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quiz 1 Flashcards

1
Q

remember, our brain is constantly working giving out small measurements. these can be reordered as potential differences that is the basis of __________________

A

electroencephalogram (EEG)

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2
Q

neural activity in response to specific types of sensory stimulation can be extracted from the EEG, giving much smaller measurements for us to see. we can only see them because …..

A

they are amplified

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3
Q

in order to view evoked responses, what two things need to be present

A

signal averaging and amplification

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4
Q

evoked response/evoked potentials (ER/EP)

A

measures the electrophysiologic responses of the nervous system to a variety of stimuli and in theory any modality can be tested

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5
Q

common ERs/EPs

A

visual evoked responses, short latency somatosensory evoked responses, short latency brainstem auditory evoked responses and cortical evoked responses

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6
Q

what are we looking at with ER/EP

A

neural responses
-remember, it is a functional test so we are looking at the functional integrity of the neural function

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7
Q

how has the usage of evoked potentials/responses changes with the introduction of advances in imaging (i.e. MRIs)

A

the usefulness of ERs/EPs has decreased and most questions regarding structures are better answered by an MRI however in some cases both an MRI and evoked potentials may be complementary
-MRI is a structural/anatomic test
-ERs/EPs are a functional test

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8
Q

auditory evoked response (AERs)

A

brain waves or electrical responses that are generated when the auditory system is stimulated by sound, but can also be through electricity or a mechanical stimuli

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9
Q

sounds that are used for AERs

A

clicks, tone bursts and speech sounds

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10
Q

clicks for AERs

A

abrupt onset, very short duration and broadband
-not a frequency specific signal as it contains energy from various frequencies, but most energy is within 1 and 4 kHz

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11
Q

tone bursts for AERs

A

short duration
-frequency specific with more energy hanging around the frequency of interest

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12
Q

what is the general rule with AERs and their stimulus intensity with response

A

the louder the stimulus intensity, the larger the AER response will be

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13
Q

what happens during an AER

A

-sound is presented through some sort of transducer
-activity from the cochlear and brain evoked by the sound is picked up by electrodes
-this evoked activity that is conveyed from the auditory structures through body tissue and fluids to the surface electrodes and from here it goes through the wire and through the technology to be analyzed

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14
Q

the electrodes we use during AERs has one side with a metal disc or adhesive patch while the other side has a DIN pin that plugs to the box or pre amp. what is the DIN pin

A

the electrical connector that belongs to a family of circular connectors that were standardized for analog audio signals

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15
Q

how can we be sure that the response is coming from the CANS if the electrodes are placed far from the generator site

A

the stimulus that is evoking the response is sound so we know that the response is from within the auditory system

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16
Q

around how long does it take for an AER to occur post stimulus

A

around 1 second

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17
Q

neural generators

A

the earliest response with the shortest latencies that are generated by the inner ear and auditory nerve
-these have smaller potentials whereas the later responses have larger potentials

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18
Q

microvolts

A

the small voltage that is used to measure brain activity making up the auditory evoked response
-activity measures from the higher regions of the CANS, such as the cerebral cortex, is larger in size than activity from the cochlea and auditory nerve

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19
Q

evoked vs. non evoked potentials

A

remember, these electrical potentials can be recorded both in response to stimulus and in ongoing manner without presence of external stimuli
-evoked is those such as the ECochG or ABR
-non evoked is those such as the EEG

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20
Q

auditory evoked potentials (AEPs)

A

represents electrical responses of the nervous system to externally presented stimuli; most will be hidden in the EEG response within the brain
-in simple words, represents brain waves generated in response to sound

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21
Q

what are AEPs generated by

A

generated by action potentials arising from many neurons within a specific region

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22
Q

how can we classify AEPs

A

characteristics determined by external or internal processes, based on the time epoch, based on relation of electrodes to generator site and based on structures in the auditory system that generates them

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23
Q

classification: characteristics determined by external or internal processes

A

exogenous : does not have to hear the signal
-earlier responses are this type
endogenous : must hear the signal
-all cortical potentials and later responses are this way

