Electrical Stimulation Fundamentals

Low Frequency Electrical Stimulating Currents (PST 410)

• Course material given by Mrs. J.O Adeleke from Bowen University

Course Outline

• Introduction to low frequency electrical stimulating currents
• Physical principles and procedures governing the use of low frequency electrical stimulating currents
• Electro-diagnosis
• Electro-analgesia
• Functional Electrical Stimulating Currents
• Current innovations in electrotherapy

Physical Principles and Procedures

• Electrical Conductivity key principles discussed with use of low frequency electrical stimulating currents
• Ohm's Law is discussed
• Electrode Placement covered
• Waveform explained
• Dose/Duration discussed
• Physiological effects detailed
• Therapeutic effects listed
• Polarity covered
• Safety considerations explained
• Electric Shock prevention and treatment
• Electrical muscle stimulation (EMS) is the stimulation of muscles used to maintain muscle viability and to restore muscle function

Electrical Muscle Stimulation (EMS)

• May include muscle strengthening
• May include reduction of muscle guarding and spasticity reduction
• May include atrophy prevention
• May include enhancement of range of motion (ROM)
• May include muscle reeducation
• Neuromuscular electrical stimulation (NMES) covered
• Electrical stimulation for tissue repair (ESTR) explained
• Functional electrical stimulation (FES) described
• Trancutaneous electrical nerve stimulation (TENS) discussed

Acronyms and Treatment Goals

• EMS: Electrical muscle stimulation used to stimulate denervated muscle to maintain muscle viability
• ESTR: Electrical Stimulation for Tissue Repair used for edema reduction, enhancement of circulation, and wound management
• NMES: Neuromuscular Electrical Stimulation is stimulation of innervated muscle to restore muscle function including reduction of muscle guarding and spasticity, atrophy prevention, enhancement of range of motion, and muscle reeducation.
• FES: Functional electrical stimulation activates muscles with electrical stimulation to perform functional activities
• TENS: Transcutaneous electrical nerve stimulation is used for stimulation for pain management

Electricity

• Described by its strength (charge), rate of flow (current), driving force (voltage), and opposition (resistance/impedance)

Resistance/Impedance

• Biological tissues possess an inherent resistance. -Resistance occurs in excitable and no-excitable tissues
• Excitable tissues include nerve, skeletal muscle, smooth muscle, and cardiac muscle -There is ability of neurons and neurotransmitters to conduct signals
• Non-excitable Tissue listed as Bone
• Impedance is "opposition" to current
• Results from the combination of resistive and capacitive reactance properties of tissue. -Capacitance provides the ability to store charge in an electric field, and oppose change in current flow -Nerve and muscle membranes are examples of capacitors
• Tissue impedance varies throughout the body, conductivity depends on water content

Conductivity

• High water content decreases impedance and improves conductance
• Healthy skin offers high impedance to current flow, the outer layer of skin, called the epidermis, contains little fluid -Moisture in the deeper layers is determined by age and number of sweat glands
• Skin resistance is inversely proportional to its temperature Increase in heat which increases moisture and salt, promoting conductivity
• Impedance can dramatically influence ability to electrically generate an adequate response in underlying muscle

Stimulating Muscle Tissue

• A greater intensity of current is needed to obtain a motor response in an area covered by adipose tissue, like the gluteus maximus muscle, -Compared with a little fat (e.g. anterior tibialis muscle)
• Increasing the current intensity to a level enough to drive current through the adipose tissue to the nerve may make the sensation of the stimulation unbearable for patient -This may rule out stimulation as a treatment option, or limit its effectiveness
• Minimizing impedance is important for all applications of electrical stimulation because this allows current intensity to be reduced and so increase patient comfort
• Cleaning the skin surface with alcohol/ methylated spirit prior to electrode application
• Wash the skin surface with soap ad rinse with water
• Remove excess body hair beneath electrodes
• Warming the region to be stimulated or warming the electrode gel
• Impedance changes in the presence of injury and disease Increase in edema, ischemia, atherosclerosis, scarring, and denervation Decrease: Open wounds and abrasions
• Positive ions known as cations are repelled from the positive electrode and migrate toward the negative electrode called cathode
• Negative ions known as anions migrate toward the positive electrode called anode
• The cathode is often active electrode because nerve activation (excitation) happens more under this electrode

Types of Current

• All therapeutic electrical stimulation units use one of three forms of current: -Direct Current (DC) -Alternating Current (AC) -Pulsed (Pulsatile) Current

Direct Current (DC)

• Continuous unidirectional flow of charged particles with a duration of at least 1 second
• One electrode is always the anode (positive) and one electrode is always the cathode (negative) for the period of stimulation
• Strong chemical effect on the tissues and can be delivered continuously to promote absorption of medication through the skin (iontophoresis) or, it can be interrupted to stimulate denervated muscle (Galvanic type current).

