audiology exam 3

• Physiologic methods acoustic immittance:

• Immittance audiometry- important audiologic tool serving the following functions in an audiologic assessment

• Sensitive in detecting middle ear disorders

• Useful in differentiating cochlear from retro cochlear disorder

• Helpful in estimating degree of peripheral hearing sensitivity and used as a cross check to pure tone audiometry

• Acoustic immittance measures:

• Typanometry- outer and middle ear function, looking at how well the bones to the eardrum are working, equivalent ear canal volume static compliance, acoustic reflex threshold ART, acoustic reflex decay ARD

• Admittance(compliance) ease with which energy will flow through the middle ear. Too less of this can be like otosclerosis.

• Impedance- resistance to the flow of energy through the middle ear. How much energy you are not allowing to the middle ear. Don’t want too much, fluid causes a lot of impedance.

• Immittance- general term encompassing both admittance and impedance. How much energy you are allowing through the middle ear. Want just the right amount.

• Measurement technique:

• Immittance audiometry is a wat of assessing sound energy floe through the outer and middle ears to the cochlea, how well the tympanic membrane and ossicles are moving

• If the middle ear system is normal sound energy will flow efficiently into the cochlea, if not energy flow to the cochlea will be reduced

• Example

• Tympanometry:

• 10 minutes, everyone should have one

• A physiological measure of middle ear function

• Defined as the dynamic measure of acoustic immitance as a function of changes in the air pressure in the ear canal

• Can identify the physical changes associated with middle ear pathology

• Used to determine whether there is a possible conductive component to hearing loss

• The tympanic membrane vibrates most efficiently when the pressure on both sides is equal

• When the pressure on both sides of the membrane is equal, most of the sondenergy will pass into the cochlea and the microphone will detect less sound in the ear canal. For a middle ear with normal function, a peak will appear on the graph at near o daPa(environmental pressure)

• 5 tympanogram types

• Instrumentation for tympanometry:

• Rubber tip is placed around a probe that includes a miniature speaker and a microphones- the speaker emits a pure tone of 226 Hz at 70 dB SPL

• An air pump creates either positive(pump pulls the eardrum out) or negative(pump pulls the eardrum in) air pressure within the canal(from +200 to -400 daPa)

• The microphones detects the change in sound pressure level of the 226 Hz tone for each change in air pressure

• We want to

• see a triangle or pyramid. Would do this to check the middle ear

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• Key terms:

• Tympanic peak measure- the pressure at which the peak of the tympanogram occurs and is assumed to be the point at which the pressure in the ear canal equals the middle ear pressure. Units = decapascals, normal range is -175 daPa to +100 daPa. Can be used in conjunction with other immittance measures to define the abnormal pathology of the middle ear system. 10 counted as an adult. Child pressure scale- +100- -150. adult pressure scale- + 100- -200. Never will see someone with abnormal positive pressure, only if you pop your ears for around five seconds. Abnormal negative is bad and no pressure is bad unless its tubes.

• Static compliance- the height of the tympanic peak pressure referenced to the baseline at +200 daPa. Altered most middle ear problems. Cannot be used in isolation as a means of diagnosis but rather in conjunction with audiometric findings, case history, and other medical/diagnostic information. Really tall peak= high immitance. If peak is shallow or small its impedance, no peak its impedance. Normal amount of mobility.

• Interpretation of static compliance- units = mmhO or cc. normal range .3-1.6-2.0. low compliance ( < .3, middle ear fluid, stiffening of ossicular chain, outer ear blockage. High compliance (>1.6, ossicular chain disruption, healed perforation. Otosclerosis or a eardrum that is really scarred.

• Equivalent ear canal volume- estimate the volume of air between the probe tip and the tympanic membrane if the tympanic membrane is intact. If the tympanic membrane is perforated or has a pe tube then the equivalent ear canal volume will include the middle ear space, volume will be abnormally large. Equivalent ear canal volume important for two reasons. Accurate measure of static compliance depends accurate estimation of ear canal volume. If a pressure seal can not be obtained, an estimation of equivalent volume can provide a clue to the cause. If the volume is high there might be a hole in the eardrum due to tubes.

• Interpretation of equivalent ear canal volume- units = cubic centimeters. Norm for children - .4-1.0cc. Norm for adults- .6-2.5 cc. low volume, probe tip against cerumen, probe tip against ear canal wall. High volume, possible tympanic membrane perforation, patent pressure equalizing tube. Want to see high volumes with someone who has tubes.

• Tympanic width- tympanic width is defined as the interval in daPa between the sides of the tympanic pressure peak at one half. The wider the tympanogram, the greater likelihood that a middle ear issue exists. Units = daPa. Normal range = <275 daPa.

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• Recording and interpreting tympanometric results:

• Based on tympanometric shape as determined by static compliance, peak pressure, and width; we can classify tympanograms into 5 distinct types

• This classification system is widely used but it is important to note that it is only applicable when measured with a 226 Hz probe tone rather than higher frequency probe tones

• Only thing that is wrong with the A's is compliance or mobility

• Type A tympanogram- indicates normal eardrum and middle ear function. Normal tympanic pressure peak and normal static compliance. Curve is characterized by a rather large inverted V.

