Exam 3 (Ch: 11 Flashcards
What is a positive electrode?
Anode
What is a negative electrode?
Cathode
Charge equation?
Q= I*t Q= Coulombs I= Current t= time
Which type of current is a series of pulses where charged particles move in only one direction?
Monophasic current
What type of current is a series of pulses where charged particles move in one direction and then the opposite direction?
Biphasic current
This type of current is bidirectional and has no net charge?
Alternating current
With an alternating current, describe the relationship b/t frequency and duration?
Frequency INCREASES the cycle duration DECREASES and
Frequency DECREASES the cycle duration INCREASES
This type of current is a continuous unidirectional flow of charged particles?
Direct current (DC)
This type of current is an interrupted flow of charged particles whereby the current flows in a series of pulses separated by periods when no current flows?
Pulsatile current
Describe on/ off time?
On time is the time during which a train of pulses occur
Off time is the time between trains of pulses where no current flows
What is the goal of on and off times?
To produce muscle contractions
What happens to a muscle during on time?
It contracts
What happens to a muscle during off time?
It relaxes
Why is off time required?
To reduce muscle fatigue
What is rise time?
The time is takes for the current to increase from zero to its peak during one phase
What is decay time?
The time is takes for the current to decrease from its peak level to zero during one phase
What is ramp up time?
The amount of time it takes for the current to amplitude to increase from zero during the off time to its max amplitude during the on time
What is ramp down time?
The time it takes for the current amplitude to decrease from its maximum amplitude during the on time to zero during the off time
What are ramps used for?
To improve patient comfort when e-stim is used to produce muscle contraction.
Allows for patient to become accustomed to the stimulation.
Ramp up/ down time in relation to ON/OFF time
Ramp up time is included in the ON TIME
Ramp down time is included in the OFF TIME
What is the time in between individual pulses?
Interpulse interval
What is the time in between phases of a pulse?
Intrapluse interval
What is Ohm’s law?
V = I*R
V- voltage
I- intensity
R- resistance
What is voltage?
The force or pressure of electricity
What is resistance?
Opposition of a material to the flow of electrical current
What can cause resistance during e-stim?
Hair, skin, amount of fat in an area
What is the amount of current per unit area?
Current density
What is impedance?
Frequency dependent opposition to current flow
In biological systems, it describes the ratio of voltage to current more accurately than resistance b/c it includes effects of capacitance and resistance
How is impedance noted & measured?
Noted by Z
Measured in Ohms
What is the delivery of ions through an electrical current for therapeutic purposes?
Iontophoresis
What is functional electrical stimulation (FES)?
Application of an electrical current to produce muscle contractions during a functional activity
What are examples of Functional Electrical Stimulation?
E-stim of dorsiflexion during the swing phase of gait
E-stim of wrist & finger flexion during grasp activities
What is neuromuscular electrical stimulation?
E-stim to motor nerves to produces contractions of the muscles they innervate
What is the place in a muscle where e-stim will produce the greatest contraction w/ the least amount of electricity?
Motor point
Where are motor points usually found?
Over the middle of the muscle belly
What are the uses of e-stim?
Pain Muscle strengthening Decreasing edema Wound care to promote epithelialization Functional E-stim Biofeedback for sensory input EMG
Interferential current (IFC)
Produced by two medium frequency (1000- 10,000 Hz) sinusoidal ACs of slightly different frequencies.
Delivered through 2 sets of electrodes through separate channels in the same stimulator
Electrodes are configured on the skin so that the two ACs intersect
Stimulates larger area than Premod, at a lower amplitude
Premodulated current (Premod)
Produced by an AC w/ medium frequency (1000- 10,000) Hz
Sequentially increasing and decreasing current amplitude
Single circuit w/ 2 electrodes
Same waveform as IFC
What are the disadvantages of a premodulated current compared to interferential current?