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24
Q

classification : time epoch

A

the time interval after which the stimulus occurs
-very early (0-1.5 msec) (ECochG)
-early (1.5-12 msec) (ABR)
-middle (12-50 msec) (MLR)
-slow (50-300 msec) (ALR)
-P300 (300+ msec) (P300)

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25
classification : based on relation of the recording electrodes to generator sites
near field : electrodes are in close proximity -uncommon as the electrode needs to be directly on the nerve far field : electrodes are some distance away -typically what is used as the electrodes will be placed on the skull
26
classification : based on structures
the receptor potentials are from the cochlear hair cells and the neurogenic potentials are from the 8th nerve and/or brainstem
27
early latency AEPs are best generated with __________whereas the late latency responses are best generated with ___________
very brief transient ; clicks
28
what are the four categories of factors that can impact the AEP measurement
stimulus, acquisition, non-pathological and waveform analysis
29
in regards to the stimulus, what are some aspects that can impact the recording
type, duration/rise time, polarity, intensity and rate
30
impacting the measurement, stimulus : type
clicks will allow for more neurons to be activated for a longer period of time, allowing for a larger response -however at low levels tone bursts may want to be used to look at those responses if the patient has a step HF loss
31
as a result of many studies, what method was found to be most effective with AEPs
the blackman setup, being a 202 -2 ms onset with no plateau then 2 ms offset
32
impacting the measurement, stimulus : duration/rise time
relating to how long we leave it on plateau for and how long it stays on until its turned off -standard click is 0.1 msec
33
the longer the duration of the stimulus, the _____ frequency specific it will be (more like a pure tone)
more
34
the shorter the stimulus, the ______ frequency specific it will be
less
35
impacting the measurement, stimulus : polarity
this relates all to how the initial direction of the pressure wavefront is and how that in turn impacts the auditory system -there is rarefaction, condensation and alternating
36
rarefaction polarity
initial direction causes the pressure wavefront to move away from the eardrum -results in outward movement of the stapes footplate and then an upward motion of basilar membrane which depolarizes the hair cells -this causes the latencies to be slightly shorter and the amplitude to be slightly higher
37
condensation polarity
initial direction causes the pressure wavefront to move towards the eardrum -results inward movement of the stapes footplate and then a downward motion of the basilar membrane, leading to the hair cells not being depolarized right away -causes the latencies to be slightly longer and the amplitude to be slightly smaller
38
alternating polarity
stimulus pressure wavefront is alternated between both rarefaction and condensation -sums up the two polarities and is routinely used during ECochG -with ANSD, we get a flat line as they are reversals
39
are the differences in latencies within rarefaction and condensation clinically significant?
no
40
impacting the measurement, stimulus : intensity
with intensity, it is important to know that there is an inverse relationship between intensity and latency -there is an increase in latency as the intensity decreases -there is a decrease in latency as the intensity increases
41
intensity with AEPs can have many unites, but the typical one we see with ABRs is dB nHL. what is important to remember with this unit
there is around a 10 dB change between this and the actual threshold -as this is based solely on ABR norms and not pure tone norms
42
what are 3 factors that impact the actual intensity and frequency information that reaches the cochlea
acoustic properties of the transducer, volume of the ear canal and middle ear transmission characteristics
43
impacting the measurement, stimulus : rate
how many stimulus is presented per second -generally will run them around 27.7 per second
44
interstimulus interval (ISI)
the time interval between successive stimuli presentations -needing to ensure that it is in accordance with the neuron rest periods -can identify by doing 1 second / rate
45
if the ISI time exceeds the refractory period, then .......
the neural can fully recover and will be responsive for the next stimulus
46
if the ISI is shorter than the refractory period, then .....
some stimuli will not contribute to the response because they are presented during the recovery period -this gives a poor response
47
fast responses such as the ECochG or ABR occur within a brief period (5-6 msec) and therefore require a __________
brief ISI
48
in regards to acquisition, what are some aspects that can impact the recording
instrumentation, electrodes, filters, amplifier, artifact rejection and signal averaging
49
impacting the measurement, acquisition : instrumentation
