Effects of electric current on human body

What is electric current What is electric current? Electric current is a flow of particles having an electric charge (electrons, positive and negative ions)…..

What is making the particles to move What is making the particles to move? Electric voltage  a difference of electric potentials. Electric potential is in fact an electric characteristic of some certain place. ….. We can compare the electric potentials to places of some “concentration” of the electric charges and electric voltage to the difference between these places. Free charged particles will be moving from highly concentrated places to places with a low concentration.

Origin of the lectric current Electric current can be present in solid substances (metals), liquids (electrolytes), and gases (ionized gases). The substance is able to conduct the electric current only on condition that contains free charged particles. Free charged particles of these substances perform only the thermal motion until the electric voltage is present. Thermal motion is a random and irregular motion of any small particle (atom, molecule). The range of the motion depends on kind of chemical bonds of the particle and surrounding matter.

If there is an electric voltage (potential difference), free charged particles start to move in the direction from the place of the highest electric potential to the place of the lowest electric potential. The movement of free charged particles from the place of highest electric potential to the place of lowest electric potential is called electric current. Free charged particles can be either negative (electrons or negative ions) or positive (positive ions).

What are AC and DC? AC is an alternating current, DC is direct current. The voltage in direct current does not change (a good example can be a battery). The voltage in AC is changing (electrical outlet). Number of cycles in 1 second is called frequency (measured in Hertz).

What does the electric current in human body? Human tissues are very sensitive to the flow of electric current. The electric current flowing through the heart causes the fibrillation of the heart, flowing through muscles it causes contractions of the muscles; if the electric current is passing through the brain it causes the loss of conciseness and seizures. The threshold of perception for current entering the hand is about 5 to 10 miliamperes (mA) for DC and about 1 to 5 mA for AC at 60 Hz.

The maximum amperage that can cause the flexors of the arm to contract but that allows a person to release his hand from the current's source is termed the let-go current. For DC, the let-go current is about 75 mA for a 70-kg man; for AC, it is about 15 mA, varying with muscle mass. AC current traveling through the chest for a fraction of a second may induce ventricular fibrillation at amperage as low as 60 to 100 mA; about 300 to 500 mA of DC is required. If the current has a direct pathway to the heart (e.g., via a cardiac catheter or pacemaker electrodes), a much lower amperage (< 1 mA, AC or DC) can produce fibrillation.

Why is AC more danger than DC? The type of current affects the severity of the injury. In general, direct current (DC), which has zero frequency, is less dangerous than alternating current (AC). The effects of AC on the body depend largely on the frequency. Low-frequency currents of 50 to 60 Hz (cycles/sec), which are commonly used, are usually more dangerous than high-frequency currents and are 3 to 5 times more dangerous than DC of the same voltage and amperage.

DC tends to cause a convulsive contraction, often forcing the victim away from the current's source. AC at 60 Hz (household current) produces muscle tetany, often freezing the hand to the current's source; prolonged exposure may result, with severe burns if the voltage is high. The human body is in fact the mixture of cells and extracellular fluid. Inside the cells is intracellular fluid. The extracellular fluid is an electrolyte that means a good conductor. The intracellular fluid is also an electrolyte. The cell membranes are isolants. DC  if the voltage that is not changing is applied …the direct current can flow through the extracellular fluids. It can not pass through the cell membranes, so it can not flow intracellulary (contrary to AC ).

Calculation of the current in circuit The value of the current flowing through any circuit is calculated by the equation I = U/R. Explanation: the higher is the voltage (U), the higher is the value of I (amperage). On the other hand the higher is the resistance (R), the lower is the value of electric current (I). Example  lets have battery having 4.5 V, the metal wire with resistance 1 W. What is the value of electric current flowing through the circuit (amperage)? Result  4,5 A.

Body resistance (measured in ohms/cm2) is concentrated primarily in the skin and varies directly with the skin's condition. The resistance of dry, well-keratinized, intact skin averages 20,000 to 30,000 ohms/cm2; for a thickly calloused palm or sole, it may be 2 to 3 million ohms/cm2. The resistance of moist, thin skin is about 500 ohms/cm2. If the skin is punctured (e.g., from a cut or abrasion or by a needle) or if current is applied to moist mucous membranes (e.g., mouth, rectum, vagina), resistance may be as low as 200 to 300 ohms/cm2.

