The Effect of Roll Circular Vection on Roll Tilt Postural Responses and Roll Subjective Postural Horizontal of Healthy Normal Subjects.

Background: Falls and related injuries are critical issues in several disease states, as well as aging, especially when interactions between vestibular and visual sensory inputs are involved. Slow support surface tilt (0.6 deg/s) followed by subjective postural horizontal (SPH) assessments have been proposed as a viable method for assessing otolith contributions to balance control. Previous assessments of perceived body alignment to vertical, including subjective visual vertical, have suggested that visual inputs are weighted more when vestibular information is near the threshold and less reliable during slow body tilt. To date, no studies have examined the influence of visual stimuli on slow roll-tilt postural responses and the SPH. Therefore, this study investigated how dynamic visual cues, in the form of circular vection (CV), influence postural responses and the perception of the horizontal during and after support surface tilt. Methods: Ten healthy young adults (6 female, mean age 23) wore a head-mounted display while standing on a tilting platform. Participants were asked to remain upright for 30 s, during which (1) the visual scene rotated, inducing roll CV clockwise (CW) or counter-clockwise (CCW) at 60°/s; (2) the platform only (PO) rotated in roll to test SPH (0.6°/s, 2°, CW or CCW); (3) a combination of both; or (4) neither occurred. During SPH trials, participants used a hand-held device to reset the position of the platform to 0.8°/s to their perceived SPH. The angular motion of body segments was measured using pairs of light-emitting diodes mounted on the head, trunk and pelvis. Segment motion, prior to platform motion, was compared to that at peak body motion induced by platform motion and when SPH had been set. Results: When the support surface was tilted 2°, peak upper body tilt significantly increased for congruent CV and platform tilt and decreased at the pelvis for incongruent CV when compared to PO, leading to significant differences across body segments for congruent and incongruent conditions (p ≤ 0.008). During PO, participants' mean SPH deviated from horizontal by 0.2°. The pelvis deviated 0.2°, the trunk 0.3°, and the head 0.5° in the direction of initial platform rotation. When platform tilt and CV directions were congruent or incongruent, only head tilt at SPH reset under congruent conditions was significantly different from the PO condition (1.7° vs. 0.5°). Conclusions: Roll CV has a significant effect on phasic body responses and a less significant effect on tonic body responses to lateral tilt. The SPH of the support surface was not altered by CV. Responses during tilt demonstrated enhanced reactions for congruent and reduced reactions for incongruent CV, both different from responses to CV alone. Tonic body displacements associated with SPH were changed less than those during tilt and were only slightly larger than displacements for CV alone. This study supports the hypothesis of weighted multisensory integration during dynamic postural tasks being highly dependent on the direction of visual cues during tilt and less dependent on tonic SPH offsets. These techniques could be used to examine vestibular and visual interactions within clinical populations, particularly those with visual vertigo and dizziness.

The Effects of Vibro-Tactile Biofeedback Balance Training on Balance Control and Dizziness in Patients with Persistent Postural-Perceptual Dizziness (PPPD).

