otometrics Madsen ZODIAC 901, Руководство пользователя

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Cartesian
tympanometry Tympanometry is the measurement of the change in the ear canal vol-
ume resulting from the tensioning of the eardrum by the application of
varying pressure in the ear canal. A tympanogram is a Cartesian graphi-
cal representation of this measurement.
Reflex tympanometry Reflex tympanometry is the measurement of the change in the ear canal
volume (the “Delta” volume) resulting from the tensioning of the ear-
drum by muscles acting on the ossicular chain following the application
of an external acoustic stimulus. The results are plotted on a Cartesian
graph with time along the
x -axis.
The difference between the tympanometric graphs generated from
measurements on healthy ears, and those obtained in cases of hearing
disorders, allow reliable diagnosis to be made of the nature of the disor-
ders. The real-time computing power of the ZODIAC 901 enables these
informative graphs to be generated quickly, repeatedly and accurately.
8.10 PRACTICAL CONSIDERATIONS
Calibration for
tympanometry The volume of air measured using acoustic-flow tympanometry can be
expected to be influenced by such variable factors as barometric pres-
sure. The ZODIAC 901 provides for the elimination of the influence of
these factors by means of an automatic daily calibration procedure, us-
ing a Madsen Electronics Precision Cavity with a known volume of 2.0
cc (2.0 ml).
Because the absolute values of acoustic impedance are influenced by
barometric pressure and other variable factors, practical tympanometry
concentrates on relative volume measurements, which are used as ana-
logs of impedance.
Ordinary
environment for
tympanometry The probe tone used to measure the ear canal volume in the ZODIAC
901 is a 226 Hz tone, which is the frequency prescribed by the Standards
CEI/IEC 1027:1991 and ANSI S3.39-1987. The electronic circuitry used to
measure the sound level in the ear cavity incorporates a highly selective
filter, which attenuates sound energy at other frequencies than 226 Hz.
This enables accurate measurements to be taken in ordinary environ-
ments without the use of a special quiet room. It enables the ear canal
volume to be measured continuously during the application of an acous-
tic reflex stimulus, which can be at a much higher level than the 85 dB
SPL used for the 226 Hz probe tone.
78 Operation Manual
PRINCIPLES OF MIDDLE-EAR ANALYSIS
Chap. 8 GN Otometrics
PRACTICAL CONSIDERATIONS
8.10 ZODIAC 901 Middle-Ear Analyzer