Interaction of Electric and Magnetic Fields With a Human Body Ján Jakuš

Electricity - results from elmg. forces between + protons and – charged electrons - in a metal wire electricity depends on a movement of free electrons in solutions electricity depends on a flow of negatively charged -Anions, which are repealed by a negatively charged –Cathode, and attracted by a positively charged +Anode. - the direction of electric current was generally aknowledged as a flow of electrons from the +Anode to – Cathode

Electric Units Electric Energy (power supply-U) is measured in VOLTS (V) Electric Current (intensity-I) in AMPERES (A) Electric Resistance (R) in OHMS (Ω) OHM´S Law is a relationship between: I= U/R, U=I.R, R=U/I Metals - the best electric conductors (of 1st order) Living bodies are 2nd order electric conductors, because contain mostly the salt watery solutions

Types of Electric Currents Direct Current (DC) – half wave shaped current. 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 (spreading). 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

Biological Effects of Electric Currents on Human Body 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 For living bodies 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 electrodiagnostic method: Chronaximetry (e.g. chronaxy for sceletal muscle 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) Therapy with stimulatory (diadynamic) currents

Stimulatory Currents in Medicine 1.Rectangular DC Currents mostly used for stimu-lation of muscles and nerves under rehabilitation 2.Faradic (Triangle) Currents used for stimulation of sceletal muscles ( i.e.muscle twitch, summation, superposition, tetanus) 3. Sinusoidally shaped AC current - vasodilation 4.Sinusoidally modulated AC currents- 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 Emer-gency Medicine Point: Condenser current under voltage U= 2-5 kV / 2-5 ms is used. Effects: Re-setting 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 „sick sinus syndrome“ (i.e. when the sinoatrial (SA) node is not working properly, and as a result is the bradycardia and collapse of patient. Point: A pacemaker device (battery operated generator of DC current) is sewed under the skin around a clavi-cula, or into an abdomen. Under X-ray method the wires with hook electrodes are introduced through caval veins into the heart right atrium, or into both the right atrium and the right ventricle . “ON DEMAND pacemaker “ It works (stimulates the heart) only when SA node is silent.

Heart Pacemaker Small d efibrilator

II. Electrolytic Effect Is a typical feature for DC current, when passing the salt solution E.g.: NaCl when dissolved in water brea-kes into Na+ + Cl - ions When DC electric current passes such solution, then Na+ cations run towards the – Cathode. Similarly Cl – anions run towar-ds the + ANODE

Methods that use Electrolytic Effect of DC Current (see also Therapeutic methods) IONOPHORESIS is an electric method which pushes drugs dissolved in water to the eye, knee, joints, skin ... Point: The method is based on the fact that ions with the same charges are repelled. Contrary, the ions with the opposite charges are attracted. E.g. Some drugs (as anesthetics) when dissolved in water create Cations+. Thus, when Anodal + current is applied, 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 AC current, mainly at frequencies above 100 kHz. As a result- a heat is produced in tissues - this property of High Frequency AC Currents is used in thermotherapeutical method named- Diathermy. Types: short wave (band 27 MHz) ultra short wave (434 MHz) microwave (2400 MHz)

Magnetic Fields Permanent (stable) magnets as Earth (it results from rotation of hot magma within the Earth core) Non-stable artificial magnetic fields – arise in a vicinity of wires (within a coil) under electricity 1.Magnetic 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) 2. 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

Patient Protection Against Electric Shock –Basic Rules At a time of Electric Recording (e.g. ENG, ECG..) or at a time of Defibrilation remember: NEVER ground a patient ! For diagnostic and treatment goals doctors must use only devices approved for their use in Medicine, being equipped with „separatory“ 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 Intensity of el. current, on the impedance (resistivity of a tissue),and on the insulation of the body against the ground. Electric shock is caused only by Electric Cu-rent, passing the electric circuit . Electric current is determined both by a Voltage and body Resistance.(OHM´S LAW)

Wishing You Merry Christmas and Very Happy and Prosperous New Year May your wishes come true With love, prof. Jakus