HEARING AND COCHLEAR IMPLANTS

Transcription

1 HEARING AND COCHLEAR IMPLANTS FRANCIS CREIGHTON, MD NEUROTOLOGY & SKULL BASE SURGERY FELLOW JOHNS HOPKINS SCHOOL OF MEDICINE NOV 9 TH, 2017 THANKS TO: CHARLIE DELLA SANTINA, HEIDI NAKAJIMA AND DOUG MATTOX

2 DISCLOSURES I have no disclosures

3 OUTLINE Hearing Physiology Basics Cochlear Implants Future Directions

4 HEARING PHYSIOLOGY

5 ANATOMY OF THE EAR External Pinna, Ear Canal Middle Tympanic membrane, Ossicles, Middle ear space Inner Cochlea, Vestibular Organs

6 EXTERNAL EAR Sound collector Important in sound localization

7 MIDDLE EAR

8 FISH STORY

9 Sound waves in the ear canal vibrate the ear drum, oscillating the middle ear bones, displacing the oval window at the base of the cochlea This transforms sound pressure waves in air into fluid compression waves in the cochlea. Thus, the middle ear bones act an impedance matcher. Impedance matching is based on: Area Ratio of tympanic membrane vs stapes footplate (20:1) Lever Ratio of malleus vs incus (1.3:1)

10 Fluid compression waves travel through the fluidfilled cochlea. Two cellular membranes Reissner s membrane and the basilar membrane partition the fluidfilled cochlea into three chambers.

11 Thus the basilar membrane is tonotopically organized As pressure waves in the scala vestibuli cross the scala media and into the scala tympani - a traveling wave appears in the basilar membrane, moving from base to apex. Base: Basilar membrane is narrow and stiff Apex: BM is wide and compliant

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14 The stereocilia contact an overlying accessory structure: the tectorial membrane 18

15 Composition of the cochlear fluids Endolymph is high in K + (150 mm); low in Na + (1-2 mm), and very low in Ca + (0.03 mm). Perilymph is low in K + (3-4 mm); high in Na + (150 mm), and Ca + + (0.6-1 mm). Stria vascularis Impermeable barrier Endolymph and perilymph are separated by an impermeable barrier of junctional complexes ( ) between all cells lining the scala media. This barrier also prevents macromolecules and drugs from entering the endolymphatic compartment. Why two different fluid compartments?

16 This large electrical difference drives cations into hair cells through ion channels (when open). This necessary to enable the cell to follow the deflection of the hair bundle at auditory sound frequencies ,000 cycles per second. The stria vascularis actively pumps K + into the endolymph (150 mm), imparting a positive charge of +80 mv. Intracellular potential of inner hair cells = 45 mv Potential electrical difference between endolymph and hair cell cytoplasm = 125 mv.

17 Connections in the CNS 3. Ventral cochlear nucleus projects bilaterally to the superior olivary complex and to the contralateral inferior collicuius. The superior olivary complex is the first site for binaural convergence (for sound localization by comparing signals from the two ears) 2. Most projections are binaurai; i.e. information crossing midline for comparison of auditory information from both ears; however there is also lots of parallel processing of auditory information 1. First relay from spiral ganglion to dorsal and ventral cochlear nuclei in rostral medulla 17

18 CATEGORIES OF HEARING LOSS Conductive Sound not conducted to the inner ear. External and middle ear Sensorineural Sound not converted to nerve impulses Inner ear and auditory nerve

19 COCHLEAR IMPLANT

20 COCHLEAR IMPLANT HISTORY 1800s: Volta 1957: Coil inserted into patient deafened from cholesteatoma Could differentiate between low and high frequencies 1960s: 3 Patients implanted at House Institute (LA, California) Differentiate between high and low frequencies Hear environmental sounds Infection led to removal After failed House implants, there was a large amount of criticism and many groups advocated against ever trying further implantation experiments

21 COCHLEAR IMPLANT HISTORY 1967: Simmons et. al showed a successful Cat model of implantation 1972: House Institute implanted first FDA approved single electrode cochlear implant Patients able to improve speech modulation, ability to hear environmental sounds, some speech discrimination 1978: Australia, Clarke et. al implanted first multichannel electrode Patients able to get some open set speech discrimination 1985 FDA approves first multichannel implant in US in adults 1990 FDA approves for children 2-18yr old 2000 FDA approves for children 12 moand older

