Review Material for Midterm Flashcards
(126 cards)
1
Q
What are Auditory Evoked Responses?
A
An Auditory Evoked Potenital or Evoked response measures the electrophysiologic responses of the auditory nervous system to a variety of stimuli.
* If its an AER than the stimlulus is auditoy. AER represent activty within the auditory system that is stimlulated or evoked by sound.
2
Q
Neural activity in response to auditory sensory stimulation can be extracted from the ___ and viewed as a ___ .
A
Neural activity in response to auditory sensory stimulation can be extracted from the EEG and viewed as a response.
3
Q
Why is the ECochG the earliest response?
A
Electrocochleography (ECochG) is used for the earliest response because the components are generated in the region of the inner ear (cochlea).
4
Q
auditory brainstem responses arise from what area(s)?
A
Components of the auditory brainstem response (ABR) arise mostly from auditory regions of the brainstem
5
Q
auditory middle latency response (AMLR) occur between what two tests?
A
AMLR occurs between the **ABR and the auditory late responses (ALRs) **
6
Q
What are the clinical applications for AER’s
A
Evaluation of..
* Hearing Sensitivity (Threshold ABR, ASSR)
* CANS for pathology (neurodiagnostics ABR)
* CAN including auditory processing (ALR,MLR,p300,MMN)
* Children with language, cognitive and other developmental disorders
* Monitoring efffectiveness of intervantion such as CI or HAs and auditory trainning because of plastcity of the CANS
7
Q
Define Filters & how are they beneficial?
A
Filters in AEP measurments selectively remove unwanted electrical requencies from the recorded signal, enahcing the clarity & accuracy of the ER’s
* Eliminate both internal (muscle or brain activity not related to AEP’s) and external noise (60hz from equipment)
8
Q
What are Low pass filters helpful for?
A
Low pass filters help to reduce electrical equipment noise (60hz mumm from equipement)
9
Q
What information is critical for filter settings used in recording AERs?
A
Frequency of the stimulus
* So you don’t filter out the frequency range of the stimuli
10
Q
What does an “Open” message mean on AER’s and what could cause this?
A
“open” means the impedance is greater than 80kOhm
How?
* Faulty electrode
* No Electrode is plugged into the receptor on pre-amp
Ex: Selecting two channel recording option for a one - channel recording montage
11
Q
what is the Best Assessment for diagnosing ANSD?
A
Auditory Brainstem Response (rate study)
12
Q
What kOhms shoudl Inter - electrode impedance be balanced at?
A
2 kOhms
13
Q
True or False
Interelectrode impedance differences should be as small as possible?
A
True
Interelectrode impedance differences should be as small as possible, ~ 2 kOhms
* Balanced inter-electrode impedance with a difference between electrodes of less than 2000 ohms or 2kohms,
14
Q
Define Impedance
A
Impedance is a material’s resistance to flow of electrical current It is measured in ohms (Ω)
15
Q
when should you check impedances
A
Impedances should be measured before and during AER recordings if there is reason to suspect a change such as:
* excessive patient movement,
* Increased electrical artifact,
* when switching between ears.
16
Q
Define Interelectrode impedance
A
Interelectrode Impedance is the opposition to alternating current (AC) flow between one electrode and another
* as small as possible, ~ 2 kOhms
17
Q
A ground electrode placed low such as on the shoulder of a baby may record a ____ reponse instaed of an AER
A
EKG
18
Q
Do Not place Ground electrodes where and why?
A
Do not place ground electrodes near the heart such as on the shoulder of a baby
An electrode located too far down the back or front may pick up an EKG response
19
Q
what two things can a good ground electrode help with?
A
a good ground electrode
* is needed to record consistently optimal responses in a varied test conditions
* one of the most impotant ways to ensure high quality AER recordings.
20
Q
What is signal averaging
A
Siganl Averaging is one technique used to increase the size of AER’s and reduce the size of the noise improving SNR
21
Q
How does Signal Averaging work?
A
- The assumption is that auditory brain activity in response to a stimulus will always be the same as the response is time locked to the stimulus. With each sim presented the brains response is recorded, and added up.
- Since noise is random over time it will cancel each other out when being averaged and with every additional response results in a better and more accurate average.
- Signal averaging helps make the AER bigger and the noise smaller, improving the signal-to-noise ratio (SNR). and with every additional average response the more clear and accurate the AER signal
22
Q
What happens with increased signal avereaging?