BACKGROUND: Patients with persistent postural-perceptual dizziness (PPPD) frequently report having problems with balance control. Artificial systems providing vibro-tactile feedback (VTfb) of trunk sway to the patient could aid recalibration of "falsely" programmed natural sensory signal gains underlying unstable balance control and dizziness. Thus, the question we examine, retrospectively, is whether such artificial systems improve balance control in PPPD patients and simultaneously reduce the effects of dizziness on their living circumstances. Therefore, we assessed in PPPD patients the effects of VTfb of trunk sway on balance control during stance and gait tests, and on their perceived dizziness. METHODS: Balance control was assessed in 23 PPPD patients (11 of primary PPPD origin) using peak-to-peak amplitudes of trunk sway measured in the pitch and roll planes with a gyroscope system (SwayStar™) during 14 stance and gait tests. The tests included standing eyes closed on foam, walking tandem steps, and walking over low barriers. The measures of trunk sway were combined into a Balance Control Index (BCI) and used to determine whether the patient had a quantified balance deficit (QBD) or dizziness only (DO). The Dizziness Handicap Inventory (DHI) was used to assess perceived dizziness. The subjects first underwent a standard balance assessment from which the VTfb thresholds in eight directions, separated by 45 deg, were calculated for each assessment test based on the 90% range of the trunk sway angles in the pitch and roll directions for the test. A headband-mounted VTfb system, connected to the SwayStar™, was active in one of the eight directions when the threshold for that direction was exceeded. The subjects trained for 11 of the 14 balance tests with VTfb twice per week for 30 min over a total of 2 consecutive weeks. The BCI and DHI were reassessed each week and the thresholds were reset after the first week of training. RESULTS: On average, the patients showed an improved balance control in the BCI values after 2 weeks of VTfb training (24% p = 0.0001). The improvement was greater for the QBD patients than for the DO patients (26 vs. 21%), and greater for the gait tests than the stance tests. After 2 weeks, the mean BCI values of the DO patients, but not the QBD patients, were significantly less (p = 0.0008) than the upper 95% limit of normal age-matched reference values. A subjective benefit in balance control was spontaneously reported by 11 patients. Lower (36%), but less significant DHI values were also achieved after VTfb training (p = 0.006). The DHI changes were identical for the QBD and DO patients and approximately equal to the minimum clinical important difference. CONCLUSIONS: These initial results show, as far as we are aware for the first time, that providing VTfb of trunk sway to PPPD subjects yields a significant improvement in balance control, but a far less significant change in DHI-assessed dizziness. The intervention benefitted the gait trials more than the stance trials and benefited the QBD group of PPPD patients more than the DO group. This study increases our understanding of the pathophysiologic processes underlying PPPD and provides a basis for future interventions.

Vestibulo-ocular reflex gain improvements at peak head acceleration and velocity following onset of unilateral vestibular neuritis: Insights into neural compensation mechanisms.

BACKGROUND AND AIMS: An acute unilateral peripheral vestibular deficit (aUPVD) due to vestibular neuritis causes deficient yaw axis vestibular ocular reflex (VOR) gains. Using video head impulse tests (vHITs), we examined phasic and tonic velocity gains of the VOR over time to determine if these differed at onset and during subsequent improvement. METHODS: The VOR responses of 61 patients were examined within 5 days of aUPVD onset, and 3 and 7 weeks later using vHIT with mean peak yaw angular velocities of 177°/s (sd 45°/s) and mean peak accelerations of 3660°/s2 (sd 1300°/s2). The phasic velocity or acceleration gain (aG) was computed as the ratio of eye to head velocity around peak head acceleration, and the tonic velocity gain (vG) was calculated as the same ratio around peak head velocity. RESULTS: aG increased ipsi-deficit from 0.45 at onset to 0.67 at 3 weeks and 7 weeks later, and vG increased ipsi-deficit from 0.29 to 0.51 and 0.53, respectively, yielding a significant time effect (p < 0.001). Deficit side aG was significantly greater (p < 0.001) than vG at all time points. Deficit side gain improvements in aG and vG were similar. Contra-deficit aG increased from 0.86 to 0.95 and 0.94 at 3 weeks and 7 weeks, and vG contra-deficit increased from 0.84, to 0.89 and 0.87, respectively, also yielding a significant time effect (p = 0.004). Contra-deficit aG and vG were normal at 3 weeks. Mean canal paresis values improved from 91% to 67% over the 7 weeks. CONCLUSIONS: Acceleration and velocity VOR gains on the deficit side are reduced by aUPVD and improve most in the first 3 weeks after aUPVD onset. Deficit side aG is consistently higher than deficit side vG following an aUPVD, suggesting that acceleration rather than velocity sensitive compensatory neural mechanisms are predominant during the compensation process for aUPVD.

