BPA Unit 4: Electrophysics Flashcards
What is a Charge?
A fundamental property of electromagnetic force and underlies the mechanisms by which living cells communicate with one another, that being depolarizing and repolarizing.
- The charge is obtained by the addition or removal of electrons and occurs when atoms of elements are acted upon by external physical forces such as friction, heat, and chemical or electrical sources. (Unit = Coulombs)
What is Ionization?
The process by which an atom or molecule acquires a negative or positive charge
What are the 4 fundamental properties of electrical charge
- There are two types of charge—positive and negative.
- Like charges repel while opposites attract.
- Charge is neither created nor destroyed.
- Charge can be transferred from one object to another.
With a charge, what does polarity refer to?
This refers to the net charge of an object - being either negative or positive
What is the difference between Anode and Cathode?
Anode is positive
{Attracts anions = negative ions}
- It has more electrons than protons
Cathode is negative
{Attracts Cations = positive ions}
- It has more protons than electrons
What is Voltage?
The force of attraction or repulsion created by an electric field represents potential energy. The greater the force, the greater the potential energy
- This force is termed voltage and represents the driving force that moves electons
- Measures in volt (V) or milivolt (mV)
What are Conductors and Isolators?
- Conductors are materials in which the ions and electrons move freely
-Tissues as muscle, nerves, and body fluid serve as conductors - Insulators are materials in which charged particles are not free to move or do not move easily
-Plastic and/or rubber
What is a current?
The movement of ions or electrons in a conductor in response to a voltage force
- Current symbol = I
- Unit = Amperre (A) or milliamperes (mA)
With Ohm’s Law, what is Resistance?
Resistance is opposition to the flow of current and comes in many forms in the body
With Ohm’s Law, what is Capacitance and Impedance?
- Capacitance is the degree to which electrical charge is stored in a system containing conductors and insulators, such as the human body
- Impedance is the resistance to the flow of alternating current, whereas resistance is specific to direct current. Gels and adhesive conductive agents on electrodes serve to decrease impedance and increase conductivity between the electrode and skin
How are currents and waveforms represented on a graph?
The horizontal axis denotes duration while the vertical axis represents the magnitude or intensity (amplitude) of the current (Ampere, mA or volts)
What is a Direct Current (DC)?
This is the continuous unidirectional flow of ions or electrons for at least 1 second
- The term direction implies flow from positive to negative or negative to positive
What are the most common clincal uses for Direct Current?
- For Iontophoresis
- Wound Care
What is an Alternate Current (AC)?
This is the uninterrupted bidirectional flow of ions or electrons and must change direction at least one time per second
What is Pulsed Current (PC)?
This is the uni- or bidirectional flow of ions or electrons that periodically ceases for a period of time before the next electrical event
With Pulsed Current what is the effect on Muscle Stimulation?
Ssed for stimulating skeletal muscle for strengthening and activity.
- Because PC is a series of pulses, muscle
fibers can be stimulated frequently, resulting in tetanic contraction
With Direct Current what is the effect on Muscle Stimulation?
DC will depolarize the muscle and cause a
single twitch, but only one. To get a tetanic contraction, the muscle must depolarize and repolarize before depolarizing again.
- DC results in a sustained state of depolarization. The muscle cannot repolarize until the DC temporarily ceases.
What is Frequency? What does low frequency and median frequency include?
This is the number of pulses or wave forms per unit of time
- Low Frequency currents currents include TENS and NMES
(Conventional/portable)
-Typically < 1000Hz or 1kHz - Median Frequency currents include Russion and Interferential (IFC)
-Typically 1 to 10kHz
What is Burst Frequency?
The generation of two or more consecutive pulses separated from the next series of consecutive pulses is termed a burst, and the time between bursts is the interburst interval 1. The frequency at which bursts are generated is the burst
frequency, while the frequency of the underlying waveform in the burst is termed the carrier frequency
What is Pulse Amplitude?
Often referred to as intensity, its the magnitude of current or voltage with respect to the isoelectric or baseline on the x-y current-time plot. Amplitude is reported in units of current (amps, milliamps, or microamps) or voltage (volts, millivolts, or
microvolts) and can be described in terms of a single phase or both phases
What is Pulse Duration?
the total time elapsed from the beginning to the end of a single pulse, including the interphase (intrapulse) interval
With Modulation of Pulsed Currents, what is On-Time?
The duration for which a
series of pulses or bursts is
delivered
With Modulation of Pulsed Currents, what is Off-Time?
The duration or time between
a series of pulses or bursts
With Modulations of Pulsed Currents, what is Duty Cycle?
The percentage of the on-time to the total time (on-time plus off-time) multiplied by 100%
Ex:
On Time = 10 sec
Off Time = 40 sec
Duty cycle = 10/50 x 100 = 20%
With Pulse Current, what is Ampitude Modulation? What are Ramps?
