Interaction of Electric and Magnetic Fields With a Human

Body

Ján Jakuš

Electricity- - results from elmg. forces between +protons and –

charged electrons

- in a wire it depends on a movement of free elec-trons

- in solutions it depends on a flow of a negatively charged -Anions, which are repealed by a negati-vely charged –Cathode, and attracted by a positi-vely charged +Anode.

- However, the direction of electric current was ge-nerally aknowledged from the +Anode to – Catho-de

Electric UnitsElectric Energy ( (power supply-U)) is measured in is measured in VOLTS (V)Electric Current (intensity-I) in in AMPERES (A))

Electric Resistance (R) in in OHMS (Ω))

OHM´S Law is a relationship between: I= U/R, U=I.R, R=U/IMetals - the best electric conductors (of 1st order)Living bodies are 2nd order electric conductors,

contain salt solutions

Types of Electric Currents

Direct Current (DC) – half wave shaped current. – half wave shaped current. Sources are batteries and rectifiers.Sources are batteries and rectifiers.

Alternating Current (AC)– sinusoidally shaped, 220V, 50Hz ( in Slovakia) USA: 120V, 60Hz

Human Body and Electricity

Body is a non-uniform space conductor where an electric current flows according to electric tissue conductivity.Body tissues have diffe-rent resistances (impedances), and therefore different conductances.

The highest el. resistance (Impedance) have the fat and bone tissues (R = 40-50 Ω/m)

The lowest el. resistance (Impedance) have a blood, liquor, lymphatic fluid (R = 0.8 Ω/m)

El. resistance for dry skin is high (R=1000 Ω/m)

El. resist. for moistured skin is low (R=50 Ω/m)

Impedance, Resistance and Reactance

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Biological Effects of Electric Currents on Human Body

Both DC and AC Currents have 3 main effects : Both DC and AC Currents have 3 main effects :

Stimulatory, Electrolytic, Thermal. I. Stimulatory – is typical for AC current with f = 50-100 Hz, but also for DC current

Max. harmless AC current is 5 mA, and for DC current is 25 mA

Stimulatory effects of DC current (a) and AC (b) are used in:

a) Chronaximetry (e.g. chronaxia for sceletal mus-cle is 1.0 msec, but for nerve is 0.1 ms. Thus, an excitability of nerve tissue is 10-times higher than that one for muscle tissue)

b) Therapy with stimulatory (diadynamic) currents

Stimulatory Currents in Medicine

1.Rectangular DC Currents mostly used for stimu- mostly used for stimu-lation of muscles and nerves in rehabilitationlation of muscles and nerves in rehabilitation

2.Faradic (Triangle) Currents used for stimulation of used for stimulation of sceletal muscles ( muscle twitch, summation, sceletal muscles ( muscle twitch, summation, superposition, tetanussuperposition, tetanus))

3. Sinusoidally shaped AC current

4.Sinusoidally modulated AC currents- relieve a pain relieve a pain

Methods of Electric Stimulation with AC Currents (see also Therapeutic Methods)

1.Electroconvulsive therapy (electroshocks)

2. Defibrilation (Cardioversion)

They are used in Psychiatry and in and in Emer-gency Medicine

Point: Condenser current 2-5 kV / 2-5 ms is used.

Effects: Re-set of either 1. brain function

or the 2. heart action

Methods of Electric Stimulation with DC Current

Pacemaking It is a useful method of treatment It is a useful method of treatment „sick sinus syndrome“ “

(i.e. the (i.e. the sinoatrial (SA) node is not working properly, is not working properly, and as a result bradycardia and collapse may appear and as a result bradycardia and collapse may appear in patient.in patient.

Point: Point: A pacemaker device (battery operated generator (battery operated generator of DC currentof DC current)) is sewed under the skin around a clavi-is sewed under the skin around a clavi-cula, or abdomen. Under X-ray method the wires with cula, or abdomen. Under X-ray method the wires with hook electrodes are introduced through hook electrodes are introduced through caval veins into the into the heart right atrium, or into both the right atrium or into both the right atrium and the right ventricle and the right ventricle ON DEMAND pacemaker- it it works (stimulates the heartworks (stimulates the heart)) only when SA node is only when SA node is silent.silent.

Heart Pacemaker

II. Electrolytic Effect

Is a typical feature for Is a typical feature for DC current, when passing the salt solution

E.g.: NaCl when dissolved in water brea-E.g.: NaCl when dissolved in water brea-kes to kes to Na+ + Cl - ions ions

When When DC electric current passes such current passes such solution, then solution, then Na+ cations run towards the run towards the – – Cathode.. Similarly Similarly Cl – anions run towar- run towar-ds the ds the ++ ANODE

Methods that use Electrolytic Effect of DC Current (see also Therapeutic methods)

IONOPHORESIS is a method of an introducing of drugs is a method of an introducing of drugs dissolved in water to the eye, knee, joints, skin ..dissolved in water to the eye, knee, joints, skin ..

Point:: The The method based on the fact that ions with themethod based on the fact that ions with the same charges are repelled. . Contrary, the ions with the opposite charges are attracted.

E.g. Drugs as anesthetics when dissolved in water create Cations+ . Thus, when Anodal + Current is app-lied, then drugs are electrically pushed to the body. Or drugs as antibiotics, aspirine or iodine salts create

Anions-. When Cathodal - Current passes the solution then dissolved drugs are pushed to the body.

III. Thermal Effect

This effect is typical for This effect is typical for AC current, mainly at mainly at frequencies frequencies above 100 kHz..

As a result- As a result- a heat is produced in tissues - this is produced in tissues - this property of property of HHigh Frequency AC Currents is used in is used in thermotherapeutical method named- thermotherapeutical method named- Diathermy.

Types: Types: short wave (27 MHz)

ultra short wave (434 MHz)

microwave (2400 MHz)

Magnetic FieldsPermanent (stable) magnets as Earth (it results as Earth (it results

of rotation of hot magma within the Earth coreof rotation of hot magma within the Earth core))Non-stable artificial magnetic fields – arise in a

vicinity of wire (within a coil) under electricityMagnetic fields with low frequency - increase

the excitability of brain, decrease the blood flow in vessels with a high diameter - aorta (this in turn, may decrease the blood pressure)

Magnetic fields with high frequency- have mainly thermal effects (used in Diathermy)

Both types of fields are used in the Nuclear Magnetic Resonance Scanning (NMRS)

Electromagnetic Field

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Patient Protection Against Electric Shock –Basic Rules

1.1. At a time ofAt a time of Recording (e.g. ENG, EKG.. (e.g. ENG, EKG..)) or or at a time of at a time of Defibrilation remember: do not do not ground a patient.ground a patient.

2.2. For diagnostic and treatment goals doctors For diagnostic and treatment goals doctors must use only devices approved for their must use only devices approved for their use in Medicine, being equipped with „use in Medicine, being equipped with „sepa-ratory“ transformes. Hence, in the time of an accident i.e. „a short circuit“- the transformer is able to disconnect the primary el. circuit , 220V, from the secondary (patient) circuit.

The harmful effect of electricity on a living body depends on on Intensity of el. current, on the on the impedance and the and the insulation of the body against the ground.

Electric shock is caused only by Electric Cu-rent, which is determined both by a Volta-ge and body Resistance.

Wishing You Merry Christmas and Very Happy and Prosperous

New Year

With love,With love,

prof. Jakus prof. Jakus