Improvement of Asymmetric Vestibulo-Ocular Reflex Responses Following Onset of Vestibular Neuritis Is Similar Across Canal Planes.

Background: We examined whether, after onset of acute unilateral vestibular neuritis (aUVN), initial disease effects, subsequent peripheral recovery and central compensation cause similar changes in vestibular ocular reflex (VOR) gains in all 3 semi-circular canal planes. Methods: 20 patients, mean age 56.5 years, with pathological lateral canal video head impulse test (vHIT) VOR gains due to aUVN, were subsequently examined with vHIT in all 3 canal planes on average 4.3 and 36.7 days ("5 weeks") after aUVN onset. Results: Lateral and anterior deficit side (DS) average gains equaled 0.41 at aUVN onset. Non-deficit, normal, side (NS) gains were 0.88 and 0.81, respectively. Mean posterior DS gain was similar at onset, 0.43, provided only gains lower than 0.6 (lower limit of healthy controls) were considered. NS posterior mean gain at onset (0.68) was less (p ≤ 0.0006) than lateral and anterior NS gains. After 5 weeks, DS lateral, anterior and posterior canal gains increased (p ≤ 0.05), on average, to 0.65, 0.59, and 0.58, respectively. NS gains increased to 0.91, 0.87, and 0.76 (p = 0.007), respectively. At 5 weeks deficit-lateral/normal-lateral canal plane gain asymmetries were significantly (p < 0.0008) reduced from 36.9 to 19.4%, deficit-anterior/normal-posterior asymmetry decreased from 28.6 to 18.1%, while deficit-posterior/normal-anterior asymmetry changed from 29.7 to 21.4%, all to circa 20%. Roll plane asymmetries decreased slightly over 5 weeks (28.6-18.1%) but pitch plane asymmetries remained significantly less (p = 0.001), not different from 0% regardless of initial DS posterior canal vHIT gain. Yaw plane asymmetry changes are identical to those of the lateral canals (36.7-19.4%). Conclusions: These results indicate that, at onset, aUVN of the superior vestibular nerve has a similar effect on lateral and anterior deficit DS VOR gains, and on posterior DS canal VOR gains if the inferior nerve was also affected at onset. The significant improvements to equal 5 week levels of DS gains and slightly greater posterior NS gain improvements, compared to lateral and anterior NS gains, yielding a common canal plane gain asymmetry of 20% at 5 weeks, suggest similar neural compensation mechanisms were active along VOR pathways. Unexpectantly, canal plane improvement was not replicated in pitch plane asymmetries.

The Effect of Unilateral Vestibular Loss on Standing Balance During Postural Threat.

OBJECTIVE: Vestibular deficit patients have an increased fall risk and fear of falling. Postural threat, known to increase balance-related fear and anxiety, influences vestibular gains during quiet standing in young healthy adults. The current study examined whether there is a similar relationship for peripheral unilateral vestibular loss (UVL) patients in comparison to age-matched healthy controls (HC). SETTING: University laboratory. STUDY DESIGN: Prospective laboratory study. PATIENTS AND CONTROLS: Eleven UVL patients, nine with vestibular neurectomy. Eleven aged-matched HCs. MAIN OUTCOME MEASURES: Subjects stood on a hydraulic lift placed at two heights: low (0.8 m, away from the edge) and high (3.2 m, at the edge). Amplitude (root mean square), mean power frequency (MPF), and mean position were analyzed for center of foot pressure (COP) and 90% ranges for angle amplitude and velocity for trunk sway. RESULTS: Group interactions were strongest for anterior-posterior (AP) COP and trunk pitch angle. AP lean away from the edge was greater in HCs than UVLs. HCs, but not UVLs had a decrease in root mean square AP COP with height. Trunk pitch sway was changed similarly. Both groups had increased trunk pitch velocity at height. Changes with height were less for roll: MPF of lateral COP increased with height for UVLs with no changes for HCs, and trunk roll amplitude decreased for both groups. CONCLUSIONS: This report provides evidence for a differential effect of height induced postural threat on balance control between UVLs and HCs presumably due to the reduced vestibular-spinal gain in UVL subjects.