common aspects is stimulus generator, electrodes, filters, amplifiers, signal average, response delay, response processing and a means to print or display results -inserts are recommended as they increase interaural attenuation, they attenuate environmental noise and they prevent ear canal collapse
50
impacting the measurement, acquisition : electrodes
these are the sensing device that detects the bioelectric activity and sends it to the pre amplifier -they are all designed to conduct electrical activity
51
two types of electrodes
disc/cup electrode: metal coated with a hole in the center to release the conducting paste, useful for very low frequency disposable electrode : self adhesive backing that comes in different sizes and shapes *other uncommon ones include ear clip or canal electrode*
52
non inverting vs. inverting electrode
non inverting: the signal is coming in and is going to be left alone inverting: the signal is coming in and gets flipped 180 degrees before it reaches the processor
53
10-20 convention with electrodes
what is used for electrode placement where the letter tells us the location and number indicates the side -odd is left, even is right -A is auris (ear), M is mastoid, C is cortex and F is forehead -those with the letter z indicate that they are on the midline
54
impacting the measurement, acquisition : filters
remove part (or parts) of something from the whole and within the AEP measurement they reject electrical activity at certain frequencies while passing energy at other frequencies
55
filtering is used to ....
eliminate as much internal noise as possible and to eliminate as much external electrical noise as possible
56
types of filters
high pass : rejects lows, allows highs to pass low pass : rejects highs, allows lows to pass bandpass : rejects energy below and above a certain cutoff, allows those between the cutoffs to pass band reject : rejects a very specific range between two cutoffs (not typically used)
57
how can inaccurate amount of filtering impact a recording
-too much can eliminate the AER response -too little can lead to high noise levels and poor AER recordings
58
impacting the measurement, acquisition : amplifiers
device that increases the strength of a signal and is critical in the AEP system -important as the signals that we are capturing are from the cochlea or 8th nerve and are very small, so without the amplifier we could not see them
59
amplifiers for AEPs need 2 things, these are
input impedance : trying to figure out how clean the measurements are by running an impedance measure common mode rejection (CMR) : the process of identifying what is common between electrodes and throwing out those common aspects so all that is left is what is different (the true response) -thought behind this is that those common signals is the noise in the environment
60
impacting the measurement, acquisition : artifact rejection
this is what takes anything that is not a true response, so an artifact, and removes it from the recording while keeping a running count of how many are thrown out -what helps create a clean and clean and true signal
61
what are artifacts within the AEP recording
electrical activity that is not part of the auditory response and should therefore not be included in the analysis of the response
62
what are the 3 common sources of artifact
electrical (activity within the circuit), electromagnetic (generated from an external or non patient source) or electrophysiologic (originating from the patient such as myogenic)
63
impacting the measurement, acquisition : signal averaging
converts the analog electrical activity from the amplifier into a series of numerical values and these values are then processed by the computer to generate the averaged response -this is what cleans the signal -a way to improve the SNR in a way (increasing the size of the response while reducing the size of the noise)
64
in regards to non-pathological, what are some aspects that can impact the measurement
age, body temperature and state of arousal -know that there is not much of an impact unless they are very young or if they are cold or hot
65
in regards to waveform analysis, what are some aspects that can impact the measurement
present landmarks, latency, amplitude, morphology and polarity direction
66
what do we mean by science vs. art
science is the number we get, the facts we get directly from the recording whereas the art means the morphology the assumptions we make based on the appearance
67
impacting the measurement, waveform analysis : latency
time interval between the exact moment of a stimulus presentation and the appearance of a change in the waveform -expressed in msec and is on the x axis
68
absolute latency vs. interpeak latency
absolute : whole time of recording interpeak : between the peaks *valuable with determining if there is a space occupying lesion*
69
impacting the measurement, waveform analysis : amplitude
finding for each wave -can do so by measuring the voltage between the peak of a wave and the trough (volley) -measured in microvolts and is on the y axis
70
impacting the measurement, waveform analysis : interaural difference of ratio
