What causes conductive hearing loss 2014,is occasional ringing in ears normal values,two causes of sensorineural hearing loss quotes,t?nis nike shox junior roxo - PDF Books

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A sensorineural hearing loss occurs when the delicate hair cells of the cochlea are damaged or missing, causing a hearing loss that may range from mild to profound.
A mixed hearing loss happens when a person has both a sensorineural and conductive hearing loss.
Auditory neuropathy spectrum disorder (ANSD) happens when the auditory nerve does not send synchronous signals to the brain.
What is a Conductive Hearing Loss?When sound waves cannot be transmitted through the outer and middle ear space, a conductive hearing loss is diagnosed. A conductive hearing loss occurs when any part of the sound transmission process is interrupted.
The actual hearing organ of the cochlea and the auditory nerves are completely unaffected in a purely conductive hearing loss. Fluid collects in the middle ear space as part of an acute or chronic middle ear infection. Conductive Hearing Loss Signs and SymptomsThe symptoms of a conductive hearing loss vary with the cause.
A? A child may not consistently turn to their name when called, particularly if the sound originates behind them. Ventilation tubes, or grommets, may be placed in the eardrum to help children with glue ear.
Treatments for Conductive Hearing LossMost forms of conductive hearing loss are curable through surgery or medication.
Occasionally, conductive hearing loss may be a permanent condition and requires treatment with hearing aids. The implanted Baha offers excellent sound quality for those with conductive hearing losses. Bone Anchored Hearing AidsIn some cases, the conductive hearing loss cannot be treated through surgery or medication. Causes of Conductive Hearing Loss: A PollWhat is the cause of your (or your child's) conductive hearing loss?
Ear Surgery for Hearing LossThe most common surgery for a conductive hearing loss is the placement of tympanostomy tubes (middle ear ventilation tubes or grommets).
A stapedectomy is a procedure performed when the stapes bone is no longer able to move freely. Ossiculoplasty is the replacement of malfunctioning middle ear bones with titanium prostheses.
CassyLu1981 3 years ago from Spring Lake, NC wow, excellent hub with great information! The outer ear consists of the auricle (unlabelled), the external auditory canal, and the lateral surface of the tympanic membrane (TM).
There are several other audiological tests that are also commonly abnormal in persons with conductive hearing loss.
Tympanometry usually is either flat (as shown below), or shows an abnormally large volume (indicating a perforation). Other tests that may be helpful in confirming conductive hearing loss are OAE testing and temporal bone CT scan. Causes include a buildup of ear wax, a foreign body in the ear canal, otosclerosis, typanosclerosis (as shown above), superior canal dehiscence (which can also cause a conductive hyperacusis), external or middle ear infections (otitis externa or media), allergy with serous otitis media (fluid in middle ear), trauma to the ossicular chain such as temporal bone fracture, tumors of the middle ear such as a glomus tumor, erosion of the ossicular chain (cholesteatoma) and perforation of the tympanic membrane.
A hole in the ear drum, which is called a tympanic membrane perforation, causes a conductive hearing loss.
It is generally attributed to previous ear infections or trauma (such as a tube insertion). The last step in the chain of signal transmission between sound in the air and movement of fluid in the inner ear is the middle ear. There are three small bones interposed between the large ear drum, and the small hole (oval window) across which sound is transmitted into the inner ear. Complete ossicular chain discontinuity usuall results in a large, flat conductive hearing loss. Characteristically, hearing aids work well for conductive hearing loss, and very good hearing results can be obtained. Surgical treatment is also generally available for conductive hearing loss as it is always due to a mechanical problem.
Most surgical treatments for otosclerosis or middle ear disease involve opening of the middle ear and repair under direct vision.
However, in our opinion (which is not representative of general opinion of ear surgeons), we think it is preferable to use a hearing aid until hearing becomes unservicable, and then move onto an implanted hearing aid, and skip the middle ear surgery part altogether.
To experience what your child may be hearing, try blocking your ears to mimic a conductive hearing loss. Your child may struggle to hear normal sounds, or complain that speech sounds soft or mumbled. En el en que farmacia venden levitra noviembre Washington comprar cialis levitra estaba a diez millas Quesne. L'Ufficio ha avviato una propria in-house programmi di istruzione e di formazione integrano gli sforzi officewide con sessioni e materiali specificamente orientata ai tipi di casi assegnati sue quattro divisioni. Il numero indagini tra le stesse e le azioni penali sono aumentati notevolmente, evidenziati, tra gli altri, i Bardzik fiscali disoccupazione e dei lavoratori premium compensazione frode SS pavimenti in calcestruzzo e Aziende, Inc.
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The Working Group on Auditory Evoked Potential Measurements was constituted (a) to review evidence and elevate the degree of consensus existing with respect to the procedural variables and instrumentation in the application of auditory sensitivity and (b) to provide a report that is highly specific in nature and intended to be a state-of-the-science update about methodology. In partial response to this mandate, the working group elected to develop a basic overview or tutorial focused on the short latency auditory evoked potentials (AEPs). Short latency AEPs are popular for the electrophysiologic assessment of otology and neurologic impairment. The short latency potentials are small amplitude, far field potentials; that is, they are recorded at some distance from their sources.
The intent of this document is not to mandate a set of standards for the measurement and evaluation of short latency AEPs. An understanding of how evoked potentials (EPs) are recorded and analyzed requires the grasp of certain principles of instrumentation.
The amplitude of surface-recorded AEPs is small in relation to the amplitude of background electro-physiological activity and electrical noise; therefore, it is necessary to improve the signal-to-noise ratio (SNR).
The accuracy with which a computer represents the fine structure, and therefore frequency content, is determined, in part, by the number of sampled points on the waveform (see Figures 1a and 1b).
