Quiz 3 (Presbycusis) Flashcards
what is presbycusis
age related HL
it is gradual, variable in age of onset & its progression rate
variable in how it progresses
what type of HL is seen in presbycusis
always SNHL because it is in teh inner ear and due to a lack of regeneration of the sensory system
two most common causes of HL
advanced age
noise exposure
presbycusis results from progressive loss of
EP, sensory cells, & other peripheral & central auditory system
results in a decline of auditory function
as inability to regenerate structures that cause audition
what was previously thought and now thought about etiology of ARHL
varied and not understood well
might be degenerative disase due to early start & noisey areas (city)
previously → cochlea was primary site & central involvement was secondary due to reduced sensory input
recently → CAS also has changes as a result of aging that is independent of peripheral involvement
incidence of ARHL
HL prevalence increases with age & is to increase as the US age continues to increase
WRS decline more rapidly in men & poorer in all aged men than women
socioeconomic & ethnic variations
African americans show lower incidence of HL in elderly population
Formula that leads to Presbycusis
genetics / (age + noise + ototoxic drugs)
why is there so much variation in HL in ARHL
because individual hearing relies on genetics
ototoxicity, noise, and age play a role on hl too
3 Variables that make it hard to study effects of pure aging on physiology & morphology
environmental noise exposure
drugs
genetics
accounts for variability seen among the elderly in hearing abilities
genetics
age-related HL is unique to aging & not a result of environmental factors (can contribute to HL)
true
where does high aerobic metabolism occur
in lateral wall of cochlea
why is high metabolism needed in cochlea
K+ maintenance bw endolymph & perilymph
EP generation
where is mechanical & metabolic damage the most common
basilar membrane at the basal turn of cochlea
ARHL is what type of HL
slowly progressive, sloping, HF SNHL
why is ARHL slowly progressive, sloping, HF SNHL
becuase damage is most common at the basilar membrane of the basal turn
presbycusis not related to environmental factors is just due to loss of cochlear hair cells
false
it is also caused by degenerative changes/pathologies of the lateral cochlear wall & not just the above
what are the three cochlear systems implicated in presbycusis
cochlear amplifier
power supply
transduction mechanism
what is the pathophysiology seen at cochlear amplifier system in presbycusis
cochlear amplifier = OHCs
loss of this reduces sensitivity by ~ 40 to 50 dB HL
this active process amplify sound vibrations in cochlea and this relies on EP found in scala media (ENDOLYMPH)
what is the cochlear battery
EP
describe EP
extracellular resting potential with +80 to +100 mV
created from stria vascularis by the Na+/K+ pump and in turn provides energy for cochlear transduction = battery of the cochlea
where is EP larger
at the base (also why we see HF HL with ARHL)
1mv = _____dB gain in cochlear amplifier
~ 1 dB
if EP drops by 30 mv, sensitivity to HF decreases by about ____ dB
30
aging effects in the cochlea can be result of
deterioration of cochlear battery (EP) & not loss of hair cells
how is research restoring EP
adding external battery by injecting current directly into scala media &/or regenerating the old batter by using stem cells to repopulate stria vascularis
these could recharge power supply to cochlear amplifier, regain some of HF sensitivity loss & reduce speech perception issues with aging
what provides the power the OHCs need to function effectively
cochlear lateral wall, including stria vascularis
what is the power supply of cochlea
cochlear lateral wall tissue including SV that generates EP
what is the power supply dependent on
K+ recycling - actively putting it back into the endolymph after it is released into perilymph through supporting cells & fibrocytes that move it through gap junctions = generating EP
describe K+ recycling during power supply in cochlea
top of OHCs has potential gradient of ~ 160 mV RP (+80mV endolymph and -80 mV in the body of the hair cells due to the resting potential of the hair cells), potential gradient causes constant flow of current from the scala media to inside of hair cells, potential changes produced by this flow of the electrical current is the cochlear microphonic
what is a cochlear microphonic
potential gradient causes a flow of current from scala media to inside of hair cells and these potential changes that are produced by the flow of electrical current is CM
what is transduction mechanism in cochlea
transduction of cochlear vibration to neural impulses
IHCs passively detect vibration that in turn excites the afferent nerve fibers of CN VIII fibers that are synapses at base of iHCs
these impulses are then sent to the brain
what are common characteristics of presbycusis
HF SNHL sloping
speech perception issues espectially in noise & reverberation
recruitment
what are the classification of presbycusis
Schuknecht’s & Killion & Fikret-Pasa
why is classifying presbycusis in older adults important
improved differential diagnosis
changes to individualized intervention that leads to improved auditory function in older adults
describe schuknech’t classificatioin of ARHL
based on postmortem eval of temporal bones
sensory presbycusis
primary loss of OHC & supporting cells
neural presbycusis
loss of afferent cochlear neurons
metabolic/strial presbycusis
loss of EP & atrophy of strial & lateral wall
mechanical presbycusis
stiffening of BM & organ of corti (no evidence)
what is the primary goal of K &FP ARHL classification and what is it based on
develop a system which appropriate amplification based on other considerations than the pure-tone audiogram
develop a system which appropriate amplification based on other considerations than the pure-tone audiogram
describe Killion & Fikret-Pasa classification of ARHL
type 1
mild - moderate SNHL (no worse than ~ 45 to 55 dB HL)
normal loudness sensation
findings consistent w/ loss of OHC fxn ONLY w/ normal IHC fxn
type 2
moderately severe HL (~ 6 dB HL)
presence of partial recruitment
assumed there is OHC loss WITH ICH loss
have issues w. speech intelligibility (especially in noise) even with the best HA’s because there is less info transmitted to the brain & fewer redundant speech cues are available
type 3
severe HL (~75 dB HL)
loudness & intelligibility are affected & recruitment is common
intelligibility becomes the primary concern
speech range that can be heard in noise is narrowed
these individuals do well when speech is presented close to UCLs
OHC, IHC & nerve fiber losses
NIHL is anatomically characterized by
loss of hair cells (initially OHCs)
loss of supporting cells
secondary neural degeneration
Presbycusis is anatomically characterized by
mostly degeneration of the stria vascularis and lateral cochlear wall
Compromised blood supply correlated with the extent of strial degeneration
Presence of mostly normal sensory cells except in the most basal and apical turns of the cochlea
NIHL is physiologically characterized by
Threshold elevations of APs of the auditory nerve, ABR, and higher level evoked responses
The distinctive feature is loss of cochlear nonlinearities
for ex: OAEs
The endocochlear potential (EP) is generally unaffected in NIHL
Degeneration of the stria vascularis is not typical in NIHL
Presbycusis is physiologically characterized by
Reduction of endocochlear potential (EP) → due to degeneration of the stria (the batter of the cochlea)
ARHL is, therefore, a ___, ______, & _____ disorder
vascular, metabolic, and neural
describe long term relationship of NIHL & ARHL
NIHL early can make ARHL worse and over time ARHL can flatten the noise notch
what is hidden hearing loss
synaptopathy (auditory nerve damage) causes it
TTS can be indicative of immediate & irreversible damage to auditory n fibers & beginnings of HHL
loss of connection from the auditory nerve to the hair cells causes HL not seen on an audiogram
may be significant contributor to classic complaint “I can hear but I can’t understand what people are saying”
HHL
