Multi-Frequency Tympanometry

Purpose

"High-frequency" tympanograms are obtained with probe tones higher than the traditional "low-frequency" 226 Hz probe tone. The "high-frequency" probe tone is usually 678 Hz. The combined use of 226 Hz and 678 Hz tympanograms is sometimes called multiple frequency tympanometry. However, this term is also used to describe various tympanometric methods that involve testing at many frequencies to arrive at the resonant frequency of the ear and other measures. Abnormally high resonant frequencies are associated with stiffening disorders, such as otosclerosis, whereas abnormally low resonant frequencies are associated with disorders that increase the mass component of the system, like ossicular discontinuity.

Materials

Tympanometer with multi-frequency capabilities

Procedures/Instruction

Separate tympanograms are obtained for susceptance (B) and conductance (G) when testing at 678 Hz instead of a single admittance (Y) tympanogram. Depending on the instrumentation used, the B and G tympanograms may be obtained simultaneously, or they may be done one after the other. In either case, the interpretation is easier when they are plotted on the same tympanogram form.

Interpretation/Site of Lesion

Normal 678 Hz Tympanograms

In contrast to 226 Hz tympanograms, 678 Hz B-G tympanograms are interpreted on the basis of their shapes and configurations (morphology). There are four types of normal 678 Hz B-G tympanograms. They are named on the basis of the number of positive and negative peaks and must also meet a criterion for tympanogram width.

1B1G

3B1G

3B3G

5B3G

The first normal type of 678 Hz tympanogram is called 1B1G because there is one peak for the B tympanogram and one peak for the G Tympanogram. The other three normal variations involve notches on one or both of the tympanograms. 

The second normal type has a notched peak on the B tympanogram and a single peak on the G tympanogram. Notice that the notch on the B tuympanogram can be viewed as two positive peaks with a negative peak between them. The convention is to count these "peaks" or "extrema." Thus, this normal variation is called 3B1G because B has three peaks and G has one peak

The third normal variation is called 3B3G because there are three peaks on both tympanograms.

the last type of normal 678 Hz configuration is called 5B3G because it has five peaks on the B tympanogram and three peaks on the G tympanogram. 

In addition to having a maximum of five peaks for B and three peaks for G, the distance between the outermost peaks of normal 678 Hz B-G tympanograms should be

1. less than or equal to 75  daPa wide for 3B3G tympanograms and less than or equal to 100 daPa for 5B3G tmpanograms
2. narrower for the G tympanogram than for the B tympanogram

Abnormal 678 Hz Tympanograms

A 678 Hz B-G tympanogram is considered abnormal if it fails to meet the criteria just outlined, if it has

1. too many peaks and/or
2. is too wide

Abnormal 678 Hz B-G tympanograms are principally associated with ossicular discontinuities but they can also occur with tympanic membrane abnormalities. We can often distinuguish between them because ossicular discontinuities usually cause significant amounts of hearing loss and appreciably alter the acoustic reflex, which is generally not the case with eardrum abnormalities. Many tympanic membrane abnormalities can be visualized otoscopically.

Management

Works Cited

Gelfand, Stanley A. Essentials of Audiology. Thieme, 2016.
DeRuiter, Mark, and Virginia Ramachandran. Basic Audiometry Learning Manual. Plural Publishing Inc., 2017