Comparison of two head autorotation tests

Changes in gain of horizontal vestibulo-ocular reflex during spaceflight

BACKGROUND:

The vestibulo-ocular reflex (VOR) is a basic function of the vestibular system that stabilizes gaze during head movement. Investigations on how spaceflight affects VOR gain and phase are few, and the magnitude of observed changes varies considerably and depends on the protocols used.

OBJECTIVE:

We investigated whether the gain and phase of the VOR in darkness and the visually assisted VOR were affected during and after spaceflight.

METHODS:

We measured the VOR gain and phase of 4 astronauts during and after a Space Shuttle spaceflight while the subjects voluntary oscillated their head around the yaw axis at 0.33 Hz or 1 Hz and fixed their gaze on a visual target (VVOR) or imagined this target when vision was occluded (DVOR). Eye position was recorded using electrooculography and angular velocity of the head was recorded with angular rate sensors.

RESULTS:

The VVOR gain at both oscillation frequencies remained near unity for all trials. DVOR gain was more variable inflight and postflight. Early inflight and immediately after the flight, DVOR gain was lower than before the flight. The phase between head and eye position was not altered by spaceflight.

CONCLUSION:

The decrease in DVOR gain early in the flight and after the flight reflects adaptive changes in central integration of vestibular and proprioceptive sensory inputs during active head movements.

Comprehensive Evaluation of Healthy Volunteers Using Multi-Modality Brain Injury Assessments: An Exploratory, Observational Study

Introduction: Even though mild traumatic brain injury is common and can result in persistent symptoms, traditional measurement tools can be insensitive in detecting functional deficits after injury. Some newer assessments do not have well-established norms, and little is known about how these measures perform over time or how cross-domain assessments correlate with one another. We conducted an exploratory study to measure the distribution, stability, and correlation of results from assessments used in mild traumatic brain injury in healthy, community-dwelling adults. Materials and Methods: In this prospective cohort study, healthy adult men and women without a history of brain injury underwent a comprehensive brain injury evaluation that included self-report questionnaires and neurological, electroencephalography, sleep, audiology/vestibular, autonomic, visual, neuroimaging, and laboratory testing. Most testing was performed at 3 intervals over 6 months. Results: The study enrolled 83 participants, and 75 were included in the primary analysis. Mean age was 38 years, 58 were male, and 53 were civilians. Participants did not endorse symptoms of post-concussive syndrome, PTSD, or depression. Abnormal neurological examination findings were rare, and 6 had generalized slowing on electroencephalography. Actigraphy and sleep diary showed good sleep maintenance efficiency, but 21 reported poor sleep quality. Heart rate variability was most stable over time in the sleep segment. Dynavision performance was normal, but 41 participants had abnormal ocular torsion. On eye tracking, circular, horizontal ramp, and reading tasks were more likely to be abnormal than other tasks. Most participants had normal hearing, videonystagmography, and rotational chair testing, but computerized dynamic posturography was abnormal in up to 21% of participants. Twenty-two participants had greater than expected white matter changes for age by MRI. Most abnormal findings were dispersed across the population, though a few participants had clusters of abnormalities. Conclusions: Despite our efforts to enroll normal, healthy volunteers, abnormalities on some measures were surprisingly common. Trial Registration: This study was registered at www.clinicaltrials.gov, trial identifier NCT01925963.

Bilateral Vestibular Weakness

Bilateral vestibular weakness (BVW) is a rare cause of imbalance. Patients with BVW complain of oscillopsia. In approximately half of the patients with BVW, the cause remains undetermined; in the remainder, the most common etiology by far is gentamicin ototoxicity, followed by much rarer entities such as autoimmune inner ear disease, meningitis, bilateral Ménière’s disease, bilateral vestibular neuritis, and bilateral vestibular schwannomas. While a number of bedside tests may raise the suspicion of BVW, the diagnosis should be confirmed by rotatory chair testing. Treatment of BVW is largely supportive. Medications with the unintended effect of vestibular suppression should be avoided.

The first demonstration that a subset of women with hyperemesis gravidarum has abnormalities in the vestibuloocular reflex pathway

OBJECTIVE

The vestibular system is a major pathway to nausea and vomiting, and the vestibuloocular reflex (VOR) is a central component; its function can be studied using the vestibular autorotation test (VAT). We hypothesize that women with hyperemesis gravidarum (HG) may have VOR abnormalities.

STUDY DESIGN

Women with HG were compared with women without HG using the VAT. Horizontal and vertical VOR gains and phases were evaluated at 3 frequency ranges: low (2.0 to 3.5 Hz), medium (greater than 3.5 to 5.0 Hz), and high (greater than 5.0 to 6.0 Hz) during pregnancy and postpartum.

RESULTS

Twenty women with HG and 48 unaffected women were evaluated in early pregnancy. Women with HG had higher horizontal gains at all 3 frequency ranges. Horizontal phase differences were also observed at medium frequencies. No VAT differences were noted postpartum.

CONCLUSION

Women experiencing HG had a higher mean VOR horizontal gain and lower horizontal phase when compared with unaffected women.

[Oculomotor response to the vertical cephalic autorotatory test in patients with benign paroxistic positional vertigo of the posterior canal]

OBJECTIVE

To evaluate the eye movement response to the head auto-rotation test (HART) in the vertical plane in patients with benign paroxysmal positional vertigo.

PATIENTS AND METHODS

DESIGN

A transversal, descriptive study. SETTING UP: Outpatient clinic in a general Hospital.

INDIVIDUALS

34 posterior canal BPPV cases with a video-oculographic diagnosis, older than 18 years old, 7 of them were not able to perform the HART.

INTERVENTION

HART was performed by a an electrooculographic system with simultaneous recording of head movement by an acelerometer in the vertical plane (Vorteq, Micromedical Instruments). The HART with eyes fixation was performed 3 times to determine its reliability.

MAIN OUTCOME MEASURES

Gain, asymmetry and phase for the vertical VOR respectively. A statistical analysis was carried out to determine the test reliability and the number of individuals with an abnormal result.

RESULTS

Gain is the only variable that showed a reproducible result in the HART for the active head movement at 1-2 Hz (test-retest reliability 0.83-0.89). The values of gain showed a moderate correlation at the frequencies 1-3 Hz (correlation 0.60-0.87). Asymmetry and phase were not reproducible variables (correlation < 0.55). Thirteen of 27 (48%) patients presented a decrease of the vertical gain, another 13 showed normal values and one case showed raised values.

CONCLUSION

Gain is the only useful variable in the vertical HART. Forty-eight percent of patients with posterior canal BPPV have a reduced vertical gain, suggesting an impairment of inferior vestibular nerve function.