Amplitude resolution depends on the numeric precision of the A-D converter, which is specified by the number of bits or places in the binary number representing its full-scale range of sensitivity. Signal averaging is necessary because the AEPs must be extracted from much larger background noise. The small amplitude of surface-recorded EPs necessitates the use of amplification prior to signal averaging. There are several specifications of the amplifier (sometimes referred to as a preamplifier) that are important. The gain of the amplifier depends on the full-scale voltage range of the A-D converter and minimum voltage input requirements.
The spectra of most EPs are concentrated such that much of the background noise can be removed via filtering. It is desirable to high-pass filter, or ac couple, to eliminate very low frequency and dc potentials.
Low pass filtering is needed because high frequency noise can be superimposed on the tracing and can obscure peak EP identification. Recording a well-defined response depends on the initial SNR, the number of samples averaged, and the extent to which the noise background is truly random.
Many artifacts encountered in EP recordings are sufficiently large in relation to the desired potential that they can be excluded on the basis of their amplitude. Earphones can be electromagnetically shielded using one or more layers of mu-metal (Elberling & Salomon, 1973), a material that tends to encourage the cancellation of the magnetic field. A particularly effective way to reduce stimulus artifacts was described by Sohmer and Pratt (1976), in which a tube is used to couple the earphone to the subject's ear and thereby create an acoustic delay line. Proper electrical wiring of the sound production and response recording systems is important, not only to minimize electrical artifacts but also to minimize electrical hazards (Pfeiffer, 1974).
Consideration must be given to the location of evoked response testing, both with regard to electrical and acoustical shielding.
The final determinant of the fidelity with which the waveform of the EP is reproduced depends on the manner in which the data are plotted. The outputting of data via analog devices, such as the X-Y plotter, requires digital-to-analog (D-A) conversion of the data in the computer's memory.
When frequency specificity is desired, sinusoidal pulses (tone pips or bursts) or band-pass filtered clicks may be used. Although no standard calibration procedure exists for clicks and other transients, a popular approach is to determine the peak equivalent sound pressure level (peSPL). Stimulus polarity does not affect the amplitude spectrum (Figure 3a), but it can affect the short latency potentials. Finally, when determining hearing levels, the psychophysical method for threshold measurement and number and rate of stimulus presentations are important factors. The efforts to date to integrate bone conduction stimulation in testing the short latency potentials have centered around the use of conventional audiometric bone vibrators with AEP test instruments (see Schwartz, Larson, & DeChicchis, 1985). The output of the vibrator is around 40 dB below that of the earphones, even when both are driven to saturating levels of output, just as in the case of pure tone audiometry. Electrocochleography (ECochG) is a term that has been applied to a family of electrophysiologic techniques directed specifically toward the recording of stimulus related potentials generated from the cochlea and eighth nerve. The record of the potentials recorded via ECochG is called the electrocochleogram (ECochGm). Coats (1974) introduced an electrode assembly that is self-retaining, although the point of recording was moved away from the eardrum and onto the floor of the ear canal. Inherent problems with this type of ear canal electrode are the difficulty of controlling placement and the relatively high electrode impedances. It will be recalled that in differential recordings a second electrode, sometimes called the reference electrode, is required, along with a ground electrode. The latency-intensity shift of the AP is demonstrated further by the ECochGm shown in Figure 8a. Both the CM and SP have very short latencies and no significant dependence of latency on intensity of stimulation. Stimulus repetition rate is an important factor in recording the ECochGm, particularly the AP.
The variability of latency is much less than that of amplitude and is relatively independent of recording technique.
Clinically, AEPs have been used in otoneurologic diagnoses and hearing threshold predictions. Originally, it had been hoped that the ECochGm waveform, as well as the input-output and latency-intensity functions, would conform to distinct patterns in cases of different pathologies of the auditory system.
Because Wave I represents the initial response of the auditory nervous system, the later waves tend to mimic its behavior, especially its dependence on stimulus parameters and the status of the middle and inner ears (Davis, 1976). The two parameters of the ABR waveform that usually are measured are amplitude and latency. The sound waves cannot get to the cochlea (and thus the auditory nerve), so sound is difficult to perceive.
This type of hearing loss is generally permanent, but may be treated with hearing aids or cochlear implants (dependent on the severity of the hearing loss). The physical transmission of sound and the cochlea are healthy, but the auditory nerve cannot effectively relay information to the brain. The "x" & "o" show the hearing for the left and right ears when sound is presented through earphones. Most causes of conductive hearing loss are treatable, but some people have a permanent condition and will require the use of hearing aids.
A problem with the outer ear, ear canal, eardrum, middle ear space, or the middle ear bones may cause a conductive hearing loss.
This is also known as "glue ear." Sound does not travel effeciently because the bones may not move freely.
If a foreign body or earwax is responsible for the problem, the obstruction is simply removed and hearing is restored to a normal state. In this case, surgery may be required to replace the middle ear bones with prostheses (see a€?ear surgery for hearing loss,a€? below). This short surgical procedure places tiny tubes into the eardrum, allowing fluid to drain into the Eustachian tubes. A tiny hole is drilled into the fixed stapes and a prosthetic that acts like a piston is surgically attached.
Children with small or missing external ears often have a small or obstructed ear canal and may also have problems with the middle ear bones. My husbad has the baha device and though it works well on the whole, background noises and things like high winds force a noise feedback from the device. My own son has a mixed hearing loss, though there was a period of time when we thought there was a more significant conductive component and we considered the Baha. We are fortunate that our son's hearing loss was detected early, so we are able to monitor it (it is progressive).
Unfortunately, we can't identify a cause of the conductive component in my son's hearing loss, as his middle ear bones appear normal and he has no fluid (he has working middle ear tubes) - so it is a permanent component to his hearing loss!
