Electrical Stimulation Flashcards
Direct Current
A continuous unidirectional flow of charged particles flowing for 1 second of longer.
Direct Currents can be completely described in terms of amplitude, direction and time.
Direct Currents are used for?
Iontophoresis
Wound Healing
Stimulating Denervated Muscle
Alternating Current
The uninterrupted flow of a bidirectional flow of charged particles.
Pulsatile Current
The unidirectional or bidirectional flow of current which ceases for a finite period of time.
Any pulsatile current could be used for TENS or NMES
Cathode
Away Road
Area of excess electrons
NEGATIVE pole
It is usually the active electrode and is BLACK
Anode
Toward Road
Area deficient in electrons
POSITIVE pole
It is usually the inactive dispersive pole and is usually RED or GREEN
Voltage or Electromotive Force
(EMF)
The “push” on electrons. Analogous tothe pressure in a hose.
Measured in volts.
1V=the EMF required to push 1 amp through 1 ohm of resistance.
Resistance
The resistance to electron flow. Analogous to the friction in a hose.
Resistance varies with properties such as length of conductor, cross sectional area, temperature and material.
Current
The number of electrons flowing past a point per unit of time.
Analogous to the volume of water flowing in a hose.
Measured in Amperes
1 AMP=6.24x10^18 electrons/sec=1 coulomb/sec
Impedance
The combinded effects of resistance and reactance (which consists of capacitive and inductive components) on current flow.
Impedance is measured in Ohms
Impedance = 1/(2piCF)
Single Pulse
An isolated electrical event separated by a finite time.
Phase: A part of a cycle.
Monophasic
A current flowing in only one direction during a pulse.
Biphasic
A current flowing in both directions during a cycle.
Polyphasic
A current changing direction more than twice during a cycle.
Symmetry
A comparison of the size and shape on both sides of the isoelectric line.
Symmetrical
A waveform which has the same size and shape on both sides of the isoelectric line.
Asymmetrical
A waveform which has a different size or shape on differing sides of the isoelectric line.
Balance of Phase Charge
A comparison of the amount of charge on each side of the isoelectric line. it is equal to the area under the curve.
If we don’t have a balanced charge we could potentially burn the patient.
Balanced
The phase charge is equal in both directions (The area under the curve is the same on both sides of the isoelectric line.) The shapes do not need to be the same.
The importance of a balanced charge is that it does not lead to a buildup in charge which could lead to patient burns.
Unbalanced
The phase charge is unequal between sides of the isoelectric line.
Physiological Effects of Electricity
Affects motor, sensory, and autonomic nerve fibers.
Can also affect muscle fibers directly.
Electricity has an effect on all tissue – all cells have membrane potentials and can be affected.
The action potential (AP) is produced by any adequate stimulus (Electrical, mechanical, thermal, chemical that reaches threshold).
There is an inverse relationship between fiber size and threshold. Therefore, large fibers are activated first.
Threshold for nerve is much less than that of muscle.
Resting Membrane Potential
RMP is -70mV -90mV
Sequence of Surface Stimulation
Sensory threshold Motor threshold Maximum motor contraction without pain Pain threshold Pain tolerance
Denervated muscle contaction
In denerveated muscle, the muscle fibers must be stimulated directly since the nerve is no longer functional.
Since the threshold is so high in muscle (-90 mV) high amounts of current are required to stimulate muscle. The treatment will be painful if sensation is intact. If sensation is not intact, there is the danger of burning the patient.
Denervated muscle requires a high amplitude, low frequency or DC to stimulate it.
Effects of Polartiy: Cathode (Negative Pole)
Under the negative pole, the interstiatial fluid will become less positive, thereby lowering the voltage difference across the cell membrane. When the difference is less than 55 mV, there will be an action potential.
The Cathode is therefore an active electrode for stimulating nerve.
Effects of Polarity: Anode (Positive Pole)
Under the positive pole, the interstitial fluid become more positive, thus increasing the voltage difference across the cell membraneand hyperpolarizing the membrane.
In the area of the anode, it therefore becomes more difficult to stimulate a nerve.
Anode Effects
Acidic Hardens Tissue Contracts Tissue Decreases Hemorrhage Decreases congestion sedative (elevates threshold)
Cathode Effects
Alkaline Softens Tissue Dilates Tissue Increases Hemorrhage Increases Congestion Stimulating
Electrode Variables
The closer the electrodes, the more superficial the treatment.
The larger the electrode, the more superficial the treatment.
If electrodes are on opposite sides of the body part, the current flow will be deeper.
If electrodes are placed over a peripheral nerve, all muscles distal to and served by that nerve will be stimulated.
Stimulation of a motor point affects only that muscle.
Generator Variables
As amplitude increases, depth of penetration increases.
As rate increases, fatigue increases.
