Reducing the number of impulses in video head impulse testing - It's the quality not the numbers

A Clinical Framework for Video Head Impulse Testing and Vestibular Evoked Myogenic Potential Assessments in Primary School-Aged Children

OBJECTIVES

This study aimed to offer normative data and age trends of an age-appropriate vestibular test protocol in a large group (n = 140) of school-aged children (6 to 13 years old) as well as to provide a practical and clinical framework for accurate performance and interpretation of vestibular test results in this specific age group.

DESIGN

The typically developing participants (mean age of 9.51 ± 2.04 years) were recruited to provide a representative group of 20 children for each of the seven age groups that were composed of children aged from 6 to 13 years in 1-year intervals. Each age group consisted of 10 boys and 10 girls. The protocol comprises the video head impulse test, and cervical and ocular vestibular evoked myogenic potential assessments to provide a child-friendly, noninvasive, short, and portable test battery, which is equally applicable in the hospital and office-practice, and which provides information on the integrity of all five parts of the peripheral vestibular system.

RESULTS

The study demonstrates that all included tests and methods, with an overall test duration of 25 min 12 sec ± 5 min 10 sec, were feasible to perform in primary school-aged children, taking into account some practical adaptations. Concerning the video head impulse test, no clinically relevant sex and age effects were noted. However, t tests revealed significant differences for the mean gain of the horizontal (right > left; t [139] = 14.563; p < 0.001) and posterior semicircular canals (left > right; t [139] = -4.823; p < 0.001) between both sides. For the cVEMP assessment, no laterality differences were observed for any of the parameters, but a significantly shorter N1 latencies in the youngest age categories (<8 years), compared with the oldest groups were observed [ F (6,118) = 8.336; p < 0.001; partial ƞ ² = 0.298]. For all oVEMP parameters, no laterality, sex, or age differences were seen. On the basis of the presented normative data, cutoff criteria were proposed with accompanying clinical recommendations to perform vestibular function testing in this target population.

CONCLUSIONS

This is the first study in a large group of school-aged children offering normative data and age trends of an age-appropriate vestibular test protocol that evaluates the integrity of all parts of the peripheral vestibular organ. The reported normative values and clinical cutoff values will enable appropriate and age-specific interpretation of clinical and scientific results. Moreover, in combination with extensive history taking, and additional vestibular testing (e.g., rotatory chair test, caloric testing) when needed, the results of this study may support clinicians in the diagnosis of side-specific and location-specific vestibular deficits, which is required for accurate counseling and referral for further follow-up and/or intervention.

Goggle Versus Remote-Camera Video Head Impulse Test Device Comparison

OBJECTIVES

This study compared remote versus goggle video head impulse testing (vHIT) outcomes to validate remote-camera vHIT, which is gaining popularity in difficult to test populations.

DESIGN

Seventeen controls and 10 individuals with vestibular dysfunction participated. Each participant completed remote-camera and goggle vHIT. The main outcome parameters were canal gain, frequency of corrective saccades, and a normal versus abnormal rating.

RESULTS

Horizontal and vertical canal vHIT gain was significantly lower in the vestibular compared with the control group; remote-camera gains were significantly lower compared with goggle gain for the vestibular group only. The devices categorized control versus vestibular canals identically except for one vertical canal. In the vestibular group, there was not a significant difference in the percentage of compensatory saccades between devices.

CONCLUSION

These data provide validation that results obtained with a remote-camera device are similar to those obtained using a standard goggle device.

Assessing long-term, vestibulotoxic side effects after gentamicin therapy in neonatal sepsis or infection using video head impulse test

Study background

Newborn infection and sepsis remain serious problems. Guideline-compliant therapy includes, among other therapeutics, calculated intravenous antibiosis with gentamicin. One of the known side effects of gentamicin is severe vestibulotoxicity, which can be detected using the video head impulse test (VHIT), which is a sensitive examination method for the detection of vestibular hypofunction in children and adults. Previous studies on the vestibulotoxicity of gentamicin in newborns were carried out using caloric testing, rotary testing, and electronystagmography. Nevertheless, there are currently no data available on VHIT examinations in children who have been treated with neonatal gentamicin therapy.

Methods

A single-center, prospective cross-sectional study, was conducted at a tertial referral center. VHIT was performed on 23 children aged 3-7 years who had received intravenous gentamicin therapy for at least five days as part of the treatment of newborn sepsis between 2012 and 2016. Main outcome was median gain and occurrence of refixational saccades as measured with VHIT. In addition, the children's parents received questionnaires to detect possible risk factors and vestibular and cochlear abnormalities.