A lot of people think of conductive hearing loss as a temporary problem or just "fluid in the ears." While those problems are significant and need to be addressed, there are also a lot of people who have permanent conductive hearing losses and require hearing aids to hear clearly! The middle ear includes the medial surface of the eardrum, the ossicular chain of bones, the eustachian tube.
These can be immensely troublesome because their removal can be difficult, and infections are common.
It is more accurate to say that there is a hearing reduction, as generally hearing is not greatly affected -- a 10 db drop is typical.
There also seems to be a weak association with increased serum calcium (de Carvalho et al, 2006) .
When these bones are fused (otosclerosis, or ossicular fixation) or broken (ossicular chain discontinuity), a conductive hearing loss is the inevitable result. When combined with a sensorineural hearing loss, this pattern may look superficially like a conductive hearing loss, because there is an air-bone gap. Persons with LVAS may develop hearing loss as well as be unusually vulnerable to inner ear disease associated with head injury. Recently some groups (Kakehata et al, 2006) are using endoscopy for repair of ossicular chain disturbances -- in our opinion, this is still very investigational and somewhat unreasonable -- when working inside a tiny space, one needs as good an exposure as one can manage. Carhart Notch 2-kHz Bone Conduction Threshold Dip: A Nondefinitive Predictor of Stapes Fixation in Conductive Hearing Loss With Normal Tympanic Membrane. Durante la noche la guarnicion tomo alarma, incendiar la fortaleza y flotaba para mas informacion por el Ohio. Y ahora general Amherst fue viagra se vende sin receta espana ascendido comandante en jefe de las mes informacio fuerzas europeas. Tres comprar viagra generica espana campanas fueron planeados para este ano general Prideaux realizar una expedicion contra Niagara, Amherst liderar la division principal en contra Ticonderoga y Crown Point, y el general Wolfe proceder el San Lorenzo contra Cataratas fue invadida Prideaux la loth julio.
Un General sito Counsel e stato nominato assistere il cialis 5 mg generico prezzo capo dell'ufficio nell'adozione e nell'attuazione delle politiche e delle procedure legali compatibili in tutto l'ufficio di presidenza. Azioni che coinvolgono di frode fiscale datore vendita cialis francia di lavoro e furto propecia uomini sussidi di disoccupazione sono perseguiti nel Distretto e Magistrature Superiori. This class of AEPs encompasses the areas of electrocochleography (ECochG) and auditory brainstem response (ABR) measurement. The stability of these potentials over subject state, the relative ease with which they may be recorded, and their sensitivity to dysfunctions of the peripheral and brainstem auditory systems make them well-suited for clinical application.
Sophisticated techniques are needed to measure these potentials because they are buried in a background of physical and physiological noise.
Rather the objective is to present a background of information that the working group believes to be requisite for a basic understanding of these measures. The first, Instrumentation—Basic Principles, presents instrumentation for both the stimulus generation and the recording and analysis methods that are common to noninvasive ECochG and ABR measurement. The sources of this activity may include muscle contractions, sensory end organ responses, and neural events from the central and peripheral nervous system. Silver, gold, and platinum have lower impedances and half-cell potentials than most other metals. Routine EP evaluations have become possible primarily through the advent and availability of relatively small and inexpensive digital computers that can efficiently perform signal averaging. This number depends on the maximum sampling rate of the A-D conversion process, which is inversely related to how long each conversion takes.
For example, suppose a 4-bit A-D converter were used to measure the voltage of a common flashlight battery, and that this A-D converter had a sensitivity of ±5 V.
Poor SNR is overcome by summing numerous digitized wave forms, each timed-locked to the stimulus.
The objective is not only to amplify the recorded potentials, but also to optimize the voltage sampling for the desired potential while rejecting unwanted signals common to each of the amplifier inputs.
One is amount of CMR, which usually is specified in decibels and is defined as the amount of amplitude reduction of common signals. Internal noise should be below 10 µV peak-to-peak to maximize SNR improvement achieved by signal averaging. However, manufacturers of EP test equipment provide few protocols for checking these parameters and typically do not give amplifier specifications in their manuals.
These potentials cause drift in the baseline of the recording and tend to make the recordings vulnerable to movement artifacts.


The use of low pass filtering also is determined by the sampling rate of the A-D converter. This may be treated via some form of post filtering or smoothing, which is a form of low pass filtering.
It is possible that an event will occur during averaging that may not be canceled by a clinically practical number of samples. Most commercially available test systems include the capability of specifying an acceptable input amplitude window or adjusting the input sensitivity while testing for samples exceeding full scale. The former is exemplified by the reception of 60 Hz noise from a fluorescent light, and the latter is exemplified by reception of 60 Hz noise induced in the amplifier circuit by radiation from a power transformer, electrical machinery, or electrical wiring around the test room.
A metal sound isolation chamber, designed especially for electromagnetic and electrostatic shielding, is ideal but not essential in every situation.
In the case of digital plotters, wherein the X and Y coordinates are changed in steps, the reproduction will be true to the form of the digitized wave, except that there will always be a slightly jagged character in the detail of the waveform due to the stepping action of the pen (somewhat like the waveform shown in Figure 1b). Some of the same considerations given to A-D conversions apply to D-A conversion although, in practice, the demands are much less in terms of dwell time and resolution. Because such stimuli are transients, their spectra are characterized by energy spread around the nominal or center frequency (Figure 3b). There are various temporal parameters associated with stimulation, particularly with regard to the use of tone bursts.
The repetition rate of the stimulus must be slow enough to prevent significant adaptation of the response. This measurement is obtained by using an oscilloscope to match the amplitude of a sine wave with the peak amplitude of the click stimulus. Therefore, it is essential to measure the starting phase of the signal to determine whether the stimulus begins with condensation or rarefaction (Figure 3a.1).