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• Type As tympanogram- characteristic peak at o daPa(normal) but peak is much shallower than a normal type A. the S subscript could stand for stiffness indicating increased impedance through the middle ear system. Interpretation- type As tympanograms are associated with any of the following pathologies, tympanosclerosis, ossicular fixation, otosclerosis. Small peak. Peak is 1.5

• Type Ad tympanogram- normal middle ear pressure with markedly increased admittance. Amplitude of peak, or compliance, is abnormally high Ear canal volume is always normal, pressure is normal. The D might stand for discontinuous or deep. Interpretation- type Ad tympanograms are associated with any of the following pathologies, flaccid or hypermobile tympanic membrane, ossicular discontinuity.

• Type B tympanogram- Bad. 5.3 configuration and flat. No identifiable point of maximum admittance or compliance. Also known as a flat tympanogram. Typically peak pressure unit a not noted on printout as even wide variations in pressure in the external ear canal can never match the pressure or fluid behind the tympanic membrane, no peak. Interpretation- associated with the following pathologies, otitis media, middle ear effusion, impacted cerumen, perforated tympanic membrane, patent(open) PE tube. perforation is abnormal.

• Type C tympanogram- abnormally negative middle ear pressure with normal or near normal admittance, the peak is occurring in the negative pressure area of the graph, ear canal volume normal. Interpretation- following pathologies, eustachian tube dysfunction, negative middle ear pressure with or without effusion.

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• Acoustic reflex:

• Reflex is an involuntary response to some external stimuli. Occurs to protect hearing.

• Acoustic reflex threshold- lowest intensity at which the acoustic reflex can be detected \acoustic reflex can inform the audiologist about the status the middle ear and can provide information about the site of lesion(cochlear vs retro cochlear)

• Two small muscles, the tensor tympani and the stapedius muscle, are involved in the operation of the middle ear mechanism

• Stapedius muscle- innervated by the Vllth nerve(facial nerve), connected to posterior side of the stapes, sole muscle responsible for the acoustic reflex in humans

• Tensor tympani- innervated by the Vth nerve, connected to malleus, in some animals this muscle is responsible for the acoustic reflex

• When a sound if of sufficient intensity, it will elicit the middle ear reflex

• In humans this sound causes the stapedius muscle to contract which stiffens the tympanic membrane and ossicular chain

• Anatomy and physiology of acoustic reflex:

• When a sound is of sufficient intensity, it will elicit the middle ear reflex

• In humans, this sound causes the stapedius muscle to contract which stiffens the tympanic membrane and ossicular chain

• When the acoustic reflex occurs, the immittance device detects a temporary increase in the impedance/decrease in the admittance of the middle ear

• Instrumentation for measuring acoustic reflex threshold:

• Rubber tip is placed around a probe that includes a miniature speaker and a microphone. The speaker emits a pure tone of 226 Hz at 70 dB

• An air pump maintains a constant pressure in the canal

• A second speaker is used to play a loud tone to stimulate the middle ear reflex

• The microphone detects the change in sound pressure level of the 226 Hz for each presentation of the loud reflex tone

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• Anatomy and physiology of the acoustic reflex:

• When a signal of intensity is presented to the right ear, a stapedius will occur in both the right(ipsilateral) and left(contralateral) ears and vice versa

• Ipsilateral- softer. Can do in both ears

• Contralateral- have to turn it up louder. 2-14 dB higher in volume than an ipsilateral reflex. Can do in both ears. Have a dip.

• To fully understand how the Acoustic reflex works, we must first understand reflex arc. 1. sound is conducted through outer and middle ear. 2. sound reaches cochlea and is conducted to 8th nerve. 3. impulses received by cochlea nucleus in brainstem. 4. impulses passed to superior olivary complex in brainstem. Impulses now sent from superior olivary to facial or impulses are sent across the brainstem to opposite superior olivary complex. 5. facial nerve innervates the stapedius muscle and impulses cause stapedius muscle ton contract

• Acoustic reflex procedure:

• A pure tone signal ranging in frequency from 500-4000 Hz is used to elicit the reflex. Tones can be presented ipsilaterally or contralaterally

• Tone is initially introduced at approximately 70 dB SPL

• If no compliance change is noted, the level should be raised by 10dB until a response is noted

• A search similar to the modified Hughson Westlake is used to determine the threshold for the reflex

• Interpretation of acoustic reflex thresholds:

• Abnormalities at any location in the acoustic reflex arc can alter the characteristics of the acoustic reflex

• Lesions in the afferent portion of the reflex arc( middle ear, cochlea, 8th nerve)produce either an absent or elevated reflex threshold in the ear to which the reflex activator signal is presented

• Mean reflex thresholds for 500, 1000, and 2000 Hz are approximately 85 dB SPL (range from 70-100 dB SPL)

• Thresholds above 100 dB SPL are considered abnormal when cochlear and conductive lesions are rules out

• No inter aural thresholds difference in normals

• Ipsilateral reflex thresholds are consistently 2 to 14 dB lower than contralateral thresholds