A
Signal averaging helps make the AER bigger and the noise smaller, improving the signal-to-noise ratio (SNR). and with every additional average response the more clear and accurate the AER signal
23
Q
what responses are generated by stimulation of afferent peripheral nerve fibers (e.g., Median nerve) by either physiological or electrical means and are used in intraoperative monitoring.
A
Somatosensory Evoked responses are generated by stimulation of afferent peripheral nerve fibers (e.g., Median nerve) by either physiological or electrical means and are used in intraoperative monitoring.
24
Q
For SER’s what are the usual stimulation sites for clinical diagnostic tests?
A
- Median nerve at the wrist
- Common Peroneal at the knee
- Posterior tibial nerve at the ankle
25
SER's are useful for what clinical diagnosis?
* Neurologic disease
* Prognosis of comatose PT's especially after postanoxic coma
* Interoperative monitoring of "at risk" somatosensory pathways
26
Why are MRI's used when assesing the auditory system?
MRI is primarily an **imaging/structural/ anatomic** test. Providing detailed information about **structural abnormalities**
27
# MRI VS ER's
why would you want to use ER's and not just MRI when assessing the auditory system?
**ER’s** assess **functionality** of the auditory system. It provides insight into the physiology of specific anatomic pathways but provides less spatial or localizing info compared to the MRI
28
The auditory evoked response is better at assessing ____ of the auditory system and the MRI is better at assessing ___ ___ within the system.
The auditory evoked response is better at assessing **functionality** of the auditory system and the MRI is better at assessing **structural problems** within the system.
29
# Near - field or Far - field
Evoked potentials recorded by electrodes close to the potential field or where the potential is generated are called ___ responses whereas those recorded by electrodes at a distance from where the potential is generated are called ___ responses.
Responses recorded from electrodes placed on the scalp are considered ___ responses whereas those recorded from intratympanic needle electrodes or on the promontory of the cochlea would be considered ____ responses.
Evoked potentials recorded by electrodes close to the potential field or where the potential is generated are called **Near - Field** responses whereas those recorded by electrodes at a distance from where the potential is generated are called **Far Field** responses.
Responses recorded from electrodes placed on the scalp are considered **Far - Field** responses whereas those recorded from intratympanic needle electrodes or on the promontory of the cochlea would be considered **Near - Field** responses.
30
AEPs can be classified according to what structures in the auditory system generates them. What are the two classifcations?
**Receptor potentials**
* cochlear hair cells - ECochG and OAEs
**Neurogenic Potentials**
* CN 8 &/or Brainstem
31
Define Far Field and when are they used?
electrodes are placed some distance away from the site of generation
* Most commonly used
* Typical in clinics
(Electrodes are located outside of the skull)
32
Define Near Field and when are they used?
electrodes are placed in close proximity from the site of generation
Used when
* measuring the response on the nerve
* Intraopertive monitoring ( electrodes placed driectly on CN8)
* Transtympanic Membrane ECochG (needle electrode is inserted though the TM and placed in the promontory)
33
Based upon the concept of near-field vs far-field responses, for which would you expect to obtain the best (largest amplitude, most detail) response?
**Near - field**
* The closer to generator site the better the response
Ex:
* Transtympanic Membrane ECochG
* Inverting electrodes placed against the tympanic membrane (TM-trode or tymptrodes)
* Directly placed in CN
34
# Exogenous VS Endogenous
do not have to hear signal
Exogenous
* think external, you dont need to process inside
35
# Exogenous VS Endogenous
must hear signal
Endogenous
* think inside, you need to process
* internal cognitive processes needed
36
# Exogenous VS Endogenous
ABR, OAE and ECochG
Exogenous
37
# Exogenous VS Endogenous
ALRs, P300,CNV,
Endogenous
38
# Exogenous VS Endogenous
influenced by cognitive processing
Endogenous
39
# Exogenous VS Endogenous
more related to the physical characteristics of the evoking stimulus
Exogenous
40
Latency is measured in what?
milliseconds (ms).
41
Define Polarity
Polarity refers to the initial direction the pressure wave moves when it first starts, measured at the surface of the transducer.
42
Rarefraction
* causes the pressure wavefront to move away from the eardrum
* This type of stimulus has a **shorter latency** as it starts immediately upon delivery.
