In Clinical Audiometry, Tympanometry is routinely carried out and is used mainly as a measure of the middle ear function. This is done by using a tympanometer to change the air pressure in the ear canal. The changing air pressure affects the position and compliance (flexibility) of the eardrum and as a result affects how the efficiency sound is admitted into the middle ear.

Both the pressure and compliance are recorded and plotted on a graph against each other. The most sound is admitted into the middle ear when the air pressure is identical on both sides of the eardrum (normal atmospheric pressure and middle ear pressure) and this is usually 0 daPa. Additionally ear canal volume

The pressure at which maximum compliance is achieved provides information about the middle ear function and how this may be related to hearing loss. It can be useful in determining differential diagnosis between sensorineural and conductive hearing losses.

Traditionally tympanograms were classified into different Types (Jerger, J. (1970). Clinical experience with impedance audiometry. Archives of Otolaryngology, 92, 311–324.). These were simply A, B and C with a number of sub types, Ad & As, C1 & C2. However more recent guidelines (http://www.thebsa.org.uk/images/stories/BSA_RP_Tymp_Final_21Aug13_Final.pdf) recommend including the shape of the curve and the various measurements obtained.

Tympanometric Shape:

The trace should have one sharp peak and it may be rounded or wide. It is possible to have two peaks where there is scarring on the eardrum and the test should be repeated to exclude artefacts. The shape of the tympanogram may be described as; normal, rounded, flat, and wide or 'W' shaped.

Middle Ear Pressure:

This is the tympanic peak pressure (highest point) on the horizontal axis. Normal is considered to be 0daPa but for adults -50 to +50 daPa is within normal limits and pressures down to -100daPa may have little clinical significance. Children's values range from +50 to -200daPa.

Compliance:

This is the value on the vertical axis and is measured in cubed centimetres or millilitres (& mmho if 226Hz probe tone is used). It is deemed the peak value once it has been corrected for the ear canal contribution (normally done by default). Normal compliance range is 0.3 to 1.6cm3 but children's lower limit can be 0.2cm3 if under 6 years old.

Ear Canal Volume:

This contributes to compliance when a 226Hz probe tone is used and is compensated for accordingly. Normal ear canal volume (ECV) for adults is 0.6 to 1.5cm3 and for children it is 0.4 to 1.0cm3. Should the probe tip be occluded (due to debris, etc) or pressed against the wall of the canal a very small ECV will be obtained and if there is an ear drum perforation then the ECV will be abnormally large. Both of these instances will cause a flat 'trace'.
 

Types of Tympanogram Results

Normal (Type A) Tympanogram

Probable normal middle ear function.
Shape: normal
Middle Ear Pressure: Normal, +/-100daPa for adults (+50 to -200daPa for children)
Compliance: Normal, 0.3 to 1.6cm3 for adults (0.2 to 1.6cm3 for children)
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)

 

Type As (Shallow) Tympanogram

Probably a less compliant middle ear system. Usually these types of tympanograms have a history of middle ear problems ranging from repeated childhood otitis media, otosclerosis or tympanosclerosis.
Shape: normal but flattened
Middle Ear Pressure: Normal, +/-100daPa for adults (+50 to -200daPa for children)
Compliance: Reduced, less than 0.3cm3
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)

Type Ad (Deep) Tympanogram

A highly compliant system
These can be seen in patients that had multiple perforations previously, or frequent insertion of grommets. It may also indicate an ossicular chain disruption.
Shape: normal but exaggerated
Middle Ear Pressure: Normal, +/-100daPa for adults (+50 to -200daPa for children)
Compliance: Increased, more than 1.4cm3 (ASHA, 1990)
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)

Flat (Type B - Low) Tympanogram

Suggestive of middle ear dysfunction.
Patients with Type B tympanograms can have otitis media. This is particularly common when a patient has a cold and is also prevalent in children. Hearing loss may be present in cases of middle ear effusion.
Shape: Flat
Middle Ear Pressure: None detectable
Compliance: None detectable
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)

Flat (Type B- High) Tympanogram

Indicative of a grommet or perforation.
Perforations can cause a drop in low-pitched hearing and can progressively get worse. The most common causes of perforation arise from ear infections, trauma and extreme pressure changes i.e. diving and flying.

There is no identifiable peak with an ear canal volume greater than 1.5 cm3.
ENT referrals are recommended in almost all cases. It is important to note that an ear with a perforation is no longer waterproof and a swimming plug may be necessary in these cases. The presence of a patent grommet also often creates slightly elevated low-pitch thresholds.
Shape: Flat
Middle Ear Pressure: None detectable
Compliance: None detectable
ECV: Large, greater than 1.5cm3 for adults (<1.0cm3 for children)

Negative Pressure (Type C)

Suggestive of Eustachian tube dysfunction.
These tympanograms usually occur after a patient has had a cold or is about to get one. Patients with repeated Type C tympanograms can be at risk of cholesteatomas. Type C tympanograms should be reviewed regularly to see the progression (improvement, the same or worsens). Type C tympanograms are subdivided into C1 or C2, this merely indicates the severity of the negative pressure. C1 denotes pressure down to -200daPa and C2 is lower.
Shape: normal
Middle Ear Pressure: Reduced, less than -100daPa for adults (less than -200daPa for children)
Compliance: Normal, 0.3 to 1.6cm3 for adults (0.2 to 1.6cm3 for children)
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)

Positive Pressure

Suggestive of acute middle ear infection
A positive pressure in the middle ear could be due to air forced into the middle by sneezing or altitude change but can also be signs of an acute middle ear infection. There is risk of the eardrum rupturing in this type.
Middle Ear Pressure: Increased, more than +100daPa for adults (more than +50daPa for children)
Compliance: Normal, 0.3 to 1.6cm3 for adults (0.2 to 1.6cm3 for children)
ECV: Normal, 0.6 to 1.5cm3 for adults (0.4 to 1.0cm3 for children)