Readings Flashcards
Impedance is understood as the resistance of an…
Alternating current circuit
Acoustic impedance is ____ dependent
Frequency
What is the Schuster Bridge?
Was able to assess the characteristics of the drum and middle ear, valuable for the distinction between conductive and perceptive deafness
What experiments did Otto Metz work on?
Temporal bone experiments
What did Metz discover that intrigued him?
The level of middle ear reflex muscles
What did Metz find about middle ear reflex’s? What was this due to?
He found nearly the same thresholds in normal hearing persons and even in most patients with rather pronounced perceptive hearing loss. This was due to recruitment.
What test did Metz establish? What was it based on? What was the advantage?
The Metz recruitment test (based on conductive system of the ear, not sensorineural)
The advantage of being objective
What did Otto Jepsen find out about the stapedius muscle vs. the tensor tympani?
The stapedius muscle is more important (facial paralysis and impedance)
Metz had the same findings on air pressure affect impedance as ____
Bekesy
Who discovered tympanometry?
K. A. Thomsen
What did Thomsen discover?
the possibility of determining ME pressure by impedance measuring
What was the problem with tympanometry back then?
It could not be made airtight
What invention allowed for airtight tympanometry?
The electro-acoustic bridge
Who designed the electro-acoustic measuring bridge?
Knud Terkildsen
What did the electro-acoustic bridge allow for?
The use of impedance audiometry
What is one of the most frequently performed and important components of the basic audiological evaluation?
Tympanometry
What does tympanometry measure?
How the ME system responds to sound energy and how it reacts dynamically to changes in atmospheric pressure
What would happen if humans didnt have a ME?
Humans would only be able to hear very loud sounds via bone conduction
What is the main role of the ME?
To act as an impedance matching system. The ME allows sounds to be transmitted more effectively through the ossicles and by concentrating sound pressure.
Are all sounds transmitted equally by the ME?
No. LF sounds below 1000Hz and HF above 4000Hz are transmitted less efficiently.
The ME transmits the most energy to the cochlea in the frequency range of ____. why?
1000-4000Hz. This is where the majority of speech cues are carried.
Tymapnometry is an ____, ____ measure of acoustic admittance of the ME as a function of air pressure in a sealed ear canal.
objective, physiological
Where do our ears operate most efficently?
atmospheric or ambient pressure
What do increases or decreases in air pressure cause?
The TM and ossicular chain stiffen, changing the admittance of sound energy to the ME.
What are the tympanogram types (picture)?
What does the tympanogram peak (static admittance) tell us?
the amount of energy that flows into the ME system
What will you hear when during a tympanogram?
You will hear decrease in sound intensity as the pressure is increased or decreased, and you should hear an increase in sound intensity at the peak of the tympanogram where admittance is greatest
A normal tympanogram has a single clearly defined peak occurring near ____
Atmospheric pressure
Problems in the middle ear cause alternations in the shape of the ____
tympanogram
What is the most common problem that affects tympanometry? What does this result in?
Fluid in the ME space (OME). This results in an increase in impedance (decreased admittance), which flattens the tymp (type b)
What causes a type C tympanogram?
ET dysfunction (negative pressure)
What can cause positive pressure?
Acute OM (AOM), which happens rarely
What type of tympanogram will result from a thinned TM?
Type Ad (ossicular discontinuity)
What type of tympanogram will result from a stiff TM?
Type As (scaring, otosclerosis)
Who invented tympanometry?
Terkildsen and Scott-Nielson
What probe tone was first chosen for tympanometry (Terkildsen & Thomsen)? why?
220Hz
Random, but also to avoid HF microphone artifacts, lower electrical line noise, and calibration ease
Explain the MFC tympanometer
- multifrequency multicomponent tympanometer
- susceptance (B); mass and spring components of admittance
- conductance (G); friction component of admittance
What frequencys do MFC tymps test?
220Hz, 678Hz, 1000Hz
When was the first ANSI standard published? What was the goal?
1987 with the goal of standardizing insrtumentation, terminology, and recording practices
What are the 4 basic tympanometric measurments required to distinguish a normal from an abnormal tympanogram?
- Equivalent ear canal volume (Vea)
- Static-compensated acoustic admittance (Ytm)
- Tympanometric peak pressure (TPP)
- Tympanometric width/gradient (TW)
What is the most popular way to describe tympanometric shape?
The classification scheme by Liden and Jerger
What conditions can affect estimates of ear canal volume?
blockages, perforation, drainage, etc
Liden and Jerger type A tymps
Normal admittance and tympanometric peak pressure
Liden and Jerger type B tymps
Abnormally low admittance with no discernible peak
Liden and Jerger type C tymps
Normal admittance with a peak occuring at negative ME pressure
Liden and Jerger type D tymps
a double peak
Liden and Jerger type Ad & As tymps
Abnormally high admittance (Ad) and abnormally low admittance (As)
Should you do tymps with ear drainage?
