Electrotherapeutic Basics Flashcards
To have current, there must be:
- a source of electrons
- a conductor of the electrons
- a driving force of electrons
ions
atoms that possess a charge
ions move from ___ concentration to ____ concentration
high; low
Electric current
the net movement of charged particles (ex ions or electrons) along a conductor
Electromotive force
The amount of potential (electrical) difference between two points ( conc of ions or electrons) in an electrical field that drives the charged particles
-measured in Volts
Driving force
- Commercial current flowing from a wall outlet produces an electromotive force of either 110-115 V or 220-240 V
- electrotherapeutic modalities then modify this voltage for specific therapeutic purposes
- in human system, the electric stimulator generates a voltage to overcome resistance (wires, tissues) allowing a current to flow along the path of least resistance
Low voltage generators
-Electrotherapeutic modalities that produce a voltage less than 150V
Coulomb (C)
The measure of electric charge equal to 6.25 x 10^18 electrons
Ampere (A)
Measure of current flow equal to 1 Coulomb (C) per second
ohm
Measure of resistance to current flow
Voltage (V)
- Measure of potential difference of EMF required to move 1 Amp (A) of current across 1 ohm of resistance
Resistance
- The ability of a medium to resist the flow of electrons through direct current
- expressed in ohms
Inductance
opposition to electron flow created by electromagnetic eddy currents generated when current is passed through a wire
Capacitance
Ability of a material to store an electrical charge
Impedance
-Resistance + inductance + capacitance
Conductors
materials that offer little resistance and allow current to flow easily
Insulators
Materials that offer high resistance to current flow
semiconductors
Materials that offer neither high nor low resistance to current flow
Electron flow
- Volt
- Ampere
- Resistance (ohm)
Water flow
- Pump
- Gallon of water/min
- length and diameter of pipe
Energy created by water flowing is dependent upon..
- pressure in the pipe
- # of gallons flowing per unit of time
Electrical power is measured in…
Watts
Watts=
Volts X Amps
W=V x A
Power (watts)=
EMF x current
(P= V x I)
- One watt is the power needed to move ( produce a current flow) one ampere of current with a force (pressure) of one volt
ohms law
- The amount of electromotive force (volts) in a circuit is equal to the current intensity (amps) multiplied by the resistance (ohms)
- V= I (amps) x R (ohms)
- I = V/R
- increase resistance = increased voltage needed to move current (I)
Series circuit
- When the same current flows through each resister, they are said to be in series
- RT=R1+ R2 + R3
- skin and fat in series
Parallel circuit
- When current flowing through a circuit has multiple pathways to follow through or around each resister
- 1/RT= 1/R1 + 1/R2 + 1/R3
- muscle, blood, tendon, ligament, bone in parallel
Types of currents capable or producing specific biological effects
- Direct (DC)
- alternating (AC)
- pulsatile or pulsed
Direct/galvanic/ or monophasic current types
- Continuous
- reversed DC current
- interrupted DC current
Continuous direct current
Unidirectional flow of electrical charges for at least one second
Reversed direct current
unidirectional flow of electrical charges for at least one second that then changes polarity
Interrupted direct current
unidirectional flow of electrical charges for at least one second that then stops for at least one second then resumes
direct current is generally used for:
- iontophoresis
- stimulating denervated muscle directly
- stimulate wound healing
Alternating/faradic/ biphasic current (AC)
- A continuous, bidirectional flow of charged particles where each cycle duration occurs in less than one second
- equal ion flow in each duration ( no net charge)
- wavelength= one cycle
- wavelength and frequency are inversely related
Rate of rise
Amount of time it takes to reach peak flow (when alternating current begins to flow in + direction)
-time dependent
Rate of fall
amount of time it takes to go from peak flow back to zero (isoelectric line)
Frequency
- # of pulses per second
- in alternating current frequency and duration (time) inversely related
AC current generally used for
- muscle strengthening
- muscle re-education
- pain modulation
- functional training (ie gait)
Pulsed/pulsatile currents
- unidirectional or bidirectional flow of electrical current that lasts less than one second and stops for a finite period (usually between 5 and 999 milliseconds) before the next pulse
- electrical current delivered discontinuously separated by a finite period of time
Types of pulsed/pulsatile currents
-Monophasic pulsed current
-biphasic pulsed current
* symmetric
* asymmetric
