the object of this invention is to propose a method and an apparatus , automated and easy to operate , that — through the recording and analysis of steady state evoked auditory potentials — allows to discriminate between the normal and abnormal hearing , identifying , in this latter case , whether the hearing disorder is of a conductive or sensorineural type . in order to use the multiple sseap technique in the neonatal screening programme to discriminate the type of hearing disorder ( if any ), an apparatus and a method are proposed , integrating the following elements : 1 ) means to independently generate two different continuous acoustic stimuli and to present them simultaneously to the patient through electro - acoustic bone and air transducers at different intensities ; 2 ) means to measure the ambient noise and , on the basis of the level measured , to regulate the execution of the screening test and the intensity of the air way stimulation ; 3 ) means to evaluate on an on - going basis the contact of the electrodes or sensors used to record the electric activity of the brain ; 4 ) means to control the process used to collect the bioelectric activity of the patient , in a synchronous manner with the generated sound stimuli ; 5 ) means for the wireless digital transfer of the bioelectric activity collected towards a computer . in order to use the apparatus for the purposes of universal neonatal screening , a computer - based methodology is implemented to efficiently detect both responses ( bone and air conducted ), which improves the signal - to - noise ratio and minimizes the duration of the hearing test , and a procedure for the automated operation that , on the basis of both responses ( bone and air conducted ) will discriminate between children without hearing disorders and those who show hearing disorders of a conductive or sensorineural type . one of the novelties of this invention is the use of the simultaneous stimulation from both the bone and air conduction modes as the basis for a system of stable state evoked auditive potentials , in order to carry out a primary hearing test ( screening ) among neonates , that may distinguish between a conductive hearing loss and a sensorineural loss ( if any ). another novelty , in the context of the design of the method and apparatus herein proposed , is the manner in which the recording conditions are monitored on an on - going basis ( ambient noise levels and the contact impedance of the electrodes ) to interact with the operator and / or the operation of the apparatus . more precisely , the use of the own active electric circuit of the neutral electrode for the on - going measuring of impedance is an original technological solution for this purpose . furthermore , the system proposed implements an original method of selective averaging , with an independent assessment of the signal - to - noise ratio and the application of a autoregressive statistical model , known as garch ( english acronym of “ generalized autoregressive conditional heteroskedasticity ”) to achieve a more efficient detection of the brain responses , which is an essential aspect , according to the invention . the method used is also original , since , on the basis of the result of the detection of one or another sseap response ( air conducted and bone way ) a conclusion can be reached in connection with the primary test , thus making a difference between normal or abnormal hearing , identifying , in this latter case , the type of disorder and the validity of the result . finally , the precise method adopted by the system , consisting of a specific purpose electronic device , which interacts with the patient and establishes a wireless communication with a laptop computer or a pda device , whose software includes all the necessary methodology to efficiently perform the primary hearing test represents a novel technological solution . description of the apparatus and method for the objective detection of auditive disorders fig1 shows the system proposed for the objective detection of auditive disorders in newborns , by means of steady state evoked auditive potentials . the system includes a device that comprises the necessary means for the simultaneous stimulation through electro - acoustic transducers for the bone and air conduction modes , and for the synchronous recording of the neuroelectric activity of the patient provoked by such stimuli . the device includes two - way wireless digital communications means to establish a connection with a computer or laptop device ( preferably , a personal digital assistant or pda ). the computer is used to perform the control functions of the device , such as the processing of the neuroelectric data , following its own automatic operation method , which is claimed in this invention . fig2 shows a detailed block diagram of the apparatus . the apparatus includes a control block that allows the digital generation of two different stimuli , and the necessary means to present them to the patient in an independent and simultaneous manner , at different intensities , by means of electro - acoustic transducers for the bone and air conduction modes . the acoustic stimulus used is generated through the following expression : s t = a − sen ( f c · t )*( 1 + p · sen ( f m · t )) a : amplitude of the modulated tone p : depth of the modulation f c : carrier frequency f m : modulating frequency the parameter a is used to weigh the amplitude of the modulated tone . preferably , at least a low frequency tone is generated for the bone conduction mode (≧ 500 & lt ; 1000 hz ) which is amplitude - modulated ( 100 % depth ) with a modulation frequency of 90 hz , while another high frequency tone (≧ 2000 hz & lt ; 4000 hz ) is simultaneously generated for the air way , which it is amplitude - modulated ( 100 % depth ) with a modulation frequency of 110 hz . these stimuli are intensity - weighed according to the electro - acoustic characteristics of each transducer ( bone and conduction modes ) and presented to the patient at constant ( but different ) intensities for each way . the apparatus also includes a channel for the collection of the neuroelectric activity ( active element g 1 of fig2 ) which is collected from the patient by means of 2 sensors or recording electrodes , which are placed on specific points of the scalp . this channel implements the necessary means to amplify such neuroelectric activity in a differentiated manner , filtering it within the desired frequency range . as shown in fig2 , a third recording electrode ( neutral ) is connected through a second active element ( g 2 ) to attenuate the interference caused by the power distribution network . this same element ( g 2 ), which is used to actively control the neutral electrode ( or “ patient &# 39 ; s ground ”) is also used to introduce in the patient , through such neutral electrode , a signal generated internally by the apparatus . the object of such signal is to evaluate the contact impedance of the recording electrodes ( za and zb ) and of the