In conventional audiometry the magnitude of conductive lesions is assessed by comparing thresholds obtained via air versus bone conduction stimuli. Unfortunately, even when the earphone and bone vibrator outputs are adjusted for equal sensation levels (for clicks), the bone conduction elicited response is delayed by 0.5 ms or more (Weber, 1983). Like the conventional earphone, the bone vibrator is an electromagnetic device and therefore emits electromagnetic waves, causing stimulus artifact.
Bone conduction testing can help in newborn screenings and other audiologic applications but, clearly, care must be taken in the use and the interpretation of results obtained.
Attempts at clinical applications of ECochG date back almost as far as the discovery of the cochlear potentials by Wever and Bray (1930), but practical applications were not realized until the late 1960s. Although the ECochGm consists of more than one electrical potential (Figure 4), the most obvious and most easily recorded component is the whole nerve action potential (AP) of the eighth nerve. One method involves inserting a needle electrode through the tympanic membrane (TM) to rest on the cochlear promontory. Combined electrocochleogram and brainstem potential recording at different sensation levels of the click stimulus.
Also, an earplug electrode of this general type compares favorably with the Coats electrode, when the latter is inserted near the entrance to the ear canal (Ferraro, Murphy, & Ruth, 1986). Two possible placements for the reference electrode are the ipsilateral earlobe and mastoid. Even prior to the appearance of the classic paper by Jewett, Romano, and Williston (1970) describing ABRs, Sohmer and Feinmesser (1967) described ECochG using essentially the same electrode placements. As expected, recordings from the TM yield the largest, most sensitive and reliable responses among the three approaches. AP latency-intensity function and corresponding ECochG tracings (recorded via an ear-canal electrode). The CM magnitude, if represented in logarithmic units, grows in direct proportion to sound pressure in decibels, usually with a slope of unity.
As illustrated by Figure 10, the amplitude of the AP decreases and latency increases with increasing rate. Effects of stimulus rate in clicks per second (CPS); for reference, the interstimulus intervals (ISI) have been computed for each rate tested (*, artifact). Fundamentally, the problem of selectively testing one ear is the same for ECochG as it is for conventional audiometry.
Standard deviations are typically less than 0.2 ms for the AP recorded from normal hearing subjects (Durrant, 1986). ECochG has been used in both of these areas, although the early work involved primarily transtympanic measurements.
Ear canal ECochG has not proven particularly useful for threshold estimation and does not provide as reliable determinations of threshold estimates as the transtympanic technique (Probst, 1983). The clinical utilities in the area of otoneurologic or differential diagnoses also have been limited for ECochG. AP latency-intensity functions for group of patients with mild-to-moderate conductive (a) and sloping sensorineural hearing loss (b). One discouraging aspect is the considerable difficulty of eliminating stimulus artifact to a degree that one is confident that only CM is being recorded. Two labeling systems have been used, one attributable to Sohmer, Feinmesser, and Szabo (1974) and the other to Jewett and Williston (1971), with the latter scheme now being used more widely. Nevertheless, there is some degree of independence between the brainstem and peripheral nerve components.
Amplitude typically is measured between a positive peak and the following negative “peak” or trough (Figure 15). The most basic is absolute latency, which is defined as the time difference between stimulus onset and the peak of the wave (Figure 15).
When the middle ear is bypassed, however, the hearing level demonstrates normal levels (brackets). The sound then travels down the ear canal, and causes the eardrum (tympanic membrane) to start vibrating.
Heavy amounts of earwax may be seen with an otoscope in some cases of minor conductive hearing loss. Fluid in the middle ear (chronic otitis media) may be treated with antibiotics or with the insertion of middle ear ventilation tubes (pressure equalization tubes) to allow the fluid to drain. A hearing test should be performed after this procedure to verify hearing has returned to normal limits.
The middle ear may be reconstructed with the use of prosthetic middle ear bones or a bone anchored hearing aid may be required to restore hearing to the damaged ear. Many children struggle with fluctuating, conductive hearing loss or have a more permanent form of conductive loss, so it is an important thing for parents to be aware of. These are most easily removed using an examining microscope, but in some instances, surgical removal is needed. It is presently thought that persons taking calcium supplements are not at increased risk, and also that there is no risk from calcium channel blocker medications. The most common ones are cholesteatoma associated with chronic ear infection (it is not a true tumor) and glomus tumors.
Certains the.se ont ete fabriques le prix du priligy en pharmacie ici, mais produits la plupart leur ont ete faites ailleurs. These potentials represent sensory or neural responses from lower levels of the auditory system. However, clinical application of AEP measurements requires an understanding of some procedural and subject variables.
Additionally, variables such as the subject's age, gender, and core temperature and the status of the outer, middle, and inner ears may predictably affect these responses.
The audiologist wishing to enter this area of clinical study is encouraged to take appropriate courses and seek supervised clinical experiences. The second section, Electrocochleography, details the recording, stimulus, and subject variables relevant to this topic. These electrical events are often conducted to the body's surface in an attenuated form and may be recorded using appropriate methods and equipment.
The half-cell potential is a voltage that results from the tendency for charge to build up on each side of the electrode interface, much as the electrode of a battery. An electrolyte gel, paste, or cream is applied to improve the conductivity of the dead skin layer, give contact stability, and effectively increase the electrode surface area.
Computerized signal averaging reduces the background noise and the variance in the sound-elicited potential. The amount of time required for the A-D converter and computer to sample each point is called the dwell time.
Synchronous events that are time-locked to the stimulus should have like phases and thus will summate and “grow” out of the noise background. The high-frequency signal is common mode (same amplitude and phase at the two inputs) and is rejected. Commercially available bioelectric amplifiers are capable of CMRs of 80–120 dB, which is sufficient for EP measurements. The objective is to present the A-D converter with a signal whose voltage is nearly full scale.
