Ear anatomy Hearing tests Audiograms

Introduction / Contents Basic Ear Anatomy Types of Hearing Loss Conductive vs. Sensorineural Audiogram Scales Frequency vs. Intensity Audiogram Symbols Contents Basic Ear Anatomy 3 Hearing Test 6 Audiogram 15 Audiogram - Examples 18 Labeling the Audiogram Page 2 May-06 Hearing Instrument Technology I

Basic Ear Anatomy The ear can be divided into 3 main divisions: 1. Outer Ear 2. Middle Ear 3. Inner Ear Inner Ear Outer Ear Middle Ear Page 3 May-06 Hearing Instrument Technology I

Outer Ear The external ear has two parts: 1. Pinna which is the outside portion of the ear that is visible on the side of the head Pinna 2. External auditory meatus (ear canal) that extends from the pinna to the tympanic membrane (abbreviated TM and is commonly referred to as the eardrum). Ear canal Page 4 May-06 Hearing Instrument Technology I

Pinna Pinna: The pinna is mostly skin and cartilage with some muscular attachments to the back The pinna collects and directs sounds down the ear canal The twists and folds of the pinna enhance high frequency (pitched) sounds and also help us to determine the direction of the sound source Sounds coming from the front and sides are slightly enhanced as they are directed into the ear canal while sounds from behind are slightly reduced. This helps us to hear what we are looking at while reducing some of the distracting background noise coming from behind. Page 5 May-06 Hearing Instrument Technology I

Ear Canal Ear Canal: The external auditory meatus is a small, twisting, tunnel-like tube that connects the pinna to the tympanic membrane. It is about one inch in length (2.5 cm) and has a diameter about the size of a pencil eraser. The outer half to two thirds of the canal is surrounded by cartilage and contains glands that produce cerumen (ear wax), while the inner one third to one half is surrounded by bone. The ear canal has a natural resonance that typically boosts sound pitches around 3000 Hertz (abbreviated Hz. and is the same as cycles per second) by approximately 10-15 decibels. Page 6 May-06 Hearing Instrument Technology I

Middle Ear 1 Middle Ear: The middle ear consists of an airfilled space between the tympanic membrane and the inner ear that contains three tiny bones linked together that connect the tympanic membrane to an opening into the inner ear. Ossicles Labyrinth The bones are: the malleus, incus and stapes Tympanic Membrane Middle Ear Space Page 7 May-06 Hearing Instrument Technology I

Middle Ear 2 Labyrinth Sounds travel down the ear canal and strike the TM, causing it to vibrate. These vibrations are then transferred through the ossicles to the inner ear Ossicles Sound sets this whole structure into vibration and the footplate of the stapes vibrates within the oval window opening of the cochlea, transferring sound energy to the fluids and tissues of the cochlea. Tympanic Membrane Middle Ear Space Page 8 May-06 Hearing Instrument Technology I

Inner Ear Inner Ear: The inner ear is comprised of two functionally separate sections: The vestibular or balance part and the cochlea, which is the hearing part. The cochlea is a coiled canal in the dense bone tissue of the skull. The shape of this canal somewhat resembles a snail shell and houses three fluid-filled membranous canals extending its full length. The cochlear connects to the auditory nerve that messages to the brain that a sound has been heard. Labyrinth Balance Nerve Middle Ear Space Hearing Nerve Cochlea Facial Nerve Page 9 May-06 Hearing Instrument Technology I

Hearing Test When we do a hearing test with conventional headphones we are testing the all three parts of the ear.. Page 10 May-06 Hearing Instrument Technology I

Hearing Test When we do a hearing test with a bone conductor we are bypassing the outer and middle ear.. Page 11 May-06 Hearing Instrument Technology I

Hearing Test The headphones and bone conductor give us different information: A sensorineural hearing loss is when the headphone (air conduction) and bone conduction sensitivity test is equal This means the problem is occurring in the inner ear or beyond A conductive hearing loss is when the bone conduction sensitivity is better than the headphone sensitivity This means the problem is occurring in the middle ear or external ear Page 12 May-06 Hearing Instrument Technology I

Hearing Test Tone tests are done by air conduction and by bone conduction. Air conduction tests evaluate the sensitivity of the entire hearing organ and are tested with earphones that are placed over the ears or inserted into the ear canal. The softest sounds heard by the subject at each pitch are recorded as the thresholds and are compared to normative values. Page 13 May-06 Hearing Instrument Technology I

Hearing Test Bone conduction is tested when air conduction testing shows a loss. They are done as in air conduction testing, except that, instead of using earphones, a small bone-conduction vibrator is placed on the mastoid bone directly behind the ear and sound is transmitted through the bones of the skull directly to the inner ear, bypassing the outer and middle ear. Thus, a difference between air and bone conduction thresholds indicates a loss caused by a problem with the outer or middle ear - a conductive loss. Page 14 May-06 Hearing Instrument Technology I

Hearing Test Why do we need to know this? Headphone sensitivity or thresholds and Bone conduction thresholds are represented differently on the Audiogram Also, a conductive and sensorineural hearing loss will have different implications for hearing aid selection and fitting Page 15 May-06 Hearing Instrument Technology I

Audiogram Audiogram is chart that hearing test is marked on low Frequency (Hz) high soft Volume measured in db/hl loud Page 16 May-06 Hearing Instrument Technology I

Audiogram Symbols are placed on the audiogram that tell us the persons bone conduction and air conduction thresholds at each frequency Right Air conduction Left Air conduction Right Bone conduction Left Bone conduction Page 17 May-06 Hearing Instrument Technology I

Audiogram Symbols are placed on the audiogram that tell us the persons bone conduction and air conduction thresholds at each frequency Right Air conduction Left Air conduction Right Bone conduction Left Bone conduction Page 18 May-06 Hearing Instrument Technology I

Audiogram Degree of hearing loss is labeled below: p 104 Sandlin Note: this may differ from Textbook to Textbook Normal Hearing Mild Hearing Loss Moderate Hearing Loss Severe Hearing Loss Profound Hearing Loss Page 19 May-06 Hearing Instrument Technology I

Examples Mild sensorineural hearing loss, right Page 20 May-06 Hearing Instrument Technology I

Examples Mild conductive hearing loss, right Page 21 May-06 Hearing Instrument Technology I