2 research outputs found
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
Mathematical methods for measuring the visually enhanced vestibulo-ocular reflex and preliminary results from healthy subjects and patient groups
Background: Visually enhanced vestibulo-ocular reflex (VVOR) is a well-known bedside clinical test to evaluate visuo-vestibular interaction, with clinical applications in patients with neurological and vestibular dysfunctions. Owing to recently developed diagnostic technologies, the possibility to perform an easy and objective measurement of the VVOR has increased, but there is a lack of computational methods designed to obtain an objective VVOR measurement.
Objectives: To develop a method for the assessment of the VVOR to obtain a gain value that compares head and eye velocities and to test this method in patients and healthy subjects.
Methods: Two computational methods were developed to measure the VVOR test responses: the first method was based on the area under curve of head and eye velocity plots and the second method was based on the slope of the linear regression obtained for head and eye velocity data. VVOR gain and vestibulo-ocular reflex (VOR) gain were analyzed with the data obtained from 35 subjects divided into four groups: healthy (N = 10), unilateral vestibular with vestibular neurectomy (N = 8), bilateral vestibulopathy (N = 12), and cerebellar ataxia, neuropathy, and vestibular areflexia syndrome (CANVAS) (N = 5).
Results: Intra-class correlation index for the two developed VVOR analysis methods was 0.99. Statistical differences were obtained by analysis of variance statistical method, comparing the healthy group (VVOR mean gain of 1 ± 0) with all other groups. The CANVAS group exhibited (VVOR mean gain of 0.4 ± 0.1) differences when compared to all other groups. VVOR mean gain for the vestibular bilateral group was 0.8 ± 0.1. VVOR mean gain in the unilateral group was 0.6 ± 0.1, with a Pearson's correlation of 0.52 obtained when VVOR gain was compared to the VOR gain of the operated side.
Conclusion: Two computational methods to measure the gain of VVOR were successfully developed. The VVOR gain values appear to objectively characterize the VVOR alteration observed in CANVAS patients, and also distinguish between healthy subjects and patients with some vestibular disorders