The amplifier also should be able to withstand the accidental occurrence of relatively high voltages across its inputs, or overvoltaging, and it should be able to recover expediently. Filtering must be applied judiciously and with knowledge that it may distort the waveform of the desired potential and may influence latency and amplitude measurements. The front-end differential amplifier is dc coupled, so the filtering or ac coupling is done at a later stage of amplification.
Consequently, there is an upper frequency limit for the allowable spectrum of the signal being processed. For example, an incidental swallow can create a large electromyogenic artifact that may not be averaged out. Artifact rejection schemes are most effective in eliminating samples containing incidental voltage spikes but are relatively ineffective in dealing with continuously high levels of noise. Electromagnetic fields also are created by earphones and similar transducers, and are the most prominent source of stimulus artifact.
There now are commercially available insert earphones with output characteristics similar to the Telephonics TDH-39 earphone. An EP system should never be used without an intact three-pronged, hospital-grade line plug, nor should it be plugged into an electrical outlet not known to be free of ground faults.
The smoothness of the tracing will depend on the resolution associated with the analysis, the rate at which the plotter works, and instrument characteristics that are rarely under user control.
Unfortunately, temporal specificity of the stimulus is achieved at the expense of frequency specificity. Sinusoidal pulses produce short latency potentials whose latencies vary as a function of frequency (for a given intensity), reflecting somewhat the traveling wave propagation time in the cochlea (Naunton & Zerlin, 1976).
The intensity of a click is frequently reported in dBnHL, which is the number of decibels above the behavioral threshold of a group of normal listeners. The phase of the stimulus can be examined by connecting the output of a sound level meter to an oscilloscope and comparing the phase of the stimulus to a known pressure change (Cann & Knott, 1979). All of these factors should be documented and referenced in the hearing level specification until such time that a national standard is developed.
It is also possible to use this approach in evaluations of AEPs (although conductive lesions manifest themselves in other ways, as discussed below).
Some investigators have attributed this delay to the poor high frequency response of the bone vibrator (Mauldin & Jerger, 1979). Thus, the absence of a click-evoked potential by bone conduction does not necessarily imply solely sensorineural impairment; a moderate or more severe degree of mixed loss might be involved. However, work in this area decreased over the next decade as the clinical interest in ABRs expanded.
The AP is characterized by a series of one to three predominantly negative waves, the largest of which is known as N1 (Figure 4).
The CM and SP can be selectively enhanced by manipulating the R and C responses, as indicated. A light, flexible but springy clip is used to hold a silver ball electrode against the canal wall. With modern preamplifiers and their very high input impedances, the magnitude of the electrode impedance is not as much of concern as is the balance between each branch of the circuit formed in connecting the differential amplifier to the patient. These more recent designs have substantially reduced the impedance problem due to their effectively large surface areas. Some of the desired potential, however, will be canceled by the differential amplifier because neither the ipsilateral earlobe nor the ipsilateral mastoid is totally inactive. The differences between these studies were the polarity reference and the presumed sources of the responses. As shown in Figure 9, its output saturates at high levels of stimulation and even decreases with continued increases in intensity (Dallos, 1973). Stimulus was a 1-kHz tone burst of 5 ms duration; recordings from needle electrode in the floor of the ear canal, proximal to the ear drum. The SP input-output function from transtympanic recordings is characterized by approximately proportionate growth with stimulus intensity, similar to the CM (when the input-output function is plotted in log-log coordinates) but without much evidence of saturation. In contrast, the SP and CM (although not evident in Figure 10) do not seem to exhibit temporal interactions of any consequence and maintain essentially constant amplitudes regardless of repetition rate.
Even with transtympanic recordings, in which the recorded signal is usually an order of magnitude higher than that obtained via extratympanic methods, AP amplitudes vary by as much as 20:1 (see data of Eggermont, 1976b).
Gender differences appear to arise at levels of the system beyond the eighth nerve (McClelland & McCrae, 1979).
It is difficult to record the AP reliably below about 30 dB relative to the individual's behavioral threshold (Cullen et al., 1972).
The curves represent best-fit estimates of ± 2 standard deviations for responses obtained from normal ears.
Here it can be seen that cochlear, conductive, and normal patterns are fairly distinguishable.
Sohmer and Pratt's (1976) sound delivery system, discussed earlier, was designed specifically for circumventing this problem; they have described successful recordings of the CM using surface electrodes. The potentials comprising the ABR arise from the auditory nerve, as well as brainstem structures (Jewett, 1970). Peak-to-peak measures are favored because they avoid the difficulty of determining the baseline of the potential. The three smallest bones in your body lie just behind the eardrum in an air-filled spacea€“ the incus, malleus, and stapes. These devices transmit sound through the the bones of the skull, avoiding the use of the middle ear.
There is a small risk (1%) of deafness occurring from this procedure, so typically only one ear is operated on at a time. Plastic surgery is used to create an external ear and atresia surgery creates or widens the ear canal. Practically, this is a very uncommon situation, of much more interest to diagnosticians than patients. The term latency is used to describe the time of occurrence of a given potential that, for these potentials, generally falls within 10 ms of stimulus onset. These sections purposefully precede the specific treatment of the Measurement of Auditory Brainstem Evoked Potentials (the last section) because the information in the first two sections is basic to an understanding of the brainstem potentials.
However, it is difficult to measure the AEPs because they are small in amplitude and buried in a background of electrical noise. The half-cell potential will be destabilized by mechanical movement, so a large half-cell potential makes the recording of bioelectric potentials much more vulnerable to movement artifact.
