Clase BERA

Name: Clase BERA
Uploaded: 2022-10-17T00:00:00.000Z
Duration: 3 h 40 min 36 s

Introduction to Auditory Brainstem Evoked Potentials

Overview of Auditory Brainstem Responses

The session focuses on understanding auditory brainstem evoked potentials, a complex term that can be broken down for clarity.

The concept relates to action potentials and nervous stimuli, which are fundamental in physiology classes.

These responses occur at the cellular level and involve synaptic activity.

Terminology and Acronyms

Various acronyms exist for auditory brainstem responses, including ABR (Auditory Brainstem Response), VERA, and PEATC in Spanish.

These terms all refer to the same phenomenon: auditory responses generated by the brainstem.

Mechanism of Response

The class aims to explain how acoustic stimuli elicit electrical responses from the brainstem.

This bioelectric activity is measurable; equipment captures these signals and converts them into waveforms for analysis.

Understanding Bioelectricity in the Brain

Communication Between Neurons

Neurons communicate through small electrical impulses, which are low amplitude signals.

An analogy is made comparing high voltage shocks versus mild sensations from low amplitude currents.

Production of Bioelectricity

Humans produce bioelectricity during synaptic activities; this is essential for neural communication.

Electroencephalogram (EEG)

Purpose of EEG

An electroencephalogram records electrical activity in the brain using electrodes placed on the scalp.

Typically, 16 to 25 flat metal discs are used to capture bioelectrical activity across different regions of the head.

Recording Process

A conductive paste is applied to enhance electrode contact with the scalp for accurate readings.

The recorded signals are amplified for better visibility since they originate as low amplitude waves.

Applications of EEG

Clinical Uses

EEG is utilized to diagnose neurological conditions such as epilepsy or sleep disorders by monitoring brain activity patterns.

Understanding Bioelectric Activity and EEG

Overview of Bioelectric Waves

The bioelectric activity captured through electrodes is amplified and visualized on a screen, allowing for the observation of different types of brain waves.

Various brain wave types are identified, ranging from Beta waves (high frequency) to Delta waves (low frequency), with Beta waves appearing more frequently as closely spaced spikes.

Brain wave patterns represent different states of consciousness; Beta indicates alertness while Delta signifies deep sleep, characterized by lower neural activity.

As attention wanes throughout the day, individuals transition from Beta to Delta waves, reflecting decreased cognitive engagement and increased fatigue.

Characteristics of EEG

The electroencephalogram (EEG) records spontaneous bioelectric activity in a resting state, which is typically low amplitude and can be measured and visualized.

Spontaneous bioelectric activity occurs in the absence of sensory stimulation (auditory, visual, etc.), forming the basis for understanding EEG readings.

The EEG reflects the central nervous system's electrical activity when no external stimuli are present.

Changes in Response to Stimuli

When stimuli are introduced during an EEG test (e.g., auditory or visual), the previously irregular wave patterns begin to change significantly.

Sensory stimulation leads to observable changes in brain wave patterns that can be extracted from the EEG data, known as evoked potentials.

Evoked Potentials Explained

Evoked potentials arise from specific sensory stimuli causing alterations in baseline bioelectric activity recorded by the EEG.

These changes manifest as larger waves that indicate heightened neural responses due to acoustic stimuli.

Techniques for Analyzing EEG Data

A group response from synapses triggered by sensory input results in distinct changes within the base bioelectric activity observed on an EEG.

Historical recognition of these phenomena led to techniques designed to extract low-voltage evoked responses from standard EEG recordings.

Computational signal averaging techniques were developed to analyze these subtle changes effectively.

Summary of Key Concepts

Understanding how various brain wave patterns correlate with states of consciousness is crucial for interpreting EEG data accurately.

Understanding Auditory Stimuli and Evoked Potentials

The Nature of Auditory Stimuli

The discussion begins with the concept of auditory stimuli, emphasizing that they are constant and synchronized, which is crucial for generating a response.

A repetitive and constant acoustic stimulus is introduced, marked in red to signify its importance in triggering responses.

Response Generation from Acoustic Stimuli

As multiple acoustic stimuli converge at a point (indicated by a red arrow), they trigger an increasingly larger response over time.

The accumulation of repeated stimuli leads to a growing wave response, referred to as the evoked potential.