Alternating Current (AC)

• An uninterrupted bidirectional flow of charged particles changing direction at least once a second
• Can also be delivered in an interrupted form referred to as bursts
• Each electrode becomes positive for one phase of the cycle and then negative as the current reverses.
• Some commercial stimulators, including interferential and Russian, use AC as their base or carrier current, which is then modified and delivered to the patient in the form of beats or bursts, respectively

Pulsed or Pulsatile Current

• Can take on the directionality characteristics of AC or DC current
• The unidirectional (like DC) or bidirectional (like AC) flow of charged particles periodically ceasing for less than 1 second (milliseconds or microseconds) before the next electrical event
• Small Interruption in current, or charge movement, between successive pulses differentiates pulsed current from AC and DC current forms
• Individual pulses delivered in a continuous series called a pulse train
• The pulse train can be delivered continuously or interrupted as in the AC and DC current forms
• Each individual pulse consists of one or more phases
• Negligible chemical effect in the tissues: -The amount of effect depends on whether the pulse is unidirectional or bidirectional
• Manipulating the characteristics of both the single pulse and the pulse train can customize treatment protocols

Pulsed Current

• Single pulse for electrical stimulation is an event that can be described in terms of the characteristics of how it occurs

Characteristics of Pulsed Current

• Single Pulse: Waveform, Amplitude, Rise time/decay time, Intrapulse interval, Duration, and Charge.
• Pulse Train: Interpulse interval, Frequency, Duty cycle, On-off-time, Ramp time, and Total current.

Ohm's Law

• The size of an electric current varies directly with the voltage and inversely with the resistance within the circuit
• An increase in resistance when voltage is constant will decrease current
• The magnitude of current therefore increases when voltage increases or resistance decreases
• High resistance requires high voltages to produce necessary current flow in the tissues
• V=IR, Voltage = Current*Resistance, Current = Voltage/Resistance

Wave Form

• A visual representation of the pulse or event
• A spatial drawing depicting the shape of the pulse
• Reflects amplitude (strength) and duration (length of time) of the pulse or even
• Classified by the number of phases; monophasic, biphasic, and polyphasic

Waveforms

• Monophasic: the entire event takes place either above or below isoelectric zero (the pulse is either positive or negative) -Isoelectric zero is the demarcation between positive and negative where there is no net charge/ baseline
• Biphasic: has two phases with one above and one below the isoelectric zero demarcation. -Biphasic waveforms can either be balanced, in which case there would be no net charge, or unbalanced in which case there would either be a positive or negative charge remaining
• Polyphasic: multiple phases occurring above and below isoelectric zero

Electric Shock

• A painful stimulation of sensory and motor nerves caused by a sudden flow, cessation of flow, or variation of intensity of current passing through the body, -Results in mild discomfort, fear of loss of consciousness, and even death in a few cases
• Intensity of shock is measured by the amount of energy passing through the body that causes the damage
• Occurs when a person becomes part of the electrical circuit
• Can result from poorly designed or faulty equipment/ appliances
• Severity Type is Mild or Severe

Mild Shock

• Intensity of shock up to 20mA
• Painful sensory stimulation
• Laboured/ irregular breathing
• No loss of consciousness

Severe Shock

• Current flow greater than 20mA
• Difficulty in letting go
• Muscular paralysis
• Fall in blood pressure
• Ceasation of respiration
• Ventricular firillation
• Death

Causes of Electric Shock

• Sudden change in current flow
• Improper earth connection
• Two pin connections
• Faulty electrical components
• Non-insulated floorings
• Faulty switch and fuse connection

Treatment of Electric Shock

• Disconnect the victim from the contact with the current source.
• Do not get shocked
• In case of mild shock, reassure the victim and allow him/her to rest
• Give water that is not hot, as it may cause vasodilation, sweating and blood pressure
• In case of severe shock, lay victim flat, ensure respiratory passages are clear, and loosen tight clothing
• If breathing has ceased, perform CPR and call for medical help

Electro Diagnosis

• Study of electrical activity in motor units when stimulated by electrical pulses
• Physiological mechanism underlying normal activity of muscle, nerve when stimulated by electrical impulses

Strength Duration Curve (SDC)

• Demonstrates the relationship between the strength of electrical impulses applied to a nerve and the minimal time required to produce a muscle contraction -As the strength of the stimulus increases, the duration decreases
• Can be plotted by gradually reducing the duration below 300 milliseconds, recording the minimum intensity of stimulation required to generate a response
• Obtained by joining points that represent the various values (intensities) along the ordinate for the various duration of the stimulus
• Normal curve has a characteristic shape
• With denervated muscle: curve shifts to the right
• Partially denervated muscle: kink is present in the curve

Normal Curve - Strength Duration Curve

• The normal curve has a characteristic shape

Complete Denervation - Strength Duration Curve

• The curve shifts to the right

Partial Denervation - Strength Duration Curve

• Curve includes a kink

Rheobase

• Intensity of the current required to produce a minimal perceptible and palpable contraction at infinite duration Pulses of 100-300 ms are used to record
• Utilization time is the duration that coincides with the rheobase

Chronaxie

• Duration required to produce a muscle contraction with a stimulus that is double the Rheobase

Advantages and Disadvantages of SDC

• Advantages: Simple, Reliable, Indicates the proportion of denervation, May show changes in innervation / denervation if plotted over time
• Disadvantages: Only a small proportion may respond, and does not tell about the site of the lesion