As pulse width (duration) increases, there is a greater depth of penetration (and more pain).
Duty cycle: best strengthening ratio is 1:3-5. Fatigue is best caused by continuous current.
Rate of Rise: A rapid rate of rise produces little accommodation. However, a slower rate of rise is more comfortable for the patient.
Contraindications for Electrotherapy
Demand type Cardiac Pacemaker Cardiac Arrhythmia Over the Carotid Artery Hypersensitive Patients Pregnancy
Precautions
Check Equipment
Change intensities slowly
Always turn down intensity before changing other parameter controls.
Avid concentration of current (Skin cuts, creases in electrode pads, poor contact of electrodes)
Avoid dispersal of current (gel dispersal outside of electrode area)
Uses of Direct Current
Used for edema reduction, iontophoresis, wound healing, fracture healing and stimulation of denervated muscle.
There is a net ionic flow and therefore a potential for electolytic burns (acidic or alkaline).
Pulsatile Monophasic
(HIVOLT)
Pulsatile Biphasic
TENS
Generally low volt, with many modulations. No net ionic flow if there is a symmetrical waveform.
Polyphasic (ex)
“Russian” - There is a 2500 Hz “carrier” signal which is turned on and off every 10 milliseconds, resulting in a series of 50 burst per second current. Used primarily for strengthening.
Interferential Frequency Current (IFC) - This machine consists of 2 electronic circuits, one at 4000 and one at 4100 Hz.
The two currents interfere with each other and produce a series of beats which is equal to the difference in frequency between the two circuits or 100 Hz. The machine is used primarily for analgesia but can be used for muscle strengthening.
Laser Contraindications
Do not treat tumors or cancerous lesions
Pregnancy
Do not apply over the Thyroid gland due to selective uptake of energy by iodine.
Do not treat bacterial infections
Do not treat patients who are on immunosuppresant drugs (weakened immune system).
Do not continue o treat if the patient feels pain or weakness.
Do not treat patients who are taking tetracycline, Retin-A, St John’s Wort, or any medications who warn to avoid bright sunlight
Laser Precautions
Do not look at the beam or allow patients to do so.
Have a “danger laser” sign at the treatment room door.
Turn the laser off before removing it from the skin.
The PT and pt. should wear protective safety goggles.
Do not treat until 2 weeks after a steroid injection.
Be careful over tattoos as dyes may absorb light and become hot.
Use care with children due to sensitive skin.
Low Frequency TENS
Rate 1-5 Hz
Pulse Width 300-400 microseconds
Amplitude to produce a visible muscle twitch within pain tolerance.
Limited to 30-45 minutes of application due to muscle fatigue.
Relief may be delayed 15-30 minutes after cessation of treatment but may be long lasting.
Mechanism is thought to be endorphin action.
Best for Chronic Pain
Hyperstimulation Analgeis TENS
Often pulsed biphasic
Pulse Width and Frequency settings usually set to maximum settings.
Amplitude set to pain tolerance.
Treatment is for 15 minutes, followed by 2-3 minutes of rest. Can repeat X 2-3
Mechanism of operation is thought to be conduction blocking.
Use when relief must be quick ad long lasting, but at the cost of being painful.
Conventional TENS
Rate 40-100 Hz
Pulse Width <200 microseconds
Amplitude between initial perception and discomfort or muscle contraction.
Can use for indefinite periods.
relief is usually rapid, but may be short term
Very effective with acute pain control (post op as measured by patient intake of pain meds).
Appears to be most effective for neurogenic pain where pain is segmental, well localized, and large afferent trunks can be stimulated.
Thought to operate via gate control at the dorsal horn.
Best for acute pain
Level I
Peripheral Nerves NSAIDs decreases synthesis of prostaglandins, which has the effect of decreasing the sensitivity of pain receptors.
Level II
Gate control at the dorsal horn.
Any modality which stimulate large diameter, mylinated afferents can potentially inhibit pain transmission using the “spinal gate.” Some methods used clinically in Physical Therapy are: TENS, Joint Mobs, traditional joint ROM and massage.
Conventional TENS
Level III
Central Mechanism of Control/Central Biasing
like Acupunture and trigger points.
Hyperstimulation
Level IV
Endorphins
Level V
Limbic System
Th possibility of modulating pain by controlling emotional of affective states has gained increasing attention lately. Several successful approaches to chronic pain include meditation, subliminal suggestion and purposeful imagination.
Ohm’s Law
Current varies directly with voltage and inversely with resistance. V=IR
Joule’s Law
Temperature rise in a conductor when current flows is directly proportional to the resistance, the square of the current in amps, and the time the current flows. Heat = 1^2RT
Charge
An excess or deficiency of electrons. Measured in Coulombs.
Capacitance
The ability to store charge. The force between 2 charges is proportional to the magnitude of each charge divided by the distance squared.
