21METhe area effect of the TM(55mm2) vs stapes footplate(3.2mm2), result in 17:1 increase sound energyLever action of ossicular chain : handle of malleus 1.3 times longer than incus long processTotal transform ratio is about 22:1(=25 dB)
51SRT (speech reception threshold) SRT is the lowest level in dB at which a patient can repeat spondee word in 50% (spondee คือคำ 2พยางค์ที่เสียงเทียบเท่ากัน เช่น eardrum)SRT should be within 10 dB of PTA
52SDS(speech discrimination score) Percentage of phonetically balanced (PB)words(monosyllable) that patient repeats correctlyTest contained 25 PB words at SRT +35 dBถ้าต่ำมากคิดถึงretrocochlear lesion
57Type A; normal ME pressure Type B; flat fluid in ME , TM perforateType C; negative pressureretract TM / ET dysfunctionType As;restric mobilityotosclerosis ,TM scar ,fixation of malleusType Ad;hyper complianceflaccid TM ,ossicular disarticulation
58Other Battery Test ABR (auditory brainstem response) EcoG (electrocochleography)OAE (Otoacoustic emissions)
65electrocochleography EcoG measures the potential arising within cochlea and auditory nerve
66EcoGFigure Electrocochleography responses recorded from the human ear canal using condensation (C) and rarefaction (R) click stimuli. The major component of the whole-nerve action potential (N1), the summating potential (SP), and the cochlear microphonic (CM) are marked. The CM and the SP can be selectively enhanced by adding (R + C) or subtracting (R − C) the recordings made using rarefaction and condensation click. Ear canal negative deflections potentials are plotted as downward deflections. (From ASHA Workgroup on Auditory Evoked Potentials. The short latency auditory evoked potentials, Rockville, Maryland, 1987, ASHA, p 9, Figure 4 [based on work from Coates, 1981]. Copyright by the American Speech-Language-Hearing Association. Reprinted with permission.)
67NormalFigure Electrocochleogram obtained with a tympanic membrane surface electrode from a normal ear: the summating potential/action potential ratio is normal at 0.13.
68Meniere’sFigure Electrocochleogram obtained from the ear of a patient with M้ni่re’s disease: the summating potential/action potential ratio is elevated (0.81).
69Otoacoustic emissions(OAEs) Confirm SNHL > 40dBAbsent in cochlea lesionPresent in neural lesionObjective test,noninvasive ,efficientLimited by conductive hearing loss
70OAEFigure 152-6A. A, Transient evoked otoacoustic emissions and B, distortion-product otoacoustic emissions from the same normal-hearing ear.
72OAEFigure 152-7B. A, Audiogram, B, transient evoked otoacoustic emissions and C, auditory brain stem responses from a patient with a 7-mm intracanalicular left-sided acoustic neuroma.
73Historical risk factors for hearing loss in newborn Family historyHyperbilirubinemia requiring exchangeCongenital infection (TORCHS)Craniofacial anormaliesBirth weight less than 1500gm
74Historical risk factors for hearing loss Bacterial meningitisApgar scores ≤ 3 at 5 minutesOtotoxic medications > 5 daysProlonged mechanical ventilator (>10days)Stigmata or others findings associated with a syndrome known to include HL