1. CSD 2230 HUMAN COMMUNICATION DISORDERS
Topic 5
Hearing Disorders and Hearing Loss
Introduction to Sound
Types of Hearing Loss

2. Sound System Source Medium Receiver Any vibrating object
Any gas, liquid or solid
Receiver
anything designed to detect the vibrations within the medium originating from the source
In order to talk about the nature and propagation of sounds, we need to define the sound system.
The sound system defines the three components necessary to establishing “sound”
Source------Medium Receiver
The source is any object that vibrates. Give some examples
Medium can be a gas, a liquid or a solid. Anything with molecules
Under this system, the vibrations of a source are passed to the molecules of the medium.
The Receiver is anything designed to detect the vibrations within the medium originating from the source.

3. A Common Sound System
Illustration of the distribution of molecules surrounding a source in an instant in time
A common example of a source and medium of a common sound system is a tuning fork vibrating in air.
If the fork has been vibrating for a while, and we could take an instantaneous picture of the air molecules near the tines, the distribution would look like fig 2.1
Define Compression and Rarefaction

4. Condensation and Rarefaction
Bands of condensation and rarefaction emanating from a sound source
Fig 3.1 is another illustration of this same thing--get them to conceptualize the graph of pressure change over time.

5. Propagation of a Disturbance Through a Medium
Fig 3.8 shows how the disturbance propagates thru the medium..
This is how sound can travel such long distances.
Notice that as time goes on, molecules farther from the source become affected by the disturbance.

6. Important Physical Characteristics of Sound
Frequency
Rate of pressure change as a function of time
Measured as cycles/sec or Hertz
The primary determiner of pitch
Intensity
Magnitude of the pressure change
Measured as the decibel (dB)
The primary determiner of loudness
Two important characteristics related to sound waves include:
frequency--the rate of pressure change over time.
Measured in cycles/sec or Hz.
Frequency is a primary determiner of pitch
Intensity--the magnitude of the pressure change.
Measured in the decibel (dB).
Intensity is a primary determiner of loudness.

7. Frequency and Intensity
Sounds a and c share the same frequency and sounds b and c share the same intensity
Use fig 2-2B

8. Loudness and Intensity
Table 3.7 has some common sounds in dB
Here are some common sounds and their decibel equivalents

9. The Hearing System
The hearing system
Fig 2.3 shows a basic schematic diagram of the entire system
Show them the major divisions of the ear (outer, middle, inner, and central).
We’ll examine each one, and then put things all together.
Basic schematic diagram of the entire auditory system

10. Putting It All Together….
Fig 6-33
Explain
Introduce concepts of hearing by AC and hearing by BC- the different pathways of sound.

11. Types of Hearing Impairment
A loss of sensitivity
Auditory nervous system pathology
Hearing impairments are of two major types:
• A loss of sensitivity--Characterized by a reduction in the sensitivity of the auditory system so that sounds need to be louder to be perceived.
• Auditory nervous system pathology--May or may not include a change in sensitivity and results in reduced ability to hear suprathreshold sounds (ie. Speech) properly.

12. Important Terms Time of onset Congenital: present at birth
Acquired: obtained after birth
Adventitious: acquired after birth
Other ways to describe a hearing loss:
Time of onset:
- congenital--present at birth
- acquired--obtained after birth
- adventitious---acquired after birth

13. Important Terms Time Course Acute: sudden onset/short duration
Chronic: long duration
Sudden: rapid onset
Gradual: changes slowly over time
Time course:
- acute---of sudden onset and short duration
- chronic---of long duration
- sudden--rapid onset
- gradual--changing slowly over time
- temporary---limited duration
- permanent---irreversible
- progressive--advancing
- fluctuating---changes in degree over time

14. Important Terms Time Course Temporary: limited duration
Permanent: irreversible
Progressive: advancing
Fluctuating: changes in degree over time
Time course:
- acute---of sudden onset and short duration
- chronic---of long duration
- sudden--rapid onset
- gradual--changing slowly over time
- temporary---limited duration
- permanent---irreversible
- progressive--advancing
- fluctuating---changes in degree over time

15. Number of Ears Involved
Important Terms
Number of Ears Involved
Unilateral: Just one
Bilateral: Both
Number of ears involved:
- unilateral
- bilateral

16. Hearing Sensitivity Loss
“The ear is not as sensitive as normal in detecting sound”
Types:
Conductive
Sensorineural
Mixed

17. Conductive Hearing Loss
“Caused by an abnormal reduction or attenuation of sound as it travels from the outer ear to the cochlea”
Conductive HL: caused by an abnormal reduction or attenuation of sound as it travels from the outer ear to the cochlea.