Correlations Between Multi-plane vHIT Responses and Balance Control After Onset of an Acute Unilateral Peripheral Vestibular Deficit.

OBJECTIVE: Previous studies reported that balance deficits in pitch (sagittal) and roll (lateral) planes during stance and gait after onset of an acute unilateral peripheral vestibular deficit (aUPVD) due to vestibular neuritis are weakly correlated with deficits in commonly explored lateral canal vestibular ocular reflex (VOR) responses. Theoretically, stronger correlations with roll and pitch balance deficits could be expected for vertical canal VOR responses. Therefore, we investigated these correlations. SETTING: University Hospital. STUDY DESIGN: Retrospective case review. PATIENTS: Thirty three patients examined on average 5 days following onset of aUPVD. MAIN OUTCOME MEASURES: Video head impulse test (vHIT) VOR gains in each vertical canal plane were converted to roll and pitch response asymmetries and correlated with patients' roll and pitch balance control measured during stance and gait with body-worn gyroscopes mounted at lumbar 1 to 3. RESULTS: Mean caloric canal paresis was 92 ±â€Š12%. Deficit side lateral vHIT mean gain was 0.4 ±â€Š0.12, anterior gain 0.44 ±â€Š0.18, and posterior gain, greater, 0.69 ±â€Š0.15. Lateral VOR response gain asymmetries (37.2 ±â€Š11.0%) were greater than roll VOR asymmetries calculated from all four vertical canal vHIT gains (16.2 ±â€Š10.2%, p < 0.0001) and correlated (R = 0.56, p = 0.002). Pitch gain VOR asymmetries were less (4.9 ±â€Š9.9%, p < 0.0001). All gait, but no stance, trunk roll angular velocity measures were correlated (p ≤ 0.03) with VOR roll asymmetries. CONCLUSIONS: This report links roll balance control deficits during gait with roll VOR deficits and emphasises the need to perform anterior canal vHIT to judge effects of an aUPVD on balance control. Pitch VOR asymmetries were weakly affected by vestibular neuritis.

Theoretical framework for "unexplained" dizziness in the elderly: The role of small vessel disease.

In this paper we postulate that disruption of connectivity in the human brain can lead to dizziness, a symptom normally associated with focal disease of the vestibular system. The specific case that we will examine is the development of "unexplained" dizziness in the elderly-an extremely common clinical problem. Magnetic resonance imaging of the brain in the elderly usually show variable degrees of multifocal micro-angiopathy (small vessel white matter disease, SVD); thus, we review the literature, present a conceptual model and report preliminary quantitative EEG data in support of the hypothesis that such hemispheric SVD leads to central nervous system disconnection that elderly patients report as dizziness. Loss of connectivity by age-related build-up of SVD could lead to dizzy feelings through one or more of the following mechanisms: disconnection of cortical vestibular centers, disconnection between frontal gait centers and the basal ganglia, and disconnection between intended motor action (efference copy) and sensory re-afference. Finally, we propose that SVD-mediated dysregulation of cerebral blood pressure is linked to dizziness during standing and walking in elderly patients with "unexplained" dizziness.

Functional Testing of Vestibulo-Spinal Contributions to Balance Control: Insights From Tracking Improvement Following Acute Bilateral Peripheral Vestibular Loss.

