HEARING IMPAIRMENT LEARNING OBJECTIVES: STUDENTS SHOULD BE ABLE TO: Recognize the clinical manifestation and to be able to request appropriate investigations Interpret lab investigations for basic management. Knowledge for rehabilitation of deaf patient. When to refer patient to the relevant specialty Divisions of the Ear Outer Ear The outer ear consists of: Pinna External Auditory Meatus Middle Ear The middle ear consists of: Tympanic Membrane Eustachian Tube Ossicles Tensor Tympani Stapedius Inner Ear The inner ear consists of: Cochlea Vestibular Auditory Nerve The auditory nerve consists of: Auditory Branch Vestibular Branch Central Auditory Mechanism The central auditory mechanism consists of: Brain Spinal Cord Audiology Audiology is the science of hearing.it. Includes all aspects, i.e.
Acoustics, Physiology of hearing, Disorders of hearing. Functional examination of hearing. Medical & surgical problems of deafness. Education & rehabilitation of deaf & hard of hearing. Hearing aids and cochlear implants. Assessment of hearing Clinical tests of hearing Finger friction test Watch test Speech tests Tuning fork tests Audiological Investigations Audiometry PTA Speech Audiometry Impedance Audiometry (Tympanometry) Acoustic reflexes Assessment of hearing Special tests of hearing Evoked Response Audiometry (B.E.R.A.) Otoacoustic Emissions (OAEs) Frequency Number of cycles per second Definitions Unit is HERTZ (Hz) named after the German scientist Heinrich Rudolf Hertz A sound of 1000 Hz means 1000 cycles per second.
Basics of Audiology Frequency range in normal hearing Normal person can hear frequencies of 20-20,000 Hz In routine audiometric testing only 125-8000 Hz are evaluated Speech frequencies Frequencies of 500, 1000 & 2000 Hz are called speech frequencies Most of the human voice falls within this range. Intensity Strength of sound which determines loudness Usually measured in decibels (db) At a distance of 1 meter intensity of Whisper --- 30 db Normal conversation --- 60dB Shout --- 90dB Discomfort in ear --- 120dB Pain in ear --- 130dB In clinical work the threshold of normal hearing is defined as 0dB. Pitch Subjective sensation produced by Frequency of sound. Higher the frequency- greater the pitch Loudness. A subjective sensation produced by intensity. More the intensity-greater the loudness Audiometry Behavioral Observation Audiometry (BOA) Visual Reinforcement Audiometry (VRA) Conditioned Play Audiometry (CPA) Standard Audiometry Pure Tone A single frequency sound- e.g. a sound of 250,500 or 1000 Hz. Complex Sound Sound with more than 1 frequency- e.g. human voice
The Decibel Pure Tone Audiometry Sound intensity (SPL) measured in decibels - A logarithmic scale of intensity of sound - 20dB is 10 times 0dB, 40dB is 10 times 20dB, 60dB is 1000 times louder than 0dB - Sound can be measured as POWER (watts/cm2) or as PRESSURE (dynes/cm2) Sound has 2 components: Frequency (pitch) cf. wavelength Hz / khz (Hertz) Intensity (loudness) cf. amplitude db (decibel) Important concept A hearing level of 0 db is an arbitrary level of hearing of a given SPL Iowa State Fair (allegedly) in 1935, 10 000 young women had their hearing measured This established the normal hearing levels for pure tone Audiometry (0 db Threshold) Pure Tone Audiometry document CHL, SNHL, baseline, preop. sooner if high risk Audiometer
Audiometer Air conduction Bone conduction PTA SPEECH AUDIOMETRY Speech Reception Threshold Discrimination Score Speech audiometry Speech reception threshold (SRT) Minimum intensity at which 50% of words are repeated correctly by pt. A set of spondee words (two syllable words with equal stress on each syllable e.g. baseball, sunlight, daydream etc.) is delivered to each ear through headphone of audiometer.
The word lists are delivered in the form of recorded tapes or monitored voice Speech reception threshold (SRT) Normally SRT is within 10 db of average of pure tone threshold of three speech frequencies (500, 1000 & 2000 Hz) Speech discrimination score Also called speech recognition or word recognition score A measure of patient s ability to understand speech A list of phonetically balanced (PB) words (single syllable words e.g. pin, sin, day, bus etc.) is delivered to patient s each ear separately at 30-40 db above his SRT. TYPES OF DEAFNESS Conductive Perceptive (sensorineural) Mixed Non-organic Common Causes of Hearing Loss
Outer Ear Middle Ear Inner Ear Auditory Nerve Central A Mechani Cerumen Impaction Microtia Anotia Foreign Body Atresia Stenosis Otitis Media Cholesteatoma Disarticulation Otosclerosis Tympanosclerosis Mastoiditis Noise Genetic Meningities Ototoxicity Anoxia Otosclerosis Skull fractures Meniere s Disease Acoustic Neuroma Meningitis Multiple Sclerosis G C A P D H Types of Hearing Loss Outer Ear Middle Ear Inner Ear Auditory Nerve Central Auditory Mechanism Conductive Hearing Loss Lesion to outer and/or middle ear Sensorineural Hearing Loss Lesion to the inner and/or auditory nerve Mixed Loss Lesion to the outer ear and/or middle ear and to the inner ear and/or auditory nerve Auditory Processing Disorder Lesion to the brain or spinal cord that affects hearing
Degrees of Hearing Loss Normal PTA Conductive Loss Sensorineural Mixed Loss Loss
Tympanometer Compliance Middle Ear Pressure Canal Volume Stapedial Reflex Tympanometry Impedance Audiometry Tympanometry procedure The EAC is sealed by the impedance probe Pressure in EAC is changed from positive to normal & then negative The reflected sound energy is measured at all the above EAC pressures
Peak at 0dPa Normal Tympanogram (Type A) Best movement of drum when no extra pressure on either side of TM Other Type A tympanograms Peak at 0dPa, but unusually high amplitude Ossicular disruption
Flat tympanogram (Type B) No Peak No best TM movement at any pressure Flat tympanogram (Type B) When tympanogram is flat, it usually means 1 of 3 things: Artefact Fluid in ME Perforation Look at EAM volume If large = perforation If normal = fluid Peak at < 0dPa Negative tympanogram (Type C) Best movement of drum when no negative pressure in EAM thus middle ear pressure must be < atmospheric
Auditory Brainstem Response/ Evoked Response Audiometry (ERA) Objective test for hearing assessment Otoacoustic Emissions Evidence of a healthy, functioning cochlea Screening tool in infants Behind the Ear Device Cochlear Implant
BAHA Sound Processor Implant & Abutment Softband (for babies from 6 weeks old or for use during a trial) THANK YOU