No
What is the main purpose of tympanometry?
To accurately estimate the ME admittance under varying ear canal air pressure
What is tympanometric compensation?
The combined admittance of the EAC and the ME are recorded, therefore, the EAC admittance must be subtracted to determine the admittance of the ME alone
What is Vea affected by?
depth of insertion of the probe tip, dimensions of the EAC, cerumen
1 cc or ml of trapped air equals the acoustic admittance of ____ in a hard walled cavity
1 mmho
The volume estimate at extreme ____ pressures is typically lower than the volume estimate at extreme ____ pressures.
negative, positive
Who is most at risk for ear canal collapse? Why)
Newborns and infants (due to highly compliant ear canals)
Where are measurements of Vea most commonly taken from? Does it overestimate Vea?
The admittance positive tail (which overestimates ear canal volume by 40%)
What must the clinician do in order to interpret Vea?
Ensure the probe tip is not blocked and perform otoscopy to determine if the TM is intact
What will a tymp look like for a blockage?
Flat or rounded
What will a tymp look like with perforations?
Irregular curves
How to differentiate between blocked vs. perforated tymps?
compare Vea to age appropriate normative values
What do Vea that are smaller than the lowest expected value for age indicate?
Blockage of the probe tip or ear canal
Static admittance commonly refers to ____
Compliance (also includes mass and resistance)
Compliance is the most dominant component at 226Hz in normal adult ears. When is this not true?
This is not the case in infants or in pathologic conditions
When is static admittance lower?
Static admittance is lower in ME conditions that increase stiffness of the ME (OME, cholesteatoma, ossicular adhesions)
When is static admittance higher?
Static admittance is higher in ME conditions that decreases stiffness of the ME (TM atrophy, ossicular disarticulation, post stapedectomy)
Compensation at the extreme positive or negative pressure baseline is used to derive the ____
Vea
The peak of the tymp after subtraction of Vea is called the ____
peak compensated static acoustic admittance (static admittance = Ytm)
What is the sharpness of the tymp peak associated with? What is it sensitive to?
ME pathology. More sensitive to ME effusion (MEE)
The presence of MEE decreases the ____ and increases the ____ of the tymp
gradient, width
How do you measure TW?
draw a horizontal line halfway between peak admittance and baseline; the intersection of this line with either side of the tympanogram is the width (measured in daPa)
When is a large TW measured?
When the tymp is rounded
When is a small TW measured?
When the tymp has a sharp peak
What happens when the ET is not functioning normally?
negative or positive pressure may develop within the ME (ET dysfunction)
Explain ET dysfunction
The ossicular chain and TM will stiffen. This means the most effective operating point of the ME will be at the pressure contained in the ME, not atmospheric pressure)
What is tympanic peak pressure (TPP)?
The ear canal pressure at which the peak of the tympanogram occurs
What is TPP an indicator of?
pressure in the ME space
Does TPP overestimate?
Yes by as much as 100% (for example, a TPP of -300daPa could occur with actual ME pressure of only -150daPa)
What is the value of measuring TPP if it overestimates?
It can detect the presence of negative or positive ME prssure because of ET dysfunction
When does positive TPP occur?
In the early stages of AOM
When does negative TPP occur?
As OME increases (the ET eventually is blocked)
What happens as MEE increases and thickens?
tymps flatten to type B
Is negative TPP provide reliable diagnostics of OME in children?
No (not by itself)
Better sound transmission occurs at ____
TPP
____ and ____ each affect tympanometry measures and need to be considered
development, aging
What three things change between 0 and 6 years of age?
- static admittance increases
- ear canal volume increases
- TW decreases
What is a patulous ET?
When the ET is abnormally open at rest, which can cause discomfort because of autophony (hearing one’s own voice and breathing) that coincides with breathing
What should be suspected when a patient complains about hearing their own voice when breathing or chewing?
patulous ET
What is a very useful alternative to a pneumatic otoscope?
Tympanometry
What are the 2 main functions of the ET?
- pressure equalization (PE)
- mucous drainage
When does the ET open?
chewing, swallowing, and yawning
Measurement of TPP is an indirect measure of ____
ET function
What are the 3 main tests of ET function?
- valsalva test
- toynbee test
- inflation-deflation procedure
Explain the valsalva test
person holds their noise and gently blows air causing a positive shift in TPP
Explain the toynbee test
person holds their nose and swallows which introduces negative pressure into the ME (more reliable than the valsalva)
Explain the inflation-deflation procedure
person is asked to swallow several times when positive or negative pressure is introduced into the ear
pre and post tymps are recorded
What are symptoms of a patulous ET?
hearing own voice, breathing, or chewing
____ has variable sensitivity to OME in children
tympanometry
What age group has very different tymps due to ear canal flaccidity?
newborns