Brian Lithgow

A new diagnostic vestibular evoked response

ObjectiveTo describe the development of a new clinically applicable method for assessing vestibular function in humans with particular application in Meniere’s disease.Study designSophisticated signal-processing techniques were applied to data from human subject undergoing tilts stimulating the otolith organs and semicircular canals. The most sensitive representatives of vestibular function were extracted as “features”.MethodsAfter careful consideration of expected response features, Electrovestibulography, a modified electrocochleography, recordings were performed on fourteen Meniere’s patients and sixteen healthy controls undergoing controlled tilts. The data were subjected to multiple signal processing techniques to determine which “features” were most predictive of vestibular responses.ResultsLinear discriminant analysis and fractal dimension may allow data from a single tilt to be used to adequately characterize the vestibular system.ConclusionObjective, physiologic assessment of vestibular function may become realistic with application of modern signal processing techniques.

Development of an ultra low noise, miniature signal conditioning device for vestibular evoked response recordings

BackgroundInner ear evoked potentials are small amplitude (<1 μVpk) signals that require a low noise signal acquisition protocol for successful extraction; an existing such technique is Electrocochleography (ECOG). A novel variant of ECOG called Electrovestibulography (EVestG) is currently investigated by our group, which captures vestibular responses to a whole body tilt. The objective is to design and implement a bio-signal amplifier optimized for ECOG and EVestG, which will be superior in noise performance compared to low noise, general purpose devices available commercially.MethodA high gain configuration is required (>85 dB) for such small signal recordings; thus, background power line interference (PLI) can have adverse effects. Active electrode shielding and driven-right-leg circuitry optimized for EVestG/ECOG recordings were investigated for PLI suppression. A parallel pre-amplifier design approach was investigated to realize low voltage, and current noise figures for the bio-signal amplifier.ResultsIn comparison to the currently used device, PLI is significantly suppressed by the designed prototype (by >20 dB in specific test scenarios), and the prototype amplifier generated noise was measured to be 4.8 nV/Hz @ 1 kHz (0.45 μVRMS with bandwidth 10 Hz-10 kHz), which is lower than the currently used device generated noise of 7.8 nV/Hz @ 1 kHz (0.76 μVRMS). A low noise (<1 nV/Hz) radio frequency interference filter was realized to minimize noise contribution from the pre-amplifier, while maintaining the required bandwidth in high impedance measurements. Validation of the prototype device was conducted for actual ECOG recordings on humans that showed an increase (p < 0.05) of ~5 dB in Signal-to-Noise ratio (SNR), and for EVestG recordings using a synthetic ear model that showed a ~4% improvement (p < 0.01) over the currently used amplifier.ConclusionThis paper presents the design and evaluation of an ultra-low noise and miniaturized bio-signal amplifier tailored for EVestG and ECOG. The increase in SNR for the implemented amplifier will reduce variability associated with bio-features extracted from such recordings; hence sensitivity and specificity measures associated with disease classification are expected to increase. Furthermore, immunity to PLI has enabled EVestG and ECOG recordings to be carried out in a non-shielded clinical environment.

Application of Vestibular Spontaneous Response as a Diagnostic Aid for Meniere's Disease.

AbstractIn this paper, we report on a new method for assisting in Meniere’s disease diagnosis. An accurate diagnosis of Meniere’s is challenging, and requires an expert opinion after observing several clinical assessments and tests over a period of time. Our proposed method is based on the analysis of the spontaneous and driven ear evoked responses recorded using Electrovestibulography (EVestG). We used the EVestG signals of 35 individuals suspected of Meniere’s and 26 age-matched healthy controls, out of which data of 14 patients with Meniere’s and 16 healthy controls were used for developing the diagnostic algorithm (training set) and the rest for testing. While recording and analyzing the test dataset, the researchers were only aware the patients suffered some dizziness, and were kept blind to the exact diagnoses till the end of study. EVestG field potentials (FPs) and their firing pattern, in response to several whole body tilt stimuli from both left and right ears were extracted. We investigated several features of the extracted FPs in response to each of side, back/forward, rotation, up/down, supine rotation, and supine up/down tilt stimulations, and selected the top five features showing the most significant differences between of the groups of the training set for every tilt. An ad-hoc average voting classifier was designed based on building five single-feature classifiers (using Linear Discriminant analysis) and taking the average of the single-feature classifiers’ votes. The results showed the side tilt data were best for the purpose of Meniere’s diagnosis; it resulted in 78% and 90% sensitivity and specificity for test dataset, respectively. The second best accuracy was achieved using back/forward tilt. The results and their implications are discussed. Overall, the EVestG side tilt results encourage the use of vestibular response as a non-invasive, robust and quick screening for Meniere’s and separating it from other types of dizziness.

