聽能障礙與輔具的應用—

從助聽器到電子耳

Chih-Hung Wang, MD, PhDDepartment of Otolaryngology-Head and Neck SurgeryTri-Service General Hospital, National Defense Medical CenterTaipei, TAIWAN, ROC

王智弘 醫師三軍總醫院 耳鼻喉頭頸外科部

Auditory System = Energy Transformation System

acoustic energy---mechanical energy---hydraulic energy---bio-electric energy

→ Outer ear ←→ Middle ear ←→ Inner ear ←

How Do We Hear?

Sound waves

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Anatomy of the Outer EarThe Outer Ear:

Auricle (pinna):is composed of a sheet of cartilage, and this is

continous with the cartilage which forms the framework of the outer 1/3 of the EAC.

Function:☆ It protects the ear canal and eardrum by repelling any

objects that strike it

☆ collect and capture the acoustic energy and direct it to the tympanic membrane

☆ the surface of the auricle can modify thespectral composition of the incomingsound

☆ localize the source of sound, using intensity and phase differences of signal at two ears

☆ beautiful to look at

Anatomy of the Ext. Ear CanalExternal auditory canal:

A narrow, slightly tortuous passage (from concha to the tympanic membrane, approximately 2.5~3 cm in the adult).

The membrane is set obliquely in the depth of the canal, in such a way that the front(anterior) wall is longer than the back (posterior) wall. (inferior wall of EAC is longerthan superior one)

.

sup.

inf.pos. ant.

ant.

sup inf.

pos

5 mm

The ear canal reinforces soundSound is directed towards the eardrum in two ways:

► Intensity of sound at eardrum is increased by 20 dB because of resonances from the externalear (concha, meatus, canal and eardrum)

► This increase in sound intensity is for high frequency sounds. In adults the peak freqeunciesare found around 2500 Hz. For children the peak intensities are at higher frequencies

Resonance

波長: 4 x L (管長) 基礎共振頻率 first harmonic4 x L x 1/3 第三共振頻率 third harmonic4 x L x 1/5 第五共振頻率 third harmonic

耳道的共振效應

In the adult, the outer cartilaginous portion of the canal runs slightly upwards and backwards, the inner bony portion running slightly downwards and forwards.

The skin covering the cartilaginous portion of the canal contains short hairs, ceruminous and sebaceous glands.

Two constrictions in the canal: one at the junction of the cartilaginous and bony portions; the other, the isthmus, 5 mm from the tympanic membrane, in the bony portion.

Function: ☆Cleaning: cilia☆Protection: cerumen, moisture☆Resonance & sound amplification:

Natural frequency in EAC: 343m/(4x0.03) = 2834 HZ 2500~4000 Hz, 2x~4x intensity

☆Sound localization:

cartilage bone

Outer 1/3 Inner 2/3

Hair Sebaceous glandCeruminous glandSweat gland

Yes NO Yes NOYes NOYes NO

Function of Ext. Ear Canal

The Eardrum & The Ossicles

☆ The middle ear acts as an impedence-matching device.

☆ Amplify sound pressure:@ Lever action: d1p1=d2p2 malleal arm: incudal arm = 1.3: 1

@ Areal ratio of the tympanic membrane to the oval window a1p1=a2p2

tympanic memb.: oval window = 14: 1→ x 18.2 → 25.25 db SPL

Exp.: Resonance in EAC: 2.5K~4k Hz: 2x ~ 4x

The Middle ear as an Impedence Transformer

The Middle Ear Cleft:The Middle Ear Cleft:

The tympanic cavity is an airThe tympanic cavity is an air--containing cavity in the containing cavity in the petrouspetrous part of the part of the

temporal bone and is lined with mucous membrane.temporal bone and is lined with mucous membrane.It contains the auditory It contains the auditory ossiclesossicles, and communicates in , and communicates in

front through the Efront through the E--tube with the tube with the nasopharynxnasopharynx and behind with the mastoid and behind with the mastoid

antrumantrum. .

Roof:Roof:A thin plate of bone, the A thin plate of bone, the tegmentegmen tympani, which is part of tympani, which is part of

the the petrouspetroustemporal bonetemporal bone

It It sepratesseprates the tympanic cavity from the the tympanic cavity from the meningesmeninges and and temporal lobe of thetemporal lobe of the

brain in the middle cranial brain in the middle cranial fossafossa..