43
Condensation
* causes the pressure wavefront to move toward to eardrum
* Wave 5 amplitude tends to be **larger** in amplitude response to condensation stimuli than for rarefaction
44
Alternating Polarity
the pressure of the wavefront stimulus is alternated on successive trails (condensation and rarefaction)
* Used in ECochG & BC
* Rule out ANSD beofre use
45
If an alternting polairty is used when ANSD is present what will happen?
ANSD will result in a flat line, you need to start with a refraction or condensation first to rule out ANSD
46
What is an example of a Non-evoked or non-event related potential?
EEG
47
What is an example of a evoked or event related potential?
ECochG
ABR
48
Disc Type Electrode
49
Disc Type Electrode
50
Disposable Electrodes
51
Disposable/ snap Electrodes
52
Tiptrode Electrode
53
Tiptrode electrode
54
TM - Trode
or
Tymptrode electrode
55
TM - Trode
or
Tymptrode electrode
56
Ear Clip/ Lobe Electrodes
57
# True or False
AERs are all separate and distinct potentials without any anatomical or waveform overlap.
FALSE
There is no distinct potentials they is some sort of over lap between on test to the next.
58
What is an Epoch and why is it an important consideration when recording AERs?
Epoch is a time window. It is the window of time in which you are viewing the responses for the AEP.
* An Epoch is a length of time (in msec) relative to a specific auditory event. If you choose an Epoch that is too short, you may not see your entire response. If you choose an Epoch that is too long your response may get lost in the bigger display with limited detail. You want to choose the best time frame for the potential of interest.
59
Late evoked responses are used to study what?
Late evoked responses are used to study **higher cortical functions**
60
The earliest responses with the shortest latencies are generated by the what?
The earliest responses with the shortest latencies are generated by the **inner ear and auditory nerve**.
61
Are late AER responses larger or smaller reposnes and does that affect the pathology identification ability?
Late AER = larger amplitude responses
* Late are looking at higher structures of the CANS
* The later/ higher up = larger responses because the more neurons involved in the response —> that is also why site location is less accurate because more neurons/structures are involved in the response.
62
Very Early
* Time Period
* Generated by
* Test Type
* Additonal Info
Very Early
* 0 - 1.5 msec
* First
* cochlea (inner ear).
* ECochG
* Includes: CM (Cochlear Microphonic), SP (Summating Potential), N1
63
Early
* Time Period
* Generated by
* Test Type
* Additonal Info
Early
* 1.5 - 12 msec
* Nerve & Brainstem
* Auditory Brainstem response
64
Middle
* Time Period
* Generated by
* Test Type
* Additonal Info
Middle
* 12 - 50 ms
* Thalamus & Auditory Cortex
* Middle Latency Response (MLR)
65
Slow
* Time Period
* Generated by
* Test Type
* Additonal Info
Slow
* 50 - 300 ms
* 1 & 2 areas of cortex
* Auditory Late Responses (ALR)
66
P300
* Time Period
* Generated by
* Test Type
* Additonal Info
P300
* 300 + ms
* 1 cortex and association areas
* associated with cognitive processing in primary and association areas
* P300 test
67
Defien Click Stimulus
Click: abrupt or rapid onset w/ a board frequency bandwidth/range (containing all frequencies)
* Gets a response from a large number of neurons = a larger amplitude response
68
ECochG and ABR are best generated by what stimulus type?
ECochG or ABR → are best generated by a click
69
Evoked responses directly depend on what?
Evoked responses directly depend on **temporal synchronization or neuronal activity**
70
for ABR using a click does the duraion of the stimulus alter the response?
No
* Because the ABR is an onset response, the duration of the stimulus should not alter the response.
But in general duration should affect response just not in this case
71
Does duration affect the frequency specificity of a response?
yes
* **The longer the duration of a stimulus the more frequency specific the stimulus will be**
* such as a pure tone, pure tones are presented for a longer duraion and gets more frequency specific information unlike a click that is abrut and get less frequency specific information.
72
what determine a clicks primary frequency emphasis?
Click primary frequency is determined by the **resonant frequency** of the **transducer**.
* For inserts it is between 1000 and 4000 Hz. (Closer to 2000 and 4000 Hz)
73
What is the click pure tone threshold frequency range?
2,000 - 4,000 hz
( or 1 - 4 khz)
74
what stimulus provides the best compromise that would maximize both frequency specificity and neural synchrony?