Background: A battery of stance and gait tasks can be used to quantify functional deficits and track improvement in balance control following peripheral vestibular loss. An improvement could be due to at least 3 processes: partial peripheral recovery of sensory responses eliciting canal or otolith driven vestibular reflexes; central compensation of vestibular reflex gains, including substitution of intact otolith responses for pathological canal responses; or sensory substitution of visual and proprioceptive inputs for vestibular contributions to balance control. Results: We describe the presumed action of all 3 processes observed for a case of sudden incapacitating acute bilateral peripheral loss probably due to vestibular neuritis. Otolith responses were largely unaffected. However, pathological decreases in all canal-driven vestibular ocular reflex (VOR) gains were observed. After 3 months of vestibular rehabilitation, balance control was normal but VOR gains remained low. Conclusions: This case illustrates the difficulty in predicting balance control improvements from tests of the 10 vestibular end organs and emphasizes the need to test balance control function directly in order to determine if balance control has improved and is normal again despite remaining vestibular sensory deficits. This case also illustrates that the presence of residual otolithic function may be crucial for balance control improvement in cases of bilateral vestibular hypofunction.

Postural Threat Modulates Perceptions of Balance-Related Movement During Support Surface Rotations.

Postural threat decreases center of pressure displacements yet increases the magnitude of movement-related conscious sway perception during quiet standing. It is unknown how these changes influence perception of whole body movement during dynamic stance. The aim of this study was to examine how postural threat influences whole-body movements and conscious perception of these movements during continuous pseudo-random support surface perturbations to stance. Sixteen healthy young adults stood on a moveable platform with their eyes closed for 7 min in a low threat (1.1 m above ground, away from edge) then high threat (3.2 m above ground, near edge) condition. Continuous pseudorandom roll platform rotations (± 4.5°, < 0.5 Hz) evoked large amplitude sway in the medio-lateral (ML) direction. Participants were asked to remain upright and avoid a fall at all times while tracking their ML body movements using a hand-held rotary encoder. Kinematic data was recorded using three markers placed on the upper trunk. Questionnaires assessed anxiety, fear and confidence. Electrodermal activity (EDA) was recorded as an indicator of arousal. Height-induced threat increased fear, anxiety and EDA, and decreased confidence. Trunk sway amplitude remained constant, while tracked movement amplitude increased at height. The gain for perceived to trunk movement was significantly increased at height across frequencies. Threat-related increases in sensitivity of sensory systems related to postural control and changes in cognitive and attention processes may lead to misperceptions of actual movement amplitudes, which may be important when examining increased fall risk in those with a fear of falling.

Spinal Surgery With Electrically Evoked Potential Monitoring and Monopolar Electrocautery: Is Prior Removal of a Cochlear Implant Necessary?

: Transcranial electric stimulation to generate motor evoked potentials in lower limb muscles is the standard technique used to monitor spinal cord efferent pathways during surgical correction for spinal deformities. Monopolar electrical cauterization is also used by default in the thoracic and lumbar area of the spine during this kind of surgery to prevent major blood loss. Owing to the high levels of current used, both techniques are considered contraindicative if the patient has a cochlear implant (CI). Here, we present a CI patient who underwent corrective spinal fusion surgery for a severe kyphoscoliotic spinal deformity on whom both techniques were used without any negative effects on the CI function. A major improvement in sagittal body balance was achieved with no loss in implant-aided hearing levels. These results add to reports that CI manufactures should review their evidence underlying recommendations that transcranial electric stimulation and upper thoracic monopolar electrical cauterization are high risk for CI users, possibly initiating verification studies.

Measurements of Trunk Sway for Stance and Gait Tasks 2 Years after Vestibular Neurectomy.