Floor:Floor:A thin plate of bone, which may be deficient and partly A thin plate of bone, which may be deficient and partly

replaced by fibrous tissue. replaced by fibrous tissue. It separates the tympanic cavity from the superior bulb of It separates the tympanic cavity from the superior bulb of

the internal jugular vein.the internal jugular vein.

Schematic diagram of the middle ear

E-tube : 17-18 mm long at birth; 35 mm in adult

Structure of Inner Ear

Anatomical two parts:

1). Bony labyrinthBony labyrinth: comprising a series of cavities within the bone

2). Membranous labyrinth: comprising a series of membranous sacs and ducts contained within the bony labyrinth.

Bony Labyrinth:Bony Labyrinth:

Vestibule:Vestibule:The central part of the bony labyrinth, lies posterior to The central part of the bony labyrinth, lies posterior to

the cochlea and ant. to the semicircular canals.the cochlea and ant. to the semicircular canals.Within the vestibule are the Within the vestibule are the sacculesaccule and and utricleutricle of the of the

membranous labyrinth.membranous labyrinth.

Semicircular canals:Semicircular canals:Within the canals are the semicircular ducts. Each Within the canals are the semicircular ducts. Each canal has a swelling at one end called canal has a swelling at one end called ampullaampulla..

Cochlea:Cochlea:Two and a half turns in the human, these Two and a half turns in the human, these coils(hollycoils(holly

bony tube) turning around a central bony tube) turning around a central ‘‘pillarpillar’’, the , the modiolusmodiolus

Anatomy of the Labyrinth

Membranous Labyrinth:

Utricle: indirectly connected to the saccule by utricular duct.

Saccule: globular in shape, saccular duct

Semicircular ducts:

Cochlear duct: triangular in cross section, connected to the saccule by the ductusreunions.

PerilymphPerilymph::

•• Primarily formed by filtration from blood vessels in the inner ePrimarily formed by filtration from blood vessels in the inner earar•• Communicates with the cerebrospinal fluid (CSF) through the cochCommunicates with the cerebrospinal fluid (CSF) through the cochlear lear

aqueduct, a narrow channel 3aqueduct, a narrow channel 3-- 4 mm long, with its inner ear opening at 4 mm long, with its inner ear opening at the base of the the base of the scalascala tympani.tympani.

•• Resembles the extracellular fluids:Resembles the extracellular fluids:( high Na+ :140 ( high Na+ :140 mEqmEq/liter; low K+:10 /liter; low K+:10 mEqmEq/liter; Protein: 200/liter; Protein: 200--400 mg%, 400 mg%, CSF: Na+ :152 CSF: Na+ :152 mEqmEq/liter; K+:4 /liter; K+:4 mEqmEq/liter; Protein: 20/liter; Protein: 20--50 mg% ) 50 mg% )

EndolymphEndolymph::

•• Produced by the Produced by the secretorysecretory cells in the cells in the striastria vascularisvascularis of the cochlea and the of the cochlea and the dark cells of the vestibular labyrinth.dark cells of the vestibular labyrinth.

•• ReRe--absorption of absorption of endolymphendolymph take place in the take place in the endolymphaticendolymphatic sac.sac.•• ResenbleResenble the intracellular fluids: the intracellular fluids:

( low Na+ :5 ( low Na+ :5 mEqmEq/liter; high K+:144 /liter; high K+:144 mEqmEq/liter; Protein: 126 mg%) /liter; Protein: 126 mg%)

Chemical Composition of the Cochlear fluids

Blood supply of the inner earBasilar artery—ant. inf. cerebellar artery—labyrinthine artery

↗ common cochlear a. --↗main cochlear a ----------------------------- ↓↘vestibulo-cochlear a ↗cochlear ramus ↑

→post. vestibular a.↓

↘ ant. vestibular a. ----------------------------------------------------------↑

Blood supply of the inner earBasilar artery—ant. inf. cerebellar artery—labyrinthine artery

↗ common cochlear a. --↗main cochlear a ----------------------------- ↓↘vestibulo-cochlear a ↗cochlear ramus ↑

→post. vestibular a.↓

↘ ant. vestibular a. ----------------------------------------------------------↑

Shearing is a particular form of bending

Inner Hair Cell Outer Hair Cell

InnervationInnervation and central connectionsand central connectionsTwo types: Two types: Afferent Afferent fibresfibres: carrying sensory : carrying sensory

information to the brain.information to the brain.Efferent Efferent fibresfibres: Pass from the brain: Pass from the brain--stem to stem to the cochlea, perhaps 1000 in numberthe cochlea, perhaps 1000 in number

As many as 95% of all afferent As many as 95% of all afferent fibresfibres make make contact with the inner haircontact with the inner hair--cells, 5% with cells, 5% with outer hair cells, and each inner hairouter hair cells, and each inner hair--cell has cell has terminals from about 10~20 afferent terminals from about 10~20 afferent fibresfibres..

