Low Frequency and Medium Frequency Currents

OBJECTIVES

Review on the difference between high, medium, and low medium frequency currents and their therapeutic/clinical implications

OBJECTIVES

Be familiar with terms used in electrotherapy current modulations particularly with WAVEFORM, (electric) PULSE, FREQUENCY, CURRENT INTENSITY, PULSE DURATION

OBJECTIVES

Enumerate the characteristics of the three types of low/medium frequency currents

Formulate guidelines in the selection and/or prescription of the most appropriate (low/medium frequency current) electrical modality

OBJECTIVES

Describe the basic design features of electrical stimulators

Be familiar with the clinical importance of the design features of electrical stimulators

OBJECTIVES

Identify the common controls present on electrical stimulator units

Be familiar with the parameters regulated by each control present on the electrical stimulator units

A review on the differences…

High Frequency CurrentsMedium Frequency

CurrentsLow Frequency Currents

HIGH FREQUENCY CURRENTS

Frequency is >6000 Hz Short wavelengths (<10 mm) Effects occur only at superficial

structures General effect = HEATING Sample modalities:

US, MWD, SWD, IRR, UVR, LASER

MEDIUM and LOW FREQUENCY CURRENTS

Frequency ranges from 1 to 6000 Hz

Longer wavelengths (>10 mm) Effects occur at deeper

structures General effects:

MFC: blocks painLFC: nerve stimulation

MEDIUM and LOW FREQUENCY CURRENTS

Sample modalities:Electrical stimulators, Diadynamics, Biofeedback, Iontophoresis, TENS, IT

Definition of some relevant terms…

ELECTRIC PULSE PULSE DURATION

CURRENT INTENSITYWAVEFORMFREQUENCY

ELECTRIC PULSE

A unit of stimulating current Otherwise known as a PHASE

(current phase)

ELECTRIC PULSE

Can be more fully described according to DURATION (pulse duration expressed in seconds), INTENSITY (current intensity expressed in amperes or volts), and SHAPE (waveform)

PULSE DURATION

Amount of time needed for the rise and fall pattern to occur at a given pulse

Expressed in SECONDS (millisecond=ms)

CURRENT INTENSITY

Rate of flow of electrons Usually expressed in AMPERES

(milliamperes = mA)

WAVEFORM

Describes the rise-and-fall pattern of a pulse

The shape of the waveform reflects the time required for the current to reach the maximum intensity

WAVEFORM

Waveforms with sudden rise in intensity are suitable for innervated muscle

Waveforms with slowly rising intensity are best suited for denervated muscle

FREQUENCY

Rate of change of an electrical pulse

Expressed in HERTZ (Hz)

Therapeutic/Clinical Uses…

MEDIUM and LOW FREQUENCY CURRENTS

MEDIUM and LOW FREQUENCY CURRENTS

Assists in functional training Assists in muscle force

generation and contraction Decreases unwanted muscle

activity Increases rate of healing of open

wounds and soft tissues

MEDIUM and LOW FREQUENCY CURRENTS

Helps maintain muscle integrity after surgery

Modulates and/or decreases pain Decreases or eliminates soft

tissue swelling, inflammation, or restriction

TYPES OF MEDIUM-LOW FREQUENCY CURRENTS

Direct CurrentsAlternating Currents

Pulsed Currents

Noted Characteristics…

QUANTITATIVE:Frequency (Hz)Pulse duration

Noted Characteristics…

QUALITATIVE:Number of PHASESShape and symmetry of WAVEFORMS

Other qualitative characteristics

Direct Current

Refers to a current passing continuously in the same direction (unidirectional current)

Direct Current (cont.)

Synonyms:Constant CurrentGalvanic Current / Galvanism

Galvanic stimulation is useful only for stimulating denervated muscles

Direct Current (cont.)

Interrupted Direct Current (IDC) is used to stimulate innervated muscles

Direct current is also used in IONTOPHORESIS

Direct Current (cont.)

2 Types of IDC:1. Long Duration IDC

> 1 ms For sensory and motor nerve

stimulation (denervated)

Direct Current (cont.)

2. Short duration IDC (Faradic-Type)

< 1 ms For pain control and nerve

stimulation (innervated)

Direct Current (cont.)

