direct current & iontophoresis

direct current

• galvanism (medical) / constant current

• mA: 1 mA = 6.24 × 10²1 electrons per second

• unidirectional flow through a conductor

• electron flow: (-) to (+)

• current flow: (+) to (-)

electrolysis

polarity testing

physiologic effects

hyperemia

• counter-irritant → pain relief

sedation

• at the ANODE, analgesic

• DC reduces NCV

Pfleuger’s (Erb’s) law

• “polar formula”

continuous direct current

• ionthoporesis

• high risk for chemical burn

• rarely used today

interrupted direct current

• flows in the same direction intermittently

• strength reduces to 0 between each period of flow

pulsed current

long interrupted direct current

• unidirectional, interrupted at regular intervals

• for denervated mm

• modulation

  • intensity is cyclically reduced to 0

  • interrupted modulation: current is turned on & off

• waveform

  • exponential progressive pulses

• factors

  • strength & duration of stimulus

rheobase

• 5-35 V (2-18 mA)

• minimal voltage, prolonged PD

• produces bare minimal & palpable contraction

• cathode / bipolar technique

Chronaxie

• 0.05-0.5 ms

• minimal time, stimulus twice the strength of rheobase

physiological effects of EPC

long IDC: denervated mm

• normal : (+) accommodation

• denervated: (-) accommodation

  • to stimulate: ↓ intensity, ↑ time (rheobase?)

effects of LIDC on denervated mm

effects of SIDC

• sensorimotor: minimal stimulation of sensory fibers

• ionic mov’t of IC & EC fluid

  • through & through faradism

surged interrupted DC

• peak intensity ↓, ↓ gradually

• no fixed current intensity — modulated

depolarized interrupted DC

• definite positive polarity

• intensity flows on reverse during interval between impulses → reduce chemical effects

Interrupted modulated DC

• intensity is cyclically reduced to zero at regular intervals

iontophoresis

• continuous DC to transfer ions

• used to avoid GI upset

• electrophoresis: movement of ions in solution

• principles:

  • ionisation

  • like charges repel

  • deeper penetration

• wave form: monophasic

• modulation: constant

• # of ions transferred is directly related to:

  • duration of tx

  • current density

  • ion concentration

Selecting the ion

• must be soluble in both fat & water

• relatively superficial, generally <1mm

indication for DC & ionthophoresis

• relief of pain

cathodal galvanism

• chronic pain due to adhesion, swelling, or pressure on nerves

• counter-irritant → VD

• max dosage (chronaxie?), short time

  • 0.5 to 0.8

  • 10 min, 1st tx → progress by 5 min to 20 min

• tx on alternate days

anodal galvanism

• relieve pain by removing H & K ions (MPS)

• low dosage, max time (rheobase?)

  • 0.15 to 0.25

  • 15 mins, 1st tx → progress by 5 to 30 mins

• can be given daily for a few days

common drugs

contraindication

• open skin

• infection

• bony areas

  • can produce burn, impedance

• loss of sensation

• dry scaly skin

• skin lesions

dangers

• shock

• burns

  • chemical

    • alkaline — cathode

    • acidic — anode

  • due to: overdosage & skin lesions

alternating current

• sinusoidal currents

• direction of flow changes in rhythmically at a specific frequency per second

• medicine = 50 Hz

surged AC

• magnitude gradually increased or decreased

• length: varies, 1-10 ms

• pulse — sine wave of each polarity

types of surged ac

sinusoidal currents

• even AC, 50 Hz

• PD: 100 ms, sine pulse

• may be surged or unsurged

physiological effects of SC

SC indication & contraindication

faradic currents

• uneven AC, 50 Hz

• PD: 1 ms, hand surged current

• produced by a faradic / induction coil