PSG: Polysomnography Board Prep ch 2
Terms
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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?
-
Jackbox
Amplifiers
Digital converter
Computer - 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?
- 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
Gain
Pen deflection - In which unit is display sensitivity expressed?
- uV
- 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?
- Seconds
- 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?
- 20%
- 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?
- Both
- Does a DC amplifier have a LFF, HFF, or both?
- HFF (NO LFF)
- What is an AC amplifier calibrated to?
- A DC voltage
- Is the signal of the cornea positive or negative?
- Positive
- Is the signal of the retina positive or negative?
- 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