18. Sensorineural Hearing Loss
“Caused by a failure in the cochlea to transduce the sound from the middle ear to neural impulses in the VIII Nerve.”

19. Sensorineural Hearing Loss
Implications include:
A reduction in the sensitivity of the receptor cells in the cochlea
A reduction in the frequency resolving power of the cochlea
A reduction in the dynamic range of the system
Sensorineural hearing loss: caused by a failure in the cochlea to transduce the sound from the middle ear (mechanical movement) to neural impulses in the VIII N. This results in a number of changes in cochlear processing including:
- a reduction in the sensitivity of the receptor cells in the cochlea
- a reduction in the frequency resolving power of the cochlea
- a reduction in the dynamic range of the system

20. Mixed Hearing Loss
“A loss with both a conductive and sensorineural component.”
• Mixed hearing loss: A loss with both a conductive and SN component.

21. Types of Hearing Impairment
A loss of sensitivity
Auditory nervous system pathology

22. Auditory Nervous System Impairment
Causes:
Disease
Disordered auditory nervous system development
AUDITORY NERVOUS SYSTEM IMPAIRMENT:
Caused by disease or disordered auditory nervous system development in children.

23. Auditory Nervous System Impairment
Kinds:
Retrocochlear disorders
Central auditory processing disorders
We tend to divide these impairments into two groups, depending on the nature of the underlying disorder.
- retrocochlear disorder--when an impairment is caused by an active, measurable disease process (tumor) or from damage due to trauma or stroke. These are structural lesions of the nervous system.
- CAPD--when an impairment is due to developmental disorder or delay or from diffuse changes (aging). These are functional lesions of the nervous system.

24. Auditory Nervous System Impairment
Auditory Characteristics:
Reduced ability to understand speech in a noise background
Problems understanding speech with reduced redundancy
Problems with localization and lateralization
Problems processing normal or altered temporal cues

25. Auditory Pathologies Outer and middle ear disorders Cochlear disorders
Conductive pathologies
Cochlear disorders
Sensorineural pathologies
Central auditory disorders
Central auditory pathologies
The causes of HL are varied. The auditory system is very complex. A lot of things can go wrong. It’s also a very sensitive system. We could spend a whole semester on just the causes of HL. We’ll just review the big ones and the more common pathologies.
We’ll make our way from the most peripheral lesions to the most central. So we will start with

26. Outer and Middle Ear Disorders
Structural defects due to embryologic malformations
Structural changes secondary to infection or trauma
OUTER AND MIDDLE EAR DISORDERS
These pathologies are commonly of two types
- structural defects due to embryologic malformations
- structural changes secondary to infection or trauma

27. Outer Ear Disorders Microtia and atresia
microtia and atresia--these are the most common congenital malformations of the auricle (pinna) and the external canal.

28. “an abnormal smallness of the auricle”
Microtia
“an abnormal smallness of the auricle”
Microtia is an abnormal smallness of the auricle. In and of itself, it doesn’t affect hearing but may signal additional malformations of the middle/inner ear.
Atresia is the absence of an opening of the external canal. This is a congenital disorder and may involve one or both ears. Sometimes the bony canal is involved, sometimes not. Although atresia can present in isolation, it is more common to occur with other auricular malformations or malformations of the middle/inner ear.
Audiogram associated with atresia--Fig 5-3
Flat, moderate, conductive HL

29. Atresia “the absence of an opening of the external canal”
Microtia is an abnormal smallness of the auricle. In and of itself, it doesn’t affect hearing but may signal additional malformations of the middle/inner ear.
Most causes for microtia and atresia are genetic syndromes or anomalies that are inherited.
Atresia is the absence of an opening of the external canal. This is a congenital disorder and may involve one or both ears. Sometimes the bony canal is involved, sometimes not. Although atresia can present in isolation, it is more common to occur with other auricular malformations or malformations of the middle/inner ear.
Audiogram associated with atresia--Fig 5-3
Flat, moderate, conductive HL

