Week 13-14 - Non-pathologic factors, Calibration, Norm data, Case report, ECochG
What are 4 criteria for normality?
False positive outcome False negative outcome Sensitivity Specificity
Advantages of Insert transducers Disadvantages of TDH & BC
Inserts ➤ less stim artifact ➤ less ringing ➤ prevent collapse EC ➤ reduce cross over ➤ reduce ambient noise ➤ better placeemnt ➤ more comfortable TDH ➤ electromagnetic artifact with 39 ➤ collapsed EC ➤ cross over BC ➤ occlusion effect ➤ restricted range ➤ stim artifact
What are considerations for collecting normative data? 4 catergories
Instrumentation ◦ Eclipse or Intelligent Hearing System ◦ Transducers, electrodes (types used & montage) Subject Characteristics ◦ Age, sex, number of subjects ◦ Audiologic & neurologic status Stimulus Parameters ◦ Mode of presentation ◦ Type of stimulus ◦ Intensity ◦ Rate ◦ Polarity ◦ Masking Acquisition Parameters ◦ Electrode array ◦ Filter settings ◦ Analysis time
ECochG, how do you measure it and why would you measure it?
Measure it similar to ABR (but maybe different montage - non-inverting inside the EC To measure the status of HC's, & distal portion of 8th nerve
What is normal pattern for SP/AP?
More robust AP vs. SP
What structure generates CM?
OHCs
what are ECochG onset, components, and blood supply?
Onset - Within 1st 2-3 msec after abrupt stimuli - Precedes ABR Components - 2 Sound evoked cochlear potentials ➤ CM (Cochlear Microphonic) · 1st recorded in 1930 (Wever & Bray) ➤ SP (Summating Potential) - 1 Compound 8th CN AP (Action Potential) (= N1, AP, Wave I) Blood Supply - Vertebrobasilar artery - Internal auditory artery - Anterior inferior cerebellar artery (AICA)
Overview of generators of ECochG
Overview of Generators of ECochG ➤CM = OHC ➤SP = HC ➤AP = distal portion of 8th nerve
CM is best evoked by what stimulus polarity?
Rarefaction & Condensation
Normal ECochG pattern?
Robust AP Preceded by distinct (yet small amp) SP
What component of ECochG is sustained throughout longer stim durations?
SP
Generally, how do different CNS drugs affect the ABR. Don't worry about memorizing all the different agents used but do be aware of the more popular ones and what their effects are. ABR, ECochG
Sedatives & hypnotics ➤ ABR & ECochG = no or minimal effect - Chloral Hydrate = most popular for quieting babies during ABR Anesthetic agents ➤ ABR & ECochG = not seriously affected - Fentanyl, Nitrous Oxide, Ketamine, neuromuscular blocker Alcohol ➤ ABR = longer III-VII; Amp no change; delayed latency (chronic use) ➤ ECochG = small CM amp (acute use)
What are sensitivity & specificity? How will narrow range of normal values affect them?
Sensitivity · Proportion of persons HAVING pathology who are classified as ABNORMAL Specificity · Proportion of persons NOT HAVING pathology who are classified as NORMAL Narrow Range of Normal Values ➤ increase sensitivity of test ➤ decrease specificity of test
Know how stimulus factors (Masking) affect the different auditory evoked potentials.
ABR ECochG 50 dB nHL to NTE
Know how stimulus factors (Mon & Binaural Stimulation) affect the different auditory evoked potentials.
ABR w/ BINAURAL stim ➤Latency = no change? ➤Amplitude = wave V increase 2x ➤Morphology = ECochG (less studied) w/ BINAURAL stim ➤CM = ➤SP = ➤AP = amp decrease; latency NO change
Know how stimulus factors (Stimulus Rate) affect the different auditory evoked potentials.
ABR w/ HIGHER rate ➤Latency = later (more for later wave) ➤Amplitude = decrease ➤Morphology = earlier waves may disappear ECochG ➤CM = no effect ➤SP = no effect ➤AP = same as ABR
Know how stimulus factors (Stimulus Polarity) affect the different auditory evoked potentials.