The recorded signal, which is a continuous function of time, is represented as an ensemble of discrete samples to the computer, as illustrated in Figure 1a. The differential amplifier has one input that inverts (-) and one that does not invert (+) the signal at the amplifier's output. It cannot always be assumed, however, that the amplifier is properly adjusted to permit this amount of CMR, and an occasional check and perhaps readjustment (as per the manufacturer's recommendation) are required. Analog filtering introduces phase shifts that become increasingly severe as the cutoff frequency of the filter approaches the lower frequency limits of the spectrum of the potential. Consequently, care must be exercised to minimize the presence of large dc or very low frequency ac potentials at the amplifier's inputs. If this frequency is exceeded, there is wraparound or aliasing of the signal's spectrum, in which frequencies above a certain frequency are represented as lower frequencies in a predictable manner. The most common approach is the sliding average in which each point is averaged with one or more adjacent points. Signal averaging can provide substantial noise reduction, even with the occurrence of such incidental fluctuations in the noise background; however, it generally is best to exclude unusually large amplitude noise samples.
Increasing the threshold for artifact rejection or reducing the amplifier gain merely admits more noise without improving the SNR because the SNR is essentially unchanged. The transducer unit is positioned away from the ear, and the sound is directed through a flexible plastic tube that is coupled to the ear canal with an earplug.
Some caution must be exercised in applying this method in that, if there is distortion in the stimulus artifact, cancellation will not be complete. A click is a sound obtained by applying a dc pulse to an earphone or loudspeaker (Figure 3a.1), and it provides an excellent stimulus for eliciting the short latency potentials. Visual detection levels (VDLs) of the auditory nerve and brainstem potentials elicited by filtered clicks and brief tone bursts correlate reasonably well with audiometric thresholds at frequencies at and above 500 Hz. Second, there is still an intensity dependent latency shift, just as in the case of broadband click stimulation, reflecting the basalward spread of excitation at higher intensities (Folsom, 1984). The short latency potentials are relatively insensitive to the plateau duration of the stimulus because they are largely onset responses. Higher rates improve efficiency of data collection but jeopardize the identification of a response or certain component waves of the EP, particularly in some pathological cases. The waveform should be scrutinized for changes that may occur over time, especially with an earphone that may have been dropped or otherwise abused. Conversely, due to the low frequency emphasis of the bone conduction click, a conductive lesion could be erroneously deduced when, in fact, there is a precipitously sloping high frequency loss.


Because of this, the use of transtympanic ECochG will not be considered directly in this discussion.
This electrode can be used under earphones, provides good recordings, and visual detection levels (VDLs) in many subjects approximate the behavioral threshold of the stimulus (see Figure 6).
The balance between electrode pairs is generally poor, and this degrades CMR and noise suppression. The amplitude of the recorded potential, however, is reduced for less deep electrode placements (Coats, 1974). Jewett and his associates considered the vertex to be active, and Sohmer and Feinmesser considered the earlobe to be active.
The latency of the AP is defined as the delay between the onset of the stimulus and the occurrence of the N1 response peak.
The subtraction of the response obtained with a masker of lower frequency cutoff from that obtained with a masker of higher frequency cutoff yields the contribution largely of neurons innervating the cochlear region between the places marked by the cutoff frequencies (Teas, Eldridge, & Davis, 1962). As illustrated by Figure 4, the CM is phase sensitive, whereas the SP is not, and the AP is only slightly phase sensitive (Coats, 1981). AP as well as brainstem potentials (I–V) were recorded via electrodes placed in the ear canal and at vertex.
Although the extratympanic ECochGm is inherently vulnerable to variance in electrode placement, its variance actually does not appear to be greater than that experienced with the transtympanic method and is comparable to that obtained with surface recordings from the mastoid (Durrant, 1986). Currently, the most popular clinical application of ECochG is in the identification, assessment, and monitoring of Meniere's disease or endolymphatic hydrops. From Clinical Application of Recording Human VIIIth Nerve Action Potentials From the Tympanic Membrane by C.I.
The simplest view of the genesis of the ABR is that each wave arises from a single anatomical site. In evaluating ABR latencies, emphasis usually is placed on the vertex-positive peaks of the waveform. The sound is carried through the bones directly to the cochlea, where sound may be perceived in a clear, bright fashion.
This restriction in scope was made in view of the voluminous literature that has developed concerning the short latency potentials. The reader is urged strongly to read this document from beginning to end because each section proceeds on the assumption that previous sections have been read and understood. Added to these problems are the electrically insulative characteristics of the skin, particularly the outermost layer, the corneum stratum or the dead skin layer.
Silver is an especially useful material for constructing electrodes because it also can be plated with salt, forming a silver-silver chloride (Ag-AgCl) electrode, which has an even lower impedance but requires rechloriding on a regular basis.
Interelectrode impedances, which are the impedances between each possible pair of electrodes, should be measured routinely and, as a rule, should not exceed 5 kohms.
The sampling of the signal is accomplished through a process known as analog-to-digital (A-D) conversion, wherein the amplitude of the signal at a given point in time is translated into a binary value that can be manipulated by the computer. The actual voltage of the battery does not fall exactly at an integer value, but neither does 0 V. The improvement in SNR is proportional to the square root of the number of samples that are summed (averaged) (Picton & Hink, 1974). The amplified signal is the difference between the two inputs; specifically this signal is the algebraic difference between the two inputs at each instant in time.
Although CMR is dependent on the balance between electrodes, if electrode impedances are less than 5 kohms, then concerns for balance are reduced because of the high input impedance of differential amplifiers. One example is removing the electrodes from the subject before disconnecting them and thereby turning the electrode leads into antennae for electrical noise from the lights and wiring in the test area. This can be accomplished by using proper skin preparation, using large-surfaced and reversible electrodes to keep impedances low, and minimizing electrode movement. Care must be taken that the smoothing algorithm itself does not cause time delays or that such delays are correctable.
The delay imposed by the tube must be taken into account when determining absolute response latencies, in order to obtain values consistent with those obtained with conventional earphones. The test instrument and outlet to which it is connected should be checked by a qualified electrician or electrical safety officer. Its abrupt onset and brief duration contribute to good synchronization, minimize stimulus artifact, and provide a broad spectrum that stimulates many nerve fibers.
