Physiology Seminar18/04/2013

PowerPoint® Seminar Slide Presentation prepared by Dr. Anwar Hasan Siddiqui, Senior Resident, Dep't of Physiology, JNMC

©Dr. Anwar Siddiqui

Tests of Hearing

Why do we test hearing ?

Is the hearing normal?

What is the degree of hearing loss?

What type of hearing loss is it?

Principles of hearing

Units for measuring sound exposure Sound Pressure Level (SPL)

• expressed in μPa or Pa• range from 20 μPa (hearing threshold) till 20 Pa (pain

threshold),

Decibel dB of sound pressure level (dB SPL) • defined as: 20 log10 p1/p0 where p1 is actually

measured sound pressure level of a given sound, and p0 is a reference value of 20μPa, which corresponds to the lowest hearing threshold of the young, healthy ear.

• In the logarithmic scale the range of human ear’s audible sounds is from 0 dB SPL (hearing threshold) to 120-140 dB SPL (pain threshold)

Principles of hearing

Table 1: Examples of sound pressure levels in relation to hearing threshold and pain threshold (in dB SPL)The range of human ear’s audible sounds goes from 0 dB SPL (hearing threshold) to 120-140 dB SPL (pain threshold)

Source / observing situation

Typical sound pressure level (dB SPL)

Hearing threshold 0 dB

Leaves fluttering 20 dB

Whisper in an ear 30 dB

Normal speech conversation for a participant

60 dB

Cars/vehicles for a close observer 60-100 dB

Airplane taking-off for a close observer 120 dB

Pain threshold 120-140 dB20dB is 10 times 0dB, 40dB is 10 times 20dB, 60dB is 1000 times louder than 0dB

Source: SCENIHR,   Potential

health risks of exposure to noise from personal music players and mobile phones including a music playing

function (2008) , Section 3.3.3.1, Page 17

Principles of hearing

Bone conduction

Air conduction

Types of hearing loss

Conductive hearing loss

Sensorineural Hearing Loss

Types of hearing loss

Mixed Hearing Loss

Central Hearing Loss

Severity of hearing loss

Degree of hearing loss Hearing loss range (dB HL)

Normal –10 to 15

Slight 16 to 25

Mild 26 to 40

Moderate 41 to 55

Moderately severe 56 to 70

Severe 71 to 90

Profound 91+

Source: Clark, J. G. (1981). Uses and abuses of hearing loss classification. Asha, 23, 493–500.

 The table below shows one of the more commonly used classification systems. The numbers are representative of the patient's hearing loss range in decibels (dB HL).

Severity of hearing loss

The American Academy of Ophthalmology and Otolaryngology (AAOO) guidelines (Revised in 1979) states:

“the ability to understand normal everyday speech at a distance of about 5

feet does not noticeably deteriorate as long as the hearing loss does not exceed an

average value of 25 dB at 500, 1000 and 2000 Hz”

Hearing Loss Causes Age- The tiny hairs get damaged and are less able to respond to

sound waves. Hearing loss can progress over the course of several years.

Loud noise-Exposure to loud noises damage the hair cells in the cochlea..

Infections-During an ear infection, fluid can build up in the middle ear.

Perforated eardrum-Depending on the size of the perforation, there may be a mild or moderate hearing loss.

Tumors- eg acoustic neuroma (vestibular schwannoma) and meningioma.

Trauma-Injuries such as a skull fracture or a punctured eardrum can cause severe hearing loss.

Medications- the aminoglycoside class of antibiotics (streptomycin, neomycin, kanamycin), large quantities of aspirin, chemotherapy drugs (cisplatin, carboplatin), Vicodin (in large quantities), macrolide antibiotics (erythromycin) can cause hearing loss.

Genes- Genetic hearing loss often begins with hearing loss diagnosed at birth

Initial Otoscopic examination

Tympanometry

BERA

EChocG

OAE (Otoacoustic Emission)

Assessment of hearing

Speech test Loud Whisper

Tuning fork test Weber Rinne Schwabach

Audiometry Speech audiometry Pure Tone Audiometry

Initial Otoscopic examination

Performed with a hand held otoscope Ear canal and tympanic membrane

are observed. Tympanic membrane is seen for:• Light reflection• Differentiation of its part• Mobility

Speech test Simplest of all Involves testing ability to hear words

without using any visual information. Patient should repeat 5 words spoken

loudly at a distance of approx. 5 metre. The whispered voice test involves the

tester blocking one of patients ears and testing hearing by whispering words at varying volumes.

Speech test

Ball Point click test

Tuning fork test

Used to differentiate between conductive and sensorineural hearing loss.

Larger forks vibrate at slower frequency. Tuning forks with frequency 256 or 512 hz

are used

Principle of Tuning fork test

CHL (OE or ME Disorder) Sounds delivered to the ear via AC will be

attenuated If the sound is delivered to the ear via

BC, bypassing the OE & ME, then the sound will be heard normally assuming there is no disorder

SNHL (OE & ME Are Free From Disorders) Sounds delivered to the ear via BC will

also be attenuated

Weber’s Test

Vibrating tuning fork is placed on the patient's forehead (or in the middle line).

The vibrations are tyransmitted by bone conduction to cochlea.

The pt. should state if the tone is heard

in the left ear, right ear, or both ears. If the sound lateralizes, the patient may

have either an ipsilateral conductive hearing loss or a contralateral sensorineural hearing loss

Weber’s Test

a b c

Interpretation

Rinne’s Test

Compares the level of air and bone conduction of the same ear.

base of a tuning fork is placed to the mastoid area (bone con.), and then after the sound is no longer appreciated, the vibrating top is placed near the external ear canal (air con.)