Results

Out of 23 children with a mean age of four years and seven months (ranging from 3 to 7 years), 11 (47.8%) indicated abnormal results in VHIT. The VHIT results were unilaterally abnormal in six children (26.1%) and bilaterally abnormal in five others (21.7%). Additionally, five of the children with an abnormal HIT had abnormalities, as found in the questionnaire results.

Conclusion

and Relevance: Almost half of the children observed after having undergone gentamicin therapy as newborns showed abnormalities in VHIT, although they did not show any clinical signs of disbalance or vestibular hypofunction. VHIT can serve as a sensitive investigation method for the early screening of post-therapeutic vestibulotoxic side effects after gentamicin therapy in children. Additionally, VHIT can enable early intervention in these children.

A review of the geometrical basis and the principles underlying the use and interpretation of the video head impulse test (vHIT) in clinical vestibular testing

This paper is concerned mainly with the assumptions underpinning the actual testing procedure, measurement, and interpretation of the video head impulse test-vHIT. Other papers have reported in detail the artifacts which can interfere with obtaining accurate eye movement results, but here we focus not on artifacts, but on the basic questions about the assumptions and geometrical considerations by which vHIT works. These matters are crucial in understanding and appropriately interpreting the results obtained, especially as vHIT is now being applied to central disorders. The interpretation of the eye velocity responses relies on thorough knowledge of the factors which can affect the response-for example the orientation of the goggles on the head, the head pitch, and the contribution of vertical canals to the horizontal canal response. We highlight some of these issues and point to future developments and improvements. The paper assumes knowledge of how vHIT testing is conducted.

Suppression Head Impulse Test (SHIMP) versus Head Impulse Test (HIMP) When Diagnosing Bilateral Vestibulopathy

The Suppression Head Impulse (SHIMP) test was introduced as an alternative to the Head Impulse Paradigm (HIMP) to overcome challenges in VOR gain calculation due to the interference of covert saccades. The objectives of this study were (1) to determine if SHIMP, compared to HIMP, reduces covert saccades in BV patients and (2) to define the agreement on diagnosing BV between SHIMP and HIMP. First, the number of covert saccades was compared between SHIMP and HIMP. Secondly, VOR gain was compared between SHIMP and HIMP. Lastly, the agreement between SHIMP and HIMP on identifying BV (horizontal VOR gain <0.6) was evaluated. A total of 98 BV patients were included. To our knowledge, this is the largest study population on SHIMP testing in BV patients. Covert saccades were significantly reduced, and a lower VOR gain was found during SHIMP compared to HIMP (p < 0.001). However, the clinical relevance of these statistically significant differences is small. In 93% of the patients, an agreement was found between the two paradigms regarding the diagnosis of BV, and both paradigms detect BV in the vast majority of patients.

Influence of predictability on saccade timing in a head impulse VOR suppression task

Gaze stabilization performance has been shown to be influenced differently when the head is either passively or actively moved in normal healthy participants. However, for a visual fixation suppression task, it remains unknown if the pattern of coordinated head and eye movement is influenced differently by passive or active head movements. We used a suppression head impulse paradigm (SHIMP), where the subject's goal was to maintain gaze stabilized on a visual target that moved with the head during rapid impulsive head movements, to evaluate gaze fixation performance in three conditions: (1) passive-unpredictable where the examiner applied impulsive head yaw rotations with random timing and direction, (2) passive-predictable where the direction of head rotation was announced and then the examiner repeatedly applied impulses in the same direction, and (3) active where the test subject self-generated their head movements. Thirteen young healthy adults performed all three conditions to assess the percentage of early saccades that initiated the gaze shift toward the final visual target position and the latency of first saccades. Early saccades were defined as those occurring within the duration of the head impulse. Results showed that active head impulses generated the greatest percentage of early saccades, followed by predictable and unpredictable. Among the two passive conditions, predictability shortened the first saccade onset latencies. Active condition onset latencies were shorter than in either of the passive conditions, showing a consistent head-leads-eye pattern defining a specific behavioral pattern that could vary across patient groups leading to insights into central neural mechanisms that control eye-head coordination.

Effect of different head impulse procedures on vestibulo-ocular reflex gain

OBJECTIVE

to study the effects on vestibulo-ocular reflex (VOR) gain using both video head impulse test (vHIT) and Suppression Head impulse test (SHIMP) either using the outward or the inwards head impulse.

METHODS

Twenty healthy subjects were enrolled in the study. They were examined using otometric vHIT and SHIMP test lateral plane using the lateral outwards head impulse ten impulses for each side and the inwards head impulse ten impulses for each side. The VOR gain resulting from the outwards versus inwards head impulse during the vHIT and SHIMP were statistically compared.