30. Outer Ear Disorders Microtia and atresia Impacted cerumen
Perforation of the tympanic membrane
Impacted Cerumen--very common cause of temporary conductive HL. Very treatable and preventable. HL that results is flat, conductive, and of varying degree.
• Perforation of the tympanic membrane--These usually occur either by trauma or secondary to OM. Give some examples of both. Perforations may or may not cause HL. If it does, the HL will be mild, flat and conductive--Fig Treatment includes spontaneous healing or tympanoplasty.

31. Outer Ear Disorders Microtia and atresia Impacted cerumen
Perforation of the tympanic membrane
Other
Other disorders of the outer ear---there are others, but not common and usually don’t affect hearing unless the auditory meatus is blocked--maybe mention collapsed canals at this point.

32. Middle Ear Disorders Otitis Media
Most common cause of transient conductive hearing loss in children
Inflamation of the middle ear
Caused by eustachian tube failure
Otitis Media--the most common cause of transient conductive HL in kids. OM is an inflammation of the middle ear. Caused by eustachian tube malfunction. When it is accompanied by middle ear effusion (fluid) it often causes a conductive HL.--Fig 6-6 shows some examples. Give a brief synopsis of the sequence.

33. Ways to Classify Otitis Media
With or without effusion
Fluid type
Serous
Suppurative
Mucoid
Ways to classify OM:
- OM w/out effusion--inflammation with no fluid
- fluid types: Serous (thin watery and sterile), suppurative (purulent--pusy, thick, infected), mucoid (thick and mucuslike).

34. Ways to Classify Otitis Media
With or without effusion
Fluid type
Duration
Acute
Chronic
Subacute
Persistent
Recurrent
- duration: acute (one bout lasting less than 21 days), chronic (persists beyond 8 weeks), subacute (duration between 3-8 weeks), persistent (fails to resolve by 6 weeks), recurrent (3 or more episodes within a 6 month period)

35. Otitis Media Facts
76-95% of all kids will have one episode of OM by age 6
Prevalence is highest during the first two years of life
50% of all kids with one episode before their first birthday will have 6 or more bouts within two years
Most episodes occur in winter and spring
Risk factors
Cleft palate
Down syndrome
Native Americans
Urban poor
Day care
Secondhand smoke
76-95% of all kids will have one episode of OM by age 6. Prevalence is highest during the first 2 years, then declines after that. 50% of all kids with one episode before their first birthday will have 6 or more bouts within 2 years. Most episodes occur in winter and spring.
Some populations are more prone to OM--kids with cleft palate or other craniofacial anomalies, Down syndrome, Native Americans, urban poor, day care kids, kids exposed to secondhand smoke.
Make the link to CAPDs. Describe treatments briefly.

36. Middle Ear Disorders
Otitis media
Otosclerosis

37. Otosclerosis
“a bone disorder that affects the stapes and the bony labyrinth of the inner ear. The disease process is characterized by resorption of bone and new spongy formation around the stapes and oval window”
Otosclerosis--a bone disorder that affects the stapes and the bony labyrinth of the inner ear. The disease process is characterized by resorption of bone and new spongy formation around the stapes and oval window.

38. Otosclerosis Facts: Hereditary
Women are more likely to develop the disorder
Usually bilateral
progressive
Very strong hereditary component. Women are more prone to the disorder. Usually a bilateral condition. Discuss treatment briefly--surgical and amplification.

39. Middle Ear Disorders
Otitis media
Otosclerosis
Cholesteatoma

40. Cholesteatoma
“an epithelial pocket that forms on the tympanic membrane. Once the pocket forms, the normal shedding of epithelium results in growth of the tumor”
Cholesteatoma--usually a secondary condition to OM. A cholesteatoma is an epithelial pocket that forms on the tympanic membrane. Once the pocket forms, the normal shedding of epithelium results in growth of the cholesteatoma, or tumor, which is capable of reabsorbing adjacent bone--which could be the ossicles or even the bony labyrinth.
Conductive HL that arise can vary. Usually the loss is conductive because the ossicles are affected.
Treatment---surgery w/or w/out ossicular replacement.

