This document discusses instrumentation used to measure acoustic signals and auditory function. It describes otoacoustic emissions, which are sounds emitted from the inner ear that can be measured in the ear canal. There are two types of otoacoustic emissions: spontaneous and evoked. Transient evoked otoacoustic emissions and distortion product otoacoustic emissions are the most clinically applicable evoked emissions. These emissions are present in normal hearing but absent in hearing loss, making them useful for hearing screening and diagnosis. The document also discusses transient evoked otoacoustic emission testing specifically, noting it is a quick, sensitive test using a small probe to detect cochlear pathology for uses such as neonatal hearing screening, differential diagnosis

1. Instrumentation
Used In The
Measurement of
Acoustic Signals
And Auditory
Function
Dr. Ghulam Saqulain
M.B.B.S., D.L.O., F.C.P.S
Head of Department of ENT
Capital Hospital, Islamabad

2. Otoacoustic Emissions
In 1978, Kemp showed that, when stimulated, the
normal ear emits sound.
These emitted sounds can be measured in the ear canal
with sensitive microphones, appropriate stimulus, and
signal averaging.

3. The fact that these responses are present in normal ears
but absent in ears with significant hearing loss has led to
the application of these techniques to the problem of
identification and diagnosis of hearing loss
(Kemp et al, 1986; Kemp et al, 1990; Lonsbury-Martin and Martin, 1990; and Lonsbury-Martin et al,
1990).

4. There are two general classes of OAEs:
Spontaneous OAEs
 They are present in about 50% of normal hearing ears.
 Their presence does not appear to be strongly related to the percept of tinnitus.
 Given these two facts, the clinical applicability of spontaneous OAEs remains extremely
limited.
There are three types of evoked OAEs:
 Transient,
 Stimulus frequency,
 Distortion product.

5. Transient Evoked Otoacoustic Emissions (TEOAE’s)
produced by brief acoustic stimuli
Distortion Product Otoacoustic Emissions (DPOAE’s)
results from inner ear distortion generated when two
or more tones of different frequencies are introduced
into the ear

6. Stimulus frequency OAEs are technically the most difficult to
extract from the stimulus waveform and have not received
much attention in terms of clinical problems.
In contrast, both transient and distortion product OAEs have
been shown to be present in the majority of normally hearing
subjects, absent in the majority of patients with hearing loss,
and easily measured in relatively short periods of time

7. – TEOAE
– TEOAE, also known as cochlear echoes, are low
intensity sounds originating from the outer hair cells in
the cochlea and can be elicited in response to click
presented to the ear through a light weight probe
– This detection by a microphone within the same probe
is a simple and rapid clinical test for the normal
functioning of the middle and inner ear.
– TEOAE testing is quick, sensitive to cochlear pathology
and involves only a small probe in the outer ear, which
makes it very acceptable to parents and babies.
– Some 2 to 3.6% screen positive.
Instrumentation

9. Function

10. Application
Neonatal hearing screening
Differential diagnosis
Monitoring cochlear damage