If skin resistance is low, few, if any, extensive burns occur, although cardiac arrest may occur if the current reaches the heart. If skin resistance is high, much energy may be dissipated at the surface as current passes through the skin, and large surface burns can result at the entry and exit points, with charring of tissues in between (heat = amperage2 × resistance). Internal tissues are burned depending on their resistance; nerves, blood vessels, and muscles conduct electricity more readily than denser tissues (eg, fat, tendon, bone) and are preferentially damaged. It is clear that much higher voltage must be used to cause at least minimal effect on human body, because of the high resistance.

Heat effects of electric current The higher the resistance is the higher production of the heat is. If there is an element with high resistance in the circuit, it is usually hot, depending on the value of electric current (amperage) in the circuit and the resistance of the element. If skin resistance is low, few, if any, extensive burns occur, although cardiac arrest may occur if the current reaches the heart. If skin resistance is high, much energy may be dissipated at the surface as current passes through the skin, and large surface burns can result at the entry and exit points, with charring of tissues in between (heat = amperage2 × resistance  Q = I2 . R. t).

Pathogenesis The type of current affects the severity of the injury. In general, direct current (DC), which has zero frequency but may be intermittent or pulsating, is less dangerous than alternating current (AC). The effects of AC on the body depend largely on the frequency. Low-frequency currents of 50 to 60 Hz (cycles/sec), which are commonly used, are usually more dangerous than high-frequency currents and are 3 to 5 times more dangerous than DC of the same voltage and amperage. DC tends to cause a convulsive contraction, often forcing the victim away from the current's source. AC at 60 Hz (household current) produces muscle tetany, often freezing the hand to the current's source; prolonged exposure may result, with severe burns if the voltage is high.

Generally, the higher the voltage and amperage, the greater the damage from either type of current. High-voltage (> 500 to 1000 V) currents tend to cause deep burns, and low-voltage to cause freezing to the circuit. The threshold of perception for current entering the hand is about 5 to 10 milliamperes (mA) for DC and about 1 to 10 mA for AC at 60 Hz. The maximum amperage that can cause the flexors of the arm to contract but that allows a person to release his hand from the current's source is termed the let-go current.

For DC, the let-go current is about 75 mA for a 70-kg man; for AC, it is about 15 mA, varying with muscle mass. A low-voltage (110 to 220 V), 60-Hz AC current traveling through the chest for a fraction of a second may induce ventricular fibrillation at amperage as low as 60 to 100 mA; about 300 to 500 mA of DC is required. If the current has a direct pathway to the heart (eg, via a cardiac catheter or pacemaker electrodes), a much lower amperage (< 1 mA, AC or DC) can produce fibrillation.

Coffee break

The pathway of current through the body determines the nature of injury. Current traveling from arm to arm or between an arm and a foot is likely to traverse the heart and so is much more dangerous than current traveling between a leg and the ground. Electrical injuries to the head may cause seizures, intraventricular hemorrhage, respiratory arrest, ventricular fibrillation or asystole, and, as a late effect, cataracts.

The most common entry point for electricity is the hand, followed by the head. The most common exit point is the foot. With AC, exit and entry are misnomers, because which site is the entry and which is the exit cannot be determined. More appropriate terms are "source" and "ground.“ Generally, the duration of current flow through the body is directly proportional to the extent of injury because longer exposure breaks tissues down, allowing internal current flow. The current flow produces heat, damaging internal tissues.

Symptoms and Signs The clinical manifestations of electrical injuries depend on the complex interaction of the factors discussed above. Physiologic functions may be altered, resulting in severe involuntary muscular contractions, seizures, ventricular fibrillation, or respiratory arrest (apnea) due to CNS injury or muscle paralysis. Thermal, electrochemical, or other damage (eg, hemolysis, protein coagulation, vascular thrombosis, dehydration, muscle and tendon avulsion) may occur.

Often a combination of these effects occurs. Burns may be sharply demarcated on the skin and extend well into deeper tissues. High voltage may cause coagulation necrosis of muscle or other internal tissues between source and ground points of the current. Massive edema may follow as the veins coagulate and the muscles swell, with resulting compartment syndromes. Hypotension, fluid and electrolyte disturbances, and severe myoglobinuria may cause acute renal failure. Dislocations, vertebral or other fractures, blunt injuries, and loss of consciousness may result from powerful muscle contractions or falls secondary to the electric shock (eg, electricity can startle a person, causing a fall).