+ balanced
+ unbalanced
Monophasic pulsed current
- flowing only in one direction
- separated by finite amount of time before next pulse becomes active
Biphasic pulsed current
- current flowing in + and - direction
- separated by finite amount of time before next pulse becomes active
symmetric biphasic pulsed current
- both positive and negative phases have same amplitude and are on for same amount of time
balanced asymmetric biphasic pulsed current
- waves look different but the area under the waves are equal
- balanced relative to amount of charge
Unbalanced asymmetric biphasic pulsed current
- positive phase and negative phase look different and have different area under the waves
- unbalance charge which leads to build up of one charge on one side
Waveform
the shape of the current intensity vs time graph
number of phases
- Monophasic
- biphasic
- triphasic
- polyphasic
symmetry of phases
- Symmetric
- asymmetric
balance of phase charge
-Balanced/unbalanced
waveform or phase shape
- Rectangular
- square
- triangular
- saw toothed
- sinusoidal
descriptive characteristics of waveforms
- waveform
- number of phases
- symmetry or phases
- balance of phase charge
- waveform or phase shape
Amplitude-Dependent characteristics of pulsed and AC currents
- Peak amplitude
- peak to peak amp
- root mean square amp
- average amp
Peak amplitude
- the max current reached for a single phase
peak-to-peak amplitude
the max current measured from the peak of the first phase to the peak or the second phase
Root mean square amplitude
-Most common mathmatical method of defining the effective voltage or current of an AC wave
Average amplitude
the mean voltage under the sine wave curve
Time dependent characteristics of Pulsed and AC currents
- phase duration
- pulse duration
- rise time
- decay time
- interpulse interval
- intrapulse interval
- Period
- Frequency
Phase duration
time from beginning of a phase to the end of a phase
Pulse duration
time from beginning of a pulse to the end of a pulse
rise time
time required from the beginning of a phase to the peak of the phase
decay time
time from the peak of the phase to the end of the phase
interpulse interval
time from the end of one pulse to the beginning of the next pulse
intrapulse interval
time from the end of one phase to the beginning of the next phase
Period
the time to complete one pulse
frequency
1/period
Amplitude modulation
- vary amplitude up and down
Pulse duration modulation
vary how much time each pulse takes
frequency modulation
modulate how many pulses per second
Ramp modulation
modulate how much time it takes to get to peak of the individual phase or pulse
Timing modulation
-Burst: a series of pulses for a finite period of time followed by a period of no current flow
Burst duration
the length of time from the beginning of the burst to the end
- usually expressed in milliseconds (msec)
interburst interval
time from the end of one burst to beginning of the next burst
burst frequency
the number of bursts per unit of time
Electrode systmes
- carbon rubber
- carbon rubber with conducting gel
- vinyl covered metal plate
Electrode considerations current density: depends on size of electrodes
- smaller electrode has higher current density
Electrode considerations current density: depends on electrode placement
- Electrodes placed closer together have higher current density superficially
- electrodes placed further apart have higher current density deeper in the tissues
Electrode placement
- monopolar:
- Bipolar
- quadrapolar
- intersecting
- non-intersecting
Tap key electrode
- to identify motor points
- to stimulate small muscles (esp face muscles)
Monopolar electrode placement
- Negative electrode= active electrode placed near tissue we are trying to stimulate
- Positive electrode= non active electrode; usually larger dispersive electrode
Bipolar electrode placement
- positive and negative electrodes equal in size
- put both over tissue you are trying to stimulate
- one wire with +/- plugs
- or one +, and one - wire
quadrapolar electrode placement
- 4 electrodes
- non-intersecting> straight across
- intersecting> diagonal from each other
Interferential current history
- The research and use of IFC: primarily in Europe
- Ho Nemec- Austrian- introduced IFC (1950)
- came to N. America in 1980s
- surveys of PTs in England, Ireland, Australia, and Canada find IFC in the top 5 therapeutic modalities used
IFC description
- a medium frequency (1000 to 10,000 Hz) current that produces unmodulated sinusoidal waves of similar amplitude that cross
- these two different carrier frequencies interfere with each other to generate an amplitude modulated beat frequency
- this beat frequency is the net difference between the two superimposed frequencies and is the stimulation frequency of the waveform