41. Middle Ear Disorders Otitis media Otosclerosis Cholesteatoma Other
Physical trauma
Barotrauma
Middle ear tumors
Glomus tumor
Other middle ear disorders
- physical trauma--results in partial or total disarticulation of the ossicular chain Fig 4-8 gives example audiogram
- barotrauma--trauma related to a sudden, marked change in atmospheric pressure. Sudden negative drops in ME pressure can rupture the TM
- Middle ear tumors--most common is a glomus tumor (vascular tumor). One symptom is pulsating tinnitus.

42. Cochlear Disorders Syndromes and inherited disorders
Syndromic disorders
Nonsyndromal disorders
SENSORINEURAL HEARING LOSS FROM COCHLEAR DISORDERS
• Syndromes and inherited Disorders--a common cause of SNHL is hereditary factors. They are of two types:
- syndromic disorders: occurring as part of a constellation of other medical and physical disorders that occur together.
- nonsyndromic disorders: autosomal recessive or dominant genetic conditions in which there is no other significant feature besides HL

43. Syndromes and Inherited Disorders Resulting in Sensorineural Hearing Loss
Table 4-3 provides an extensive list of syndromes and inherited disorders resulting in SNHL.

44. Types of Nonsyndromic Disorders
Dominant
Dominant progressive
Dominant progressive with adult onset
Recessive hereditary SNHL
X-linked
The nonsyndromic disorders that result in SNHL can be dominant (only one gene of the mating pair carries the gene that is expressed), dominant progressive (dominant inheritance with progressive HL), dominant progressive with adult onset, recessive hereditary SNHL (this is the most commonly inherited loss in which both mating pairs are carriers of the gene but both genes must be inherited for the HL to be expressed), and X-linked.

45. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Noise induced HL---very common cause of SNHL in adults. Right up there with presbycusis. This can happen with a one-time exposure to a very loud sound or long-time exposure to constant, softer sounds.

46. Noise Induced Hearing Loss
The degree of SNHL depends on
The intensity of the noise
The spectral composition of the noise
The duration of exposure
Individual susceptibility
Effects of noise are cumulative. How damaging sounds are to the cochlear are dependent on
- the intensity of the sound--obviously, the higher the intensity, the more damage there will be.
- the spectral composition of the sound---higher frequency sounds are more damaging than lower frequency sounds.
- duration of exposure--longer the duration, more damage. Discuss damage risk criteria Fig 4-4.
- individual susceptibility---genetic predisposition, environmental chemicals.
The SNHL is centered at 3K and is progressive over time. Fig 4-10

47. OSHA Damage Risk Criteria

48. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Other trauma--physical trauma that causes a fracture of the temporal bone and leakage of endolymph. Give triad of symptoms (unconsciousness, bleeding, SNHL).
Infections

49. Infections Congenital Cytomegalovirus HIV Rubella Syphilis
Toxoplasmosis
--we discussed congenital infections most commonly associated with SNHL that included:
- cytomegalovirus
- HIV
- rubella
- syphilis
- toxoplasmosis
Remember that CMV is the leading cause of nongenetic congenital hearing loss in infants and young children.

50. Infections Acquired Herpes Zooster Oticus (Chicken Pox) Mumps Syphilis
Acquired infections: can be caused by viral or bacterial infections--and by fungi
Some common acquired viral infections that can cause HL
- Herpes Zoster Oticus--caused by a virus that also causes chicken pox. The virus can lie dormant for years in the CNS. At some point the virus can be reactivated (shingles). SNHL can result, varying degree usually high frequency.
- Mumps----HL is rare but can occur related to encephalitis. HL is almost always unilateral and, in fact, mumps is the single most common cause of unilateral SNHL. HL is profound.
- syphilis--occurs in the secondary or tertiary stage of the disease. The HL is fluctuating and generally progressive. Really affects speech discrim.

51. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
Ototoxicity--certain drugs and chemicals are toxic to the cochlea (so is blood, for that matter). Acquired ototoxicity results from the ingestion of certain drugs that are given for medical purposes. Ototoxicity can result from excessive exposure to certain environmental toxins. Congenital ototoxicity results from the effects of drugs administered to the mother during pregnancy.

