Low Frequency and Medium Frequency Currents OBJECTIVES n

Low Frequency and Medium Frequency Currents

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

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

OBJECTIVES Describe the basic design features of electrical stimulators n Be familiar with the clinical importance of the design features of electrical stimulators n

OBJECTIVES Identify the common controls present on electrical stimulator units n Be familiar with the parameters regulated by each control present on the electrical stimulator units n

A review on the differences… High Frequency Currents Medium Frequency Currents Low Frequency Currents

HIGH FREQUENCY CURRENTS Frequency is >6000 Hz n Short wavelengths (<10 mm) n Effects occur only at superficial structures n General effect = HEATING n Sample modalities: n n US, MWD, SWD, IRR, UVR, LASER

MEDIUM and LOW FREQUENCY CURRENTS Frequency ranges from 1 to 6000 Hz n Longer wavelengths (>10 mm) n Effects occur at deeper structures n General effects: n n MFC: blocks pain

MEDIUM and LOW FREQUENCY CURRENTS n Sample modalities: n Electrical stimulators, Diadynamics, Biofeedback, Iontophoresis, TENS, IT

Definition of some relevant terms… ELECTRIC PULSE DURATION CURRENT INTENSITY WAVEFORM FREQUENCY

ELECTRIC PULSE A unit of stimulating current n Otherwise known as a PHASE (current phase) n

ELECTRIC PULSE n 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 n Expressed in SECONDS (millisecond=ms) n

CURRENT INTENSITY Rate of flow of electrons n Usually expressed in AMPERES (milliamperes = m. A) n

WAVEFORM Describes the rise-and-fall pattern of a pulse n The shape of the waveform reflects the time required for the current to reach the maximum intensity n

WAVEFORM Waveforms with sudden rise in intensity are suitable for innervated muscle n Waveforms with slowly rising intensity are best suited for denervated muscle n

FREQUENCY Rate of change of an electrical pulse n Expressed in HERTZ (Hz) n

Therapeutic/Clinical Uses… MEDIUM and LOW FREQUENCY CURRENTS

MEDIUM and LOW FREQUENCY CURRENTS Assists in functional training n Assists in muscle force generation and contraction n Decreases unwanted muscle activity n Increases rate of healing of open wounds and soft tissues n

MEDIUM and LOW FREQUENCY CURRENTS Helps maintain muscle integrity after surgery n Modulates and/or decreases pain n Decreases or eliminates soft tissue swelling, inflammation, or restriction n

TYPES OF MEDIUM-LOW FREQUENCY CURRENTS Direct Currents Alternating Currents Pulsed Currents

Noted Characteristics… n QUANTITATIVE: n Frequency (Hz) n Pulse duration

Noted Characteristics… n QUALITATIVE: n Number of PHASES n Shape and symmetry of WAVEFORMS n Other qualitative characteristics

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

Direct Current (cont. ) Synonyms: n Constant Current n Galvanic Current / Galvanism n Galvanic stimulation is useful only for stimulating denervated muscles

Direct Current (cont. ) Interrupted Direct Current (IDC) is used to stimulate innervated muscles n Direct current is also used in IONTOPHORESIS n

Direct Current (cont. ) 2 Types of IDC: 1. Long Duration IDC n > 1 ms n For sensory and motor nerve stimulation (denervated)

Direct Current (cont. ) 2. Short duration IDC (Faradic. Type) n < 1 ms n For pain control and nerve stimulation (innervated)

Direct Current (cont. ) Physiological effects: n Sensory stimulation n Hyperemia n Electrotonus n Relief of pain n Acceleration of healing n Tissue destruction

Alternating Current n Defined as continuous or uninterrupted bidirectional flow of charged particles

Alternating Current (cont. ) 2 Types: 1. Sinusoidal Current n Evenly alternating sine wave currents of 50 Hz n For pain relief, edema, and improvement of circulation

Alternating Current (cont. ) 2. Diadynamic Current n Rectified monophasic sinusoidal current n For pain relief, tissue healing, muscle reeducation and improvement of circulation

Pulsed Current n Defined as the uni- or bidirectional flow of charged particles that periodically ceases for a finite period of time

Pulsed Current (cont. ) Types: 1. Symmetrical Biphasic 2. Balanced Asymmetrical Biphasic 3. Unbalanced Asymmetrical Biphasic 4. Monophasic

GUIDELINES… Selecting, Prescribing, or Purchasing the MOST APPROPRIATE Electromodality

GUIDELINES… Determine your treatment goals n Note for the presence of contraindications n n 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 n Consider the requirements for maintenance of the modality n

BASIC DESIGN FEATURES and CONTROLS… Electrical Stimulators

BASIC DESIGN FEATURES Path from power source to the unit (plugs and cables) n Control knobs and/or buttons n Electrodes (with cables) n Alternative power source n Safety features n

BASIC DESIGN FEATURES n Controls or adjustment knobs/buttons for: n Frequency n Intensity n Mode (continuous or pulsed) n Pulse Duration and Intervals n Treatment Duration

Basic Electrode Systems 1. 2. 3. Malleable metal electrodes Electrodes that conform to the body surfaces Water Bath

Malleable Metal Electrodes Made of tinplate or aluminum with pad of lint, cotton gauze or sponge at the end n Pad/gauze/sponge is wet with water before being applied to skin n Electrodes kept in place with bandages / straps n