ABR w/ RAREFACTION polarity ➤Latency = earlier ➤Amplitude = increase (maybe) ➤Morphology = ? ECochG ➤CM = R & C out of phase ➤SP = no effect ➤AP = same as ABR
Know how stimulus factors (Stimulus Intensity) affect the different auditory evoked potentials.
ABR w/ intensity INCREASE ➤Latency = earlier ➤Amplitude = increase ➤Morphology = more prominent ECochG w/ intensity INCREASE ➤CM = latency NO change; amp INCREASE ➤SP = only recorded at HIGH intensity; depend on electrode site ➤AP = same as ABR
Know how stimulus factors (Stimulus Frequency) affect the different auditory evoked potentials.
ABR ➤Latency = HF earlier; LF later ➤Amplitude = same...? ➤Morphology = HF sharp peak; LF rounded peak ECochG ➤CM = waveform resembles pure tone stim of single polarity ➤SP = follows envelope of stim ➤AP = same as ABR
Know how stimulus factors (Stimulus Duration) affect the different auditory evoked potentials. How to differentiate SP & AP?
ABR ➤Latency = later w/ stim rise time INCREASE ➤Amplitude = ? ➤Morphology = ? ECochG ➤CM = no effect ➤SP = no effect ➤AP = same as ABR Differentiate SP & AP Extend stim duration SP will persist AP only appear immediately following stim onset
What are analysis time for ABR click, TB, ECochG only, & ECochG/ABR combo platter?
ABR click = 10-15 msec TB ABR = 20-25 msec ECochG only = 5 msec ECochG/ABR combo platter = 10-15 msec
Explain Cochlear Microphonic (CM) characteristics origin recording site mechanism of production polarity
AC (alternating current) potential Characteristics - follows waveform of stimulus - Pure tone stim (Tone Burst) produces CM like a sine wave of same frequency Origin - Arises from OHCs (Dallos, 1973) Recording site - Outside recording = reflects OHC activity from BASAL END of BM Mechanism of CM production - Not clearly defined - Maybe velocity / acceleration of HC movement & displacement of BM Polarity - Best evoked by single polarity (i.e., condensation, rarefaction) 0 Alternating will cancel out CM
What is the CM?
AC potential that follows the stimulus
How is ECochG affected by increase in stim intensity?
AP latency decrease (earlier) AP amplitude increase SP not seen at lower intensity levels
Know how nonpathologic characteristics and what they affect evoked potential recordings. (short version)
Age - infancy & childhood = delayed latency, smaller amp - advancing age = delayed latency, smaller amp Body temperature - hypothermia = delayed latency, smaller amp (but CM no latency change) - hyperthermia = earlier latency? less studied Attention & state of arousal - awake vs. sleep = no difference Effects of drugs - ototoxic = damage OHC; change in ECochG; ABR to monitor effects if behavioral not possible - CNS (sedative & anesthetic) = below - sedative = no or minimal effect - anesthetic agents = not seriously affected - alcohol = latency delayed; longer III-VII; CM amp smaller Muscular artifact - can be obscured
nonpathologic characteristics Infancy & Childhood ABR & ECochG
Age: - 27-28 wks conceptional age = can measure ABR (prominent wave I - may be delayed) - 35-38 wks = ECochG measured (delayed latency & small amp) - 0-18 mo = other waves emerge (III & V latency shorten) - 18-24 mo = adult-like ABR Overall: - ABR incomplete at birth (only I, III, V) - interwave latency longer (5 msec)
Know how to write a case report. You should have at least 4 parts; background information, results, impressions, and recommendations. You will be given all the information you need to write a report.