Blackman
75
What polairty Can be used at high intensities to reduce stimulus artifact
Alternating Polarity
76
Stimulus intensity is measured in what unit?
dB (decibels)
77
what happens to Latency & amplitude if intensity increases?
As stimulus intensity increases, AEP waves show shorter (decreases/faster) latencies and larger amplitudes.
* Intensity ↑ Latency ↓ & Amplitude ↑
78
what happens to Latency & amplitude if intensity decreases?
As stimulus intensity decreases, AEP waves show longer latencies (increase/slower) and smaller (decrease/smaller) amplitudes.
* Intensity ↓ Latency ↑ & Amplitude ↓
79
The actual intensity reaching the cochlea is dependent on what?
1. The acoustic properties of the transducer
2. the volume of the ear canal
3. Middle ear transmission Characteristics
80
The stimulus rate affects what?
affects both the **latency** and the **amplitude**
81
What is the correct stimulus rate for all test circumstances?
There is no single correct rate or one that is appropriate for all test circumstances
82
What is the general rule of stimulus rates?
Rates above 30/sec latency increases and amplitude decrases.
83
83
what stimulus rate do we run?
We run at about 27.1 or 27.7/sec
84
What is Interstimulus interval (ISI)
time interval between successive stimuli presentations
* is the time between each stimulus being played.
85
why are ISI's important for AEP's?
If the ISI is too short (shorter than the refractory period), it may lead to **incomplete neural recovery**, affecting the response by **increasing latency or decreasing amplitude**.
* If the ISI time period exceeds the refractory period, then the neural unit can fully recover and will be responsive to the next stimulus.
86
electrode effects may alter what in the AER's?
* Latency
* Amplitude
* Morphology
* Polarity
87
The what electrodes are most commonly used in AER measurements
Disc & Disposable
88
Where is the non-inverting electrode loacted?
VERTEX
Cz or the midline forehead near Fz
89
Where is the inverting electrode loacted?
earlobe or mastoid of the stimulus side. (A1 or A2)
90
Filtering of the physiological response is used to:
1. **Eliminate** as much **internal noise** (electrical activity coming from the patient) as possible
2. **Eliminate** as much of **external electrical noise** (e.g., 60Hz) as possible
This is distinguished from any filtering of a stimulus transduced through an earphone.
91
what Two characteristics of amplifiers have direct influence on successful AER recordings
Input Impedance
&
Common Mode Rejection
92
Briefly describe the role of amplifiers in an auditory evoked potential system AND how does Common Mode Rejection work within that system
Amplification: increases the strength of an electrical or acoustical signal.AEP's are very small and amp is needed for interpretation
CMR: allows the electrode to pick up what is common to each electrode (noise) and cancel it out (uses the inverting and non-inverting) while retaining the evoked responses at the two electrode sites, because they are different. = a more clear AEP response
93
What is Artifact rejection
The process of eliminating non-AEP signals from the recording to ensure a clean and accurate waveform.
94
Why do Auditory Evoked Responses?
Patients who cannot be assessed validly with behavioral audiometry, including
* Newborn infants
* Difficult-to test-children
* Patients with developmental disorders
* Patients with cognitive impairment
* Persons with false or exaggerated hearing loss
* Very Sick Patients or Sleeping or unconscious patients
* Patients who are anesthetized and undergoing surgery that puts the auditory system at risk
* Comatose patients with severe head injury who have central nervous system damage
95
Absolute Latency
Time interval between the exact moment of stimulus presentation and the appearance/ peak of the waveform in milliseconds
96
Absolute latency is the ___ ___ and ___ ___ and provides the ____ of ABR interpretation.
Absolute latency is the **most robust** and **reliable characteristic** and provides the **mainstay** of ABR interpretation.
* "mainstay" means the most important or central part of something
97
What is the normal wave I ABR latency?
Wave I ≈ 1.6 msec after stimulus onset
* Replicate within 0.1 msec
98
What is the normal wave III ABR latency?
Wave III at ≈ 3.7 msec after stimulus onset
* Replicate within 0.1 msec
99
What is the normal wave V ABR latency?
Wave V at ≈ 5.6 msec
* Replicate within 0.1 msec
100
Interpeak Latency
The time period between peaks
101
What is the normal ABR interpeak latency Wave 1 -3?