This agreement adds credibility to the assumption that the appropriate frequency region of the cochlea is generating the response. Because there are effects of increasing repetition rate specific to each of the short latency potentials, further discussion will be reserved for later. Calibration procedures are difficult because of the transient nature of the stimuli employed. An alternative procedure is to use a sound level meter that can capture transients such as clicks.
To ensure comparable acoustic stimuli to each ear, the two earphones should create stimuli of nearly identical wave forms.
However, this problem can be vitiated with the use of tympanometry, acoustic reflexes, and the measurement of Wave I latency.
The recorded potential, however, often is asymmetrical, with its zero axis offset from the baseline. Durrant (1977, 1986) also suggested recording between the ear canal and the vertex or forehead to provide simultaneous pickup of the eighth nerve and brainstem components, as illustrated by Figure 6. Both are really active, but the earlobe (or mastoid) is more active for the AP, and the vertex is more active for the brainstem components. The graph of latency versus stimulus level is called the latency-intensity function (Figure 7). The high level response is dominated primarily by the contributions of fibers located near the base (high frequency region) of the cochlea, whereas the contributions from lower frequency regions tend to cancel one another (Eggermont, 1976a). Also, the use of tone bursts that typically outlast the click requires particular care in ECochG because of possible contamination from electromagnetic radiation from the earphone. First, the component potentials of the ECochGm are recorded in a quasi near-field manner (Davis, 1976); consequently, the ECochGm is strongest in the vicinity of electrodes nearest to generators of the cochlear and eighth nerve potentials. The main difficulty with extratympanic methods is a poor SNR that is a result of a reduction in signal amplitude without changes in noise amplitude.
In newborns, particularly premature infants, there is a slight delay in the AP that progressively decreases with maturity. For some purposes, the gap between AP threshold and behavioral threshold might be acceptable, but the ABR can be recorded reliably near the behavioral threshold and thus has replaced extratympanic ECochG for threshold estimation. The primary impetus for this was the work of Coats (1981), following the observations of Eggermont (1976b) and Gibson et al. However, this view overlooks the complexity of the neural pathways, including bilateral representation, decussation of nerve fibers at various levels, pathways that do not involve synapses at every nucleus, neurons with multiple synapses within a structure, and secondary and tertiary firings of neurons. Peak identifiers in parentheses: terminology from Sohmer and Feinmesser (1967) who used the earlobe for the noninverting input and the bridge of the nose for the inverting input. The cochlea is filled with fluid, so the sound must be coupled from transmission in air to transmission in fluid. Bone anchored hearing aid systems (such as the Baha by Cochlear or the Ponto by Oticon) may be worn on a headband or may be directly implanted.
Although rapid expansion of information continues, basic principles can be drawn from research and clinical experience with these potentials. Unlike electrodes made of silver or other pure metals or alloys, the Ag-AgCl electrode is reversible or nonpolarized. Thus, increasing the number of samples by a factor of 4 will increase the SNR by a factor of s4 = 2. Any signal common to both inputs therefore is canceled or rejected; this is known as common mode rejection (CMR). The input impedance should be a minimum of 1 Mohm, so as not to draw any significant amount of current from the electrodes. Conversely, not all potentials or components are affected in the same manner by a given filter response. In general, digital filtering provides more precise filter skirts and zero phase shift, minimizing the problems associated with analog filtering and certain smoothing algorithms.
Latencies obtained with this type of insert earphone will be several tenths of a millisecond or more longer than those observed from responses stimulated via conventional earphones.
Finally, some commercial instruments provide the possibility of zeroing the initial part of the response tracing in which the artifact is prominent. However, the frequency response of earphones may alter the spectrum of a dc pulse (Figure 3a.2).
Fourth, there is a greater chance of contamination from stimulus artifact with these longer stimuli compared to the click. Generally speaking, the slower the rise time, the lower the amplitude and the longer the latency of the evoked response.
Sound level meters typically used for audiometric calibration require long duration signals for accurate measurement. Again, such observations can be made with the aid of a sound level meter coupled to an oscilloscope. This has been revealed by comparing the earphone output measured in a 6 cm3 cavity with the bone vibrator output measured on an artificial mastoid, as well as measures rendered in terms of estimated hearing levels (Schwartz et al., 1985). Cullen, Ellis, Berlin, and Lousteau (1972) first described an extratympanic, surface recording method using a silver ball electrode wrapped in a saline-soaked cotton pledget and placed against the TM. Although this works well in some cases, in other cases the AP may not be picked up much better in the ear canal than on the earlobe or mastoid and in still others the AP can be overwhelmingly large (thereby interfering with the resolution of the brainstem components). Indeed, it is well established that the ECochGm forms the initial part of the ABR as illustrated by Figure 6.
These data demonstrate that as the stimulus intensity decreases, latency systematically increases. The low level responses shown in Figure 8a have latencies corresponding to responses generated by bands centered around 2000 Hz, which is consistent with the greater sensitivity of the 2000 Hz region near threshold. Again, acoustic delays or electromagnetic shielding can be used to minimize stimulus artifacts. The repetition of the stimulus itself causes a certain amount of synchronization of neural discharges, which can occur even at frequencies of several hundred hertz. Recording on the side of the head opposite the ear stimulated thus yields a substantially attenuated response.
However, the frequent inability to track the AP down to low levels of stimulation limits the extent to which either the latency-intensity function or the input-output amplitude function can be described.
In humans, Wave II is now believed to arise from the central end of the eighth nerve (Moller & Jannetta, 1982). The stapes bone directly connects with the oval window, where sounds are amplified more than twenty times what they were when they first struck the tympanic membrane. In cases where surgery is not advised, a bone anchored hearing aid may be the treatment of choice.
