A tympanogram is a graphical representation derived from a tympanometry test, which assesses the function of the middle ear and the mobility of the eardrum. This diagnostic tool is non-invasive and provides insights into how effectively sound is transmitted through the ear. Healthcare professionals, particularly audiologists and ear, nose, and throat specialists, use tympanograms to help diagnose various conditions such as middle ear infections, fluid accumulation, or issues with the Eustachian tube. The test is quick, involving the placement of a small probe in the ear canal to measure the eardrum’s response to subtle pressure changes.
Understanding the Tympanogram Graph
The tympanogram presents data on a graph with two primary axes. The horizontal axis, or X-axis, represents air pressure in the ear canal, measured in decaPascals (daPa). This pressure ranges from -400 to +200 daPa. The vertical axis, or Y-axis, indicates the eardrum’s compliance or admittance, which is its ability to move, measured in milliliters (mL) or cubic centimeters (cm³).
The plotted line, or curve, on the graph illustrates how the eardrum’s movement changes in response to these pressure variations. The highest point on this curve is known as the peak, which signifies the pressure at which the eardrum is most compliant. Additionally, the width of the curve, sometimes referred to as the gradient or tympanometric width, indicates the stiffness of the middle ear system.
Interpreting a Normal Tympanogram
A healthy middle ear system is represented by a Type A tympanogram. This type is characterized by a distinctive “mountain peak” or “tent” shape on the graph. The peak of a normal tympanogram is located near 0 daPa, within a range of +50 to -50 daPa, indicating that the middle ear pressure is balanced with atmospheric pressure.
For adults, the peak height, representing eardrum compliance, falls within a range of 0.3 to 1.6 mL or cm³. This range signifies appropriate mobility of the eardrum and the small bones within the middle ear.
Identifying Common Tympanogram Shapes
Variations in tympanogram shapes can indicate different middle ear conditions. A Type B tympanogram appears as a flat or nearly flat line with no discernible peak. This shape suggests limited or no movement of the eardrum, due to fluid accumulation behind the eardrum, such as in otitis media with effusion. A flat line can also be caused by a perforated eardrum or a complete blockage of the ear canal, such as from excessive earwax.
A Type C tympanogram features a peak that is shifted towards the negative pressure side of the graph, at -150 daPa or more negative. This shift suggests negative pressure within the middle ear, a common sign of Eustachian tube dysfunction. This can arise during or after a cold, or due to allergies, as the Eustachian tube struggles to equalize pressure.
The Type A_s_ tympanogram, also known as a shallow or stiff tympanogram, maintains the general Type A shape but exhibits a reduced peak height. This indicates decreased compliance or increased stiffness of the middle ear system. Conditions like otosclerosis, which involves the hardening of the middle ear bones, can lead to this type of tracing.
Conversely, a Type A_d_ tympanogram, referred to as a deep or disarticulated tympanogram, also resembles a Type A shape but shows a high peak height. This suggests an overly mobile or flaccid eardrum. Such results can point to a disarticulation of the ossicles, meaning the small bones in the middle ear have separated, or a very thin and flexible eardrum. While these patterns offer strong indicators, only a qualified healthcare professional can provide a definitive diagnosis based on a comprehensive medical evaluation.