Tympanometry is a non-invasive test designed to evaluate the function of the middle ear. This procedure assesses how well the eardrum (tympanic membrane) and the small bones of the middle ear move in response to changes in air pressure. It provides information about the middle ear system’s ability to transmit sound energy effectively. Healthcare professionals use this test to identify various conditions that might affect hearing.
How Tympanometry Works
Tympanometry involves a specialized instrument called a tympanometer. A healthcare professional places a small, soft-tipped probe snugly into the ear canal, creating an airtight seal. This probe has a tiny pump, a speaker, and a microphone. The pump gradually changes the air pressure within the sealed ear canal, typically ranging from positive to negative pressure, measured in decapascals (daPa).
As pressure changes, the speaker emits a low-frequency sound tone, usually 226 Hz for adults. The microphone measures how much sound is reflected back from the eardrum. This indicates the eardrum’s mobility and how well sound energy passes through the middle ear. These measurements are then plotted on a graph called a tympanogram.
Key Measurements and Their Indicators
Tympanometry provides several objective measurements that offer insights into middle ear health. Middle ear pressure, measured in daPa, ideally matches the atmospheric pressure outside the ear. This reflects the function of the Eustachian tube, which connects the middle ear to the back of the throat and helps equalize pressure. Deviations from normal pressure (typically around 0 daPa) can suggest issues with Eustachian tube function.
Compliance, also referred to as admittance, quantifies the eardrum’s mobility or stiffness. It indicates how readily sound energy is transmitted through the middle ear system. Compliance is plotted on the vertical axis of the tympanogram and is usually measured in milliliters (ml) or millimhos (mmho). A healthy middle ear system exhibits a specific range of compliance.
Ear canal volume (ECV) is also measured, providing an estimate of the air volume between the probe and the eardrum. This measurement is particularly useful in identifying conditions where the eardrum’s integrity is compromised or the ear canal is obstructed. For adults, a normal ECV typically ranges from 0.6 to 2.5 ml, while for children, it ranges from 0.4 to 1.0 ml. An abnormally large ECV can indicate a perforated eardrum or a patent tympanostomy tube.
Common Abnormalities Detected
Tympanometry is a valuable tool for identifying several middle ear abnormalities. Middle ear fluid, often associated with otitis media with effusion (OME), is one common condition detected. When fluid accumulates behind the eardrum, it dampens the eardrum’s movement, causing it to become stiff. This stiffness results in a characteristic flat line on the tympanogram, known as a Type B curve, assuming a normal ear canal volume.
Eustachian tube dysfunction occurs when the tube connecting the middle ear to the nasopharynx does not open and close properly, leading to pressure imbalances. This can cause negative pressure to build up in the middle ear space. Tympanometry reveals this as a peak shifted significantly to the negative pressure side of the graph, which is characteristic of a Type C tympanogram.
A perforated eardrum is another condition that tympanometry can identify. In such cases, air from the ear canal passes directly into the middle ear space, preventing the pressure changes from affecting the eardrum’s mobility. This results in a flat Type B tympanogram, but it is accompanied by an abnormally large ear canal volume measurement, indicating the presence of a hole.
Ossicular chain discontinuity refers to a break or separation in the tiny bones (ossicles) of the middle ear. This can lead to excessive movement or flaccidity of the eardrum. Tympanometry may show an abnormally high peak in compliance, often classified as a Type Ad tympanogram. Conversely, otosclerosis, a condition where the ossicles stiffen, reduces the eardrum’s mobility. This results in a shallow peak on the tympanogram, known as a Type As curve, indicating reduced compliance.
Interpreting Tympanogram Types
A tympanogram is categorized into different types based on its shape. A Type A tympanogram represents normal middle ear function. It is characterized by a sharp, inverted V-shaped peak located near 0 daPa, indicating that the eardrum moves normally and the pressure in the middle ear is equal to the external ear canal pressure.
Type B tympanograms, characterized by a flat line, suggest conditions like middle ear fluid or a perforated eardrum. Type C tympanograms, with a peak shifted significantly to the negative pressure side, indicate negative middle ear pressure often associated with Eustachian tube dysfunction. These conditions are detailed in the ‘Common Abnormalities Detected’ section.
While these classifications provide general interpretations, a medical professional is necessary for a definitive diagnosis and to correlate the findings with a patient’s overall clinical picture.