Decoding the Tympanogram - Harmonious Hearing

Introduction

Tympanometry was first developed by Terkildsen in the1950s. Tympanometry is one of the routine diagnostic tests used to measure the movement of the eardrum, pressure changes within the middle ear, and the volume of the ear canal. All these movements measured by a tympanometer are recorded on the graph, which is known as the tympanogram. Tympanometry (acoustic immittance testing) is one of the most rapid, simple, and not invasive tests used to rule out middle ear infections. This test is not indicated in infants below seven months due to the presence of highly compliant ear canals.

What Are the Elements of a Normal Tympanogram?

A thorough understanding of the tympanogram and basic knowledge of interpretation of the data of different elements of the tympanogram (graphical presentation) is important. Different parts of the tympanogram are:

1. ECV (External Canal Volume): External ear canal volume ranges from 0.5 to 1.2 cc (cubic centimeters).

• Small Volume: It indicates the presence of a foreign material, ear wax (cerumen), or other material in the ear canal. It may be also due to the faulty placement of the probe.
• Large Volume: It indicates a hole or perforation in the pressure-equalizing tubes of the eardrum.

2. Peak: It denotes the peak compliance of the eardrum that is measured in cubic centimeters.

3. R (Right Ear): “R” on a graph denotes the tracing of the right ear.

4. L (Left Ear): “L” on a graph denotes the tracing of the left ear.

5. D (daPa): The unit daPa (deca-pascals) denotes the peak pressure location.

6. Pressure Tracing: The peak curve on a graph denotes the pressure tracing.

7. Positive Values (like + 200): Positive values like +200 daPa on a graph denote positive pressure in the ear canal.

8. 0 (Zero): Zero on a graph denotes the atmospheric pressure within the ear canal.

9. Negative Values (like - 400): Negative values like - 400 denote the negative pressure of air in the external ear canal.

10. GR (Gradient): It denotes the width of the tracing. A gradient of more than 150 daPa indicates fluid accumulation in the middle ear. An increased gradient (more than 150 daPa) in combination with decreased compliance of the eardrum (less than 0.2 cubic centimeters) indicates middle ear effusion in ninety-five percent of cases.

How Are Tympanograms Classified?

Liden and Jerger classified different systems of the tympanogram that are used very commonly nowadays. There are three different types of tympanogram as described by them:

• Type A: The type A tympanogram presents a conical tent (teepee) like appearance on a graph. It denotes the disease-free or normal middle ear with no build-up of free fluid. It shows no signs of any physiological abnormalities disrupting the sound transfer mechanism from the middle ear to the cochlea (a snail-shaped organ in the inner ear).

• Type B: Type B tympanogram presents with a flat line on a graph indicating the infections in the middle ear and the build-up of fluid behind the eardrum. This type of tympanogram is usually seen in cases of a perforated eardrum. It indicates an increase in the volume of the external ear canal (ECV).

• Type C: This type of tympanogram shows a teepee or conical tent appearance in a graph shifted more towards the negative side of the graph. It indicates negative pressure build-up within the middle ear. It is mostly seen in cases of allergic sinusitis, sinus infections, nasal congestion, severe cold or flu, and ear infections.

How Is the Tympanometry Procedure Performed?

Tympanometry procedure is performed using a set of instruments like:

• Tympanometric Probe: A tympanometry probe consists of a tiny speaker that gives probe signals and a small microphone to monitor the pressure of the sound. The probe is used to seal the external auditory canal. The probe tips are available in various sizes.

• Pneumatic System: It is used to create air pressure changes in the ear canal between the probe tip and the ear drum. A positive force (+200 daPa) moves the eardrum inwards and the negative pressure (- 400 daPa) forces the eardrum outwards.

• Acoustic-Immittance Measurement System: It helps to convert the sounds in the speaker and the microphone into the immittance units.

• Acoustic-Reflex Activator System: It produces noise signals in one or both ears.

• Recorder: Recording equipment records the sound wave that is reflected from the ear drum. The tympanometer measures the reflected sound energy and the process is done by varying the air pressure produced by the probe. The results are recorded on the graph called the tympanogram which is then assessed by the doctor.

What Are the Indications of Tympanometry?

Tympanometry is used in the diagnosis of various conditions like:

• Acute or chronic otitis media (middle ear infections).

• In cases of perforated eardrums.

• In the evaluation of functions of the middle ear (during ear infections).

• Patulous eustachian tube.

• In the evaluation of the type of hearing loss.

• Ear ossicle fixation or dysfunction.

When Is Tympanometry Contraindicated?

Tympanometry test should be avoided in:

• Patients with skull base fractures or head trauma.

• In patients who had undergone recent ear surgery.

• Infants younger than seven months have compliant ear canals (which may give faulty results as the bony region of the ear is not yet completely developed).

What Are the Advantages of Tympanometry?

A few advantages of the tympanometry test are:

• It is a simple and rapid test.

• It is easily tolerated by patients of all ages.

• It is a non-invasive procedure.

• It does not require any other expensive equipment or a sound-treated room.

Conclusion

Tympanogram is a graphical presentation of the tympanometric test or acoustic immittance test, which is done to evaluate the volume of the external ear canal, movement of the eardrum, and pressure changes within the middle ear due to ear infections. It is quite a reliable, safe, simple, and non-invasive technique developed to rule out ear infections, and conductive hearing loss, and to evaluate the integrity of tympanic membranes. Tympanometry is an exciting and newer diagnostic tool in the healthcare field for instant and informative diagnosis of ear infections. It has also served as a boon in conducting various auditory screening programs in different sectors for early diagnosis of middle ear infections. However, further innovative research is needed to study tympanometric testing at multiple frequencies.