Patent No. 5601091 Audiometric apparatus and associated screening method

 

Patent No. 5601091

Audiometric apparatus and associated screening method (Dolphin, Feb 11, 1997)

Abstract

An audiometric screening apparatus and associated method provides fast, low-cost, noninvasive screening of a subject's hearing. The apparatus includes a signal processor for generating a stimulus signal and a probe electrically coupled to the signal processor and insertible in a subject's ear. The probe includes a transmitter to transmit the stimulus signal into the ear and a receiver for receiving a first response signal from the subject's ear. An electrode, electrically coupled to the signal processor, is attached to the subject's scalp for sensing a second response signal. The signal processor processes the first response signal to provide an evoked otoacoustic emission signal and processes the second response signal to provide an auditory evoked potential signal.

Notes:

BACKGROUND

The present invention relates generally to the field of audiometric apparatuses and associated screening methods. In particular, the invention relates to audiometric apparatuses and auditory screening methods for providing rapid, low-cost, comprehensive, non-invasive screening of a subject's hearing.

Language acquisition in infants requires a critical period of hearing capacity which spans the frequency range of human speech. The critical period extends from birth to about two to three years of age, when infants typically begin to talk with some level of proficiency.

Approximately three to five percent of newborn infants suffer from some degree of hearing impairment. These impairments can be devastating to the social, emotional and intellectual development of the affected infants. Early identification of hearing impairments in infants allows for early intervention to minimize significant speech and language deficiencies. Infants are usually unable or unwilling to participate in known behavioral auditory examinations. Moreover, delaying auditory screening until infants can verbally respond is often too late for heating impaired infants and results in long term problems.

Federal, state and private agencies have attempted to implement universal auditory screening of infants for over twenty years. A major impediment to the implementation of universal auditory screening of infants has been the cost and complexity associated with the tests. Current infant screening tests are time consuming and require expensive devices and trained specialists to conduct the tests and interpret results. As such, universal auditory screening of infants is presently economically infeasible.

Various entities have developed audiometric devices which may be useable for screening an infant's hearing. These existing devices generally fall into one of two categories. Devices in the first category are configured to elicit auditory evoked potentials (AEPs), which are electrical responses of cells within the auditory pathway of the brain to an acoustic stimulus. Such devices typically utilize the non-invasive auditory brainstem response (ABR) test for auditory screening of infants. An earphone provides an acoustic stimulus, specifically a brief click or toneburst, to the subject's ear. Electrodes attached to the subject's scalp receive auditory evoked potentials from the scalp, which are recorded as an electroencephalogram waveform. Analysis of these brainwave patterns are used to determine if the auditory system is functioning normally.

Devices in the second category utilize the evoked otoacoustic emission (OAE) test for auditory screening. An earphone provides a brief acoustic stimulus to the subject's ear. A microphone disposed in the subject's ear adjacent the earphone receives an OAE from the ear, which is recorded as an acoustic signal. Analysis of the OAE waveform provides an indication of the functional integrity of the middle and inner ear, which together comprise the auditory periphery.

A number of limitations exist with respect to existing audiometric screening devices. One limitation is that some existing devices are complicated and require extensive training to operate. Another limitation is that other devices only provide a pass/fail indication and lack a visual display. Yet another limitation is that two separate devices are required to perform both the ABR or OAE tests. An operator typically makes a subjective determination of the acceptability of the ABR or OAE test results based on a visual examination of the response waveforms. Because existing audiometric devices do not allow for rapid, low-cost, non-invasive, comprehensive screening of infants, such devices do not adequately address the need for universal auditory infant screening.