Premodulated current uses only two electrodes in a single channel
It does not cover as large an area
Uses a modulating current of increasing amplitude
Russian protocol
Developed by Kots, used for training Russian Olympic athletes
Intended for quadriceps muscle strengthening
Uses AC w/ medium frequency (2500Hz) delivered at 10ms long bursts
50 bursts per second w/ a 10ms interval b/t bursts
AKA- medium-frequency burst AC
What is the magnitude of the current or voltage and is also known as the “intensity” or “strength” of the stimulation?
Amplitude
What is a variation in peak current amplitude over time?
Amplitude modulation
What is the period of time immediately after nerve depolarization when no action potential can be generated?
Absolute refractory period
What is the period of time after depolarization in which the nerve membrane is hyperpolarized and a greater stimulus than usual is needed to produce an AP?
Relative refractory period
What is propagation?
The movement of an AP along a nerve axon, aka conduction
This rapid propagation of an electrical signal along a myelinated nerve axon, w/ the signal appearing to jump from one Node of Ranvier to the next?
Saltatory conduction
What is the minimum current amplitude, with long pulse duration, required to produce an AP?
Rheobase
What is the minimum duration an electrical current at twice rheobase intensity needs to be applied to produce an AP?
Chronaxie
What is the reversal of the resting potential in excitable cell membranes, where the inside of the cell becomes positive relative to the outside?
Depolarization
Name the fatty tissue that surrounds the axons of neurons, that allows electrical signals to travel more quickly?
Myelin
What are the small, unmyelinated gaps in the myelin sheath covering myelinated axons?
Nodes of Ranvier
What can Biphasic pulsed current be used to control?
control pain, decrease spasticity, and strengthen innervated muscles
It has not been found to prevent atrophy in denervated muscles
If a patient cannot use self-adhesive electrodes, what other types could they use?
Blue-gel electrodes are used for patients with sensitive skin.
Conductive garments can be used when the area to be treated is large (e.g. whole hand)
Carbon rubber electrodes with gel are economical alternatives to standard adhesive electrodes because they can be reused on multiple patients when cleaned properly.
Action potentials/ Amplitude
The greater the current amplitude, the more nerve fibers can be stimulated to produce an action potential. Action potentials are all or nothing, and amplitude does not affect the speed. Rise time does not decrease threshold potential
What is the electrical difference b/t the inside of a neuron & outside when the neuron is at rest, with the inside being negative relative to the outside?
Resting membrane potential
What causes more action potentials to be stimulated?
Increased frequency
What is it called when the nerve gradually becomes less responsive to stimulation?
How can this response be reduced?
Accommodation
Modulation of the current
What current amplitude and duration would stimulate sensory nerves?
Low amplitude and short duration
Which type of currents may be more comfortable for contracting smaller muscles?
Asymmetric biphasic
Which type of currents may be more comfortable for contracting larger muscles?
Symmetrical biphasic
What current amplitude and duration would stimulate motor nerves?
Longer durations with high amplitudes
What does frequency indicate?
Number of pulses per second.
What does pulse duration indicate?
Duration of a single pulse.
What does interpulse interval indicate?
Length of time between pulses.
How could pulse duration of a current be decreased without changing the frequency?
If the frequency stays the same interpulse interval increases
pulse duration must decrease
To get the same number of pulses to occur per second
Depolarization of nerves at rest?
The outside of the cell is more positive than the inside due to the greater concentration of positively charged sodium ions outside the cell.
Contraindications for E-stim
Pacemaker
Unstable arryhythmias
Placement of electrodes over carotid sinus
Over areas where venous or arterial thrombophlebitis is present
Pregnancy- over or around lower back
Precautions for E-stim
Cardiac disease
Patients w/ impaired mentation or impaired sensation
Malignant tumors
Areas of skin irritation or open wounds
Resistance
Ability to oppose a charge
Capacitance
ability to store up charge and oppose the change of current flow
Accomodation
nerves get used to the sensation and become less responsive
Poor conductors of current
Bone, fat, tendons, fascia
B/c of low water content
Strong conductors of current
Muscle and nerve
Nerve will be excited first then muscle
What type of estim is used for SENSORY stimulation?