Preliminary report: neural firing patterns specific for Meniere’s disease

ObjectiveTo describe the application of a new, objective diagnostic test for Meniere’s disease.IntroductionElectrovestibulography (EVestG) is a complex, newly-developed test paradigm that searches for neural firing patterns that may be diagnostic for particular neural disorders. EVestG system was previously “trained” to distinguish Meniere’s disease from other patients on a set of training data. In this paper we illustrate its diagnostic application in a new group of unknown subjects.SettingCollaborative Academic Bioengineering Research Centre.Study designProspective, blinded human Clinical Trial.MethodsIn an attempt to understand the specific neural firing patterns that may objectively characterize latent Meniere’s disease, two hundred fifty-six consecutive patients who presented for electronystagmography testing were asked to undergo EVestG testing. Ten subjects actually completed testing but data were too noisy to permit analysis for one patient. Complete data were available for nine patients with either a clinical diagnosis of either Meniere’s disease (4 patients) or some other vestibular disorder (2 vestibular neuritis, 2 benign positional vertigo and 1 non-specific dizziness). None of the patients were experiencing attacks of vertigo within a week of EVestG testing. Ten normal control subjects with no history or symptoms of ear disease were also tested. EVestG was performed in a separate engineering research facility by investigators who were unaware of their clinical diagnosis. If EVestG suggested that the probability of Meniere’s disease was 0.5 or greater Meniere’s disease was considered present by the objective testing. The objective and clinical diagnoses were compared.ResultsEVestG testing correctly identified three of four Meniere’s disease patients and rejected the diagnosis in 9 of the 10 controls. Two of the 5 dizzy, non-Meniere’s patients were incorrectly identified as Meniere’s disease. The sensitivity and specificity of EvestG testing were 75% and 80%, respectively. EVestG results were statistically significantly different for Meniere’s patients versus the other dizzy patients and controls (Univariate ANOVA difference contrasts p = 0.0340) even in this small sample.ConclusionThe EVestG protocol appeared to show promise as an objective, diagnostic test for Meniere’s disease, but our sample size is too small to generalize widely.Level of evidenceN.A. Prospective Human clinical trial.

Investigation of a New Weighted Averaging Method to Improve SNR of Electrocochleography Recordings

Goal: The aim of this study was to investigate methods to improve signal-to-noise ratio (SNR) of extratympanic electrocochleography (ET-ECOG); a low SNR electrophysiological measurement technique. The current standard for ET-ECOG involves acquiring and uniform averaging ~1000 evoked responses to reveal the signal of interest. Weighted averaging is commonly employed to enhance SNR of repetitive signals in the presence of a nonstationary noise, yet its efficacy in ET-ECOG has not been explored to date, which was the focus of this study. Methods: Conventional techniques used to compute signal statistics required for weighted averaging were found to be ineffective for ET-ECOG due to low SNR; therefore, a modified correlation coefficient-based approach was derived to quantify the “signal” component. Several variants of weighted averaging schemes were implemented and evaluated on 54 ECOG recordings obtained from seven healthy volunteers. Results: The best weighted averaging scheme provided a 17% (p <; 0.05) SNR increase [signal amplitude to standard deviation (STD) of the noise ratio] compared to uniform averaging, and further improved to 22% (p <; 0.05) when variance of the noise was incorporated as a cost factor. The implemented weighted averaging schemes were robust and effective for variants of ET-ECOG recording protocols investigated. Conclusion: Weighted averaging improved SNR of low amplitude ET-ECOG recordings in the presence of nonstationary noise. Significance: SNR improvements for ECOG have significant benefits in clinical applications; the variability associated with biofeatures extracted can be reduced, and may lead to shorter recordings. Methods described in this study can easily be incorporated in other low SNR repetitive electrophysiological measurement techniques.