Tympanogram interpretation

Tympanogram Interpretation
Audiograms

Measures energy transfer of ear as f(x) of air pressure
Low frequency tone is played
Pressure of middle ear measured
TM compliance is measured
Ear canal volume is measured

To begin testing, the probe, fitted with an appropriately sized eartip, is positioned at the opening of the ear canal. For operator convenience, the probes of the Auto Tymps are equipped with either signal lights (GSI 38) or an easy to read display (GSI 37) to keep the operator informed of the test status at all times. Even inexperienced instrument users can obtain reliable results with confidence. When a tight seal is obtained, a known quantity of sound energy is introduced to the ear. By introducing a known amount of sound energy to the ear, a measurement of the energy not transmitted into the middle-ear system is recorded. The amount of sound energy transmitted is equal to the amount of sound energy introduced, minus the amount of sound energy that returns to the probe microphone. The amount of energy transmitted is directly related to the compliance of the system. Compliance (labeled in cm3 of equivalent volume) indicates the amount of mobility in the middle ear. For example, the more energy returned to the probe, the less energy admitted, and thus a low compliance measurement. Low compliance measurements indicate a stiff or obstructed middle ear (See Figure 3). Of course, the opposite is true for a high amount of energy transmission, indicating a flaccid or highly mobile system.
At this point, the probe introduces a pressure of + 200 daPa to the middle ear canal. Decapascals, or daPa is a measurement of air pressure; whereby, 1.02mm H20 = 1.00 daPa. This positive pressure forces the tympanic membrane inward and the approximate ear canal volume is recorded. This volume gives a baseline from which the compliance curve is drawn. The pressure is now varied in the negative direction, while constantly monitoring the compliance of the system. The pressure continues toward the negative direction until a pressure peak has been detected and -100 daPa has been reached or until a pressure of -400 daPa is present in the ear canal, whichever comes first. Once the pressure is equalized on both sides of the tympanic membrane, the point of peak compliance is stored, as is the pressure at which peak compliance occurs.
A tympanogram is a graphic representation of the change in compliance (Y or vertical axis) of the middle-ear system as air pressure (X or horizontal axis) is varied. Valuable diagnostic information is obtained from both the graphic and quantitative data (See Results Section).

1. Ear Canal Volume (0.2-2.0), measured in cm3, indicates the volume from the probe tip to the tympanic membrane at a pressure of +200 daPa. Ear canal volume < 0.2: cerumen or probe malposition. Ear canal volume > 2: PE tubes or perforation.
2. Compliance Peak (0.2-1.4), expressed in daPa, indicates the amplitude of the peak. This value can vary from NP (no peak, when compliance < 0.1) to 6.0 cm3. If <0.2, 'stiff'; if > 1.4, 'hyperflaccid.'
3. Pressure Peak (-150 to 100), measured in cm3, indicates the pressure at which equalization occurs on both sides of the tympanic membrane. It also indicates the pressure at which peak compliance or maximum mobility is attained. This corresponds to the value on the horizontal axis of the graph. Pressure peaks more negative than –150 indicative of poorly functioningeustachiantube or possibly some fluid. Extreme positive pressures possibly at the onset of AOM
4. The Scale of Reference, measured in cm3, is dependent on the amplitude of the tymp peak measurement. This scale is either 1.5 cm3 or 3.0 cm3. Should the peak measure 1.5 or less in amplitude, the scale reading will be 1.5 cm3. If it is 1.6 or greater, the scale will read 3.0 cm3. The change in scale size merely allows a greater distribution of the graph on the chart. A tymp peak reading of "NP" will automatically cause the scale reading to be 1.5, which is indicative of no peak.
5. Normal Box indicates the range of pressure peak and compliance peak values associated with normal middle-ear function. (-150 daPa to +100 daPa, 0.2 cm3 to 1.4 cm3 per ASHA, 32, Suppl. 2, 1990, 17-24).
6. Gradient (60-150 child, 50 to 110 adult), expressed in daPa, is the tympanometric pressure width at 50% of the compliance peak. The width of the pressure curve; the range of pressures needed for mobility Infants may show higher gradient values due to the mobility of their ear canals. Wide gradients indicate presence of fluid. Narrow gradients associated with a flaccid middle ear system. Near zero gradient: viscous effusion.
7. Acoustic Reflex, expressed as a yes (normal)/no, dB HL or dB HL and a curve, signifies the level at which the acoustic reflex causes the stapedial muscle to contract. This value will depend upon the level or intensity at which the acoustic reflex is detected at a given frequency. "NR" indicates no reflex occurred at the level tested. "NT" indicates test aborted prior to completion. (negative if hearing loss is present)

In assessing the results of tympanometry, they should be analyzed with respect to:
(1) Ear Canal Volume. (2) Compliance (peak amplitude)
(3) Gradient (tymp width) (4) Middle-Ear Pressure (peak pressure)
Each result is a piece of the puzzle and provides information on a possible cause for any abnormality. The gradient acts as an adjunct to the tymp and ear canal volume measurements by helping to differentiate between tymps with similar peak values. A larger than-normal gradient value can indicate the presence of fluid in the middle ear when other parameters are within normal limits.
The configuration of the tympanogram itself indicates the compliance of the middle ear system. In the physiologically stiffened ear, the variation in mobility will be less, indicating a limited movement at the point of equalized pressure. A hyperflaccid condition, indicative of a scarred membrane is illustrated by a sharp peak.

