[Universal neonatal screening as an application of automated audiological techniques]

Current audiological diagnostics

Today's audiological functional diagnostics is based on a variety of hearing tests, whose large number takes account of the variety of malfunctions of a complex sensory organ system and the necessity to examine it in a differentiated manner and at any age of life. The objective is to identify nature and origin of the hearing loss and to quantify its extent as far as necessary to dispose of the information needed to initiate the adequate medical (conservative or operational) treatment or the provision with technical hearing aids or prostheses. Moreover, audiometry provides the basis for the assessment of impairment and handicap as well as for the calculation of the degree of disability. In the present overview, the current state of the method inventory available for practical use is described, starting from basic diagnostics over to complex special techniques. The presentation is systematically grouped in subjective procedures, based on psychoacoustic exploration, and objective methods, based on physical measurements: preliminary hearing tests, pure tone threshold, suprathreshold processing of sound intensity, directional hearing, speech understanding in quiet and in noise, dichotic hearing, tympanogram, acoustic reflex, otoacoustic emissions and auditory evoked potentials. Apart from a few still existing gaps, this method inventory covers the whole spectrum of all clinically relevant functional deficits of the auditory system.

Notched-Noise Embedded Frequency Specific Chirps for Objective Audiometry Using Auditory Brainstem Responses

It has been shown recently that chirp-evoked auditory brainstem responses (ABRs) show better performance than click stimulations, especially at low intensity levels. In this paper we present the development, test, and evaluation of a series of notched-noise embedded frequency specific chirps. ABRs were collected in healthy young control subjects using the developed stimuli. Results of the analysis of the corresponding ABRs using a time-scale phase synchronization stability (PSS) measure are also reported. The resultant wave V amplitude and latency measures showed a similar behavior as for values reported in literature. The PSS of frequency specific chirp-evoked ABRs reflected the presence of the wave V for all stimulation intensities. The scales that resulted in higher PSS are in line with previous findings, where ABRs evoked by broadband chirps were analyzed, and which stated that low frequency channels are better for the recognition and analysis of chirp-evoked ABRs. We conclude that the development and test of the series of notched-noise embedded frequency specific chirps allowed the assessment of frequency specific ABRs, showing an identifiable wave V for different intensity levels. Future work may include the development of a faster automatic recognition scheme for these frequency specific ABRs.

[Universal newborn hearing screening. Methodical aspects]

BACKGROUND

In order to prepare for the introduction of a universal newborn hearing screening program on a larger scale, TEOAE and ABR were recorded on automated screening instruments from both ears of 501 newborns at the University Hospital Heidelberg over a period of 13 months. The parents of children in whom OAE and ABR could not be detected in both ears, were requested to allow a complete exploration of the auditory status of the children at the department of pediatric audiology.

SUBJECTS AND METHODS

Internally available data networks were used for the acquisition and evaluation of data and for the organization of tracking and follow-up. Of the children 35% exhibited risk factors for congenital hearing impairment.

RESULTS

The pass rate was 98.7% for the exclusion of binaural and 91.6% for monaural hearing disorders (TEOAE or ABR detectable). On the basis of the data it can be shown how pass rates can be optimized by selecting a suitable moment for the examination and by prescribing a minimum number of test repetitions (3 for TEOAE and 2 for AABR).

CONCLUSION

Quality control of screening programs should include these parameters and, in particular the number of repetitions of test measurements in all screening steps.

On the single sweep processing of auditory brainstem responses: click vs. chirp stimulations and active vs. passive electrodes

We have recently shown that click evoked auditory brainstem responses (ABRs) single sweeps can efficiently be processed by a hybrid novelty detection system. This approach allowed for the objective detection of hearing thresholds in a fraction of time of conventional schemes, making it appropriate for the efficient implementation of newborn hearing screening procedures. It is the objective of this study to evaluate whether this approach might further be improved by different stimulation paradigms and electrode settings. In particular, we evaluate chirp stimulations which compensate the basilar-membrane dispersion and active electrodes which are less sensitive to movements. This is the first study which is directed to a single sweep processing of chirp evoked ABRs. By concentrating on transparent features and a minimum number of adjustable parameters, we present an objective comparison of click vs.chirp stimulations and active vs. passive electrodes in the ultrafast ABR detection. We show that chirp evoked brainstem responses and active electrodes might improve the single sweeps analysis of ABRs.Consequently, we conclude that a single sweep processing of ABRs for the objective determination of hearing thresholds can further be improved by the use of optimized chirp stimulations and active electrodes.

Evoked response denoising using nonlinear diffusion filtering of single-trial matrix representations

Recent progress in mathematical image processing shows a remarkable success when applying numerical methods to ill-posed partial differential equations (PDE). In particular, nonlinear diffusion filtering (NDF)process is an approach that belongs to such family of differential equations. It has been successfully applied in many recent methods for image processing and computer vision areas, particularly in denoising, smoothing, segmentation, and restoration. In this paper we focus on a novel NDF application, namely denoising of single-trials of auditory brainstem responses (ABRs) and the analysis of transcranial magnetic stimulation (TMS) responses.We show that by applying NDF on a matrix-form image of single-trials, we were able to denoise the single-trials, resulting in a better extraction of information over the ongoing experiment; morphology, eg. the latency of the single-trials according to different stimuli paradigms at different stimulation intensity levels. It is concluded that NDF represents a novel and useful approach for the analysis of single-trials in brain imaging.

Ultra-fast quantification of hearing loss by neural synchronization stabilities of auditory evoked brainstem activity

Recently, we proposed a new novelty detection paradigm for the fast detection of hearing thresholds using single sweeps of auditory evoked potentials as efficient approach to newborn hearing screening. Such a method might prevent currently used time consuming averaging procedures which require the state of spontaneous sleep, sedation, or narcosis of the newborns when using such systems in universal newborn hearing screening programs. In this study, we present an evaluation of new feature for such novelty detection schemes, namely the synchronization stability of auditory evoked brainstem activity. For this, large-scale correlates of the neural group synchronization at the brainstem for stimulation levels above the hearing threshold are detected as novel event. This novelty detection paradigm allows for the adaptive inclusion of individual measurement conditions using the spontaneous EEG. For the individual patient, at the challenging stimulation level of 30dB(HL) the synchronization stability allowed the discrimination of stimulated from the non-stimulated condition in a fraction of time of conventional devices. It is concluded that the proposed feature following the novelty detection paradigm might be used for the ultra-fast detection of hearing thresholds and is thus ideally suited for the use in efficient universal hearing screening programs.

Kongenitale Schwerhörigkeit

BACKGROUND

About 50% of congenital non-syndromic hearing impairment is caused by genetic factors. Research on the genetics of deafness has revealed a vast number of relevant genes. Mutations in the GJB2 gene have been shown to be the most common in several populations.

METHODS

Mutation analysis of the genes for connexin 26, 30 and 31 (GJB2, GJB6 and GJB3) was performed in 67 patients with profound hearing loss.

RESULTS

Of the participants, 9% had two pathogenic mutations in the GJB2 gene. Pedigree information indicates that in these families further offspring have a 25% to a 100% chance of having hearing impairment.

CONCLUSIONS

Patients with non-syndromic hearing impairment should be offered molecular diagnostics of the GJB2 gene. Genetic counseling is mandatory for mutation carriers in order to advise them on the individual consequences of the gene test results.