Malleable Metal Electrodes (cont. ) n 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 n Used with sponge pads or thin layer of conducting gel n Kept in place with strap or adhesive tape n

Electrodes that Conforms to the Body Surface Less efficient in passing current than metal electrodes n Has lower impedance than polymer electrodes n

Water Bath Used for hand, forearm, foot and leg which is placed between the electrodes n Provides a large area for the indifferent electrode & for applying muscle stimulating currents n Current density depends on location of electrodes n

Methods of Electrode Placement 1. 2. 3. UNIPOLAR BIPOLAR QUARDRIPOLAR

Unipolar Motor Point Stimulation One small active electrode & one large dispersive electrode n Site of stimulation: motor point for stronger response n

Unipolar Motor Point Stimulation Same amount of current passes thru each electrode n Smaller sized electrode has higher current density (stronger effect) n

Unipolar Motor Point Stimulation (cont. ) Used for innervated and denervated muscles Indications: n n Peripheral nerve injuries n Tendon transplants

Unipolar Motor Point Stimulation (cont. ) Contraindications: n Cases wherein active motion is prohibited n Patients with pacemakers n Directly over superficial metal implants

Unipolar Motor Point Stimulation (cont. ) Contraindications: n Active bleeding over treatment site n Malignancies over treatment site

Unipolar Motor Point Stimulation (cont. ) Precautions: n Sensory loss over treatment site n Open wounds n Extreme edema

Bipolar Motor Point Stimulation Equally sized electrodes n Effect of stimulation is dependent on electrode placement n Current density is equal in both electrodes n Effective for stimulating muscle groups or very large muscles n

Bipolar Motor Point Stimulation (cont. ) n Used for innervated and denervated muscles Indications: n Peripheral nerve injuries n Inhibition of muscle activity due to joint pain and effusion

Bipolar Motor Point Stimulation (cont. ) Indications (cont. ): n UMN lesions to decrease spasticity & facilitate active contraction n Disuse atrophy n Immobilization n Orthopedic & neurological cases with LOM

Bipolar Motor Point Stimulation (cont. ) Contraindications & Precautions: n Same as Unipolar application

Quadripolar Motor Point Stimulation Electrodes from two or more circuits positioned so that currents geometrically intersect n Used for Interferential Stimulation Technique (MFC) n

Quadripolar Motor Point Stimulation (cont. ) Indications: n Pain & muscle spasm n Edema n Hematoma n Chronic ligamentous lesions n Urinary stress incontinence

Quadripolar Motor Point Stimulation (cont. ) Contraindications & Precautions: n Same as Unipolar application

Importance of Stimulation Parameters n 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 n IONTOPHORESIS / DIRECT CURRENT

Importance of Stimulation Parameters (cont. ) 2. 3. Very fast change of rate n HIGH FREQUENCY CURRENTS Rate of change between nos. 1 & 2 n LOW & MEDIUM FREQUENCY CURRENTS

Importance of Stimulation Parameters (cont. ) n The current intensity determines the extent of physiological changes n 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. ) n A single pulse is described by their: 1. Duration n 2. Intensity n 3. Seconds / Milliseconds / Microseconds Milliamps / Volts Shape n Illustrates the change of intensity with time

Importance of Stimulation Parameters (cont. ) n 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 n Generally, watery tissue such as blood, muscle and nerve has low ohmic resistance n

Current Flow in the Tissues (cont. ) Bone and fat has higher ohmic resistance n The epidermis has the highest ohmic resistance, which is determined by: n n Thickness & nature of skin n Inter-electrode distance

Current Flow in the Tissues (cont. ) This electrical resistance can be reduced by: n Washing & wetting the surface n Warming the skin

Skin Irritation as an Adverse Response Skin irritation may be caused by: n Electrical reaction n Electrochemical response n Allergic response to electrodes, gel, or tape

Skin Irritation as an Adverse Response (cont. ) Skin irritation may be caused by: n 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 n Disruption of stimulating devices due to proximity of diathermy output n Skin irritation n Electric shock n

Contraindications to Electrical Stimulation Strong muscle contraction might cause joint/muscle damage; detachment of thrombus; spread of infection; and hemorrhage n Stimulation of autonomic nerves might cause altered cardiac rhythm or other autonomic effects n

Contraindications (cont. ) n Currents might be unduly localized due to open wounds or skin lesions n Currents might provoke undesirable metabolic activity in neoplasms or in healed tuberculous infections

Contraindications (cont. ) n 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 n Check the patient for contraindications n Explain the treatment fully to the patient n

Principles of Application (cont. ) n Collect the necessary equipment n ES, electrodes, wiring n Soap & water for cleaning the skin n Contact gel / sponge, tape / straps / Velcro

Principles of Application (cont. ) Position the patient in the comfortable position n The skin should be uncovered & examined for any contraindications to treatment n Test the equipment as appropriate; demonstrate the technique to the patient n

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 n Select appropriate treatment parameters n

Principles of Application (cont. ) Always turn all intensity dials to zero before beginning the treatment n Place the electrodes as appropriate for the treatment n

Principles of Application (cont. ) Increase intensity until desired result is produced n Never lift the active electrode from the skin or replace it without turning the intensity to zero n

Principles of Application (cont. ) Terminate the treatment; check the skin condition n Keep a full record of the treatment n