasks. Future work will need to determine the effect of a training time on the improvement in balance control using such a prosthetic device and the ideal position and velocity auditory feedback combination.