The vast majority of the The vast majority of the fibresfibres of the cochlear of the cochlear nerve (about 30,000 of them) are afferent nerve (about 30,000 of them) are afferent and their cell bodies are in the and their cell bodies are in the spiral spiral ganglionganglion in the in the modiolusmodiolus. .

The The modioulsmodiouls contains many small canal, the contains many small canal, the most central of them carrying most central of them carrying fibresfibres from the from the apex of the cochlea, while the outermost apex of the cochlea, while the outermost canal carry canal carry fibresfibres from the basal part of the from the basal part of the cochlea. cochlea.

Travelling waveTravelling wave::

Travelling waveTravelling wave::

Response to a 150 Hz tone

Response to a 1.5 kHz tone

Response to a 15 kHz tone

Response to a pulse sequence

Low frequency traveling wave in 3-D

High frequency traveling wave in 3-D

Tuning CurveTuning CurveThe frequency sensitivity of a hair cell can be displayed as a tuning curve

PHYSICAL PROPERTIES OF SOUND

Chih-Hung Wang, MD, PhDTri-Service General Hospital, National Defense Medical Center

王智弘

三軍總醫院耳鼻喉部 國防醫學院耳鼻喉學系

Nature of sound

• The sensation of sound is determined by the interaction of sound waves with the hearing system.

• The normal human ear has an auditory sensitivity which ranges from 20-20,000 Hz.

Humans: 20- 20,000 Hz Whales: 20- 100,000 Hz Bats: 1500- 100,000 Hz Frogs: 600- 3000 Hz Fish: 20- 3000 Hz Crickets: 500- 5000 Hz

Production of sound

► Sound is a form of energy

► The vibration of an elastic body (tuning fork, piano string, vocal cords) gives rise to the propagation of pressure waves [ a sequence of increases (compressions) and decreases (rarefactions) in pressure].

►When the vibrating object is a sound source, these pressure waves are known as sound waves.

►Sound wave: Energy transmission by media Longitudinal wave = pressure wave

縱波: 波傳遞時，介質振動的方向與波行進方向平行

橫波:波傳遞時，介質振動的方向與傳遞方向互相垂直

At rest Compression Rarefaction

Characters of sound

1). Frequency: one double vibration is called a cycle. The frequency of sound is determined by the number of complete cycles per second and is expressed in hertz (Hz).

► Pitch: Psychoacoustics terms► Octave: at twice the frequency: ► Fundamental frequency: the basic underlying sine wave► Harmonics: the higher frequencies based on multiples of a

fundamental frequency.

•The lowest component of the waveform is known as the FUNDAMENTAL

•The second harmonic is twice the fundamental frequency, the third harmonic is three times the fundamental frequency, and so forth.

2). Period: the time for one double vibration= second/ per cycle

3). Wave length: the distance for one cycle = m/sec

4). Phase: the phase of a sine wave corresponds to itsdistance form zero at the moment in which thevibration begins (onset) and is usually defined interms of time (period) or angular measure.

If you strike a tuning fork and rotate it next to your ear, you will note that the sound alternates between loud and soft as you rotate through the angles wherethe interference is constructive and destructive.

interference

The arrow indicates one cycle of the sound. The time it takes to complete a cycle is the period. Frequency is the inverse of this, the number of cycles in a second. The distance sound travels during one period is the wavelength.

P = 1/f λ = S/fThe upside down y is λ (lambda): wavelength

P = period, f = frequencyS = the speed of sound

20℃、海平面上，聲音的速率: 343 m/s 溫度的變化:『v = (331 + 0.6T) m/s 』

在水中，20℃時聲音的速率: 1,482 m/s

鋼鐵材質中則大約5,960 m/s。

Sine wave

• The waveform produced by simple harmonic motion is the SINE WAVE

• the simplest type of sound wave is one which has only one frequency and is constant in amplitude

Beats

When two waves with the same amplitude but different frequency are added together a phenomenon called "beating"

occurs.