Measure wave 1-3 (~2 msec)
102
What is the normal ABR interpeak latency Wave 3-5?
Measure wave 3-5 (~2 msec)
103
What is the normal ABR interpeak latency Wave 1-5?
Measure wave 1-5 (~4 msec)
104
Interaural Latency Differences
Comparing your wave 5 latencies from your left to your right ear.
105
What is a normal Interaural Latency Difference?
When hearing sensitivity is similar in both ears, the **latency of Wave V** should differ by no more than **0.2 to 0.4 msec** between the ears.
* exceed 0.2 or 0.4 msec = abnormal
106
# True or False
High impedance in one electrode and a low impedance in another is acceptable becuase they will equal each other out.
FALSE
High impedance in one electrode and a low impedance in another can **create an electrical imbalance** at the input to a differential amplifier
* Imbalance can cause excessive interference from sources of the electrical artifact
* Low inter-electrode impedance is very important for common mode rejection to work well.
107
The impedances can sometimes be lowered by...
* Pressing on the electrode for several minutes
* Moving the electrode slightly to get a better contact with the prepped skin
* Adding more electrode conducting paste/gel
* Securing the electrode snugly with additional tape
* Removing electrodes with higher impedances and re-prepping the skin
108
all electrodes should have similar impedance values within ___
all electrodes should have similar impedance values within **2kOhms**
109
# The test enviorment
How to Reduce Impedance & Improve Recordings
* The pre-amplifier (pre-amp) of the ER equipment should not be placed near the isolation transformer, a computer monitor, or other electronic equipment
* Turn off any unnecessary computer monitors and fluorescent lights (do not just put them on “dim” mode)
* If possible, ensure you are using a designated and grounded electrical outlet
* It can help eliminate unwanted noise from the tracings
* If the patient is sitting in a chair that can be operated electrically, unplug the chair
* Turn off all cell phones (do not just set them to “silent”)
110
An electrode box has a minimum of how many jacks?
minimum of **3** receptacles or jacks
* Non-inverting, inverting, and ground - this constitutes **one channel recording**
111
Two channel recording boxes will have how many jacks?
Two channel recording boxes will have **5 or 6 jacks**
* 1 shared noninverting (Cz or Fz)
* 2 inverting electrodes (e.g., A1 and A2)
* 1 ground
* 1 jumper cable - need a jumper
112
One Channel VS two channels
One:
* 3 jacks
* no jumper cable
Two:
* 5 to 6 jacks
* Perform both ipsi and contra recordings simultaneously'
* Jumper cable
113
Define ABR
ABR is a complex response to particular types of external stimuli that represent neural activity generated at several anatomical sites.
114
# ABR
Wave 1 neural generators
Distal 8th nerve (spiral ganglion)
* farther from the brain and closer to the cochlea.
115
# ABR
Wave 2 neural generators
Proximal 8th Nerve w/ some contribution from distal 8th nerve
* Proximal - closer to BS
* Distal - closer to cochlea
116
# ABR
Wave 3 neural generators
Neurons in the cochlear nucleus and possibly fibers entering the CN
117
# ABR
Wave 4 neural generators
Unknown
* but 3rd order neurons in SOC are most likely
118
# ABR
Wave 5 neural generators
May be related to activty in **lateral lemniscus and inferior colliculus**
119
Slow the rate =
Slow the rate = earlier latency, cleaner the wave form
120
Faster the rate =
Faster the rate = prolongation (longer Latnecy
121
____ is flipped and you get phase cancelation, and what is incommon cancels and you are left with the signal of interest.
Inverting Electrode
* used in common mode rejection
122
__ and __ Tend to have very large amplifier gain
ECochG and ABR tend to have very large amplifer gain
123
What subject factors affect AEP?
Age
* not adult like configuraton until age of 2
* ECochG → Lates in maturation (earlys mature before lates in a decesnding pathway)
124
Briefly Tell me how you would run a neurological ABR
Do a high intensity
* do a slow, medium & fate rate
* Replicate the runs
* look peak and interpeak abonromalities (longation and that indicative of a retrcocohlear parhology)
125
Briefly Tell me how you would run a Threshold ABR
* high intensity ABR
* rule out ANSD with R or C
* Lowest level you can get a wave 5 = threshold
* (repliacte each wave)
* +/- your correction factor
* Use clicks and tone burts to estimate frequency
