Motorized head impulse rotator in patients with vestibular schwannoma.

CONCLUSION: Motorized head impulse rotator is an effective technique to assess peripheral vestibular function. Approximately a quarter of patients with vestibular schwannoma (VS) had preserved preoperative responses. Vestibular disability could not be predicted based on vestibulo-ocular reflex (VOR) performance during motion stimuli, or in the caloric test. OBJECTIVES: To explore motorized head impulse rotator for evaluation of angular horizontal VOR in patients with VS, and to compare these responses to those of the caloric test and the symptoms. PATIENTS AND METHODS: We prospectively recorded head and eye position during unpredictable motorized head impulses in 38 patients with VS. We calculated gain and asymmetry of VOR (mean +/- 95% CI), and the results were compared to those of the caloric test and a questionnaire regarding dizziness, hearing and quality of life. RESULTS: The VOR during motorized impulses was abnormal in 71% of patients. Asymmetry in gain correlated significantly (p < 0.001) with unilateral weakness in the caloric test. Preoperative gain was significantly lowered to 0.83 +/- 0.08 on the ipsilateral side compared to 0.98 +/- 0.06 on the contralateral side. Postoperative gain on the operated side of 0.53 +/- 0.05 was significantly different from preoperative gain (p < 0.001). Findings in vestibular tests did not correlate with subjective sensation of dizziness.

Motorized head impulse rotator for horizontal vestibulo-ocular reflex: Normal responses.

OBJECTIVE: To characterize the horizontal angular vestibulo-ocular reflex using a new motorized head impulse rotator and electro-oculography technique. DESIGN: Prospective case-control study. PARTICIPANTS: We included 22 healthy volunteers with unpredictable, horizontal motorized head impulses with a mean velocity of 170 degrees/s and a mean acceleration of 1550 degrees/s2. We recorded head and eye position and calculated gain, asymmetry, and latency of the vestibulo-ocular reflex. All subjects underwent testing twice while viewing a far (140 cm) target to evaluate the repeatability of the measurement. In addition, 8 of these subjects underwent testing while viewing a near (15 cm) target. We reported findings as mean +/- SD. RESULTS: The mean gain during the 30-millisecond interval before peak head velocity and during the interval when head velocity ranged from 100 degrees /s to 120 degrees/s was 1.08 +/- 0.10. The mean asymmetry in gain between sides was 3.7% +/- 2.8%, and the mean latency of the vestibulo-ocular reflex was 3.4 +/- 6.3 milliseconds. There was a statistically significant correlation between consecutive gain measurements for each subject (r = 0.59; P=.004). The mean gain for the near target was 1.26 +/- 0.10 and was significantly higher than that for the far target (P = .002). CONCLUSIONS: The vestibulo-ocular reflex measurements using our novel system are comparable to those achieved using other techniques. These results suggest that a motorized head impulse rotator with electro-oculography allows reliable and fast measurement of the vestibulo-ocular reflex. In addition, the method is safe, repeatable, and thus could be a useful tool in the clinical assessment of the vestibulo-ocular reflex.

Postural control after vestibular schwannoma resection measured with visual feedback posturography.

BACKGROUND: Vestibular symptoms after surgery diminish rapidly, but the simultaneous progress in active postural control has not been fully addressed. OBJECTIVES: The aim was to evaluate the progress in postural control in operated vestibular schwannoma (VS) patients with visual feedback posturography (VFP). METHODS: 36 consecutive patients with unilateral VS were studied with the VFP pre-operatively, 1 month and 3 months after the surgery. The accuracy and velocity of active postural control movements to distant targets in VFP was measured and compared to that of healthy controls. RESULTS: The hold percentage within the targets was significantly reduced in the VS patients compared to the controls (pre-operatively p = 0.005; postoperatively at 1 month p = 0.002 and at 3 months p = 0.017). The sway velocity (SV) within the targets among patients with VS was significantly increased pre-operatively (p = 0.009), at the 1-month (p = 0.004) and at the 3-month follow-up visits (p = 0.016). All the postural control parameters except SV tended to improve slightly postoperatively. The consecutive VFP measurements in individual VS patients correlated statistically significantly (p < 0.001 for all parameters). The abnormality in the pre-operative VFP results correlated statistically significantly with that of postoperative VFP (p = 0.001). CONCLUSIONS: The VFP is an objective and repeatable method, which can be used to assess and follow up the active postural control in individual patients with VS. Persisting abnormality in the VFP seems to be an indication for more aggressive vestibular rehabilitation to normalize the disturbed postural control.

Postural control measured by visual feedback posturography.

The objective was to study the applicability and repeatability of visual feedback posturography (VFP) in assessing postural control of 23 healthy subjects. The subjects had to move their center of gravity (COG) marker on a computer screen to chosen targets by leaning their body on the platform, and the accuracy, velocity, and side difference of these movements were measured. The intraclass correlation coefficients for all parameters during repeated tests were significant (r = 0.93 - 0.96; p < 0.01). Hold percentage within the targets and COG marker velocity to the targets did not change significantly during repeated tests. Balance index and hit delay were significantly smaller during the 4th and 5th than during the 1st test session (p < 0.05), but they did not change significantly between the other test sessions. The normative limit for side difference in postural control was 22%. VFP can be used to follow active postural control due to its high test-retest repeatability. However, learning effects in some parameters must be taken into account when applying VFP repeatedly in different patient populations to assess the progress in postural control.