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(Z) Impedance vs. Admittance (Y) Resistance(R) Conductance(G) Mass Reactance(Xm) Mass Susceptance(Bm) Stiffness Reactance(Xs) Stiffness Susceptance(Bs) Z = (R2 + Xt2)1/2 Y = (G2 + Bt2)1/2 Mass and Stiffness Reactance 1.2 1 Reactance 0.8 0.6 0.4 0.2 0 100 500 1000 Frequency 4000 Resonant Freq. Xm Xs Mass and Stiffness Susceptance 1.2 1 Susceptance 0.8 0.6 0.4 0.2 0 100 500 1000 Frequency 4000 Resonant Freq. Bs Bm RESISTANCE AT THE EARDRUM 1000 900 800 700 600 500 400 300 200 100 0 0.01 R (Ohms) 0.1 1 Frequency (kHz) 10 100 Reactance at the Eardrum 1000 500 0 -500 -1000 -1500 -2000 -2500 -3000 -3500 -4000 0.01 X (Ohms) Reactance 0.1 1 10 Frequency (kHz) Tympanogram: A plot of middle ear admittance as a function of ear canal pressure Pressure is swept from +200 to -200 or -400 dPa Should see peak at point where pressures are equal Static Admittance Height of tympanogram peak Adults 3-10 yrs A As Ad 0.30 to 1.70 < 0.30 >1.70 0.25 to 1.05 < 0.2 > 1.05 Gradient = hp/ht Tympanogram types: A: peak between +100 and -200 dPa: normal C: peak beyond -200 dPa: neg pressure B: no peak flat tymp: effusion As: peak but shallow: stiff: otosclerosis Ad: peak off scale: floppy: dysarticulation Tympanogram Types Physical Volume Test Measure of volume of air enclosed under probe Adults 3-10 yrs. Intact TM: 0.9 to 2.0 0.3 to 0.9 TM Perf/Tube: > 2.0 >1.0 Blockage: small volume 6 Admittance (mmhos) 5 4 3 2 1 0 -300 -200 -100 0 100 200 Air Pressure (daPa) Perf Eff Clog The Acoustic Reflex Stapedius contraction as measured change in compliance Reflex arc: peripheral ear, VIIIth n. Cochlear nucleus Superior Olivary Complexes Medial Nuclei of VII VIIth nerves to both middle ears R MN 7 L SOC CN 8th IE ME OE 7th CN MN 7 SOC CN 7th CN 8th IE ME OE Clinical Tests using Acoustic Reflexes: A.R. Threshold: how intense sound must be to elicit the reflex? A.R. Decay: Is the degree of a contraction maintained throughout a 10 second stimulus? AR Threshold: to pure-tones, 0.5, 1, 2, 4 kHz = lowest level at which change in admittance can be read ipsilaterally or contralaterally should be between 65 and 90 dB SL. The Boxes Probe Right (Measured) Ear/ Condition Contralateral Right ear Reflex Stimulated Contralaterally Ipsilateral Right ear Reflex Stimulated Ipsilaterally Left Left ear Reflex Stimulated Contralaterally Left ear Reflex Stimulated Ipsilaterally Vertical Right Contralateral Ipsilateral Left Present Present 7th Nerve Absent Absent Diagonal Right Contralateral Ipsilateral Left Present Absent 8th Nerve Absent Present Horizontal Right Contralateral Ipsilateral Left Absent Present Brainstem Absent Present Inverted L Right Contralateral Ipsilateral Left Absent Present Absent Absent Conductive/8th Impinging on 7th Eustachian Tube Function Test: To see how well the Eustachian tube can resolve the pressure differences introduced with the bridge. Note tympanogram peak pressure introduce pressure into canal Have patient swallow water recheck tympanogram peak pressure

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