neutral electrode ( zt ). the output ( s 1 ) of the active element g 2 is recorded by another signal recording channel of the apparatus , and is used as the basis for the on - going impedance monitoring methodology which is claimed as part of this invention . the apparatus includes a microphone that picks up the ambient noise level , which is recorded by the g 3 channel through the active element . finally , the control block of the apparatus allows the synchronization between the stimuli generation process and the collection of the neuroelectric activity , so that , at each digitized time window or interval corresponding to such neuroelectric activity there is an exact number of cycles of tone stimuli generated , to allow the subsequent detection of the signal or sseap . this block also controls the real time , 2 - way and wireless transmission between the apparatus and the computer . the method used in this invention guarantees the automatic operation of this apparatus , so that it can be used with neonates to assess the auditory sensitiveness and to early detect eventual disorders , differentiating them from a diagnostic point of view . it consists of the following stages : 1 ) positioning in the head of the patient of the recording electrodes and the electro - acoustic transducers for the bone and air conduction stimulation modes ; 2 ) start - up and self - test of the apparatus ; 3 ) on - going measuring of the impedance of the recording electrodes and the ambient noise levels ; 4 ) interactive check of the adequate conditions to perform the test , on the basis of the information obtained in the previous stage ; 5 ) simultaneous bone and air conduction stimulation modes , with synchronous recording of the neuroelectric activity ; 6 ) transformation of each one of the neuroelectric records obtained in the previous step within the domain of frequency , by means of a fourier analysis ; 7 ) independent selective averaging for each spectral response or sseap by means of an interactive analysis of each record , on the basis of its signal - to - noise ratio ; 8 ) statistical determination of the presence or the absence of each one of the responses obtained by stimulation in the bone and air conduction modes ; and 9 ) diagnosis decision about the normal conditions of the auditory sensitiveness or the type of auditive disorder ( if any ) taken on the basis of the presence of both responses and / or the selective absence of one or another of the responses . steps 1 to 5 are performed by the apparatus , and steps 6 to 9 are carried out by programming a proprietary methodology in a general purpose portable computer . this allows to update and / or improve the method used by this invention to detect the responses . the selective averaging method used in this invention consists of collecting and averaging , on an independent basis for each response or sseap , only those neuroelectric records which have an adequate signal - to - noise ratio . one of the peculiarities of this method consists of the fact that , on the basis of the spectrum analysis of each recorded interval , the validity of the record is independently determined for each sseap , by comparing the amplitude of the spectrum component of the response ( at the relevant modulating frequency ) with that of the residual noise measured from n spectrum components found around it . the rejection criterion is based on a value of the signal - to - noise ratio that is lower than one . this is independently performed for each sseap ( bone and air modes ), so that the same neuroelectric record collected might be valid for a signal and rejected for the other one . in order to improve the signal - to - noise ratio of the sseap , a method is used to model the noise present at the artifact - free averaged neuroelectric records , based on a autoregressive statistical model , ar / garch . in this case , the response is modelled in the average of the n artifact - free segments , using the formula : where y t is the signal , c is the average , φ i are the autoregressive coefficients φ i , c and ε t the innovations . the variance of the innovations is : then , we can calculate the parameters of the model ( 0 . 1 0 . 2 0 . 3 ), using the maximum plausibility method . the following step of the method consists of detecting the signal . once the coefficients of the model have been calculated , we can separate the autoregressive process from the garch process that is responsible for the background noise . this way , if we calculate the spectrum of the autoregressive process only , we will obtain a spectrum which is free from background noise , which simplifies that identification of the signal . the spectrum is calculated as : in the last step , we use the hotelling &# 39 ; s t2 stadigraph ( t2h ) whose degrees of freedom have been modified according to the number of spectrum components used for the calculation , in order to determine whether the spectrum component at the modulation frequency of the stimulus ( sseap ) is significantly different from the adjacent spectrum components ( noise corresponding to that signal ), and therefore , to determine the presence or absence of response . finally , the following criteria are used by the method of this invention to complete the hearing test and reach the final conclusions : 1 ) if both signals ( bone and air modes ) reach a stable statistical significance ( after n successive calculations ) by means of a hotelling &# 39 ; s t2 stadigraph , it can be concluded that the auditory sensitiveness is normal ; 2 ) if the response found through the bone conduction mode is significant , and in the absence of the air way response , it can be concluded that the disorder or hearing loss is of a conductive type , 3 ) in the absence of both responses , it can be concluded that the hearing loss is of a sensorineural type , and 4 ) in the absence of a bone conducted response and in the presence of an air response , the result is doubtful , and the test should be repeated .
the invention relates to a method and apparatus for the objective detection of auditive disorders , by recording arising potentials of a steady state with simultaneous acoustic stimulation via the bones or the airway to be used in newborns . the apparatus comprises the necessary means for the independent generation of two different sound stimuli presented to the subject simultaneously via osseous and airway electroacoustic transducers , the synchronous recording of the cerebral electrical activity of the subject , the continuous evaluation of the contact of the electrodes , the interactive measurement of the levels of ambient noise , and the wireless digital transmission of the bioelectric activity towards a computer . the method according to the invention statistically processes and detects the potentials provoked by the osseous - airway stimulation , automatically providing a categorical final result , according to the presence or absence of the auditive sensitivity disorders , the type of disorder , and the validity of the result .