Characteristics of Evoked Responses

The evoked response signifies a stable reaction over time, contrasting with random activity when no stimuli are present.

Summation or averaging of stimuli enhances the evoked response above baseline bioelectric activity, making it more discernible.

Measuring Bioelectric Activity

An example illustrates measuring bioelectric activity in the absence of external stimuli, highlighting randomness without any defined pattern.

Introducing an external auditory stimulus aims to evoke a sensory response from the subject's nervous system.

Enhancing Clarity in Measurements

Multiple acoustic stimuli are presented simultaneously (indicated by green arrows), aiming to elicit a clear electrical response from the baseline activity shown in blue.

Increased stimulation results in larger waves that can be measured more effectively, allowing for better clarity and understanding of the responses elicited by sensory inputs.

Distinguishing Between Types of Activity

The distinction between evoked responses (in red) versus baseline bioelectric activity (in blue), where the latter appears random without any structured pattern.

To achieve stable responses over time with defined patterns, it is essential to provide numerous stimuli consistently.

Practical Applications and Considerations

Auditory evoked potentials are non-invasive and comfortable for subjects; ideally suited for use with infants who may not require sedation during testing.

Electroencephalogram (EEG) Classification and Responses

Classification of Potentials

The classification of potentials in EEG is based on latency, which refers to the time taken for a response to appear after an acoustic stimulus.

Another classification method is anatomical origin, identifying where in the auditory pathway the response occurs.

Electrode Placement and Measurement

Electrodes are placed at various points on the head; however, they measure bioelectric activity from distant locations like the brainstem rather than directly at the source.

Historically, invasive methods were used to measure potentials by inserting electrodes into the ear canal, but modern techniques utilize non-invasive approaches.

Types of Responses

The focus will be on short-latency responses evoked by acoustic stimuli, typically occurring within 1 to 10 milliseconds.

Short-latency responses are crucial as they provide insights into immediate neural processing following auditory stimulation.

Latency Categories

Responses can be categorized into short-latency (1–10 ms), medium-latency (15–80 ms), and long-latency (80–300 ms).

Ultra-long latencies (300–700 ms) are also noted but are less relevant for this discussion as they pertain more to cognitive processes.

Subcortical vs. Cortical Processes

Responses can be divided into subcortical processes (early and medium latencies occurring in the brainstem) and cortical processes (late latencies occurring in the cortex).

Understanding Auditory Potentials and Their Latencies

Types of Potentials: Exogenous vs. Endogenous

The discussion begins with the distinction between late latency cognitive potentials and short latency potentials, emphasizing that the vertical axis indicates the onset of acoustic stimulation and how long it takes for a wave to appear after stimulus delivery.

Exogenous potentials require an external stimulus (e.g., auditory stimuli delivered through headphones), while endogenous potentials arise from internal cognitive processes without external sensory input.

An example of endogenous potential is recognizing a spelling error during reading, which generates a response independent of external stimuli.

Cognitive Processes and Attention

Red elements in the previous slide represent responses typically triggered by exogenous sensory stimulation, whereas upper cortical processes are cognitive functions occurring without external stimuli.

Sensory potentials do not necessitate attention to the acoustic stimulus; they occur automatically upon presentation, unlike cognitive potentials that require focused attention.

Early latency responses can be elicited passively, but late latency cognitive responses demand active concentration on specific stimuli.

Characteristics of Auditory Responses

Early auditory responses manifest within 5 to 6 milliseconds post-stimulus; although they can last up to 10 milliseconds, focus will be on the first five waves.

The initial five peaks in auditory response are crucial for analysis; these peaks are labeled using Roman numerals I through V based on their timing relative to stimulus presentation.

Wave Generation and Latency Measurement

The significant peaks in waveforms correspond to specific latencies measured from when an acoustic signal is presented until a response occurs.

Each peak's timing is critical; for instance, Wave I appears approximately 1.62 milliseconds after stimulus onset, while subsequent waves show increasing latencies.

Neural Synchronization in Response Generation

Waves I and II originate in the acoustic nerve—Wave I being closer to the cochlea than Wave II.

Wave III arises from cochlear nuclei within the auditory system anatomy discussed earlier.

Understanding Auditory Responses and Stimuli

Overview of Auditory Waves

The auditory response involves synchronized answers to analyze acoustic stimuli effectively, with waves 1, 2, and 3 originating from the same side as the stimulus.

