Page 997 - TNFlipTest

Toronto Notes 2019 Hearing Otolaryngology OT11 Speech Audiometry
Speech Reception Threshold
• lowesthearinglevelatwhichpatientisabletorepeat50%oftwosyllablewordswhichhaveequal emphasis on each syllable (spondee words)
• SRTandbestpuretonethresholdinthe500to2000Hzrange(frequencyrangeofhumanspeech) usually agree within 5 dB; if not, suspect a retrocochlear lesion or functional hearing loss
• usedtoassessthereliabilityofthepuretoneaudiometry
Speech Discrimination Test
• percentageofwordsthepatientcorrectlyrepeatsfromalistof50monosyllabicwords
• testedat40dBabovethepatient’sSRT,thereforedegreeofhearinglossistakenintoaccount
• patientswithnormalhearingorCHLscore>90%
• rollovereffect:adecreaseindiscriminationassoundintensityincreases;typicalofaretrocochlearlesion
(e.g. acoustic neuroma)
• investigatefurtherifscoresdiffermorethan20%betweenears,asasymmetrymayindicatea
retrocochlear lesion
• bestpredictorofhearingaidresponse:apoordiscriminationscoreindicatessignificantneural
degeneration and hearing aids may not be the best option for the patient
Impedance Audiometry
Tympanogram
• theEustachiantubeequalizesthepressurebetweentheexternalandmiddleear
• tympanogramsgraphthecomplianceofthemiddleearsystemagainstapressuregradientrangingfrom
to –400 to +200 mmH2O
• tympanogrampeakoccursatthepointofmaximumcompliance:wherethepressureintheexternal
canal is equivalent to the pressure in the middle ear
• normalrange:–100to+50mmH2O
High
Type A Type B Type C
Low– O +– O +– O +
Air Pressure
• Normal pressure peak at 0
• Note: with otosclerosis, peak is still at
0 mmH2O but has a lower amplitude
• Note: with ossicular chain discontinuity,
peak is still at 0 mmH2O but has a higher amplitude
Figure 17. Tympanograms
Static Compliance
Air Pressure
• No pressure peak
• Poor TM mobility indicative of
middle ear effusion (OME) or perforated TM
Air Pressure
• Negative pressure peak
• Indicative of Eustachian tube dysfunction
or early stage otitis media without effusion
• volumemeasurementreflectingoverallstiffnessofthemiddleearsystem
• normalrange:0.3-1.6cc
• negativemiddleearpressureandabnormalcomplianceindicatemiddleearpathology
• inatypeBcurve,earcanalvolumesof>2ccinchildrenand>2.5ccinadultsindicateTMperforation
or presence of a patent ventilation tube
Acoustic Stapedial Reflexes
• stapediusmusclecontractsinresponsetoloudsound
• acousticreflexthreshold=70-100dBgreaterthanhearingthreshold;ifhearingthreshold>85dB,reflex
likely absent
■ stimulating either ear causes bilateral and symmetrical reflexes
■ for reflex to be present, CN VII must be intact with no CHL in monitored ear ■ if reflex is absent without CHL or severe SNHL, suspect CN VII lesion
• acousticreflexdecaytest=abilityofstapediusmuscletosustaincontractionfor10sat10dB ■ normally, little reflex decay occurs at 500 and 1000 Hz
• withcochlearhearingloss,acousticreflexthresholdsare25-60dB
• withretrocochlearhearingloss(acousticneuroma),absentacousticreflexesormarkedreflexdecay
(>50%) within 5 s
Compliance