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Basics Of Electrode Application > Electrodes > Flashcards

Electrodes Flashcards

0
Q

What is impedance mismatching?

A

The input impedance of electrode pairs is not similar.

This allows current to pass through to the amplifier and can lead to artifact.

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1
Q

What do electrodes in PSGs do

A

Conduct bio potentials from the patient to the recording circuit.
Lower impedance allows higher conductance and produces higher amplitude waveforms

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2
Q

What is common mode rejection

A

It is the cancellation of voltages equal to both input electrodes.
Impedance mismatch impairs common mode rejection.

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3
Q

When is Optimal signal quality possible?

What is the ideal impedance range?

What is the upper limit?

A

Impedances are low enough to maximize amplitude
Take advantage of common mode rejection
And avoid impedance mismatching.

Range from 1-5ohms regardless of the amplifier used although its effect is less pronounced in some recent high input impedance amplifier designs

Standard electrode impedance upper limit is 5ohms for EEG & EOG
10ohms for EMG & ECG

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4
Q

What is signal averaging time for pulse oximetry?

A

3 seconds or less

Pulse oximetry does not reflect gas exchange and therefore can not detect changes in PaCo2

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5
Q

What is capnography?

What are the two types and how do they work?

What is the normal range?

A

Capnography is used to measure the patients CO2 level

Transcutaneous PCO2- the electrode is placed directly on the skin and heated to 42-45 degrees C. It measures the transpired PCO2 , which fairly accurately reflects tissue PCO2.
Preferred for monitoring neons yes in ICU however only accurate in other with good tissue perfusion.

35-45mmhg

End tidal is commonly used in children and some adults. Uses a nasal or nasal/oral cannula or tight fitting mask to produce numerical and graphical displays of CO2 levels. It reflects the CO2 in the lungs and blood at end of expiration

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6
Q

What is the montage of a standard PSG?

A

Channel LOC, ROC, Chin EMG, Frontal EEG, Central EEG, occipital EEG, left anterior tibialis, right anterior tibialis, ECG, Snore, Pressure Flow, Thermal Flow, Thoracic effort belts, Abdominal effort belts, CPAP, SpO2.

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7
Q

What are Sensitivities , Filter setting & Sampling rates of EEG&EOG?

A

EEG & EOG sensitivity 5-7uv/mm
High filter 35Hz
Low Filter 0.3Hz
Sampling rate=500Hz.

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8
Q

What is the sensitivity, filter settings and sampling rates for EMGs

A 
EMG chin & Legs
Sensitivity 10uv/mm
High filter 100Hz 
Low Filter 10Hz  
Sampling rate 500Hz.
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9
Q

What is the sensitivity, filter settings and sampling rates for ECGs

A

ECG sensitivity 20uv/mm
High filter 70Hz
Low Filter 0.3Hz
Sampling rate=500Hz.

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10
Q

What are Sensitivities , Filter setting & Sampling rates of Snore?

A 
Snore
Sensitivity 20uv/mm
High filter 100Hz 
Low Filter 10Hz  
Sampling rate=500Hz.
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11
Q

What are Sensitivities , Filter setting & Sampling rates of Pressure & Thermal Flow?

A 
Flow 
Sensitivity 20uv/mm
High filter 15Hz 
Low Filter 0.1Hz  
Sampling rate 100Hz.
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12
Q

What are Sensitivities , Filter setting & Sampling rates of Effort Belts

A 
Effort Belts
Sensitivity 10-100uv/mm
High filter 15Hz 
Low Filter 0.1Hz  
Sampling rate 100Hz.
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13
Q

What are Sensitivities , Filter setting & Sampling rates of CPAP?

A

CPAP

DCx

High filter 5Hz

Sampling rate 100Hz.

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14
Q

What are Sensitivities , Filter setting & Sampling rates of SpO2?

A

SpO2

DCx

High filter 5Hz

Sampling rate 25Hz.

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15
Q

What is Nyquist theory?

A

The theorem states that a sampling rate of a minimum 2x the frequency of the original data being measured is needed to be able to adequately reconstruct a signal.

200Hz is the recommended minimum setting.

Recommended setting is 500Hz

16
Q

What is a differential amplifier?

A

Differential amplifiers
Designed to distinguish between the desired physiologic voltage at the exploring electrode site & all other unwanted voltages from the body & the external environment using common mode rejection.

17
Q

What is aliasing

A

If a sample is set lower than the frequency band width being recorded, the reconstructed data may be distorted this is aliasing.

Using a higher sampling rate will increase data resolution but will also require more memory

AASM has recommended sampling rates for each type of signal ring acquired.

18
Q

What is a montage?

What are the types?

A

In PsG terms, montage is a common term to describe the array of electrode derivations for acquiring, recording, and displaying data.

Acquisition montages identify the location and the storage rate (sampling rate) for each acquired channel.

The display montage defines the way the data will be viewed, such as the order of signal display, channel sensitivity, filters etc

19
Q

Display montages can be bipolar or referential.

Explain these terms

A

Bipolar montages display the difference between two active electrodes. Eg f4 - c4

Referential montages display the difference between one active electrode and one reference electrode.

20
Q

Where are reference electrodes placed?

A

Typically placed in an area where there is very little bioelectrical activity. Such as the mastoid process.

21
Q

Can anyone viewing a PSG change the derivations or montages without permanently modifying raw data?

A

Yes
Digital recording systems are designed to collect & store each signal separately.

Referencing all EEG signals to a common electrode (typically Cz) is the most common method of collection/recording.

It is accomplished by digitally subtracting activity originating in the common reference (Cz) from a pair of electrodes.

22
Q

What are the AASM guidelines for the performance of mslt?

A

5 nap opportunities separated by 2 Hr intervals. The only time that a shorter four nap test is acceptable is in pts with narcolepsy, who have had at least 2 REM periods during the study.

23
Q

What are the AASM guidelines for the performance of MWT?

A

MWT consists of 40 min trials and measures the patients ability to resist the urge to fall asleep.
Protocols vary but consensus is that an individual MWT trial is ended at sleep onset
3 epochs of 1 or one epoch of any other stage of sleep.

24
Q

What are Zaleplon & Zolpidem?

A

Sedatives that are used to treat insomnia by aiding in the initiation and maintenance of sleep
Result is a shortened sleep latency and increased sleep efficiency. They do not decrease stage REM sleep.

25
Q

What is a low frequency filter?

A

Low frequency filter also called a high pass filter, attenuates components below the filter setting & allows those above the setting to pass through.

Basics Of Electrode Application (4 decks)

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