App. 1.3 Acoustic Reflex Testing; App. 1.3.1 Acoustic Reflex Quick Check - Madsen zodiac Reference Manual

App. 1 MADSEN Zodiac immittance methodology and features
How to perform the maneuver
1. Instruct the patient to block the nostrils by pinching the nose using the thumb and index finger.
2. Instruct the patient to swallow a few times. It may help to provide some water to drink.
App. 1.3 Acoustic Reflex testing
The term "Acoustic Reflex" refers to the stapedius reflex, a middle ear muscle contraction which is normally elicited bin-
aurally by particularly loud sounds. The acoustic reflex is assessed through the measuring of an acoustic admittance change
as the ear is stimulated with different loud pure tones or with filtered noise. As the stapedius muscle contracts, tension in
the ossicular chain stiffens the middle ear, and consequently compromises the acoustic energy flow through the middle
ear. The probe microphone detects this change as the acoustic energy remaining in the ear canal is increased. The res-
ulting graph shows the admittance change on the vertical axis and time on the horizontal axis. The properties of the reflex
are determined from a curve deflection referenced to an initial baseline. The baseline is the total ear admittance without
any stimulus applied.
It is important to note that the change in admittance, which results from the functioning of the reflex mechanism, is very
small. It is further diminished if the eardrum is tensioned by a static pressure differential between the ear canal and the
middle ear. Therefore, measurements are made with an ear canal air pressure applied, corresponding to the tym-
panometric peak pressure.
Tympanometric features ► 141
See
Always perform tympanometry before attempting to assess the acoustic reflex. Atmospheric pressure (0 daPa) is used in
case no tympanometric peak data is available. The tympanometric peak data is probe tone specific. In case of baseline
instability due to a hyper-flaccid eardrum, a pressure offset of 20-30 daPa in the same direction as TPP displacement may
be used. A pressure offset of this magnitude will stabilize the flaccid eardrum without obscuring the reflex induced admit-
tance change.
Due to the physiology of the neural pathways involved, acoustic reflexes can be elicited either with stimulation of the ipsi-
lateral (probe ear) or contralateral ear. This means that the acoustic reflex is a binaural phenomenon. This is used for dia-
gnostic purposes since different configurations of reflex integrity, when comparing ipsi- and contralateral measurements,
suggest different sites and types of lesions.
Acoustic reflex tests are used to indicate, or, in conjunction with other audiological tests, confirm disorders such as ret-
rocochlear pathology, brain-stem lesions, Bell's palsy, conductive hearing loss, cochlear hearing loss, etc.
Many different features of the acoustic reflex may be studied. Clinically, the most common are the
Threshold
(see
App. 1.3.1 Acoustic reflex quick check
Acoustic Reflex Screening is not a threshold search, but provides useful information about presence/absence of acoustic
reflexes within normal stimulus levels.
Normal hearing individuals or individuals with symmetrical sensorineural hearing loss, where there is no suspicion of ret-
rocochlear pathology may be tested with a condensed screening protocol to indicate normal acoustic reflex behaviour. A
single stimulus frequency (1000 Hz is recommended) with 226 Hz probe tone is presented ipsilaterally. If the reflex is not
detected within normal stimulus levels in relation to the pure tone audiogram, a complete and thorough acoustic reflex
threshold investigation is recommended.
144
.
Acoustic reflex threshold ► 145 Acoustic Reflex Decay
) and the
Acoustic Reflex
Acoustic reflex decay ► 145
(
Otometrics - MADSEN Zodiac
).