Immitance

• the opposition to the flow of energy through a system
• -sound strikes system and a portion is reflected back depending on the stiffness of the system.
• -reflected wave carries info about the status of the middle ear
• -harder surface has higher impediance

• greater amount of energy reflected back
• -otis media or otosclerosis

• will reflect less energy
• -ossicular chain disruption

• how much energy is going into the system/how easy energy flows through
• -ear with high impedance will have a low admittance

• a measure of impedance or admittance in order to get info about middle ear status
• -fluid no fluid in middle ear?
• -evaluate eustachian tube
• -facial nerve function
• -determine nature of hearing loss
• -predict audiometric findings

no compliance or impedance measure

• -if compliance is high impedance is low
• -compliance is highest in centre of eardrum and lowest at edges
• -negative and positive pressure push the eardrum in or out
• -different pressures change the compliance of the eardrum and the impedance
• -you push air in or out of the system to see when the eardrum is maximally compliant by monitoring tone changes

• measurement of the mobility of the middle ear when pressure in the canal is varied from +200 to -400 daPa
• -tells us 2 things
• 1.middle ear drum peak pressure (normal is -150 to 50 daPa)
• 2.where the eardrum moves best (normal is 0.3 to 1.6) lower than 0.3 is stiff and higher than 1.6 is flaccid

• -can infer volume of ear canal in cubic cm
• -determine immittance ad +200daPa then immittance at most compliant point. The difference between the two = the equivalent ear canal volume(air space in canal)
• -range of normal= 0.9 to 2.0 adults and 0.25 to 0.9 kids

peak pressure within normal range, height of peak tells us flaccid (Ad) if peak is too high and stiff if the peak is too low (As)

• flat low volume, with no peak pressure meaning no drum movement
• -lower than normal compliance

peak pressure out of normal range, ear infection possibly

• -They help you make sense of info you already know
• -normal ears will have AR's at 500,1000,2000Hz at 65 to 95 db. higher than this is disordered
• -elevated AR thresholds could mean conductive loss
• -AR thresholds can help differentiate cochlear from retrocochlear pathology.
• -with cochlear loss ARs are severe but present
• -with retrocochlear lesions AR thresholds are not present

• The lowest possible intensity required to elicit a middle ear muscle contraction
• -reflex triggered in both ears
• -contraction of the muscle results in temporary increase in impedance of middle ear
• -if your drum is too stiff to move there is no reflex-if no reflex:inner ear, nerve, brain stem problems
• -when reflex occurs impedance and sound pressure increase