Electric Acoustic Stimulationand Hearing Preservation :Atraumatic SurgicalTechniques and OutcomeDr Zeeshan Ahmad Department of ENT,M.S.(ENT,PGY1) NMCH,Patna. 18-10-2012
Cochlear Implant History#Pre-1960’s - beginning studies of electrical stimulation on humans#1960’s - active research of electrical stimulation in human ears#1970’s - first wearable implants designed for long-term stimulation#1980’s - commercial development of the cochlear implant device began
#1985…continued - United States Food & Drug Administration (FDA) granted the first approval for implantation in adults #1990 - FDA granted approval for cochlear implants in children #1999 - Electric Acoustic stimulation first described by C. Von Ilberg & J Kiefer of Frankfurt University. Same year first EAS implant was done.
ELECTRIC STIMULATION: A cochlear implant converts everyday sounds into coded electrical pulses. These pulses stimulate the auditory nerve. The brain interprets these signals as sound. Mid and high frequency sounds are picked up by the microphone of theDUET 2 Audio Processor and are converted into a special code.
ELECTRICSTIMULATION: This code is sent to the coil and is transmitted across the skin. The implant interprets the code and sends electrical pulses to the electrodes in the cochlea. The auditory nerve relays these signals to the brain
ACOUSTIC STIMULATION: Acoustic amplification turns up the volume on the sounds that the cochlea is still able to hear. For EAS, only the low frequencies are amplified. Low frequency sounds are picked up by the microphone and are digitally processed. Sounds are amplified by the loudspeaker located in the ear hook and are relayed via the ear mould to the ear canal.
ACOUSTIC STIMULATION: Sounds reach the undamaged areas of the cochlea responsible for processing low-frequency sound. The auditory nerve sends the signals to the brain.
The importance of highfrequency hearing Our brain relies extensively on high frequency sounds to clearly decipher and understand spoken words, especially at a distance or in noisy places. High frequencies deliver the additional vital details of sound – making the sounds you hear richer, fuller and crisper in every way. Hearing high frequency sounds clearly can enrich your awareness and enhance your experience.
High frequency hearing loss Did you know that many words begin and end with high frequency sounds? That explains why, when you lose high frequency hearing, words seem to merge together and become indistinguishable from one to the next. In addition to human speech, your environment is full of many other high frequency sounds, without which you can’t get a complete sense of a situation.
Let’s see a typical audiogramfor an individual with highfrequency hearing loss.Someone with severe to profound highThe red line shows a persons hearingfrequency hearing loss would strugglethe of toThe closer the line is to the bottom hear atprofile - how much sound they canhear the sounds above the hearing loss.audiogram, the greater red linedifferent frequencies.(speech, birdsong, music, telephone
Indications and Criteria forEAS(a)Audiological criteria ◦ below 1.5 kHz – No or moderate HL ◦ above 1.5 kHz – Severe to profound SNHL
Indications and Criteria forEAS(b)Speech recognition• The patients monosyllable word score should be ≤ 60% at 65dB SPL in the best aided condition.
Indications and Criteria forEAS(c)Additional criteria No progressive hearing loss(10/2, 15/1 in 1yr) No autoimmune inner-ear disease No hearing loss as a result of meningitis, otosclerosis or ossification No malformation or obstruction of the cochlea Maximum air–bone gap 15dB HL No external ear contraindications to
SURGERY :-The EAS surgeries are aimed atpreserving the anatomical structures andpreserving the cochlear function. Stepsare as follows:- Pre-incision measures ◦ Antibiotic prophylaxis ◦ Systemic corticosteroids Posterior tympanotomy ◦ A standard mastoidectomy is done ◦ Anatomy identified
SURGERY :- Endosteum or Round Window exposure at the Cochleostomy site ◦ Currently, RW approach is mostly used Topical steroid application ◦ Dexamethasone 1mg/ml or Triamcinolone 40 mg/ml ◦ Allowed for minimum 30 minutes
SURGERY :- Placing the Implant ◦ Subperiosteal pocket created ◦ Well for Implant created ◦ Bone dust and blood removed ◦ New gloves ◦ Subcutaneous fat autografts taken ◦ Implant inserted into the implant well ◦ Electrode array is coated with Hyaluronic acid and Steroid
SURGERY :- Inserting the Electrode Array ◦ Electrode tip is placed in the opening(RW or Cochleostomy) and introduced into the Scala Tympani supero-posterior to antero-inferior ◦ Slowly to prevent intracochlear pressure build-up ◦ Inserion is stopped when predefined length is reached or resistance is felt ◦ tip touching the ST Modiolar wall avoided ◦ Opening closed with previously taken antibiotic soaked Fat Autografts.
SURGERY :- Securing the Electrode and Closing the Retroauricular Incision in Three Layers ◦ Care is taken that Ossicular Chain is not touching with any component
Electrode design for HP For hearing preservation the Electrodes are designed to create least trauma to intracochlear structures ◦ Thinner caliber 0.25mm at tip and 0.8mm at entry site ◦ More flexible Tip regions ◦ Tailoring the insertion depth
Outcome of EAS HEARING PRESERVATION ◦ The success of EAS Implant depends upon the RLFH(Residual Low Frequency Hearing). ◦ The cochlear hybrid implant using 6mm and 10mm elctrodes resulted in long term hearing preservation in 75% of subjects. ◦ Studies using Med-El elctrodes showed a successful HP in 12/18 subjects with complete hearing loss in 3/18 subjects.
Outcome of EAS SPEECH PERCEPTION with EAS ◦ EAS significantly improves speech perception in quiet and in noise compared to acoustic hearing only. ◦ In a study by Gstoettner et al EAS treatment yielded an improvement in speech perception in quiet from 24% preoperatively to 71% after 12 months.
Outcome of EAS Music appreciation and Subjective benefit with EAS ◦ EAS users perform better on melody and instrument recognition than CI users. ◦ Subjective benefit of EAS was assessed with APHAB(Abbreviated Profile of Hearing Aid Benefit). ◦ Observed with EAS fitting and improved gradually with experience.