Tympanograms can be characterized by their shape and location. The key characteristics affecting the pathology diagnoses are; pressure peak, compliance (maximum displacement) and width (gradient) of tympanograms.
Cases of otitis media can easily be detected by a depressed compliance peak amplitude and a negative pressure peak. (In general, the shape of the peak is more sensitive/specific vs peak pressure or peak compliance - the more rounded the peak, or ultimately an absent peak, the higher the probability that an effusion is present. Nelson 16h ed) The results provide an objective and tangible means for a simple diagnosis. The example tymps that follow are analyzed and the results could be interpreted as stated below each chart.

Ears can be classified into three basic groups on the basis of the configuration of the tympanogram.
in general a peak that is pointy and sharp has a low probability of effusion. A more rounded peak has a higher probability of effusion
Type A. The peak compliance occurs at or near atmospheric pressure indicating normal pressure in the middle ear. There are three subgroups.
- A - normal shape reflects a normal mechanism
- AD - A deep curve with a tall peak indicates an abnormally compliant middle ear, as seen in ossicular dislocation or erosion, or loss of elastic fibers in the tympanic membrane, thin tympanic membrane (ie healing post rupture)
- AS - A shallow curve indicates a stiff system, as in otosclerosis or middle ear effusion
Type B - No sharp peak, with little or no variation in impedance over a wide range:
- normal volume -> middle ear fluid (non-compressible), sclerosis
- with abnormally small volume -> faulty probe, usually probe against wall or cerumen
- with abnormally large volume -> tympanic membrane perforation or PE tube
Type C - Peak compliance is significantly below zero, indicating negative pressure (sub-atmospheric) in the middle ear space. This finding is often indicative of eustachian tube dysfunction.
Type D: Notching: shows a dip in the peak. Indicates scarred eardrums or hypermobile TM

Type A curve
Normal Ear Canal Volume
Normal Middle-Ear Mobility
Normal Middle-ear Pressure (o)
Normal GR

Poorly Functioning Eustachian Tube

Type C Curve
Normal Ear Canal Volume
Restricted Mobility (low amplitude)
Abnormal Middle-ear Pressure (very negative)
Borderline wide GR

POSSIBLE CAUSE
Poorly functioning Eustachian Tube
Possibly Some Fluid

Partially Blocked Eustachian Tube

Normal Ear Canal Volume
Normal Middle-ear Mobility
Slightly Negative Middle-ear Pressure
Normal GR

POSSIBLE CAUSE
Partially Blocked Eustachian Tube

Possible Nasal Congestion

Normal Ear Canal Volume
Normal Middle-ear Mobility
Positive Middle-ear Pressure
Normal GR

POSSIBLE CAUSE
Patient has a cold

Type As curve

Glue Ear

Normal Ear Canal Volume
Restricted Mobility
Normal Middle-ear Pressure
Borderline-or-Wide GR

POSSIBLE CAUSE
Glue-ear
Otosclerosis; stiff ossicular chain
Severely Scarred Tympanic Membrane
Plaque over Tympanic Membrane

Serous Otitis Media with Air Pockets
(Serous OM without airpockets would show a flat line)

Type B curve

Normal Ear Canal Volume
Restricted Mobility
Negative Middle-ear Pressure
Abnormally Wide GR

POSSIBLE CAUSE
Serous Otitis Media
Small Air Pockets Present

Ossicular Disarticulation/Discontinuity

Type AD curve
Normal Ear Canal Volume
Extremely Hyperflaccid Middle-ear
Normal Middle-ear Pressure
Narrow GR

POSSIBLE CAUSE
Ossicular Disarticulation
More Detailed Testing Indicated

Scarred Tympanic Membrane

Normal Ear Canal Volume
Hyperflaccid Middle-ear System
Normal Middle-ear Pressure
Normal-or-Borderline Narrow GR

POSSIBLE CAUSE
Minor Scar Tissue in Tympanic Membrane

Tympanic Membrane Perforation

Abnormal Ear Canal Volume (large)
No Mobility
No Middle-ear Pressure
No GR

POSSIBLE CAUSE
Open Perforation
Patent Pressure Equalization (P-E) Tube

Serous Otitis Media

Normal Ear Canal Volume
No Mobility
No Middle-ear Pressure
No GR

POSSIBLE CAUSE
Fluid-filled Middle-ear (Serous Otitis Media)
Compliance Peak May be Present at a Much More Negative Pressure Than -400daPa

Effusion

Reference
http://www.grason-stadler.com/tymp.html