Rinne’s TestInterpretation

Schwabach’s Test

compares the patient's bone conduction to that of the examiner's

If the patient stops hearing before the examiner, this suggests a sensorineural loss

If the patient hears it longer than the examiner, this suggests a conductive loss

This test is contingent on the examiner having normal hearing…..

Tuning fork test summary

Audiometry

Audiometry (from the Latin audīre, "to hear", and metria, “to measure) is a branch of Audiology, and is the science of measuring hearing acuity for variations in sound intensity and frequency.

An audiometer is the device used to produce sound of varying intensity and frequency.

Ear Phone to testAir conduction threshold

Response switch

Bone oscillator to testBone conduction threshold

Pure Tone Audiometry A pure tone is a tone having a single

specific frequency. The frequency of the tone is determined by the rate or speed at which the sound source vibrates

Pure tone audiometry is the use of pure tones to assess an individual’s hearing.

The results of this testing are plotted on the audiogram.

Pure tones are generated by an audiometer and presented to the patient via headphones or, in some cases, through loudspeakers.

Can be air conduction audiometry or bone conduction audiometry

Pure Tone Air Audiometry procedure The audiologist present pure tones of one

frequency to the patient, initially at an intensity level that it is assumed they can hear quite well.

The intensity (loudness) of the tone is decreased in 10 to 15 dB steps.

This is continued, with tones being presented for one to two seconds, until the patient no longer responds.

The intensity is then raised in 5 dB steps until the patient responds, decreased again and increased again in 5 dB steps until the patient responds.

This lowest audible intensity is defined as the patient’s threshold for the particular frequency and is marked as such on the audiogram

Pure Tone Air Audiometry procedure

Interaural attenuation and masking At certain intensity levels, the signal

presented to the test ear will cross over and be heard in the non-test ear. The inter-aural attenuation rate, or the intensity difference at which a sound will be heard in the non-test ear, is approximately 40 dB for air conduction signals presented through circumaural earphones.

the masking noise used for pure tone audiometry is narrow-band noise;generally the same frequency as the pure tone being presented to the test ear.

Pure Tone Air Audiometry procedure

Pure Tone Air Audiometry audiogram

Pure Tone Air Audiometry audiogram

Pure Tone Air Audiometry audiogram

Sensorineural impairment Conductive disease

Tympanometry

Tympanometry is an examination used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction bones by creating variations of air pressure in the ear canal.

In evaluating hearing loss, tympanometry permits a distinction between sensorineural and conductive hearing loss, when evaluation is not apparent via Weber and Rinne testing

Principles of Tympanometry

Introduces a pure tone into ear canal through 3-function probe tip• Manometer (pump) varies air pressure against

TM (controls mobility)• Speaker introduces 220Hz probe tone• Microphone measures loudness in ear canal

Principles of Tympanometry

Normal tympanogram (Type A)

• Peak at 0 daPa• Best movement of drum when no extra pressure on either side of TM

Other Type A tympanograms

Peak at 0daPa, but unusually high

amplitude

? Ossicular disruption

Peak at 0daPa, but unusually low

amplitude? Stapes fixation

Flat tympanogram (Type B)

When tymp is flat,

usually means 1 of 3

things:

1. Artefact

2. Fluid in ME

3. Perforation

Look at EAM vol.

If large = perforation

If normal = fluid

Negative tympanogram (Type C)

Can be further divided into:

C1 – peak between 0 and -200 daPa

C2 – peak less than -200daPa

Otoacoustic Emission

They are low intensity sounds produced by outer hair cells of a normal cochlea

Can be elicited by a very sensitive microphone placed in EAC (External Ear Canal)

Absent when OHC are damaged Thus serve to test cochlear functioning

OAE’s

spontaneous evoked

Transient(click)

Distortion product(paired tones)

Otoacoustic Emission

USES of OAE’s

As a screening test for neonates

Distinguish cochlear from retrocochlear HL

To test hearing in mentally challanged and uncooperative individuals after sedation

(Note- sedation doesn’t interferes with OAE’s)

ElectroCochleoGraphy (EChocG)

It measures electrical potentials arising in the cochlea and VIII nerve in response to auditory stimuli within first 5 millisec

Response is in the form of • Cochlear microphonics (CM)• Summation potential and (SM)• Action potentials (AP)

Two methods are widely used:• Transtympanic• Extratympanic

ElectroCochleoGraphy(EChocG)

Transtympanic membrane electrodes: These are needle electrodes, which are placed over the promotory by penetrating the ear drum

Intrameatal electrodes: These electrodes are placed in the external auditory canal.

ElectroCochleoGraphy (EChocG)

Normal electrocochleogram from the tympanic membrane to clicks presented in alternating polarity at 80 dB HL. The amplitudes of the Summating Potential (SP) and Action Potential (AP) can be measured from peak-to-trough (left panel), or with reference to a baseline value (right panel).

mean SP/AP amplitude ratio to click stimuli for normal subjects is approximately 0.25 + 0.10 standard deviations (SD). An SP/AP amplitude ratio greater than 45 % (2 SDs above the norm) is considered to be enlarged.

ElectroCochleoGraphy (EChocG) usage

Objective identification and monitoring of meniere’s disease and endolymphatic hydrops (EH): Enlarged SP reflects pathologic condition of EH. SP-AP amplitude ratio is more consistent with the presence of meniere’s disease. On average, SP-AP ratio of 0.45 or greater is considered abnormal.

Intraoperative monitoring: Surgical operation on brainstem or cerebellum may bear risk of damage to the auditory system. ECochG recording during surgery assess the functional integrity of the peripheral and brainstem pathway directly during operation.

BERA

To be dealt in subsequent seminar by Dr. Saif

Final Thought

“Tests are not infallible, they are only as good as those taking, administering and

interpreting them…”

Sorry can’t hear you!!!!!!!!!

………………Thank You

Any Queries?