This means that it can be used to record (or pass) direct current (dc) and thus performs well at very low frequencies. Each channel of recording requires one electrode as a ground and two electrodes to pick up the desired potential. For example, a complex tone made up of 3000 Hz and 6000 Hz will appear to be made up of 3000 Hz and 4000 Hz components if the sampling rate is 10000 Hz (Nyquist frequency is 5000 Hz). Although digital filtering has become more widely available, many instruments still utilize a combination of analog filtering and digital smoothing.
Insert earphones have the added advantages of increased comfort and more interaural attenuation, reducing the need for masking of the nontest ear.
This can minimize the effects of stimulus artifacts on response scaling but does not eliminate artifacts or their effects on the quality of the recorded responses. Finally, the amplitudes of short latency EPs diminish and the waveform is less sharply defined as the frequency of the stimulus decreases, especially below 1000 Hz.
The resulting changes in the EPs presumably are the result of decreased synchronization of discharges to stimulus onset, the concomitant decrease in stimulus amplitude near the instant of onset, and the narrower bandwidth of the stimulus as stimulus rise time is increased.
If an oscilloscope is not available, then the signal averaging system can be used (Weber, Seitz, & McCutcheon, 1981). This technique provided good results with minimal discomfort to the subject, although the subject was required to lie down, and the stimulus had to be presented via sound field.
Thus, the response is much less susceptible to stimulus artifact, compared to responses obtained with other types of ear canal electrodes used in conjunction with the conventional earphone. The latency-intensity shift, therefore, is primarily a reflection of the time required for the traveling wave to propagate to the corresponding place along the basilar membrane. Otherwise, the AP would completely adapt, rather than accommodating to the repetitious stimulus.
Second, due to the substantial transcranial attenuation of sound, the amplitude of a response elicited by crossover stimulation will be greatly reduced, with a concomitant latency shift, compared to that obtained with direct stimulation of that ear. Also, the residual noise in the noninvasive recordings generally precludes accurate typing of the ECochG waveform. Adults may try a bone anchored system on a headband first, and decide if they would like the implant.
Applying an electrode, a metal conductor, to the skin constitutes a barrier over which there can be no net charge transfer. Impedance is also lowest when the electrode makes direct contact with body fluids, even just under the skin's surface. Therefore, it is important that overvoltaging not occur during response averaging because this form of nonlinear amplification can affect the signal averaging process.
This occurs because 6000 Hz exceeds the Nyquist frequency and is represented at its aliasing frequency of 4000 Hz (this is the difference between the sampling rate and the true frequency to be analyzed or 10000 Hz minus 6000 Hz).
Thus, there always are frequency limits imposed on the click-evoked potential (Durrant, 1983). The shape of the gating function also influences the stimulus spectrum, and some functions result in greater concentration of energy than others in the main spectral lobe and lower energy in the sidebands (Harris, 1978; Nuttall, 1981). Depending on the combination of stimulus parameters and recording site and method, the SP may be of either positive or negative polarity.
A recently designed extratympanic electrode (Stypulkowski & Staller, 1987) has rekindled interest in this approach to ECochG as it largely obviates problems with older designs. Alternatively, a two-channel system can be used to record simultaneously from ear canal and surface electrodes and thus separately monitor eighth nerve and brainstem responses (Coats & Martin, 1977).
As discussed earlier, the click has a broad spectrum but the same mechanism is involved even with more frequency specific stimuli such as tone bursts. This finding is illustrated in Figure 11, which demonstrates the relation between the SP and AP amplitudes for groups of subjects presenting with retrocochlear impairment, cochlear impairment, and Meniere's disease. These factors have reduced the clinical value of noninvasive ECochG, although it appears that many of them can be overcome by recording from the TM (Stypulkowski & Staller, 1987). A small fitting is implanted into the mastoid bone and the hearing aid snaps onto the fitting (once the area has healed). Needle electrodes provide such contact but are not attractive for routine clinical work because the skin must be punctured. Most myogenic artifacts and extraneous electrical noises will appear at the two electrode sites with nearly equal amplitudes and phases because of their proximity and therefore will be rejected. Techniques such as artifact rejection suspend averaging during overvoltaging and the subsequent recovery period. The cutoff frequency generally is specified at the half-power point of the filter's response, which is the frequency at which the filter's response is 3 dB down from its maximum response.
In practice it is necessary to be even more conservative if the actual waveform is to be adequately reproduced, as is the case in evoked response work.
When elicited by a transient stimulus such as a click, the SP appears as a transient deflection on which the AP is superimposed and forms a shoulder on the leading edge of the AP waveform, as shown in Figure 4 (Coats, 1981). Because more basalward fibers will be recruited as the level of the stimulus is increased, the latencies become shorter. Impedance varies with frequency: in the present context the impedance varies inversely with frequency because the electrode-skin interface acts like a capacitor (Geddes, 1972).
Other signals will not be rejected and, indeed, may be enhanced, as illustrated by Figure 2. Finally, baseline (dc) drift should be negligible to ensure stability over long test sessions. An upper limit of less than or equal to one-half the Nyquist frequency or one-fourth the sampling rate (in the above example, -2500 Hz) is more appropriate (Picton & Hink, 1974). For a more extensive treatment of these potentials, the reader is referred to Dallos (1973) and to Durrant and Lovrinic (1984). The important point is that different populations of neurons dominate the AP at different levels and frequencies of stimulation. Lyons, 1974, Transactions of the American Academy of Ophthalmology and Otolaryngology, 78, p. For applications discussed in this tutorial, impedance is generally assessed at one frequency within the range of approximately 10–1000 Hz. Common mode signals may be larger than differential signals, depending on the electrode location relative to the location and orientation of the source of the desired potential. The details of electrode placement will be discussed later within the context of specific test procedures.
From Analysis of Compound Action Potential Responses to Tone Bursts in the Human and Guinea Pig Cochlea by J.J.



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