Physiological effects: Sensory stimulation Hyperemia Electrotonus Relief of pain Acceleration of healing Tissue destruction

Alternating Current

Defined as continuous or uninterrupted bidirectional flow of charged particles

Alternating Current (cont.)

2 Types:1. Sinusoidal Current

Evenly alternating sine wave currents of 50 Hz

For pain relief, edema, and improvement of circulation

Alternating Current (cont.)

2. Diadynamic Current Rectified monophasic

sinusoidal current For pain relief, tissue healing,

muscle re-education and improvement of circulation

Pulsed Current

Defined as the uni- or bi-directional flow of charged particles that periodically ceases for a finite period of time

Pulsed Current (cont.)

Types:1. Symmetrical Biphasic2. Balanced Asymmetrical

Biphasic3. Unbalanced Asymmetrical

Biphasic4. Monophasic

GUIDELINES…

Selecting, Prescribing, or Purchasing the MOST

APPROPRIATE Electromodality

GUIDELINES…

Determine your treatment goals

Note for the presence of contraindications

Determine the usual conditions of or problems presented by patients of the facility/area

GUIDELINES…

Consider the market availability of the modality and its cost

Consider the requirements for maintenance of the modality

BASIC DESIGN FEATURES and CONTROLS…

Electrical Stimulators

BASIC DESIGN FEATURES

Path from power source to the unit (plugs and cables)

Control knobs and/or buttons Electrodes (with cables) Alternative power source Safety features

BASIC DESIGN FEATURES

Controls or adjustment knobs/buttons for:Frequency IntensityMode (continuous or pulsed)Pulse Duration and IntervalsTreatment Duration

Basic Electrode Systems

1. Malleable metal electrodes2. Electrodes that conform to

the body surfaces3. Water Bath

Malleable Metal Electrodes

Made of tinplate or aluminum with pad of lint, cotton gauze or sponge at the end

Pad/gauze/sponge is wet with water before being applied to skin

Electrodes kept in place with bandages / straps

Malleable Metal Electrodes (cont.)

If unequal in size, the smaller electrode is active & most effects will occur here; the other electrode is the indifferent or dispersive electrode

Electrodes that Conforms to the Body Surface

Made of carbon-impregnated silicone rubber

Used with sponge pads or thin layer of conducting gel

Kept in place with strap or adhesive tape

Electrodes that Conforms to the Body Surface

Less efficient in passing current than metal electrodes

Has lower impedance than polymer electrodes

Water Bath Used for hand, forearm, foot

and leg which is placed between the electrodes

Provides a large area for the indifferent electrode & for applying muscle stimulating currents

Current density depends on location of electrodes

Methods of Electrode Placement

1. UNIPOLAR2. BIPOLAR3. QUARDRIPOLAR

Unipolar Motor Point Stimulation

One small active electrode & one large dispersive electrode

Site of stimulation: motor point for stronger response

Unipolar Motor Point Stimulation

Same amount of current passes thru each electrode

Smaller sized electrode has higher current density (stronger effect)

Unipolar Motor Point Stimulation (cont.)

Used for innervated and denervated muscles

Indications:Peripheral nerve injuriesTendon transplants

Unipolar Motor Point Stimulation (cont.)

Contraindications:Cases wherein active motion is prohibited

Patients with pacemakersDirectly over superficial metal implants

Unipolar Motor Point Stimulation (cont.)

Contraindications:Active bleeding over treatment site

Malignancies over treatment site

Unipolar Motor Point Stimulation (cont.)

Precautions:Sensory loss over treatment site

Open woundsExtreme edema

Bipolar Motor Point Stimulation

Equally sized electrodes Effect of stimulation is

dependent on electrode placement

Current density is equal in both electrodes

Effective for stimulating muscle groups or very large muscles

Bipolar Motor Point Stimulation (cont.)

Used for innervated and denervated muscles

Indications:Peripheral nerve injuries Inhibition of muscle activity due to joint pain and effusion

Bipolar Motor Point Stimulation (cont.)

Indications (cont.):UMN lesions to decrease spasticity & facilitate active contraction

Disuse atrophy ImmobilizationOrthopedic & neurological cases with LOM

Bipolar Motor Point Stimulation (cont.)