In "bathtub accidents" (typically, when a wet [grounded] person contacts a 110-V circuit--eg, from a hairdryer or radio), cardiac arrest may occur without burns. Lightning rarely, if ever, produces entry and exit wounds and seldom causes muscle damage or myoglobulinuria, because the duration of current is too short to break down the skin and tissues. Lightning flashes over the person, producing little internal damage other than electrical short-circuiting of systems (eg, heart asystole, brain confusion, loss of consciousness, neuropsychologic sequelae). Some form of amnesia generally results.

Neuropsychologic damage, pain syndromes, and sympathetic nervous system damage are the most common long-term sequelae. Cardiopulmonary arrest is the most common cause of death. Toddlers who suck on extension cords can burn their mouth and lips. Such burns may cause not only cosmetic deformities but also growth problems of the teeth, mandible, and maxilla. An added danger is labial artery hemorrhage, which results when the eschar separates 7 to 10 days after the injury; hemorrhage occurs in up to 10% of cases.

Symptoms and Signs - CONCLUSION Depend on the pathway of electric current through the body. Conduction from arm to arm or arm to foot is much more dangerous than the conduction between legs or leg and the ground since the current may traverse the heart. Electrical injuries to the head cause loss of conciseness, seizures, respiratory arrest. In Czech republic in half of electric injuries at home children under 5 y are insulted. High voltage vs. low voltage injuries (special category  bathtub accidents) ……..

Treatment Contact between the victim and the current source must be broken. The best method is to shut off the current, if it can be done rapidly (eg, by throwing a circuit breaker or switch, by disconnecting the device from its electrical outlet); otherwise, the victim must be removed from contact with the current. For low-voltage (110 to 220 V) currents, the rescuer should first well insulate himself from ground and then use an insulating material (eg, cloth, dry wood, rubber, leather belt) to pull the victim free. If lines could be high voltage, no attempt to disengage the victim should be made until the power is shut off. High- and low-voltage lines are not always easily differentiated, particularly outdoors.

Once the victim can be safely touched, he should be rapidly examined for vital functions (eg, radial, femoral, or carotid pulse; respiratory function; level of consciousness). Airway stabilization is the first priority. If spontaneous respiration is not observed or cardiac arrest has occurred, immediate resuscitation is required (see Ch. 206). Treatment of shock and other manifestations of massive burns is discussed in Ch. 276. Once vital functions have been reestablished, the full nature and extent of the injury must be evaluated and treated. Dislocations, fractures, and cervical-spinal and blunt injuries should be sought. If myoglobinuria is present, fluid replacement and alkalinization therapy is essential to reduce the risk of renal tubular myoglobin precipitation (see Ch. 276). Mannitol or furosemide may be indicated to increase renal flow. Tetanus prophylaxis is required for any burn.

Baseline assessment for all electric injuries includes an ECG, cardiac enzymes, a CBC, and urinalysis, especially for myoglobin. Cardiac monitoring for 12 h is indicated if there is any suggestion of cardiac damage, arrhythmias, or chest pain. Any deterioration in the level of consciousness mandates a CT or MRI scan to rule out intracranial hemorrhage. Victims of lightning injuries may require cardiac resuscitation, monitoring, and supportive care. Fluid restriction is the rule because of potential brain edema. Children with lip burns should be referred to a pedodontist or oral surgeon familiar with the evaluation and long-term care of such injuries.

Treatment – CONCLUSION Separating the patient from the current source  cut off the source (circuit breaker or switch, disconnecting the device from its electrical outlet). For low voltage (110-220 V), the rescuer should first ensure that he himself is well insulated from ground, and then use an insulating material to pull the person free. If it is suspected that higher voltage lines are involved, it is best to leave the victim alone until the power can be shut off. rapid cardiopulmonary resuscitation (ABC) care in hospital  treatment of myoglobinuria + hyperkalemia, treatment of fractures, treatment of burns.

Prevention Education about and respect for electricity as well as common sense are essential. Any electric device that touches or may be touched by the body and may be life threatening should be properly grounded and incorporated into circuits containing protective circuit-breaking equipment. Ground-fault circuit breakers, which trip when as little as 5 mA of current leaks to ground, are excellent and are readily available. Preventing lightning strikes involves using common sense and proper protection devices, knowing the weather forecast, and having an escape route to an appropriate shelter in storms. Prevention : respect in dealing with electricity proper design, installation and maintenance of all electric devices education and care about children

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