The aim of this study was to investigate changes in balance control for stance and gait tasks in patients 2 years before and after vestibular neurectomy (VN) performed to alleviate intractable Meniere's disease. Amplitudes of trunk sway in roll and pitch directions were measured for stance and gait tasks in 19 patients using gyroscopes mounted at the lower-back. Measurements before VN and 2 years later were compared to those of healthy age-matched controls (HC). We also examined if changes in trunk sway amplitudes were correlated with patients' subjective assessment of disability using the AAO-HNS scale. For patients with low AAO-HNS scores 0-2 (n = 14), trunk roll and pitch sway velocities, standing eyes closed on foam, increased 2 years post VN compared to HC values (p < 0.01). Trunk sway amplitudes remained at levels of HC for simple gait tasks, but task durations were longer and therefore gait slower. For complex gait tasks (stairs), balance control remained impaired at 2 years. In patients with AAO-HNS high scores level 6 (n = 5), balance control remained abnormal, compared to HC, 2 years postoperatively for all stance, several simple and all complex gait tasks. Trunk sway in the pitch and roll directions for stance tasks was correlated with clinical (AAO-HNS) scores (p ≤ 0.05). These results indicate that VN leads to chronic balance problems for stance and complex gait tasks. The problems are greater for patients with high compared to low AAO-HNS scores, thereby explaining the different symptoms reported by these patients. The lack of balance recovery in VN patients to levels of HCs after 2 years contrasts with the 3 months average recovery period for acute vestibular neuritis patients and is indicative of the effects of neurectomy on central compensation processes.

Balance Changes in Patients With Relapsing-Remitting Multiple Sclerosis: A Pilot Study Comparing the Dynamics of the Relapse and Remitting Phases.

Aims: To compare balance changes over time during the relapse phase of relapsing-remitting multiple sclerosis (RRMS) with balance control during the remitting phase. Methods: Balance control during stance and gait tasks of 24 remitting-phase patients (mean age 43.7 ± 10.5, 15 women, mean EDSS at baseline 2.45 ± 1.01) was examined every 3 months over 9 months and compared to that of nine relapsing patients (age 42.0 ± 12.7, all women, mean EDSS at relapse onset 3.11 ± 0.96) examined at relapse onset and 3 months later. Balance was also compared to that of 40 healthy controls (HCs) (age 39.7 ± 12.6, 25 women). Balance control was measured as lower-trunk sway angles with body-worn gyroscopes. Expanded Disability Status Scale scores (EDSS) were used to monitor, clinically, disease progression. Results: Remitting-phase patients showed more unstable stance balance control than HCs (p < 0.04) with no worsening over the observation period of 9 months. Gait balance control was normal (p > 0.06). Relapsing patients had stance balance control significantly worse at onset compared to remitting-phase patients and HCs (p < 0.04). Gait tasks showed a significant decrease of gait speed and trunk sway in relapsing patients (p = 0.018) compatible with having increased gait instability at normal speeds. Improvement to levels of remitting patients generally took longer than 3 months. Balance and EDSS scores were correlated for remitting but not for relapse patients. Conclusions: Balance in remitting RRMS patients does not change significantly over 9 months and correlated well with EDSS scores. Our results indicate that balance control is a useful measure to assess recovery after a relapse, particularly in patients with unchanged EDSS scores. Based on our results, balance could be considered as additional measurement to assess recovery after a relapse, particularly in patients with unchanged EDSS.

A comparison of balance control during stance and gait in patients with inflammatory and non-inflammatory polyneuropathy.