Refraction 折射

▶In the first, the beam crosses the boundry between warm and cool at a right angle. All thathappens is the wavelength changes. It gets shorter, since the speed of sound is lower inthe cool air.

▶ Look at the beam that strikes the boundry at an angle.The wavefront that has just crossedactually has two wavelengths; long for the part still in the warm air, short for the part inthe cold.This makes it skewed. All later waves just propagate off this crooked wavefront,in a new direction.

Resonance

5). Amplitude: The difference between normal (atmospheric) pressure and the pressure in the presence of a sound wave. It varieswith time between positive and negative values and is expressed inpascals (newtons/m2).The lower limit to the hearing threshold at 1k Hz:

2 x 10-5 newton/m2= 20 µPa

► The measurement of amplitude of the sound wave:Pressure: Newton/m2 or dyne/cm2

Intensity: power : watt/m2 or watt/cm2

Exp: 1k Hz: (power) 1 x10-16 watt/cm2 =(pressure) 0.0002 dyne/cm2

or 2 x 10-4 dyne/cm2

Intensity being proportional to the square of the amplitude of sound pressure (I ∞ P2)

Pascal

Amplitude and waveform

•Amplitude of sounds as loudness.

•The shape of a sound is its waveform

•The shape of the curve is very important in establishing thetimbre of the sound..

20

40

60

80

100

dB

1 4010kHz

Normal Loss of OHC Loss of IHC & OHC

Tuninig curve of single nerve fiber

sound_zh_TW.jar

Measurement of Sound

MKS CGS

Length m cm

Mass Kg g

Time second second

sound wavepressure

intensity

Newton/m2 dyne/cm2

watt/m2 watt/cm2

F=ma Newton: 1N = 105 dyne

0 bel =1 x 10-12 watt/m2 (I0: a tone which is only just audible= a threshold sound) 1 bel =10 x 10-12 watt/m2

3 bel =10 x 10 x 10 x 10-12 watt/m2 (a whisper is 1000 times more powerful thana threshold sound = raised to the power of three)

Bel systemBel system=Intensity (power) system, named

after the scientist

Alexander Graham Bell

BelIL = log I/I0

Decibel system

Decibel system: for clinical purposes, the bel has been broken down into ten smaller units known as decibels (dB)

dBeL = 10 log I/I0 I: the intensity to be measured I0: threshold sound = 1 x 10-12 watt/m2 = 1 x 10-16 watt/cm2

Exp: when noise is 1 x 10-14 watt/cm2

dBeL= 10 log 1 x 10-14 watt/cm2 / 1 x 10-16 watt/cm2 =20 dBSimilarly, a whisper (3 bels) = 30 dB = 103 x threshold sound

A conversational voice (6 bels) = 60 dB = 106 x threshold sound A loud shout (9 bels) = 90 dB = 109 x threshold sound

Loudness: Psychoacoustics terms

Intensity being proportional to the square of the amplitude of sound pressure

(I (power)∞ p2 )

dBSPL = 20 log P/P0P=power

Exp.: A: 0.002 dyne/cm2: dBSPL=20 log 0.002/0.0002= 20B: 0.02 dyne/cm2: = 40C: 0.004 dyne/cm2: = 26

BelIL = dBelIL/10 = dBSPL/20

Auditory threshold

• 1). dB SPL (sound pressure level): a value in decibels which express the pressure of sound in relation to a reference pressure which for conventional purposes is the minimum pressure required for the perception of a 1000-4000 Hz sine wave in the average adult.

• 2). dB HL (hearing level): the minimum intensity at which a person can hear at a specific frequency (e.g. 1000 Hz ) in relation to a basic value (0 dB HL) which represents minimum hearing in normal hearing subjects.

•3). dB SL (sensation level): the level of hearing in dB HL above threshold for the subject being tested.

基本上我們使用音量來表示聲音的強弱，但是前述兩種計算音量的方法，只是用數學的公式來逼近人耳的感覺，和人耳的感覺有時候會有相當大的落差，為了區分，我們使用「主觀音量」來表示人耳所聽到的音量大小。例如，人耳對於同樣振福但不同頻率的聲音，所產生的主觀音量就會非常不一樣。若把以人耳為測試主體的「等主觀音量曲線」（Curves of Equal Loudness）畫出來，就可

以得到下面這一張圖：