Dr. Rashi Goel (PT)

Assistant Professor

DY Patil College of Physiotherapy

Pimpri, Pune

Definition

Use of electrical energy as a medical treatment

Electricity is an element of PT modalities most frightening and least understood

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Matter

Mass + occupies space Basic unit of matter- atom

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States of matter

Solid- lattice formation Liquid Gas

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Cohesive force- attracts molecules of the substance to one another

Kinetic force- force of movement of the molecules

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Properties of matter

Adhesion Surface tension Viscosity Density Elasticity

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Adhesion

Attachment of a substance to the surface of another substance

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Surface Tension

The cohesive forces between liquid molecules

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Viscosity

Quantity that describes a fluid's resistance to flow

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Density

Mass per unit volume

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Elasticity

Tendency of solid materials to return to their original shape after being deformed

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ATOM

A central nucleus surrounded by a cloud of electrons revolving in definite orbits

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Structure of atom

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Nucleus

Proton Neutron

Electron

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Molecule

Electrically neutral group of two or more atoms held together by chemical bonds

A substance that is the smallest particle of a compound and still contains all the characteristics of that compound

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Elements

a substance that is made entirely from one type of atom

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Compounds

Substance formed by the union of two or more elements, the union taking place via the electrons of the atoms involved to form a molecule of the compound

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Compounds

Covalent Electrovalent

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Molecule/Compound

A molecule is formed when two or more atoms join together chemically

A compound is a molecule that contains at least two different elements

All compounds are molecules but not all molecules are compounds

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Electron theory

Electric Charges:

Electrons have a –ve charge Protons- =+ve Neutrons- no charge

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An electrically neutral atom has the same number of protons and electrons

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Atomic no.= no. of protons in the nucleus

Atomic mass= no. of protons + no. of neutrons

Isotopes eg. Carbon

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Electricity

Electricity is the force created by an imbalance in the number of electrons at two points

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Static electricity

Simplest form of electricity

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Causes of static electricity

Static electricity is usually caused when certain materials are rubbed against each other, like wool on plastic or the soles of your shoes on the carpet

This causes electrons to be pulled from the surface of one material and relocated on the surface of the other material

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Try-

run a comb through your hair to charge the comb with static electricity

The comb can then be used to attract neutral pieces of tissue

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The material that loses electrons ends up with an excess of positive (+) charges

The material that gains electrons ends up an excess of negative (-) charges on its surface

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Electric field of a charged body

A zone of influence

Lines of force

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Properties of lines of force

I. Straight lines

II. Repel one another

III. Pass more easily through conductors than insulators

IV. Concentrate over that part of the surface over which they can exert an influence

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Electrical Potential

When compared to neutral potential of the earth

Unit- Volt High potential= strong repelling power

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Capacitance

The ability of tissue (or other material) to store electricity

Unit is Farad, microfarad

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Potential Difference

Difference in concentration of electrons between two points

Electrons will not move unless a potential difference exists

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EMF

Force producing the force

Electrons flow from more negative to less negative body until both are at same potential

Unit is Volts

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Current electricity

An electric current occurs when there is a flow of charged particles in a conductor

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Conductors

Materials that permit free movement of electrons

Composed of large numbers of free electrons

Offer little resistance to current flow Good conductors

Metals (copper, gold, silver, aluminum)Electrolyte Solutions

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Insulators

Materials that resist the flow of electrons Contain few free electrons Insulator materials

Air, Wood, Glass

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Electromagnetic Radiation

Produced by movement of electrons within the atom

Excited state

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Resistance

The opposition to flow of current

Measured in Ohms

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Intensity

Magnitude of current- rate of flow of electrons through the conductor per second

Measured in Amperes

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Ohm’s law

V = IR (V is voltage, a measure of the driving

force which is equal to the I x R where I is the Ampere (the amount of current flow) and R is the resistance

The Ampere is equal to the Voltage divided by the Resistance.

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Application of Ohm’s law to AC and DC currents Thermal effects of an electrical current

Joule’s law: Q= I2RT

I= current in amperes R= Resistance in ohms T= time in seconds

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Main supply

Produced by Dynamo Principal of Dynamo

Live wire- at high potential Neutral wire- at zero potential connected

to earth

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Electrical supply

Alternating sinusoidal current of 50 Hz at 220- 240 voltage

GRID SYSTEM

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Wiring in houses

Light and power circuits In parallel or in ring main Sub-circuits

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Numericals

2 formulae

EMF= VI V= IR

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Watt= 100W V= 240V R=?

Watt= 2000W V=240V R=?

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Results

1. I= 0.417A R= 576 ohm

2. I= 8.333A R=28.9ohm

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Over current/Excess current

A situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment

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Causes for over current

Short circuits Excessive load Incorrect design

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Short Circuit

Resistance of circuit reduces- due to:

If insulation becomes worn out 2 supply wires come in contact Connection between live wire and earth

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Fuse

Weak point in the circuit which blows if a very high intensity of current is passed

Low melting point

Safety device

Live wire

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Fuse

Silver wire- fusible material Metal caps Glass tube Metal clips

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Cartridge fuse

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Why a fuse blows off?

1. Resistance too low

2. Wattage too high

3. Several parallel circuits from one supply point eg. Adaptors

To prevent overheating and fire

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When a fuse blows what to do?

1. Disconnect the apparatus

2. Switch off the main supply

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Dangers

Short circuits Electric shocks

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3 Pin Plug & Socket

Earth pin- longest

Live- brown Neutral- blue Earth- yellow and green

Easily distinguished

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One way to enter One way to exit

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Earthing

Precaution against earth shock

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Earth shock

Connection between live wire of the mains and earth

Earth circuit Eg.

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Precautions for earth shock

Water and gas pipes- out of reach of apparatus & patients getting treatment

Floor should be dry Floor of insulating material/mat placed Fuses on live wire

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Electric shock

Physiological reaction or injury caused by electric current passing through the human body

Painful stimulation of sensory nerves caused by a sudden flow, cessation or variation in the current passing through the body

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Causes of electric shock

Sudden increase in the current

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Effects of electric shock

Minor- frightened and distressed Major- Fall in BP, Loss of consciousness,

stoppage of respiration, cardiac arrest, ventricular fibrillation due to electrical stimulation of the heart

Death caused by an electric shock is called electrocution/ electrical execution

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Electrical currents flowing at <1mA will not be felt and is referred to as microshock

Shock from a current flow >1 mA is called macroshock

Currents b/w 1 - 15 mA: a tingling sensation or perhaps some muscle contraction

Currents b/w 15-100 mA: a painful electrical shock

Currents b/w 100 and 200 mA may result in fibrillation of cardiac muscle or respiratory arrest

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Severity of shock-

1. High voltage/ High current

2. Duration

3. Resistance of the body

4. Path taken by current- lethal if current flows through the heart muscle

5. Type of current

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Under dry conditions, resistance offered by the human body is- 100,000 Ohms

Wet or broken skin- body's resistance is 1,000 Ohms

high-voltage electrical energy quickly breaks down human skin, reducing the human body's resistance to 500 Ohms

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Treatment of electric shock

Disconnect the person from the source of supply

Switch off the current at once

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Precautions to be taken

Self test all equipments before using on patients

Check all connections Check all control knobs Intensity to be increased slowly Regular servicing of the equipments Patient should not touch electrical

equipments

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Electric shock as a medical therapy

Electroconvulsive therapy/ ECT- psychiatric illness

Defibrillation– for fibrillation/ irregular heart rhythms

For pain relief- TENS For hyperhidrosis- Iontophoresis

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