Contraindications & Precautions:Same as Unipolar application

Quadripolar Motor Point Stimulation

Electrodes from two or more circuits positioned so that currents geometrically intersect

Used for Interferential Stimulation Technique (MFC)

Quadripolar Motor Point Stimulation (cont.)

Indications:Pain & muscle spasmEdemaHematomaChronic ligamentous lesionsUrinary stress incontinence

Quadripolar Motor Point Stimulation (cont.)

Contraindications & Precautions:Same as Unipolar application

Importance of Stimulation Parameters

The effect of electrical stimulation on the tissue will depend on the rate of change of the electrical pulse:

1. No change / Slow change in electric pulse IONTOPHORESIS /

DIRECT CURRENT

Importance of Stimulation Parameters (cont.)

2. Very fast change of rate HIGH FREQUENCY

CURRENTS3. Rate of change between nos.

1 & 2 LOW & MEDIUM

FREQUENCY CURRENTS

Importance of Stimulation Parameters (cont.)

The current intensity determines the extent of physiological changes When stimulating a muscle at a

constant frequency the only way to increase the force produced is to recruit more motor units by increasing the intensity of stimulation

Importance of Stimulation Parameters (cont.)

A single pulse is described by their:

1. Duration Seconds / Milliseconds /

Microseconds2. Intensity

Milliamps / Volts 3. Shape

Illustrates the change of intensity with time

Importance of Stimulation Parameters (cont.)

The relationship between time and current intensity is the rate of change in current

Current used in Galvanic current and Iontophoresis

Current used for Nerve Stimulation

Current used for producing Single Nerve Impulse

Current used for TENS & Faradic Stimulators

Surged current producing Muscle Contraction

Current Flow in the Tissues

The quantity of current that flows in the tissues and the path it follows will depend on the impedance of that pathway

Generally, watery tissue such as blood, muscle and nerve has low ohmic resistance

Current Flow in the Tissues (cont.)

Bone and fat has higher ohmic resistance

The epidermis has the highest ohmic resistance, which is determined by:Thickness & nature of skinInter-electrode distance

Current Flow in the Tissues (cont.)

This electrical resistance can be reduced by:Washing & wetting the surfaceWarming the skin

Skin Irritation as an Adverse Response

Skin irritation may be caused by:Electrical reactionElectrochemical responseAllergic response to electrodes, gel, or tape

Skin Irritation as an Adverse Response (cont.)

Skin irritation may be caused by:Mechanical irritation caused by shearing forces between adhesive substances and the skin

Hazards in Electrotherapy Chemical damage due to

inadequate skin protection when direct or interrupted current is used

Disruption of stimulating devices due to proximity of diathermy output

Skin irritation Electric shock

Contraindications to Electrical Stimulation

Strong muscle contraction might cause joint/muscle damage; detachment of thrombus; spread of infection; and hemorrhage

Stimulation of autonomic nerves might cause altered cardiac rhythm or other autonomic effects

Contraindications (cont.) Currents might be unduly

localized due to open wounds or skin lesions

Currents might provoke undesirable metabolic activity in neoplasms or in healed tuberculous infections

Contraindications (cont.)

Current is not evenly phasic, leading to possible skin damage or irritation, especially if there is loss of sensation

Principles of Application Conduct general safety checks

with respect to the equipment Check the patient for

contraindications Explain the treatment fully

to the patient

Principles of Application (cont.)

Collect the necessary equipmentES, electrodes, wiringSoap & water for cleaning the skin

Contact gel / sponge, tape / straps / Velcro

Principles of Application (cont.)

Position the patient in the comfortable position

The skin should be uncovered & examined for any contraindications to treatment

Test the equipment as appropriate; demonstrate the technique to the patient

Principles of Application (cont.)

Wash the skin over the region of electrode contact. Soaking the skin for 3-4 min either in a bath or with a warm, damp pad may reduce skin resistance

Select appropriate treatment parameters

Principles of Application (cont.)

Always turn all intensity dials to zero before beginning the treatment

Place the electrodes as appropriate for the treatment

Principles of Application (cont.)

Increase intensity until desired result is produced

Never lift the active electrode from the skin or replace it without turning the intensity to zero

Principles of Application (cont.)

Terminate the treatment; check the skin condition

Keep a full record of the treatment