Electrical Stimulus and Ohm's Law

• Principles of Electrical Stimulation is also known as Electrotherapy.
• Different types of stimuli can be differentiated.
• Stimuli characteristics can be demonstrated.
• Different Types of Electrical Stimulation can be identified.
• Electrical Current can be defined.
• Factors Affecting Current Flow can be analyzed.
• Electrical Current Types can be classified.

Types of Stimuli

• Electrical stimuli are one type of stimulus.
• Chemical stimuli are a type of stimulus.
• Mechanical stimuli are a type of stimulus.
• Electromagnetic stimuli are another type of stimulus.
• Electrical stimulus is preferred in therapeutic uses because it is similar to stimuli inside the body.
• Electrical stimulus intensity and duration can be easily controlled.
• Electrical stimuli can produce a response without nerve damage.

Characteristics of Stimuli to Depolarize a Nerve

• Amplitude needs to be strong.
• Rise time needs to be fast.
• Phase duration needs to be long.

Electrical Stimulation

• Neuromuscular electrical stimulation activates skeletal muscle for strengthening.
• Functional electrical stimulation activates skeletal muscle for reeducation or movement training for functional use.
• Electrical muscle stimulation is used for denervated muscle.

Current

• Current involves of ions or electrons in a conductor due to voltage.
• The flow of current is directly proportional to voltage.
• Current is the quantity/amount of ions or electrons flowing at a given time.
• The international unit is the ampere (amp or A).
• Therapeutic applications use milliamperes (mA, or thousandths of an ampere).

Ohm's Law

• The magnitude of current flow is directly proportional to voltage and charge.
• Resistance opposes current flow.
• Ohm's Law states I = V/R.
• Current (I) in amperes is proportional to the voltage force (V).
• Current (I) is inversely proportional to the resistance (R) to the voltage force.
• Being aware of factors that affect biological resistance is important when applying ES for therapeutic use.
• Calloused or dry skin presents high resistance, reducing current flow.

Factors Affecting Current Flow Through a Conductor

• Conduction characteristics of the material affect current flow.
• More electrons mean less resistance and better current flow.
• Blood and nerves have more free electrons compared to skin or bone.

Conductors and Insulators

• Ions or electrons require materials that permit movement.
• Materials where ions/electrons move freely are conductors.
• Metals and water are examples of conductors.
• Muscle, nerve, and bodily fluid act as conductors in the body.
• Materials where charged particals are not free to move are insulators.
• Rubber and plastic are typical insulators.
• The more free electrons, the better the conductor.
• Conductors and insulators often exist together.
• An extension cord uses metal wire to conduct current and plastic coating insulate.
• Fat is an insulator in the human body.
• Greater cross sectional area of a path, leads to less resistance of current flow.
• Nerves having large diameter depolarize before nerves having smaller diameters.
• Increased temperature increases electron movement, decreasing resistance and the need for higher output intensities.

Types of Electric Currents

• Direct Current
• Alternating Current
• Pulsed Current

Direct Currents

• Direct currents are uninterrupted and flow one-directional of electrons.
• Electrons travel from the cathode (negative pole) to the anode (positive pole).
• Examples: galvanic and Iontophoresis.
• A battery has a positive pole lacking electrons as well as a negative pole with excess electrons.
• Electrons flow from the negative pole through a wire.
• When the poles have an equal amount of electrons there won't be current flow and the battery is dead.

Variations of Direct Current

• DC variations must remain unidirectional and uninterrupted to be called DC.
• Interrupted DC ceases flow after 1 second before resuming in the same direction for one second.
• Reversed DC ceases flow after 1 second before resuming in the opposite direction for one second.
• Interrupted reversed DC is a combination of both interrupted and reversed DC.

Alternating Currents (AC)

• In an AC, the direction of flow changes cyclically from positive to negative.
• A cycle duration is measured from the originating point on the baseline to its terminating point and shows is required to complete one cycle.
• The number of times the current reverses direction in 1 second represents the current's number of cycles per second (frequency) and is expressed in hertz (Hz).

Pulsed Currents

• Pulsed currents flow unidirectional (monophasic) or bidirectional (biphasic) and are interrupted by periods of noncurrent flow.
• Current flows for microseconds (1/1,000,000 of a second, µsec) or milliseconds (1/1000 of a second, msec).

Monophasic Pulses

• Monophasic pulses have only one phase per pulse that flows in only one-direction.
• The current flows from the cathode (negative electrode) to the anode (positive electrode).
• High-voltage pulsed stimulation uses a monophasic current

Biphasic Currents

• Biphasic currents consist of two phases on opposite sides of the baseline.

Biphasic Current Types

• Symmetrical currents are mirror images on each side of the baseline and have no net positive or negative charges.
• Balanced Asymmetrical are shaped to allow for anodal (positive) or cathodal (negative) effects and have no net positive or negative charge.
• Unbalanced Asymmetrical currents have positive or negative effects.
• Unbalanced Asymmetrical currents can cause skin irritation if used for long durations given of their imbalance.
• Symmetrical or balanced asymmetrical pulses physiological effects of positive and negative current flow cancel over time.
• Unbalanced asymmetrical pulses may lead to residual physiological changes based on imbalances in charges.
• Symmetrical biphasic waveforms are more comfortable due to their low charge per phase.
• Neuromuscular stimulation units deliver asymmetrical biphasic current.
• Transcutaneous electrical nerve stimulators use a balanced asymmetrical current.

Explore therapeutic applications of electrical stimulus and Ohm's Law. Understand nerve depolarization, current flow, and factors affecting resistance. Key concepts include direct current, Ohm's law and electrical stimulation types.