wanting to see that there is symmetry between both sides
71
impacting the measurement, waveform analysis : morphology
the pattern or overall shape of the recording
72
clinical utility of AEPs
evaluation of hearing sensitivity, evaluation of CANS for pathology, evaluation of the CANS including auditory processing, evaluation of children with language/cognitive/other developmental disorders, monitoring effectiveness of intervention -they show high correlation to physiological changes in the auditory pathway
73
why use AEPs
-evoked responses contribute importantly and in many ways to the early detection and accurate diagnosis of auditory dysfunction and to effective intervention for HL and other types of auditory disorders -auditory evoked responses play a vital role in the identification, diagnosis and management of HL in children and adults
74
advantages with using AEPs
-automated evoked response measurements and analysis makes possible universal newborn hearing screening -cortical auditory evoked responses can be used in documentation of central nervous system maturation and development in infants following intervention with HAs or CIs -auditory evoked responses often greater sensitivity to certain types of auditory dysfunction than behavioral audiometry, including neural dysfunction -auditory evoked responses offer greater specificity for detection and diagnosis of dysfunction in specific regions of the auditory system than behavioral audiometry
75
what populations of people can AEPs be recorded on if they cannot have valid threshold testing
newborns, difficult to test children, patients with developmental disorders, patients with cognitive impairments, persons with false or exaggerated HL, very sick patients/unconscious patients/sleeping patients, patients who are anesthetized and comatose patients
76
how to prepare for conducting the test
patient instructions, patient arousal state, patient medications, makeup/hair/clothing and then electrode placement and impedances
77
steps for electrode preparation
-skin surface will be scrubbed with a mildly abrasive substance (NuPrep) in order to remove dead skin, debris and oil -alcohol wipes can be used to remove some things prior to recording however it takes time to dry
78
importance with electrode placement
ensure consistent placement in the accurate position -secure and consistency attachment throughout the test session
79
mounting the electrodes
disposable electrodes : pre gelled and no further gel is required -do not press them in the middle as the gel will then be dispersed -gently pull on the electrode a few seconds after application and it should remain adhered to the skin reusable electrodes : should always apply a conductive electrode gel (10-20 paste) and then use medical tape to hole them in place
80
electrode impedances
a small current is applied to one electrode and the amount of cross over is determined in a second electrode to determine interelectrode impedance -low and balanced impedances contribute to high quality AER by limiting internal amplifier noise, reducing effects of external electrical interference and maintain higher common mode rejection ratios
81
desired impedance levels
-should be within 3-5 kOhms (down to 1 for reusables) -should not differ by more than 2 kOhms
82
if impedances are too low this means
there is not a direct connection between the two electrodes and may lead toa short circuit at the amplifier output
83
what does it mean when there is high impedances
can occur if there is a fault electrode or if no electrode is plugged into the receptor on the pre amp
84
what are some ways to lower impedances
pressing on the electrode for several minutes, moving the electrode slightly to get better contact, adding more electrode conducting paste, securing the electrode snugly with additional tape and removing the electrodes with higher impedances and re-prepping the skin
85
ways to reduce impedance and improve recordings : test environment
-turn off any unnecessary monitors or light -ensure you are using the designated and grounded electrical outlet -if chair is operated electrically, unplug it -always choose the largest size of ear tip
86
ways to reduce impedance and improve recordings : electrodes
-braid electrodes or tape them to help prevent noise from getting in the recording -do not mix electrode type -all electrode wires should run towards the top of the head with the transducer wires running down (they should not mix)
87
what do we mean when we say electrode montage
this is when we use the 10-20 convention, basically another way to talk about the electrode placement
88
our reference electrode will be a ___________ electrode
inverting
89
two channel recording
both ipsi and contra ear recordings can be performed simultaneously -can be done through the usage of jumpers
90
in a two channel recording, how can we differentiate the two
there is absent/reduced wave 1 and 2 in the contralateral response, plus longer latencies on the contralateral measurements

AUDE 6470 (2 decks)

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