The amplitude modulation is used to gradually or progresssively increase and decrease the amplitude of a current to the desired intensity. For example, when stimulating muscles
- The terms rise time and fall time are used to describe the time required for the leading and trailing edge of a single phase
- Ramps are specific to the increase or decrease in the amplitude of a series of pulses
What is the difference between Phase Charge and Pulse Charge?
- Phase Charge: the number within one phase of a pulse
- Pulse Charge: the cumulative charge of all phases within a single pulse
With Biphasic Waveforms, what is does it mean for it to be Symmetrical?
The sum of current amplitude and duration of the first phase (i.e., phase charge) are identical to the second, the phases are termed symmetrical
With Biphasic Waveforms, what is does it mean for it to be Asymmetrical?
- If the amplitude and duration characteristics between the two phases of the biphasic waveform differ in any manner, the phases are termed asymmetrical
With Biphasic Waveforms, what is does it mean for the phases to be balanced?
If the area under the curve of the first phase is equal to that of the second phas
With Biphasic Waveforms, what is does it mean for the phases to be unbalanced?
If the phases are not of equal area
What are the Different Physiological Responses to Electrical Current?
- Electrochemical Effect
- Electrothermal Effect
- Electrophysical Effect
With Direct Current (DC), what are the Electrochemical Effects?
- Cathode: Sodium Hydroxide (NAOH) = Alkaline reaction, increases in water
-The Skin softens - Anode: Hydrocloridic Acid (HCL) = Acidic reaction, decrease in water
-The Skin hardens
What are the Electrothermal Effect?
- As charged particles move through a conductor, the friction encountered by the particles results in
microvibration of the conductor’s elements. This
friction and vibration reflect kinetic energy created by moving parts, and heat is a product of this energy. - Because the skin resists the transcutaneous delivery of current, accumulation of heat at the skin is a
concern
What are the Electrophysical Effects?
- Depolarization of the nerve cell is generated
- The nerve impulse is generated
- Increases the permeability of the cell membrane to Na+ causing a reduction in the resting membrane potential and depolarizing the nerve cell
- In the resting state, the cell membrane is kept negative inside
- Electrical potential is maintained principally by sodium and potassium
What is the Response of Excitable Tissues to Stimulation?
Depolarization of the cell membrane of excitable tissues (nerves and muscles) requires sufficient electrical current amplitude and duration
With the Reponse to excitable tissues to stimulation, what is the difference between Rheobase and Chronaxie?
Rheobase: The minimum strength (mA) of a stimulus of very long duration that is capable of eliciting a minimally detectable motor response
Chronazie: The duration (usec or msec) of a stimulus two times the rheobase strength capable of eliciting a minimally detectable motor response
What is the requirement of doing Electrical Stimulation of Denervated Muscle?
- This requires large pulse duration for the depolarization of the sarcolemma
With Peripheral Nerve Fibers, what is the Function of Type A (alpha)
Proprioception, motor
- Diameter is 12-20um
With Peripheral Nerve Fibers, what is the Function of Type A (Beta)
Touch, Pressure
- Diameter is 5-12 um
With Peripheral Nerve Fibers, what is the Function of Type A (Delta)
Pain, Temperature
- Diameter is 2-5 um
With Peripheral Nerve Fibers, what is the Function of Type C (Dorsal Root)
Pain
- Diameter is 0.4-1.2 um
When would you use Russian? What type of Waveform is it?
Use:
- Activation of skeletal muscles for strengthening and endurance (NMES)
Waveform:
- Burst-modulated AC
When would you use High Volt? What type of Waveform is it?
Use:
- Pain Modulation
- Wound/Tissue healing
Waveform:
- Twin-peak monophasic pulsed
When would you use Interferential or Premodulated? What type of Waveform is it?
Use:
- Pain Modulation
Waveform:
- Amplitude Modulated AC
When would you use Microcurrent? What type of Waveform is it?
Use:
- Wound/Tissue Healing
Waveform:
- Low-Intensity DC (Microamperage current)
When would you use Symmetrical BiPhasic: Square or Triangular? What type of Waveform is it?
Use:
- Activation of skeletal muscles for strengthening andn endurance (NMES)
or
- Functional electrical stimulation (FES)
Waveform:
- Symmetrical biphasic: Square or triangular
Which of the following is electrode placement application is the MOST appropriate application of electrodes when treating deeper structures?
A. Place only one electrode on the patient
B. Place the electrode close together
C. Place the electrode farther apart
D. Place the electrode parallel to each other
C. Place the electrode farther apart
Which of the following would be considered a contraindication for the use of electrical stimulation (E-stim)?
A. Edema reduction
B. Open wounds
C. Trunk or heart region in patients with pacemaker
D. Muslce weakness
C. Trunk or heart region in patients with pacemaker
