PRINCIPLES OF OPERATION
4
D-0115690-C (OM001)
– Otowave 102 Operating Manual
3.
PRINCIPLES OF OPERATION
Please note:
This operating manual is not intended as a training manual for tympanometry. The reader should
consult standard audiology texts for the theory and application of the screening tests provided by this
instrument.
3.1.
COMPLIANCE MEASUREMENT
The Otowave 102 measures the compliance of the tympanic membrane and middle ear by playing a continuous
226Hz tone into the ear canal at a level calibrated to give 85dB SPL into a 2ml cavity. The sound level this
produces in the ear canal is measured using a microphone and the compliance calculated from the result. In
line with normal audiometric practice compliance is displayed as an equivalent volume of air in ml.
3.2.
TYMPANOGRAM
To record the tympanogram the compliance is measured while the air pressure in the ear canal is varied from
+200daPa to -400daPa by means of a small pump. The compliance peaks when the air pressure is the same
on both sides of the tympanic membrane. The changing compliance with pressure is displayed as a graph.
3.3.
STAPEDIAL REFLEX MEASUREMENT
Using the same principle it is also possible to establish whether a stapedial reflex is present. In this case, the
226Hz tone is used to measure the compliance of the ear, while a short tone at a different frequency is
presented (the reflex stimulus). The level of this stimulus is increased in steps until the stapedial muscles
respond causing the tympanic membrane to become stiffer, or a preset maximum level is reached. When the
change in compliance exceeds a predetermined threshold this constitutes a reflex and the change in
compliance at that level when the stimulus is applied is displayed as a plot against time.
The stapedial reflex is measured at the static ear canal pressure that produces the maximum membrane
compliance, so reflex measurements are taken after the tympanogram is measured when the peak compliance
pressure has been established.
The Otowave model 102-1 measures stapedial reflex at 1000Hz, while the model 102-4 measures at 500Hz,
1000Hz, 2000Hz and 4000Hz. The maximum level for the reflex stimulus may be preset, along with the step
size in dB between the three preceding lower levels of stimulus.