Background info _____ was seen for ABR evaluation on 5/11/2022. Prior history includes: ______. Audiometric test results indicated ______. ME measures indicated ____ and ipsi & contra AR _____. OAE were ____. ABR testing completed with AC clicks presented to each ear through insert earphones at rates of 17.1 and 65.1 per second and an intensity level of 70 dB nHL. Copies of marked waveforms and a summary table of absolute and interwave latencies are enclosed Results Results of ABR testing are interpreted as ______. The abnormal findings for LE are based on prolonged absolute latencies for Waves III & V and prolonged I-III & I-V interwave latencies. Impressions Normal ABR results for the RE and abnormal for the LE. Recommendations Recommendation is made that imaging studies and medical follow-up be obtained
What stimuli can you use to evoke ABR's?
Broadband (i.e., click, chirp) Frequency-specific (i.e., tone-burst, NB chirp)
How would you determine a normal vs. abnormal ABR for retrocochlear pathology? If an abnormality is found, what information can this provide as to the location of a tumor?
By comparing absolute, interwave latencies interaural latency difference to norms Tumor may be located where the prolongation of interwave latency is found
What components of ECochG are affected by stimulus frequency?
CM & AP
Calibration What is it? Why? When? How? What to calibrate?
Calibration = adjustment of equipment or application of defined correction factor when using equipment Why - To meet performance criteria - to ensure properly functioning equipment When - periodically How - Need additional equipment (i.e., oscilloscope - device to view electrical signal) - Consult evoked response manual to get equipment specifications - Manufacturer offer for free What to Calibrate - Amplifier (no need oscilloscope) - Stimulus Rate - Stimulus Polarity - Stimulus Intensity
AP amplitude is largest for what type of stimulus?
Click (brief onset)
What does ECochG consist of?
Cochlear Microphonic Summating Potential Action Potential
Explain Summating Potential (SP) characteristics origin effect of rapid rate & HF stim
DC (direct current) potential Characteristics - Shift in baseline recording - Same direction & just prior to compound AP of 8th CN Origin - HC - Precise source in cochlea unknown ⇒ Distortion products associated w/ irregularities in BM & HC displacement ⇒ Subsequent generation of electrical current ⇒ Both IHC & OHC activity Rapid Rate & High Freq Stim - Unlike AP, clearly observed w/ extremely RAPID stim - Prominent recording w/ HF TB stim
What is SP?
DC potential that does NOT follow the stimulus
What structure generates AP?
Distal portion of the 8th nerve
3 Problems with relying on published norms
1) Inflexibility in test protocol - Follow stimulus parameters, analysis techniques (wave peaks vs. shoulders) PRECISELY 2) Few carefully defined & published norm data bases for threshold ABRs - Also for ECochG, MLR, LLR, P300 3) For certain ABR applications, data bases might be more appropriately obtained from pts not necessarily normal - Those who simply do not have the pathology of interest - E.g., data from pts w/non-tumor hearing impairment to help differentiate b/w cochlear vs. retrocochlear
Abnormal ECochG patterns (2)?
1) Little or no response of AP (under typical measurement conditions) - Most common reason for reduced ECochG = Cochlear pathology (> 1kHz region) 2) SP amp abnormally LARGER than AP amp - Associated w/Meniere's disease (endolymphatic hydrops)
What are uses of ECochG?
1) Objective identification of Ménière's disease (endolymphatic hydrops) 2) Identification of CM for Auditory Neuropathy 3) Enhancement of Wave I & Identification of I-V interwave interval ⇒ in presence of HL or less than optimal recording conditions 4) Monitoring of cochlear & auditory nerve function ⇒ During surgical procedures at risk for permanent damage in ear
4 Problems with generating own norms
1) Time-consuming 2) Require Normal subjects - Minimally young adult males & females 3) Must consider age of subjects 4) If changes to setting (i.e., filter) or transducer => must do norms over
What to include in ABR report? How many pages?
