electrotherapy basics

electric charge

property of matter measured in coulombs, results from either too many or too few electrons

every estim device delivers

charge

electric charge does what to ions

moves ions and activates nerves - sensory, motor or pain

voltage

force of attraction of repulsion

attraction of charge

opposite ion charges attract - how we activate nerves

repulsion of charge

like charges repel - how we deliver medication

charge cannot be

created or destroyed, but it can be transferred

current

flow of ions or electrons - in the wire this is electrons, in the body this is ions

closed circuit, loop

need 2 electrodes on a patient to get a closed circuit and feel charge

higher voltage

more current

less voltage

less current

polarity

idea of being positive or negative

anode

positive electrode, usually the red wire

cathode

negative electrode, usually the black wire

due to properties of charge and polar effects of ions

the anode attracts acid (HCl) and the cathode attracts base (NaOH)

which wire is at higher risk of skin irritation

cathode wire because it is basic and the skin is acidic

Ohm's law

I =V/R

to get the most current, we want to

keep resistance as low as possible

low resistance would include features like

good electrodes, clean skin, minimal hair

when current increases/resistances decreases

cathode reacts worse at skin because of acid/base mix

ways resistance can increase

electrode dries out, skin gets dry (feels less of a tingle)

reasons resistance can decrease

sweating (feel strong pain)

constant voltage device

monitors the amount of voltage and adjusts the current to keep the voltage constant - likely to create polar effects and could burn skin

constant current device

monitors current level and adjusts voltage level to maintain - much safer for patient use/skin

conductance

ability to conduct electrcitiy

resistance

resistance to the flow of current (want to keep it low)

old wires, dry electrodes, hair, oily or dirty skin can all

increase resistance

resistance is measured in

Ohms

capacitance

ability to store electrical charge - we have to overcome this

in the body, what has capacitance

skin, nerves

capacitance is measured in

Farads

overcome capacitance by

high voltage, high current or pulsed current

pulsed current allows

charges to jump across and overcome capacitance

by increases area of estim and voltage

you can overcome capacitance and resistance to increase current and effectiveness of estim

impedance

combination of resistance and capacitance - must be overcome for estim to have an effect

to decrease impedance of skin

clean skin with a wet paper towel

wiping skin with alcohol wipes can

increase skin impedance by drying out electrode or leaving residue on skin

to produce some effect in the human body, we need

closed circuit, minimized impedance, proper electrode placement, voltage applied