Wave 5 indicates activity in the midbrain contralateral to the stimulation; for example, stimulating the right ear produces waves on both sides but reflects left-side midbrain activity.

The discussion focuses on identifying points generating responses for five key auditory waves.

Stimulation Techniques

Effective auditory testing requires an acoustic stimulus delivered through transducers like audiometric headphones or silicone inserts.

A short click stimulus (0.1 milliseconds) is used, covering a frequency range from 250 Hz to 4 kHz, primarily focusing between 2000 Hz and 4000 Hz.

Click stimuli produce large and robust waveforms but are not frequency-specific; they represent a range rather than pinpointing specific frequencies.

Comparison of Stimulus Types

Other stimuli similar to clicks include "secure" sounds that generate larger and more defined responses compared to traditional clicks.

The choice between using click or secure stimuli depends on their ability to evoke clearer neural responses during testing.

Optimal Stimulus Characteristics

An optimal click stimulus generates synchronous neural activity across many neurons, resulting in larger and well-defined waveforms.

To achieve robust responses, multiple acoustic stimuli must be presented; around 2000 total stimuli are recommended for effective averaging of results.

Stimulation Rate Considerations

Understanding Stimulus Presentation and EEG Response

The Importance of Stimulus Balance

A balanced stimulus presentation is crucial for effective evocation; using inferior stimuli (e.g., below 37) can slow down the test, making it less effective.

High stimulation rates can alter wave morphology, leading to unclear patterns in EEG readings. An ideal stimulation rate is suggested to be around 45.1 stimuli per second.

Averaging Stimuli for Clarity

Visual representation shows that increasing the number of stimuli (from 50 to 25,000) improves waveform clarity and stability.

Fewer averaged stimuli result in a spiky waveform with poor pattern recognition; more stimuli lead to clearer and more robust waveforms.

Noise vs. Signal in EEG Readings

The presence of noise in EEG recordings interferes with the desired bioelectric activity; distinguishing between background activity and evoked responses is essential.

Increasing stimulus quantity reduces baseline bioelectric activity, enhancing the visibility of evoked responses while minimizing noise.

Effects of Stimulation Intensity on Waveform Characteristics

Higher intensity acoustic stimuli (80 decibels) produce clearer waveforms compared to lower intensities (20 decibels), which delay response times and reduce amplitude.

Understanding Auditory Response Latency

Relationship Between Stimulus Intensity and Latency

As stimulus intensity increases, latency values decrease; this indicates a faster response time. The amplitude of the response also increases significantly above 70 decibels, while latency remains stable.

The study examines auditory responses at varying intensities from 10 to 80 decibels, focusing on the latency of wave 5, which is crucial for auditory interpretation.

Importance of Wave 5 in Auditory Testing

Wave 5 is highlighted as the most significant waveform in auditory testing due to its role in assessing auditory function. Further interpretation will be discussed in the next class.

At an intensity of 80 decibels, wave 5 appears after approximately 5.7 milliseconds; however, at lower intensities (e.g., 10 decibels), it takes longer (10.5 milliseconds) to appear.

Effects of Noise on Wave Morphology

High noise levels can obscure wave morphology, leading to potential misdiagnosis due to poor visibility of low-amplitude waves.

Providing a sufficient rate and quantity of stimuli reduces background noise and enhances wave morphology for better analysis.

Preparing for Auditory Testing

A brief pause is taken before continuing with practical aspects of conducting auditory exams. The next session will cover how to analyze test results effectively.

Equipment Setup for Auditory Exams

An overview is provided regarding the necessary equipment setup for conducting auditory tests, including electrodes and amplifiers that enhance signal clarity.

Proper insertion devices are essential for delivering acoustic stimuli effectively during testing procedures.

Patient Comfort and Environmental Considerations

Ensuring patient comfort is critical; patients should be relaxed and ideally reclined during testing to prevent temperature loss that could affect results.

Ambient noise must be minimized; while some background sound may be acceptable, excessive noise can interfere with accurate readings during tests like emissions acoustics.

Managing Electrical Noise During Tests

It's important to avoid electrical interference from devices such as cell phones or Bluetooth during testing as they can distort waveform morphology.

