App. 1 MADSEN Zodiac immittance methodology and features
146
MADSEN Zodiac
An initial positive or negative air pressure is applied to the ear through the probe. Due to the eardrum perforation, the
pressure will be applied to both the ear canal and middle ear cavities. The patient is then instructed to swallow some
water, which typically causes a functioning Eustachian tube to open. Any pressure equalization through the tube will show
as a sudden pressure drop toward, but not necessarily reaching, atmospheric pressure (0 daPa). This is repeated until the
pressure is equalized or until the test time has elapsed. The pressures at which the tube opens and closes are reported as
test results.
Typically, an initial build-up of positive pressure will cause the Eustachian tube to open spontaneously. To avoid
premature spontaneous pressure equalization related to positive pressure build-up, the pump speed should be kept at a
maximum of 50 daPa/s.
The pressure range available for positive and negative pressures (including 400 daPa and -600 daPa) is commonly used in
ETF-P testing.
App. 1.5 Susceptance and Conductance, B/G
The
admittance (Y)
of the ear consists of the contribution of
the two components
Susceptance (B)
and
Conductance (G)
.
The admittance magnitude is the vector length derived from
the Cartesian graph as shown.
App. 1.5.1
Susceptance, B
Susceptance
is determined by the ease with which energy flows through the
Compliant elements
of the ear and the ease
of energy flow through the
Mass elements
of the ear.
•
Compliant elements
are the tympanic and round window membranes, the ossicular ligaments, the middle ear
muscles, and the air in the ear canal and middle ear.
•
Mass elements
are the ossicles and the slugs of air in the middle ear mastoid air cells (moving as units without
compression or expansion).
The
compliance
and
mass
contribution to the total
Susceptance
is frequency dependent.
•
Compliant Susceptance
is greater with low frequencies and gradually decreases with higher frequencies.
