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PSG: Polysomnography Board Prep ch 2


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What electrical component does an electrode act as?
A capacitor
What does the abbreviation ADC stand for?
Analog-to-digital converter
What 4 components are part of the signal pathway?
Digital converter
What is the purpose of the ADC?
Converts analog signals from the patient, to digital values to be read by the computer
*What is "sampling rate"?
The rate at which the computer program samples the analog information to convert it to a digital signal.
*What is the "Nyquist principle"?
The sampling rate must be at least twice as fast as the fastest frequency that will be recorded.
What is the ASET standard for the Nyquist Principle?
Sampling rate needs to be at three times faster than the HFF setting (~90-105)
What is the normal sampling rate for EEG channels?
200+ per second
What is the normal sampling rate for respiratory channels?
10 per second
What is meant by the term "aliasing"?
Low sampling rate causing a tracing that is not smooth
What is meant by "sampling skew"?
When all channels are not sampled simultaneously
How is sampling skew avoided?
Each amplifier having its own ADC, or
Sample and hold method
What is "ADC precision"?
Vertical resolution
What are the 2 types of sensitivity, in relation to the recording?
Amplifier sensitivity
Display sensitivity
Is the amplifier sensitivity kept relatively high or low?
Is the amplifier sensitivity in the hardware or the software?
Hardware (but may be accessed through the software)
What does the display sensitivity do?
Makes the waveform larger or smaller on the screen itself
What are other terms for "display sensitivity"?
Zoom factor
Pen deflection
In which unit is display sensitivity expressed?
What does the abbreviation "HFF" stand for?
High-frequency filter
What does the abbreviation "LFF" stand for?
Low-frequency filter
Wht is the 60-hertz filter also know as?
Notch filter
What are filters?
Electrical devices that allow us to zero in on the frequencies we want to see and reduce those we don't want to see
What is the high-frequency filter also known as?
Low pass or low cut filter
What is the purpose of the high-frequency filter?
Reduces high-frequency interference
What is the low-frequency filter also known as?
High pass or high cut filter
What is the purpose of the low-frequency filter?
Reduces low frequency interference
What is the purpose of the 60-hertz filter?
Eliminates 50- or 60-hertz frequency artifact from the amplifier output
What is the "time constant"
The amount of time it takes for the signal to fall to 37% of the original amplitude of a calibration signal
In which unit is the time constant measured?
What other filter does the time constant act as?
Low filters
What kind of bandpass does an amplifier filter have?
Wide bandpass
What are the HFF and LFF of the amplifier filters?
LFF below 0.1 Hz
HFF above 100 Hz
What are three units of measurement used in filtering?
Hertz (Hz)
Seconds (sec)
Decibels (dbl)
What is the normal value for LFF on a digital filter?
0.3 Hz
What is the normal value for HFF on a digital filter?
35 Hz
At a LFF of 0.3 Hz (or HFF of 35 Hz), how much is the amplitude of the low (high) frequencies reduced?
At what point is the 60 Hz filter applied?
Only when 60 Hz artifact is noted
If you change the filters on an EEG filter, what do you to the other EEG channels?
Change the filters on all the EEG channels to the same value
What does a faster TC do?
Reduces amplitude of slow frequencies
What does the term "drop" refer to in relation to TCs?
Decay time
What does the term "rise" refer to in relation to TCs?
Rise time
What does the term "low cut" refer to in relation to TCs?
Same as high pass filter
What is the the 60 Hz filter in Europe?
50 Hz
What frequency range does the notch filter filter out?
58-62 Hz
Do you need a longer or a shorter TC for airflow?
Longer TC because it takes more time for waveform to drop to 37%
What is the formula for the relationship between TC and LFF?
LFF = 1/(2pi x TC)
What is the 60 Hz filter also known as?
Line filter
What is the purpose of the low frequency filter?
Designed to reduce the amplitude of frequencies at and below the selected frequency
What is the purpose of the high frequency filter?
Designed to reduce the amplitude of frequencies at and above the selected frequency
What is the purpose of a high frequency response curve?
To show how much the amplitude is affected by useng a HFF
What is a differential amplifier (AC amplifier)?
Instrument used to process common mode rejection using inputs from exploring and reference electrodes
What is common mode rejection?
A method of processing input signals in which any identical voltages are eliminated, while dissimilar voltages are recorded
Which frequencies do AC amplifiers process?
Relatively fast signal frequencies (EEG)
Which frequencies do DC amplifiers process?
Relatively constant or slowly fluctuating voltages
Does an AC amplifier have a LFF, HFF, or both?
Does a DC amplifier have a LFF, HFF, or both?
What is an AC amplifier calibrated to?
A DC voltage
Is the signal of the cornea positive or negative?
Is the signal of the retina positive or negative?
What is the acceptable EMG impedance?
<30 kohms
What is G1?
Exploring electrode
What is G2?
Reference electrode
What is "gain"?
A measure of the ability to change the magnitude of the input voltage
What is "sensitivity"?
The amount of output (pen deflection) to a given input voltage
What is Ohm's law?
V = SD
V = voltage
S = sensitivity
D = pen deflection
What does the device calibration do?
Calibrates a known voltage to the ADC so it can assign the proper voltage to incoming signals
**What voltage is used on the device calibration?
50 uV
What is checked on a calibration wave?
-Electrical baseline
-Mechanical baseline
-Pen damping
-Time axis
What do you check electrical baseline?
See if there is any movement off the horizontal line
How do you check mechanical baseline?
Spacing between channels should be even
How do you check damping?
Tip of waveform should not be too smooth or too sharp
How do you check the time axis?
The waveforms should be in line vertically

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