INTRODUCTION: We compared changes in balance control due to chronic inflammatory demyelinating polyneuropathy (CIDP) and non-inflammatory (non-inf) polyneuropathy (PNP) to each other and with respect to healthy controls (HCs). Differences in patients' subjective impressions of balance capabilities were also compared. METHODS: Balance control of 11 CIDP patients (mean age 61.1±(sd) 11, 8 male) and 10 non-inf PNP patients (mean age 68.5±11.7, all male) was examined and compared to that of 18 age- and gender-matched healthy controls. Balance control during stance and gait tasks was measured as trunk sway angles and angular velocities with body-worn gyroscopes. Patients' subjective impressions of balance were obtained using the Dizziness Handicap Inventory (DHI). The Neuropathy Impairment Score in the Lower Limbs (NIS-LL) was used to measure clinical disease status. RESULTS: Non-inf PNP patients had slightly lower NIS-LL (13.5±7.2 vs. 17.9±15.1) and DHI scores (22.6±17.1 vs 27.6±16.3). Gait tasks showed a significant decrease in gait speed with respect to HCs for both patient groups but reduced trunk sway for non-inf PNP patients. Trunk sway during tandem walking and walking on the heels was greater for both groups than that of HCs. Sway during 2-legged stance tasks with eyes closed on a firm or foam surface was also greater than for HCs. DISCUSSION: Compared to HCs both groups of patients have significantly greater sway for most stance and gait tasks accompanied by reduced gait speed. As for HCs, non-inf PNP patients reduced trunk sway with slower gait speed. In CIDP patients this compensatory strategy was absent, possibly due to a greater deficit of efferent and motor nerve fibers. An interpretation of these findings is that CIDP patients have reduced ability to decrease trunk sway with slower gait speed and is possibly associated with an increased risk of falls.

The Effect of Peripheral Vestibular Recovery on Improvements in Vestibulo-ocular Reflexes and Balance Control After Acute Unilateral Peripheral Vestibular Loss.

BACKGROUND: Patients with an acute unilateral peripheral vestibular deficit (aUPVD), presumed to be caused by vestibular neuritis, show asymmetrical vestibular ocular reflexes (VORs) that improve over time. Questions arise regarding how much of the VOR improvement is due to peripheral recovery or central compensation, and whether differences in peripheral recovery influence balance control outcomes. METHODS: Thirty patients were examined at aUPVD onset and 3, 6, and 13 weeks later with four different VOR tests: caloric tests; rotating (ROT) chair tests performed in yaw with angular accelerations of 5 and 20 degrees/s; and video head impulse tests (vHIT) in the yaw plane. ROT and vHIT responses and balance control of 11 patients who had a caloric canal paresis (CP) more than 90% at aUPVD onset and no CP recovery (no-CPR) at 13 weeks in caloric tests were compared with those of 19 patients with CP recovery (CPR) to less than 30%, on average. Balance control was measured with a gyroscope system (SwayStar) recording trunk sway during stance and gait tasks. RESULTS: ROT and vHIT asymmetries of no-CPR and CPR patients reduced over time. The reduction was less at 13 weeks (36.2% vs. 83.5% on average) for the no-CPR patients. The no-CPR group asymmetries at 13 weeks were greater than those of CPR patients who had normal asymmetries. The greater asymmetries were caused by weaker deficit side responses which remained deficient in no-CPR patients at 13 weeks. Contra-deficit side vHIT and ROT responses remained normal. For all balance tests, sway was slightly greater for no-CPR compared with CPR patients at aUPVD onset and 3 weeks later. At 13 weeks, only sway during walking eyes closed was greater for the no-CPR group. A combination of 5 degrees/s ROT and balance tests could predict at onset (90% accuracy) which patients would have no-CPR at 13 weeks. CONCLUSIONS: These results indicate that for ROT and vHIT tests, central compensation is observed in CPR and no-CPR patients. It acts primarily by increasing deficit side responses. Central compensation provides approximately 60% of the VOR improvement for CPR patients. The rest of the improvement is due to peripheral recovery which appears necessary to reduce VOR asymmetry to normal at 13 weeks on average. Balance control improvement is more rapid than that of the VOR and marginally affected by the lack of peripheral recovery. Both VOR and balance control measures at onset provide indicators of future peripheral recovery. For these reasons VOR and balance control needs to be tested at aUPVD onset and at 13 weeks.

Differences in head impulse test results due to analysis techniques.