SUMMARY OF THE INVENTION

The present invention contemplates audiometric screening apparatuses and associated methods for providing rapid, low-cost, comprehensive, non-invasive screening of a subject's hearing. An advantage of performing auditory screening using apparatuses incorporating the principles of the invention is that a behavioral response from the subject is not required. Thus, such apparatuses can be used to screen subjects who are unable to respond (e.g., infants) or unwilling or difficult to test (e.g., unconscious or mentally handicapped persons). Another advantage is that the invention is particularly useful in the area of auditory screening of infants. Except for initial infant preparation, the apparatus provides a fully automated screening procedure which includes stimulus presentation, response signal acquisition, signal analysis and interpretation of results. Nurses, technicians or hospital volunteers only require minimal training to perform auditory screening of infants. Thus, the cost of administering such auditory screening tests is reduced, encouraging universal screening of newborn infants.

The invention features an audiometric apparatus for screening a subject's hearing. The apparatus includes a signal processor for generating a first stimulus signal. A probe is electrically coupled to the signal processor and insertible in a subject's ear. The first stimulus signal comprises an amplitude modulated modulated acoustic signal which may include at least one paired tonal stimulus or at least one triple tonal stimulus. The probe includes a transmitter to transmit the first stimulus signal into the ear and a receiver for receiving a first response signal from the subject's ear. At least one electrode, electrically coupled to the signal processor, is attached to the subject's scalp for sensing a second response signal. The signal processor processes the first response signal to provide an OAE signal and processes the second response signal to provide an AEP signal. The signal processor processes the first and second signals in parallel. Moreover, the signal processor may process signals simultaneously to provide simultaneous OAE and AEP signals.

An input device is electrically coupled to a control processor to enable a user to request the signal processor to perform OAE and AEP tests. A display is electrically coupled to the control processor for displaying one or more characteristics of the OAE and AEP signals.

The apparatus may further include the capability to perform acoustic reflectivity (AR) tests. Such tests measure the degree to which sound across a range of frequencies is reflected off of the tympanum. The signal processor generates a second stimulus signal which is transmitted into the subject's ear by the transmitter. The receiver receives a third response signal from the subject's ear, and the signal processor processes the third response signal to provide a AR signal. The AR signal indicates the presence of fluid in the middle ear cavity and other pathologies.

The invention also features a portable audiometric apparatus for screening a subject's hearing. The portable apparatus includes a hand held housing and a docking station for receiving the housing. The docking station includes a battery charger for recharging the signal processor and a printer. A signal processor disposed within the housing generates a first stimulus signal. The first stimulus signal comprises an amplitude modulated signal, which may include at least one paired tonal stimulus or at least one triple tonal stimulus. A probe, electrically coupled to the signal processor, extends from the housing and is insertible into a subject's ear. The probe includes a transmitter to transmit the first stimulus signal into the ear and a receiver for receiving a first and second response signals from the subject's ear. The signal processor processes the first response signal to provide an OAE signal and processes the second response signal to provide an auditory indication signal. The auditory indication signal may be a tympanometry signal or an AR signal.

An input device electrically coupled to a control processor to enable a user to request the signal processor to perform OAE and auditory indication tests. A display is electrically coupled to the control processor for displaying one or more characteristics of the OAE and auditory indication signals.

The invention also features an auditory screening method for providing comprehensive screening of a subject's hearing. An electrode is attached to a subject's scalp. A probe, including a transmitter and a receiver, is inserted in the subject's ear. A stimulus signal is transmitted into the subject's ear. The stimulus signal comprises an amplitude modulated signal, which may include at least one paired tonal stimulus or at least one triple tonal stimulus. A response signal is received from the subject's ear via the probe. The response signal is averaged over a plurality of intervals to produce a plurality of subaverages. The subaverages are weighted based on a derived estimate of response content and combined to produce an auditory indication signal.

More specifically, the subaverages are inversely weighted based on the variance and content of the response signal. Further, the inversely weighted subaverages are combined according to the following steps: (i) performing a Fourier transform for each subaverage, (ii) determining real and imaginary components of the Fourier transform at specified frequencies, (iii) independently estimating variance of each component, and (iv) determining the probability of an auditory indication signal using an F statistic.