22 COCHLEAR IMPLANT COMPANIES In US there are 3 companies with FDA approved devices Cochlear Corp Med-El Advanced Bionics

23 WHO GETS A COCHLEAR IMPLANT? Advanced Bionics 2006

24 AUDIOLOGIC CRITERIA FOR COCHLEAR IMPLANTATION IN ADULTS (USA) Mainly depend on speech discrimination with best-fit conventional hearing aids Worse than 40% of CNC Words in better ear Worse than 60% HINT/Q Sentences in better ear Worse than 50% HINT/Q Sentences in worse ear Typically > 70 db PTA

25 CNC WORDS & PHONEMES Consonant Nucleus Consonant 50 words 3 phonemes / word CNC Word Score = %correct words CNC Phoneme Score = % correct phonemes Examples: Response Word Phoneme neck (N E CK) neck 1 3 geese (G EE S) fleece 0 2 heat (H EA T) mat 0 1

26 HINT SENTENCES Sentences They heard the funny noise He found his brother hiding The dog played with a stick Hearing In Noise Test Each word worth 1 point, scored as %correct For CI patients, used both with added noise (HINT/Noise) and without (HINT/Quiet)

27 CID SENTENCES Central Institute for the Deaf 20 sentences Scored on % key words correct Examples: Where are you going? Do you want an eggfor breakfast? It would be much easier if everyone would help. Context helps understanding - CID scores higher than HINT/Q

28 Auditory Development of Hearing-Impaired Infants Age at Implant: Months Pre Months Postimplant Normal Hearing IT-MAIS (in %) Chronological Age (in months) Robbins et al, 2004

29 Auditory Development of Hearing-Impaired Infants 90 Age at Implant: Months Pre Months Postimplant 100 Normal Hearing IT-MAIS (in %) Implanted Months Chronological Age (in months)

30 Auditory Development of Hearing-Impaired Infants 90 Age at Implant: Months Pre Months Postimplant 100 Normal Hearing 80 IT-MAIS (in %) Implanted m Implanted m 10 0 Implanted m Chronological Age (in months)

31 Statistics in US Deafness and CI Background q ~ 1 million deaf individuals or 0.38% of US population q About 4000 babies are born deaf each year Cochlear Implants as of 2012 q US: 96,000 people q Worldwide: 324,000 people

32 Cochlear Implants Microphone Picks-up sound Speech Processor Converts sound into digital signal NIH Medical Arts Electrode Array Stimulates auditory nerves Transmitter/ Receiver Converts signal into electrical pulse

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34 COCHLEAR IMPLANTATION - TECHNIQUE Advanced Bionics 2006

35 COCHLEAR IMPLANTATION - TECHNIQUE Advanced Bionics 2006

36 COCHLEAR IMPLANTATION - TECHNIQUE Advanced Bionics 2006

37 COCHLEAR IMPLANTATION - TECHNIQUE Advanced Bionics 2006

38 COCHLEAR IMPLANTATION - TECHNIQUE incus Advanced Bionics 2006

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43 FUTURE DIRECTIONS Fully Implantable Cochlear Implants Auditory Brain Stem Implants

44 FULLY IMPLANTABLE COCHLEAR IMPLANTS Short Comings of Current CIs ² All CIs still require an external device Sound ² Fully Implantable CI Removes cosmetic stigma of device Allows CIs to be worn during showering/swimming Possible improvement in sound localization Microphone ² There are multiple components that must be redesigned in order to create a functioning FICI

45 Background on FICI 1. Rechargeable and implantable battery 2. Miniaturized speech processor 3. Implantable Microphone

46 Can We Use the Intracochlear Pressure Wave as an Input for a Microphone?

47 PVDF Sensor Worm

48 Testing Set-Up 5.0 mm PDMS Round Window Metal Coated PVDF Film Purpose of PDMS Encapsulation 1.Insulation from Wet Environment 2.Ease of Insertion into the Cochlea LDV Reflector on Stapes PVDF Microphone

49 Microphone in EAC Speech Microphone in EAC Music PVDF Sensor Speech PVDF Sensor Music

50 AUDITORY BRAIN STEM IMPLANT

51 WHY WE DO IT