RESULTS

Twenty healthy subjects, 10 Males and 10 females with a mean age 35±11.7. Paired t- test showed no statistical significance difference in the mean VOR gain of right lateral semicircular canal (1.1±.12) using outwards versus (1.03 ± .22) inwards head impulses, nor for the left lateral semicircular canal mean VOR gain (1.1 ± .22) using outwards head impulse (1.1 ± .3) for inwards head impulse in vHIT. Paired t- test showed no statistical significance difference in the mean VOR gain of right lateral semicircular canal (0.96 ± 0.2)using outwards versus (1.04 ± 0.2) inwards head impulses, nor for the left lateral semicircular canal mean VOR gain (0.98 ± 0.25) using outwards head impulse (1.1 ± 0.28) for inwards head impulse in SHIMP test. No statistical significant difference was found between the VOR gain resulting from the right versus the left semicircular canal.

CONCLUSION

The starting head position does not affect the VOR gain using both vHIT and SHIMP tests.

Relevance of Artifact Removal and Number of Stimuli for Video Head Impulse Test Examination

OBJECTIVE

To evaluate the effect of artifacts on the impulse and response recordings with the video head impulse test (VHIT) and determine how many stimuli are necessary for obtaining acceptably efficient measurements.

METHODS

One hundred fifty patients were examined using VHIT and their registries searched for artifacts. We compared several variations of the dataset. The first variation used only samples without artifacts, the second used all samples (with and without artifacts), and the rest used only samples with each type of artifact. We calculated the relative efficiency (RE) of evaluating an increasingly large number of samples (3 to 19 per side) when compared with the complete sample (20 impulses per side).

RESULTS

Overshoot was associated with significantly higher speed (p = 0.005), higher duration (p < 0.001) and lower amplitude of the impulses (p = 0.002), and consequent higher saccades' latency (p = 0.035) and lower amplitude (p = 0.025). Loss of track was associated with lower gain (p = 0.035). Blink was associated with a higher number of saccades (p < 0.001), and wrong way was associated with lower saccade latency (p = 0.012). The coefficient of quartile deviation escalated as the number of artifacts of any type rose, indicating an increment of variability. Overshoot increased the probability of the impulse to lay on the outlier range for gain and peak speed. Blink did so for the number of saccades, and wrong way for the saccade amplitude and speed. RE reached a tolerable level of 1.1 at 7 to 10 impulses for all measurements except the PR score.

CONCLUSIONS

Our results suggest the necessity of removing artifacts after collecting VHIT samples to improve the accuracy and precision of results. Ten impulses are sufficient for achieving acceptable RE for all measurements except the PR score.

Diagnosing vestibular hypofunction: an update

Unilateral or bilateral vestibular hypofunction presents most commonly with symptoms of dizziness or postural imbalance and affects a large population. However, it is often missed because no quantitative testing of vestibular function is performed, or misdiagnosed due to a lack of standardization of vestibular testing. Therefore, this article reviews the current status of the most frequently used vestibular tests for canal and otolith function. This information can also be used to reach a consensus about the systematic diagnosis of vestibular hypofunction.

Comparison of three video head impulse test systems for the diagnosis of bilateral vestibulopathy

INTRODUCTION

A horizontal vestibulo-ocular reflex gain (VOR gain) of < 0.6, measured by the video head impulse test (VHIT), is one of the diagnostic criteria for bilateral vestibulopathy (BV) according to the Báràny Society. Several VHIT systems are commercially available, each with different techniques of tracking head and eye movements and different methods of gain calculation. This study compared three different VHIT systems in patients diagnosed with BV.

METHODS

This study comprised 46 BV patients (diagnosed according to the Báràny criteria), tested with three commercial VHIT systems (Interacoustics, Otometrics and Synapsys) in random order. Main outcome parameter was VOR gain as calculated by the system, and the agreement on BV diagnosis (VOR gain < 0.6) between the VHIT systems. Peak head velocities, the order effect and covert saccades were analysed separately, to determine whether these parameters could have influenced differences in outcome between VHIT systems.

RESULTS

VOR gain in the Synapsys system differed significantly from VOR gain in the other two systems [F(1.256, 33.916) = 35.681, p < 0.000]. The VHIT systems agreed in 83% of the patients on the BV diagnosis. Peak head velocities, the order effect and covert saccades were not likely to have influenced the above mentioned results.

CONCLUSION

To conclude, using different VHIT systems in the same BV patient can lead to clinically significant differences in VOR gain, when using a cut-off value of 0.6. This might hinder proper diagnosis of BV patients. It would, therefore, be preferred that VHIT systems are standardised regarding eye and head tracking methods, and VOR gain calculation algorithms. Until then, it is advised to not only take the VOR gain in consideration when assessing a VHIT trial, but also look at the raw traces and the compensatory saccades.