tympanometry - exam 2 Flashcards
tympanometry
measures the extent to which sound energy is transferred through the outer & middle ear
determined by mobility of the TM as a function of varying pressure in the ear canal
indication of middle ear status
why is tympanometry important
determine middle ear function
middle ear disorders risk factors for health, education, &/or development of speech & language
very useful for infants & young children & hard to test populations
immittance
impedance, admittance, & compliance
acoustic compliance
mobility of the TM in response to air pressure in the ear canal
acoustic impedance
the opposition to the flow of sound energy through an acoustic system
inverse of admittance
ohms
impedance - mass & stiffness
mass & stiffness of ME system are freq dependent
mass changes have more effect on high freq
stiffness changes have more effect on low freq
ME system is stiffness dominated
low freqs therefore admitted less
admittance
the ease w/ which sound energy flows through an acoustic system
inverse of impedance
mmhos
basics of measurement
probe tone is introduced into hermetically sealed ear canal
SPL of the signal in the EC is measured - indirect measure of energy passed or opposed
high SPL
higher impedance to the flow of energy
lower admittance
low SPL
lower impedance to the flow of energy
higher admittance
what probe tone do we use for pediatric & adults
226 Hz
because at 226 Hz, mmhos = cm cubed
admittance & volume are interchangeable in our measurements
what probe tone for infants (under 3 mos)
1000Hz
ME mechanics different in children than adults
plane of measurement
at the probe tip = end of ear canal
ideally want TM because we want measurement of the middle ear not the ear canal
not possible so we must derive it by compensating for the ear canal
normal peak admittance for adults
0.37-1.66 mmhos
normal peak pressure for adults
-100 -50 daPa
normal ECV for adults
0.9-2.0 ml
peak admittance
occurs when the pressure on either side of the TM are equal
ear canal volume
estimate of volume between probe & TM
in a compensated tympanogram - ECV is given
too large ECV
perforation of TM
open PE tube
absence of hermetic seal
too small ECV
clogged probe tip
probe tip against canal wall
impacted cerumen
clogged PE tube
type A
everything normal
type As
shallow
normal peak pressure
reduced peak admittance
increased stiffness, middle ear effusion
type Ad
deep
normal peak pressure
higher than normal admittance
scarred or flaccid TM, ossicular discontinuity
type B
essentially flat - no peak pressure or admittance
when volume is high - middle ear effusion, cholesteatoma, TM perforation
when volume is low - impacted cerumen or obstruction in EC
compensated
compensating for ECV
tails @ 0
uncompensated
tails @ ECV
Type C
negative pressure peaks beyond -100 daPa
eustachian tube dysfunction, middle ear effusion
contra indications for tympanometry
recent surgery
abnormal otoscopic findings
- blood or discharge in the outer ear
- pain upon contact
- otitis external (infection of the outer ear canal/swimmers ear)