Interference
-When two waves are brought into the same location, the amplitudes combine and are increased or summative
Constructive interference
two waves produced in phase or originate at the same time
- amplitudes combine with resultant amplitude increased
Destructive interference
Two waves produced out of phase or originate at different times
- amplitudes combine with resultant amplitude decreased
- if perfectly out of phase, amplitudes will cancel each other with resultant amplitude of 0
beat effect
produced by waveforms that have two different frequencies but combine at the same location
- the blending of waves results in both constructive and destructive interference and is termed heterodyne (different power-greek)
- the heterodyne effect is seen as rising and falling waveform
- the peaks correspond to the beat frequency and is the stimulation frequency of the waveform
- the beat frequency is the difference between the two original frequencies
four petal effect
- IFC : 4 electrodes crossing causing this effect
- electric field lines flowing perpendicular to generator 1 and generator 2
IFC: stimulating current pattern
- when electrodes are placed in a square pattern, electric field is produced that looks like a four petal flower
- maximum interference is at the center
Constant (bipolar) IFC
-Both carrier frequencies are fixed
Variable (quadripolar) IFC
- One carrier frequency is fixed while the other varies in frequency creating a variable or sweep frequency
- This is used to minimize pt accommodation to the current
Scanning IFC (quadripolar with vector scanning)
-The ability to move the entire petal of stimulation so as to effect a larger treatment area
Stereodynamic IFC
Three distinct circuits that blend and create a distinct wave
High voltage pulsed current: history
- Lehmann- “high-voltage electro galvanic stimulator”
- Term “ galvanic” was erroneuous in that current was not direct or continuous current but rather pulsed
- Proper term should be high-voltage pulsed current (APTA, 1990)
HVPC: biophysical characteristics
- Twin peaked, monophasic, pulsed current
- driven by characteristically high EMF (current) from 150-500 volts
- 150 volts= high volt stimulator
- HVPC pulses generally fixed
- some allow for adjustment of interspike interval
- pulse frequency: 1-200 pps (pair of monophasic spike like waveforms
HVPC: twin-peak monophasic pulse
- pair of monophasic spike-like waveforms
- almost instantaneous rise followed by exponential decline
- pulse duration: short
- 100-200 usec
HVPC: Tissue impedence
- capacitance= charge/voltage
- high volt source > less capacitance
- low capacitance > low tissue impedance > more comfortable
HVPC: strength duration curve
- need for high voltage output due to extreme shortness of pulse duration at its peak in keeping with classic strength duration curve
- shorter pulse duration- higher current amplitude
HVPC: versatility
High voltage output and monophasic pulsed waveform allows for
- electric nerve/muscle stim
- wound healing
Russian current history
-Yakov Kots – Russian physiologist
1977 – Russian – Canadian exchange symposium
-Revolutionary claims
*An electrically produced human muscle contraction, using this new type of stimulation, could generate up to 30% more force then that generated by a MVC
*Application of such current is painless
*Short-term training could produce lasting gains in mm strength of up to 40% in healthy subjects
-1980s -first russian current stimulator electro-stim 180 produced in US and canada
-Clinical importance:
* if kot’s claim is correct, could train individuals without need of voluntary contractions
Russian current: biophysical characteristics
- Time modification of continuous sine-wave having carrier frequency of 2,500 pps
- burst modulated for fixed 10 msec periods
- Fixed IPI of 10 msec
- Burst frequency of 50 bursts per second (bps)
Russian current: net physiological effects
- total number of bursts/sec (burst frequency) determine magnitude of effect
- at nerve/muscle memebrane level, each bursts leads to motor nerve depolarization and tetanic contraction
Russian current: physiological and therapeutic effects
- depolarizes both motor and sensory neurons simultaneously
- muscle contraction will be painless
- higher current amplitudes can be used
- will stimulate deeper motor neurons
Russian current: motor unit activation
- preferential activation of type II motor units
Russian current: motor unit recruitment deficiency
- during max voluntary muscle contraction
- unable to recruit large #s of large, type II fast-twitch motor units or get them to fire fast enough to develop max muscle force
- with Russian stimulation, higher current amplitudes that are painless stimulate larger pool of type II motor units