1) copies of actual ABR waveforms 2) test parameters 3) latency values numerically & marked on waveforms Limit report to ONE page
Explain Action Potential (AP) characteristics Intensity related amplitude increase intensity related latency decrease N2 of ECochgh
Far-field representation of compound AP of 8th CN Characteristics - Reflects synchronous firing of many 8th nerve fibers - Amp largest for transient stim w/ abrupt & rapid rise times (i.e., click) - AP amp INCREASE & latency DECREASE with stim intensity INCREASE Intensity Related Amplitude Increase - Due to increased # of 8th nerve fibers contributing to response ⇒ More neuroelectric activity summating at essentially the same time - Synaptic properties of HCs affect AP latency & amp ⇒ Rate of Excitatory Postsynaptic Potentials Intensity Related Latency Decrease - Due to reflecting more basal origin of cochlear activity ⇒ BM traveling wave for HIGHER intensities extends in that direction N2 of ECochG (= Wave II) - Originate more from apical end of cochlea - N2 occurs with LOW intensity stim - N1 occurs for HIGH intensity stim - Generator = proximal end of 8th nerve???
nonpathologic characteristics Advancing age & gender ABR & ECochG
Gender Effect - Females • Shorter latency & larger amplitude for later waves (III, IV, V, VI) • Interwave latencies shorter Age Effect (both ABR & ECochG maybe) - 25 -> 55 years (delay latency of ~0.2 msec) - small amp Age & Gender Effects Can interact & affect ABR
nonpathologic characteristics Body temperature ABR & ECochG
Hypothermia ABR = delayed latency, small amp (ABR disappears with severe hypothermia) - due to delayed synaptic transmission, decreased axonal conduction velocity ECochG = CM (only small amp, no latency change); SP (variable change); AP (same as ABR) Hyperthermia Less studied Maybe earlier latency
Temperature correction factor for hypothermia? Temperature correction factor for hyperthermia?
Hypothermia Every 1 C DECREASE body temp (37C) = I-V + 0.2 msec Hyperthermia Every 1 C INCREASE body temp (37C) = I-V - 0.15 msec
What are 2 general types of abnormal ECochG results?
Little or no response of AP Large SP & small AP
How do measurement factors like stim freq, rate, and gender effect play a role in newborn ABR?
Stimulus Frequency - ABR elicited with LF stimuli more important for generating ABR in newborns (than adults) - Animal models - found change in tonotopic organization of cochlea with maturation Stimulus Rate - w/ increase rate - more pronounced increased in latency in newborns (than adults) Gender Effects Mixed findings
Know when you would need to mask for EP testing and what your results would look like if you were supposed to have masked and did not.
When there is a potential for cross over of stimulus sound to the NTE Usually one normal ear and one dead ear If not properly masked, you would see ABR responses from dead ear (amount that has been crossed over)
Know when you would want to do bone conducted ABRs and what this information will tell you.
When we need to bypass ME (i.e., OM, atresia) When we need to find out the type of HL
Define Chloral Hydrate
➤ most popular sedative for quieting children during ABR testing ➤ typical dosage = 50 mg/kg of body weight (max 1000 mg) ➤ administered by physician or RN ➤ NOT affect ABR
Define ototoxic
➤ Damage to ear brought by a drug which depends on many factors (i.e., duration of administration, type of infection, age of patient, etc.) ➤ Can use ABR to monitor effects of drug if behavioral testing not possible
Why should we do temperature correction in ABR?
➤ Monitoring deleterious changes in neurologic status - CNS changes reflected by increase in ABR latency ➤ Must rule out body temp change before stating neurologic change
How do you establish normative data? For ABR what categories we need for norm data?
➤ Must establish & define how to analyze waveform amplitude & latency (diagrams to aid) E.g., Choose peaks, shoulders, etc. ➤ Use cutoff criterion for normality - 2-2.5 standard deviations above mean value for normal subject group ➤ Some equipment has software to aid in creating a normative database - Saves latency, amplitude info into database - Provides descriptive statistics (mean, standard deviations) For ABR - latency values (I, III, V) - minimally - interwave latencies - amp for wave I & V (V/I ratio)
What is an abnormal SP/AP ratio?
➤ SP/AP ratio = 0.45 or greater ➤ SP amp is more than 45% of AP amp **indicative of Ménière's disease** **SP/AP area ratio maybe better?**