Study On Hearing Loss Detection Methods Based On Sweep-tone Auditory Brainstem Response

Hearing is an important channel for human beings to perceive and understand the world around them.Hearing loss seriously affects the quality of life of patients,and the patients are common.Detecting hearing loss early and adopting active treatment measures can reduce the probability of newborns becoming deaf-mute children,prevent depression in the elderly and reduce their risk of Alzheimer’s disease.Auditory brainstem response(ABR)audiometry is currently the most reliable objective detection method widely used in clinical practice,which can assess the functional status of auditory neural pathways and test hearing thresholds.However,the amplitude of the ABR signal is very weak and its frequency range is large,which brings difficulties to the signal acquisition and analysis.At present,the click ABR is the gold standard for ABR detection in clinical practice,but the click stimulus does not consider the delay characteristics of the human cochlear basilar membrane,resulting in a certain attenuation of the evoked response.The emerging chirp stimuli can theoretically make up for the shortcomings of click.Many researchers have designed a variety of chirps based on different models,but these models are all derived from average data with a limited number of samples.Moreover,as an evoked electroencephalogram(EEG)signal,the ABR is submerged by other physiological signals(including spontaneous EEG,electromyography(EMG),electrooculogram(EOG),etc.)appearing in the electrodes due to its weak amplitude.Hence,a clear ABR signal requires thousands of repeated stimuli followed by superposition averaging,which leads to long test time.Furthermore,the interference introduced by the electromagnetic field in the environment is much larger than the ABR signal and its frequency is within the ABR frequency band,which limits that the ABR test can only be performed in a shielded room.To improve the efficiency of the ABR test,the key is to increase the target signal as much as possible while reducing background noise,thereby increasing the signal-to-noise ratio.Therefore,to reduce the background noise,this study designed an active-shield circuit,which was placed in the front end of the acquisition device,to suppress the power line interference as well as electrode lead jitter interference caused by the electromagnetic field.Then,to increase the target signal,this study attempted to design two sweep-tone stimuli(the primary sweep-tone and the improved sweep-tone),defined and tested the Sum polarity method from the perspectives of improving the stimulus type and selecting the optimal stimulus polarity respectively.The specific research contents are as follows:Firstly,given that the recordings are easily mixed into the external interferences caused by the electromagnetic field during physiological signal acquisition,this study designed an active-shield circuit,which was placed at the front end of the acquisition device.In this study,the Active-shield method was evaluated by comparing the results with conventional hardware methods(including No-shield,GND-Shield,and BiasShield).The electrocardiograph(ECG),EOG,and EMG experiments in a normal laboratory showed that the Active-shield method could effectively suppress power line interference(50 Hz attenuation can reach more than 30 d B compared with that of the No-shield method).The EMG experiment in a shielded room showed that the Activeshield method can completely eliminate the electrode lead jitter interference.The above results demonstrated that the Active-shield method can eliminate external electromagnetic interference in the source and obtain high-quality raw data directly.Then,the existing chirp models are based on the indirect measurement of the characteristics of the living human cochlea to derive the average delay data of the basilar membrane.On the contrary,this study designed a primary sweep-tone stimulus based on the data from literature that was obtained by directly measuring the average delay characteristics of the cochlear basilar membrane of human cadavers and then deriving the corresponding data of living people.The experimental results showed that the primary sweep-tone ABR had better waveform differentiation and shorter formation time than the conventional click ABR.Next,in view of the existing chirp models based on the average delay data of the human cochlear basilar membrane with a limited number of samples,ignoring the individual differences amongst subjects,this study further improved the primary sweeptone stimulus,and synthesized the appropriate sweep-tone for each specific subject under a specific stimulus intensity.The experimental results showed that the(improved)sweep-tone ABR achieved a higher amplitude compared with those elicited by the conventional click and tone-bursts.When the stimulus level or rate was varied,the sweep-tone ABR consistently elicited a larger response than the corresponding click ABR,which implied the sweep-tone ABR could detect lower thresholds when used for hearing threshold estimation.Moreover,the sweep-tone ABR appeared earlier than the click ABR under the same conditions,which indicated that using the sweep-tone stimulus would save test time.Specifically,the mean wave V amplitude of the sweeptone ABR was 1.3 times that of the click ABR at 70 d B n HL and 20/s,in which the former could save 40% of test time.Finally,considering the difference in the physiologic basis of the positive and negative polarity stimuli on the auditory system,it is unclear whether conventional alternating polarity used to eliminate stimulus artifacts would adversely affect the ABR characteristics.This study proposed a new polarity method,named Sum polarity,and then through experiments compared the ABRs elicited by the common stimulus types(click,tone-burst,and sweep-tone)under different stimulus polarity methods(positive,negative,alternating polarity,and Sum polarity).The experimental results showed there was no significant difference among the click ABRs under the four polarity methods;low-frequency tone-burst ABRs were easily affected by stimulus polarity,with the effect decreasing as the stimulus frequency increased;the difference between the sweep ABRs under alternate polarity and Sum polarity methods was not obvious.This study verified the feasibility of the Sum polarity,which offers another choice for eliminating stimulus artifacts in evoked potential acquisition.According to the analysis of the experimental results,this study suggested the optimal polarity selection for each stimulus type.In summary,to eliminate the external electromagnetic interference mixed in the physiological signal acquisition,this study designed an Active-shield circuit to reduce background noise introduced by the external electromagnetic field as much as possible,thus avoiding the dependence on the shielded room.Aiming at the problems in ABR detection,such as unsatisfactory stimuli,long test time,and dependence on a shielded room,this study designed the sweep-tone stimulus and tested the Sum polarity method to maximize the ABR signal,which were made from the perspectives of improving stimulus types and selecting the optimal stimulus polarity respectively.The increased ABR signal not only saves the test time,but also helps clinicians to make the diagnosis more quickly and accurately.