Chapter 2 Flashcards
Polarity
Refers to the positive or negative nature of a measured signal
Voltage
Refers to electromotive force expressed in a measurement of volts
Current
Refers to the flow of electricity in a circuit
Resistance
Refers to anything that restricts or deters the flow of a current
Differential amplification
Differential amplifiers are required because the signal frequencies generated by the head are also being generated by othere sources
Using the head as a signal source
Virtually all bio electric activity is based on the concentration and flow of ions across the cellular membrane.
This transmembrane potential is based on the concentration of ions (charges) inside the cell to those outside of the cell
CMRR
The ability of the differential amplifier to perform the function of eliminating unwanted signals is called common mode rejection ratio or CMRR
What is the modern EEG amplifier generally have the common mode ratio set at
5000 to 10,000 or more
DC (direct current) voltage
Is defined as the potential that exists as a value between two terminals, as in a battery. Direct-current always flows in one direction from naked terminal to the positive terminal. DC potentials me either be positive or negative.
AC (alternating current)
A voltage is referred to as an AC voltage if it’s potentially between the two connecting terminals alternating charges polarity. AC waveforms may take many complex shapes. the brainwave recording is a good example of how complex AC waveforms
Frequency
Frequency refers to how often or how frequent a wave repeats itself
Hertz or Hz
The number of times there is a polarity change with a return to original condition in one second
Time and frequency are
Reciprocal to each other or as one increases the other decreases
EEG frequency bands
The rhythmicity of EEG signals gives a means of Quantitatively describing EEG records, because the frequency of a rhythm can be measured
Delta waves
Delta waves
Theta waves
4-8Hz
Alpha waves
8-13Hz
Beta waves
> 13Hz
Equations in electronics
If E = voltage, I = current and R = resistant then:
E= IR
I=E/R
R=E/R
Electrical safety in the diagnostic environment is a high priority for several reasons
- Technicians and other medical personnel assume medical responsibility for the welfare of patients seen in the testing environment and during diagnostic procedures
- Patients are usually connected to multiple pieces of electrode diagnostic equipment simultaneously
- Fluids are typically in abundance in the testing environment
- Patient seen in the testing center are often sick or weakened condition and cannot ambulate as they normally would
- Patients with heart conditions are often susceptible to lower levels Electrical activity
To ensure proper safety from excessive leakage current, loss of instrument current ground, and other hazardous electrical possibilities, the following procedure should be taken:
- Ensure that all diagnostic equipment is equipped with a 3-pronged grounded
- Maintain periodic maintenance on diagnostic equipment
- Do not use extension cords with diagnostic equipment
- Do not use a direct patient ground leads when executing portable procedures
- Check all equipment for Frayed, loose, or torn wires
- Report abnormal interference patterns as this may indicate poor ground of the instrument
- Ensure that the testing area is dry free, from spills ,and that the patient has a low resistance ground To earth
- Always power on the equipment before the patient is hooked to the equipment. Likewise, always remove all interfaces between the patient and electrodiagnostic equipment before turning off the equipment.
AC frequencies range from
Essentially DC through infinity
Limitation is defined by
Numbers for lowest and highest frequencies
The range of frequency included by
The lower where in the higher figure it’s called the band width of the system
In EEG the frequency of interests are
DC (0Hz) to 100Hz
AC coupled by calibrators
Have a cutoff frequency above DC
The frequencies at the upper and lower it ends at the bandwidth referred to
70% values
There are three controls on a narrow diagnostic instrument
Low-frequency filters, high-frequency filters, and 60Hz filters
Low frequency filters
The primary of the LFF is attenuation of frequencies below a certain point, while allowing frequencies above this point to pass relatively unobtrusive
LFF
Low-frequency filters
HFF
High frequency filters
Time constant
It’s the time required for a capacitor to charge to 63% of its full charge
The decay time constant, or Falltime constant is:
It’s the time required for a capacitor to discharge to 37% of the full charge
60Hz Rejection filter
60Hz Rejection filter
The cutoff frequency is
The frequency above which the significant attenuation
Alternating current power wiring
When the AC power comes into the building it passes through a substation and is transformed from very high voltage to a low potential to be used inside the building
Thermistors
Nasal and oral thermistors are used in polysomnography to record airflow from the nose and mouth
Thermistors are sensitive to changes in temperature