Preparation and Placement of Electrodes in Auditory Testing

Importance of Proper Grounding

The significance of a well-grounded electrical setup is emphasized to prevent noise interference during auditory testing. Proper grounding helps maintain the integrity of the data collected.

Electrode Configuration

A total of four electrodes are typically used: one active (positive) electrode placed on the forehead, two negative electrodes positioned on each mastoid (right and left), and a ground electrode that can be placed on the forehead or cheek.

Skin Preparation for Electrode Placement

Before placing electrodes, skin preparation involves using gauze to create friction along with an exfoliant. If an exfoliant isn't available, damp gauze can suffice to prepare the skin adequately.

Ensuring Good Impedance Levels

After preparing the skin, disposable electrodes are applied. If impedance levels are not optimal, additional moisture or conductive paste may be added to enhance conductivity at electrode sites.

Verification of Electrode Positioning

Once electrodes are attached, impedance must be checked to ensure it remains between 0 to 5 kΩ for each electrode with no more than a 2 kΩ difference among them. This step is crucial for accurate readings during stimulation.

Calibration and Setup for Auditory Equipment

Use of Insertion Earphones

The setup includes insertion earphones that require calibration with appropriate adapters before use. These earphones should fit snugly within the user's ear canal for effective sound delivery.

Securing Equipment During Testing

To prevent dislodging during testing, insertion earphones come equipped with clips that attach securely to the user’s clothing, ensuring stability throughout the procedure.

Final Checks Before Testing

After positioning all equipment, it's essential to verify that everything is correctly set up—ensuring proper separation between active and ground electrodes as well as maintaining clear pathways free from obstruction by cables.

Challenges in Measuring Bioelectric Activity

Complexity in Impedance Measurement

The process of measuring impedance is highlighted as one of the most challenging aspects of auditory examinations. Accurate measurement is critical for reliable results in bioelectric activity detection.

Impact of Skin Condition on Readings

It’s noted that excessive moisture or oiliness on the skin can hinder accurate readings from electrodes placed on areas like the forehead due to poor contact quality affecting signal capture.

Cleaning Techniques Prior to Electrode Application

Exfoliation Process

Effective cleaning involves using an exfoliating paste designed to remove dead skin cells and excess oils from areas where electrodes will be placed. This ensures better adherence and signal quality when recording bioelectrical activity.

Post-Cleaning Procedures

Electrode Impedance and Preparation Process

Ideal Impedance Range

The ideal impedance range for electrodes is between 0 to 3 kΩ, with a maximum allowable difference of 2 kΩ between electrodes. If one electrode shows 1 kΩ, the other should not exceed 3 kΩ.

Importance of Cleaning

Proper cleaning of the skin area where electrodes will be placed is crucial. This process must be done meticulously to ensure accurate readings and avoid having to repeat the setup if impedances are out of range.

Types of Electrodes Used

Various types of electrodes are discussed, including disposable ones (white) and reusable cup electrodes (yellow with a gold coating). The latter helps reduce electrical noise during measurements.

Electrode Placement Techniques

Correct placement of electrodes is essential; for instance, positive electrodes may go on the forehead while negative ones are positioned on the mastoid bone. The arrangement affects how stimuli are delivered and responses recorded.

Simultaneous vs Sequential Testing

While it’s possible to prepare both ears simultaneously by placing all necessary equipment, evaluations should ideally be conducted one ear at a time for accuracy in results. This method streamlines preparation without interrupting testing flow.

Cleaning and Gel Application

Exfoliation Process

Before applying electrodes, each area must be cleaned thoroughly but only within the small region corresponding to each electrode's surface area—not excessively over larger areas like the entire forehead. Proper exfoliation ensures better contact and signal quality.

Conductive Gel Usage

A small amount of conductive gel should be applied after cleaning; excessive gel can interfere with readings or cause poor adhesion of the electrode to the skin surface. Proper application enhances conductivity between skin and electrode.

Understanding Bioelectric Activity Capture

Circuit Configuration

The configuration involves using color-coded wires: red for right (positive), blue for left (negative), white for vertex, and black for ground—forming an electric circuit that captures bioelectric activity effectively from brainstem regions during tests.

Impedance Measurement Dial

Electrode Impedance and Signal Filtering Techniques

Understanding Electrode Impedance

The speaker discusses the process of adjusting electrode impedance, starting from a low value and gradually increasing it. When the impedance reaches 1 kOhm, specific electrodes light up, indicating successful detection.