BACKGROUND: Different analysis techniques are used to define vestibulo-ocular reflex (VOR) gain between eye and head angular velocity during the video head impulse test (vHIT). Comparisons would aid selection of gain techniques best related to head impulse characteristics and promote standardisation. OBJECTIVE: Compare and contrast known methods of calculating vHIT VOR gain. METHODS: We examined lateral canal vHIT responses recorded from 20 patients twice within 13 weeks of acute unilateral peripheral vestibular deficit onset. Ten patients were tested with an ICS Impulse system (GN Otometrics) and 10 with an EyeSeeCam (ESC) system (Interacoustics). Mean gain and variance were computed with area, average sample gain, and regression techniques over specific head angular velocity (HV) and acceleration (HA) intervals. RESULTS: Results for the same gain technique were not different between measurement systems. Area and average sample gain yielded equally lower variances than regression techniques. Gains computed over the whole impulse duration were larger than those computed for increasing HV. Gain over decreasing HV was associated with larger variances. Gains computed around peak HV were smaller than those computed around peak HA. The median gain over 50-70 ms was not different from gain around peak HV. However, depending on technique used, the gain over increasing HV was different from gain around peak HA. Conversion equations between gains obtained with standard ICS and ESC methods were computed. For low gains, the conversion was dominated by a constant that needed to be added to ESC gains to equal ICS gains. CONCLUSIONS: We recommend manufacturers standardize vHIT gain calculations using 2 techniques: area gain around peak HA and peak HV.

Vibro-tactile and auditory balance biofeedback changes muscle activity patterns: Possible implications for vestibular implants.

BACKGROUND: The two different types of balance prostheses being developed, implants and vibro-tactile/auditory feedback prostheses, rely on different measures to prove efficacy (those based on vestibular ocular reflexes versus balance control, respectively). Here we provide evidence that examining muscle activity might provide a useful alternative for both. METHODS: The muscle activity of 6 bilateral vestibular loss (BVL) and 7 age-matched healthy controls (HC) was examined while standing eyes closed on a foam support surface. Pelvis and upper trunk angular movements were recorded in the roll and pitch planes. Surface EMG was recorded from the lower leg, trunk and upper arm muscles. BVL subjects were first assessed without feedback of pelvis sway, then received training with combined vibro-tactile and auditory feedback, before being re-assessed with feedback. RESULTS: Feedback reduced the amplitudes of pelvis and shoulder sway to values of HC without feedback. Both the level of background EMG activity and the EMG area amplitudes changed when feedback was provided in a manner consistent with the reduced amplitude modulation of muscle synergies of HC. CONCLUSIONS: The results of this study indicate that changed muscle synergy amplitudes underlie improvements in sway achieved by BVL subjects. The concept of this investigation may provide a means to prove efficacy for different types of balance prostheses, including implants.

Benefits of multi-session balance and gait training with multi-modal biofeedback in healthy older adults.

Real-time balance-relevant biofeedback from a wearable sensor can improve balance in many patient populations, however, it is unknown if balance training with biofeedback has lasting benefits for healthy older adults once training is completed and biofeedback removed. This study was designed to determine if multi-session balance training with and without biofeedback leads to changes in balance performance in healthy older adults; and if changes persist after training. 36 participants (age 60-88) were randomly divided into two groups. Both groups trained on seven stance and gait tasks for 2 consecutive weeks (3×/week) while trunk angular sway and task duration were monitored. One group received real-time multi-modal biofeedback of trunk sway and a control group trained without biofeedback. Training effects were assessed at the last training session, with biofeedback available to the feedback group. Post-training effects (without biofeedback) were assessed immediately after, 1-week, and 1-month post-training. Both groups demonstrated training effects; participants swayed less when standing on foam with eyes closed (EC), maintained tandem-stance EC longer, and completed 8 tandem-steps EC faster and with less sway at the last training session. Changes in sway and duration, indicative of faster walking, were also observed after training for other gait tasks. While changes in walking speed persisted post-training, few other post-training effects were observed. These data suggest there is little added benefit to balance training with biofeedback, beyond training without, in healthy older adults. However, transient use of wearable balance biofeedback systems as balance aides remains beneficial for challenging balance situations and some clinical populations.