52. Ototoxicity Some antibiotics that are often ototoxic:
Amikacin
Dihydrostreptomycin
Garamycin
Gentamicin
Kanamycin
Neomycin
Netilmicin
Streptomycin
Tobramycin
Viomycin
Here is a list of antibiotics that often ototoxic--Fig ??. Most of these drugs are ok in small doses, but at high doses are damaging to the ear.

53. Ototoxicity Chemotherapy Carboplatin Cisplatin
Drugs that cause reversible hearing loss
Quinine
Salicylates (aspirin)
Loop diuretics
Drugs that may be harmful during pregnancy
Accutane
Dilantin
Thalidomide
Carboplatin and cisplatin are drugs commonly used during chemotherapy for cancer treatment.
The HL due to ototoxicity is usually permanent, SN, bilateral and symmetrical. HL usually results from damage to the outer Hcs at the basal end (high freq). The loss progresses to the lower freqs with additional exposure to the drugs.
Some ototoxic drugs cause reversible HL--especially at lower doses. These include:
- quinine--used to treat malaria
- salicylates--aspirin
- loop diuretics--used to promote the excretion of urine.
Finally, some drugs when given to the mother during pregnancy have a teratogenic effect of the auditory system of a developing embryo. These include
- accutane--used to treat acne
- dilantin
- quinine
- thalidomide

54. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
Meniere’s Disease
Meniere’s Disease--endolymphatic hydrops. Triad of symptoms includes tinnitus, vertigo, and SNHL. The cause for the hydrops is unknown, usually, but has been attributed to allergy, vascular insult, physical trauma, syphilis, viral insult.

55. Meniere’s Disease Symptoms Tinnitus Vertigo
Unilateral sensorineural hearing loss
The HL is most often unilateral, SN and fluctuating. In the early stages, the HL is restricted to the low frequencies---eventually becomes flat.
Fig 6-14 shows audiogram. Speech recognition is usually very poor.

56. Cochlear Disorders Syndromes and inherited disorders
Noise induced hearing loss
Other trauma
Infections
Ototoxicity
Meniere’s Disease
Presbycusis
Presbycusis--decline in thresholds due to aging. The leading contributor to HL in adults. Estimates are that 25-40% of those over 65 have this.
Structures throughout the system degenerate with age. Changes in the hair cells, the stria vascularis (which provides the cochlea with a blood supply and nutrients), the spiral ligament (suspends the cochlear structures on the basilar membrane), and the cochlear neurons are known to occur.
The HL from presbycusis is bilateral, usually symmetrical, progressive, and SN. Mostly centered in the high frequencies. Fig Discuss gender differences. Speech discrim is variably affected.

57. Central Auditory Disorders
VIII Nerve tumors
Other diseases of the VIII Nerve
Neural disorders
Cochlear neuritis
Diabetes mellitus
Brain Stem disorders
Infarcts
Gliomas
Multiple sclerosis
Temporal Lobe disorders

58. CNS DISORDERS
The nature of the HL that accompanies CANS disorders vary as a function of location of the lesion--more peripheral, more apparent. Disruption in speech perception also gets more subtle as the lesion becomes more central.
• VIII N. Tumors--These are benign, encapsulated tumors that arise from the VIII cranial nerve. They are almost always unilateral and slow growing. They usually form one the vestibular branch of the nerve. The effects of these tumors are variable. Auditory symptoms might include tinnitus, HL, and problems with balance. Speech perception is usually more affected than what would be predicted bases on the audiogram.
• Other tumors, cysts, and aneurysms can affect the VIII nerve and the cerebellopontine angle.
• Neural disorders:
- cochlear neuritis--inflammation of the VIII nerve due to viral attack on the cochlear portion of the nerve. HL is sudden and severe. Speech discrim is very poor. Sometimes a complication of syphilis.
- diabetes mellitus--chronic complications can include neuropathy and generalized degenerative changes in blood vessels. The inner ear can be affected.
• Brain Stem Disorders--these include infarcts, gliomas (fast growing tumors), and multiple sclerosis.
• Temporal-Lobe Disorder--audition may be affected, although more typically receptive language processing is affected while hearing thresholds per se are ok.