Short pulses and low current amplitudes
What type of estim is used for MOTOR stimulation?
Longer pulses and high amplitudes
C-fibers
large diameter, unmyelinated SLOWEST
pain and temp
A-gamma or A-delta
smaller diameter, myelinated SLOWER
A-alpha
large diameter, myelinated FAST
motor
Estim for muscle strength
Effective in strengthening muscles
Encourage patient to actively contract when electrical current is felt
Electrically stimulated contractions are more fatiguing/ longer rest period after contractions
Works via Overload or Specificity principles
Contraction must be at least 50% of max voluntary contraction/ Highest gains w/ 100% max voluntary contraction
Estim for muscle endurance
Prolonged periods of stimulation with more lower force contractions
Pt. must have intact CNS, if not must have intact PNS to use Neuromuscular Estim
Results in increased strength in muscles available for recruitment
NMES is integrated into….
Functional Electrical Stimulation
ie- tibialis anterior during heel strike to prevent foot drop
Estim for spasticity
Focus on stimulating the antagonist muscle (reciprocal inhibition)
Stimulation of both the agonist and antagonist provides a more realistic movement pattern
Can be used to improve swallowing
Can be used for urinary continence- transcutaneously, percutaneously, transvaginal probe
Functions like an orthotic device
ie- stimulates rotator cuff muscles to decrease subluxation better than using solely a sling
Estim for denervated muscle
Used to decrease muscle atrophy and fibrosis
Usually done with a direct current
Estim and the gate control theory
Estim activates A-beta fibers
These fibers signal reach the CNS first flooding the “gate” thus decreasing the perception of pain
Short pulse width (50-80msec) medium frequency level (100-150pps)- sensory level amplitude
Estim and Endogenous Opoids
Repetitive stim of motor or A-delta fibers at twitch can stimulate Endogenous opoids
Long pulse width (over 100 msec) @ 2-10pps, twitch level amplitude
Estim applications for pain
Tens (pulsed biphasic)- high or low pulse width
IFC- must cross 2 channels
Premod current- current mixed up inside of the machine
Amplitude setting is either at sensory or twitch
How estim assists w/ tissue healing?
Increased protein synthesis & cell migration
Anti-bacterial
Increased blood flow
Improve tissue oxygenation
Parameters of estim for tissue healing
Monophasic wave form w/ bias polarity and long duration treatment at sub sensory intensity Low intensity DC (microcurrent) Hi-Volt (HVPC)- Monophasic pulsed 60-90 V 60-125pps 40-100msec Subsensory level 45-60 minutes daily
How estim decreases edema?
Negative charge repels the negatively charged large proteins molecules to block movement out of the BV, estim is used to provide muscle contraction causing movement of fluids
Passive drug delivery (transdermally) without electrical current
Substances can diffuse across the stratum corneum
Very low penetration 3-20 mm (not deeper than superficial musculature
Takes 1/2 day to multiple days
ie- transdermal patches or NSAIDs
Iontophoresis
Uses small amounts of electrical current changes to change the transcutaneous permeation of charged and non-charged particles
Iontophoresis application
Choose lower current level for the longest delivery time
-more comfortable/ reduces irritation and alkaline reaction
Select the charge of the active electrode based on the charge of the medication to be delivered
Placed electrode directly over the target tissue no closer than 1 inch to the dispersive
Iontophoresis pretreatment
Equipment check
Plug into power source
Position patient
Inspect skin- wash or shave area of electrode placement if necessary
Secure electrodes
Turn power on, select and set all current parameters
Iontophoresis delivery
Adjust intensity
Ask patient where they feel the current/ how does it feel?
Make adjustments as needed
Stay w/ pt. the first few minutes to observe reaction to treatment
Check w/ pt. and be prepared to problem solve
Iontophoresis post treatment
Turn amplitude to ZERO Turn off power Remove electrodes Inspect the skin of treatment area Ask pt. how they feel