It is crucial to ensure that the impedance between electrodes does not exceed 2 kOhms. If one electrode shows an impedance of 1 kOhm, the others should ideally be below this threshold to maintain balance.

High impedance readings (over 5 kOhms) necessitate removing and cleaning the electrodes before reapplying them to achieve accurate results. Balanced impedance across all electrodes is essential for reliable measurements.

Signal Filtering Techniques

The importance of signal filtering is highlighted; clear waveforms are necessary for accurate analysis. Unfiltered signals can appear jagged or unclear.

Before conducting tests, appropriate filters must be selected based on frequency ranges of interest. Frequencies below 30 Hz and above 3000 Hz can contaminate results.

Two types of filters are discussed: high-pass filters (allowing high frequencies while blocking low ones) and low-pass filters (allowing low frequencies while blocking high ones). This helps in isolating relevant data.

Practical Application of Filters

A high-pass filter set at 30 Hz allows only sounds above this frequency to pass through, effectively eliminating lower frequencies that may interfere with results.

Conversely, a low-pass filter set at 1500 Hz permits sounds below this threshold while blocking higher frequencies, ensuring focus on desired data ranges between 30 Hz and 1500 Hz.

Evaluation Methodology

After preparing the skin and confirming electrode impedances are balanced, various tests can be conducted to evaluate specific frequency responses or broader ranges (e.g., from 500 Hz to 4000 Hz).

Intensity levels for stimulation typically start high (80 dB), decreasing progressively during testing. The goal is to observe response waves at different intensities until they stabilize around a normal range.

Observational Analysis

The appearance of five distinct waves during testing is critical; these should first emerge at higher intensities before being observed at lower levels as intensity decreases.

Visual inspection focuses on wave morphology, amplitude measurement, and latency timing—key factors in assessing auditory responses accurately.

Equipment Setup Overview

Final setup includes selecting stimulus type (alternating polarity), presentation speed (45 stimuli/second), using insertion headphones for both ears, averaging over multiple trials (2000), and setting stimulation intensities appropriately.

Understanding Auditory Responses and Influencing Factors

Sample Collection and Analysis

The process of taking auditory samples requires the user to be calm or asleep. Once the sample is obtained, analysis can focus on latency and amplitude, identifying key waves (1, 3, and 5) along with the auditory threshold based on the last intensity evoking wave 5.

Factors Affecting Auditory Potentials

Age significantly influences auditory responses; newborns under 18 months show altered responses due to incomplete myelination processes.

In adults, age-related loss of myelination also affects response times.

Gender Differences in Latency

There are notable differences in latency between genders; women generally exhibit better latencies compared to men. Body temperature also plays a role—lower temperatures can slow down response times.

Importance of Temperature Management

It is crucial to keep subjects warm during evaluations as a drop in body temperature can lead to slower tracing results.

Conductive Alterations Impacting Responses

The auditory brainstem response (ABR), generated by the eighth cranial nerve, is influenced by conductive alterations which affect latency. Sensory or neural hearing loss will also produce specific changes in latency and amplitude.

Sleep Considerations During Evaluation

Physiological sleep does not typically affect ABR results; thus, it’s recommended that young children arrive for evaluation sleep-deprived to ensure they fall asleep during testing.

Limitations of Click Stimulus Evaluations

Click stimulus evaluations primarily estimate hearing sensitivity within frequencies ranging from 2000 Hz to 4000 Hz. Other tests are needed for lower frequencies.

Complementary Testing Methods

Additional tests such as frequency-specific assessments are necessary for comprehensive audiometric evaluations beyond what click stimuli provide.

Application Beyond Humans

These types of examinations are not limited to humans; they are also utilized in veterinary medicine, indicating their broader applicability across species.

Next Steps: Preparing for Interpretation

Review Recommendations

Students should review material before the next class focused on interpreting examination results and understanding their clinical significance.

Addressing Questions

Students are encouraged to raise any questions or doubts regarding the material through forums or emails prior to the next session for clarification.

Handling Situations During Testing

Managing Sleep Interference

If an elderly subject falls asleep during testing, gentle nudging may help without causing abrupt awakening. Generally, snoring does not interfere with test outcomes unless it disruptively affects acoustic emissions.