Maico MI 24 Operating Instructions Manual

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Maico MI 24 Operating Instructions Manual Manual pdf 23 page image

Operating Instructions MI 24, MI 24h216 How to measure the Stapedius reflex6.1 The basics of the Stapedius reflex measurementWhile tympanometry measures thechange of the compliance caused bychanging pressure in the outerauditory canal, the Stapedius reflexmeasurement works with a changingcompliance caused by contraction ofthe Stapedius muscle in the middleear. The contraction - called Stapediusreflex - causes a decrease incompliance and is caused by loudacoustic stimuli. Regardless whetherthe acoustic stimulus is active on theleft or on the right or on both sidesthe Stapedius reflex is alwaysbinaural, i.e. it occurs in both ears atthe same time. The Stapedius reflex is caused in ears of adults with normal hearingwith sound pressure levels between 70 and 105 dB.In the probe ear, the reflex method continuously measures the compliance with thepressure which was caused before the highest compliance measurement.Simultaneously the stimulus ear is irritated by the sound which causes the contractionof the Stapedius muscle.The ipsilateral reflex measurement uses the same ear for theprobe and the stimulus. The contra-lateral measurementuses different ears for the probe and the stimulus. Theacoustic stimulus is applied to the ear opposite the probeear.If the applied stimulus causes a reflex, the impedancemeasuring instrument registers a decrease in compliancein the “probe ear” which indicates a Stapedius reflex atthe actual test frequency and the test level. The test levelwhich was set when the reflex occurred is called reflexthreshold and is shown in dBHL (dB hearing level).6.2 Preparing the patientIn addition to the general introduction described inchapter 4.2, explain to the patient that loud test sounds will occur during the reflexhearingnerveear canalmiddleearbonesear drummiddle eareustachian tubecochleamusculusstapediusFigure 16The middle earFigure 18Contralateral testFigure 17Ipsilateral test