bioelectricity, physiological response to electric current Flashcards
define static electricity
-where there is a build up of either positive or negative charges on an object & this surplus charge can either repel or attract other objects which have an excess charge
define current
the rate of flow of charge
what are the units of current?
Amps
what are Coulomb forces?
-type of force that exists between electrically charged objects
-the attractive / repulsive forces
-like charges repel and opposite charges attract
what is earthing?
earthing involves connecting electrical devices, appliances, or structures to the ground or earth.
-earthing is used to prevent electrical accidents by providing a path for excess electrical current to flow safely into the ground, rather than through a person’s body or critical equipment.
what can a build up of static electricity cause?
sparking - sudden discharge of electricity
- may have a visible flash of light
-can be dangerous in the presence of flammable gases eg oxygen
what kind of conditions are electrostatic effects much more prominent in?
dry conditions w/ low humidity - since any moisture in the air can drain away excess charge through attachment to water molecules
what are examples of precautions that should be taken against static discharge in a clinical setting?
-maintain humidifiers in operating theatres - prevents build up of static electricity
-use antistatic flooring
-use anti-static rubber for masks, tubing etc
- all electrotherapy equipment should be properly earthed, which will prevent electric shocks by displacing excess current into the ground rather than people
describe conductors
-materials that allow electricity to flow through them easily
-they have many free electrons that move freely within the material when an electric field is applied
-eg metal, copper
describe insulators
-materials that do not allow electricity to flow through them easily
- dont have free electrons, making it difficult for electric current to pass through the material
eg plastic, wood, rubber
-insulators are used to prevent the flow of electricity & can protect against electric shocks etc
why is the human body a reasonably good conductor?
as it contains water (which contains ions) & electrolytes which are substances that can conduct an electrical current
-also sweat is very rich in electrolytes
-therefore, electric current can flow easily through the body
does a material with a high resistance have a low or high current flow & why?
- a material with a high resistance has a low current flow
-this happens as the resistance opposes the movement of electric charge through the material
does a material with low resistance have a high or low current flow?
a high current flow, as there is minimal resistance to the movement of electric charge through the material
what are the 2 types of electric currents that are distinguished by the direction of electric flow?
-unidirectional - d.c
-alternating a.c
describe unidirectional current / d.c
-electric charge flows continuously in one direction.
-The flow of charge is constant and does not change direction over time
-d.c is typically produced by batteries
describe alternating current / a.c
-the flow of electric charge reverses direction periodically, oscillating back and forth.
-AC is produced by generators, power plants, and electrical outlets in homes and buildings
what unit is electrical resistance measured in?
Ohm
define voltage
the energy source required to produce a current, and the size of current depends on the resistance offered by the material in which the current flows
describe ohms law
The current (I) flowing through a conductor is directly proportional to the voltage (V) applied across it and inversely proportional to the resistance (R) of the conductor.”
V=IxR
describe the current flowing through wet skin (resistance = 1000 ohms) and dry skin (resistance = 100,000)?
-dry skin has higher resistance than wet skin, which means it resists and limits the amount of electric current
-wet skin has a much lower resistance than dry skin, water increases the conductivity of the body - making it easier for an electric current to flow through the body - high current flow
when exposed to an external a.c current of 50Hz for 1 second, what physiological affects are observed at different threshold currents, 5mA, 10-20 mA, 50mA, 100-300mA, 6 amps etc?
5 milliamps - accepted value for maximum harmless current
10-20mA- sustained muscular contraction
50mA - pain - possible fainting and exhaustion
100-300mA - ventricular fibrillation - may be fatal
6 Amps - sustained ventricular contraction, paralysis and burns
what factors determine how the body will respond to electrical current ?
the magnitude of the current
-the duration of exposure to the current
-the path taken by the current
what value of Hz is the human body most sensitive to?
10-60 Hz
why are most physiological responses neuromuscular responses?
as the nerve cells tend to fire at frequencies close to 50/60 Hz
-note neuromuscular responses are less likely to occur for higher a.c current frequencies
what are the physiological effects of higher frequencies of current?
mostly thermal - due to the joule heating - this can be used clinically
what is electrocautery?
-the sealing of open blood vessels for the control of bleeding
-uses high frequency currents to produce localised heating
what is electrosurgery?
-surgery that involves devices for cutting through tissue using a hot tip
-frequencies of 500-600 kHz are most effective
what kind of path can a current only flow through?
only through a closed path
what is the purpose of the dispersive plate in electrosurgery?
serves as a crucial safety measure to complete the electrical circuit and safely return the electrical current to the electrosurgical generator.
-NB patient safety
what would a typical delivery system (of electrotherapy) look like?
- actual device - generates a.c current
-tip of probe - connected to one terminal
-other terminal connected to a dispersive plate eg a big electrode around thigh
what are examples of precautions that need to be taken when using devices in electrotherapy?
-tip of the probe should be quite small, while the dispersive plate should be quite large (could be placed below the buttocks, or around the thigh)
why should the probe tip be moved rapidly?
as if you keep the probe tip in the same spot, the heat could damage the underlying tissue
what are microshock hazards?
potential danger posed by small electric currents passing through the body
define microshock
- applies to situations where tiny currents are applied directly to the heart, such as through invasive medical procedures
- Even though the current is small, it can disrupt the heart’s electrical activity, potentially leading to arrhythmias or other cardiac complications
what kind of patients are said ti be microshock sensitive?
patients with pacemakers, inserted catheters, any internally placed conductor
what is the second condition for microshock risk?
is that the patient is grounded in some way - if this is the case, the connection to the ground provides a path for the current to flow through the patient
if a patient is isolated from the ground (ie not grounded), can a current flow?
no current will flow
- similar to a bird sitting on a high voltage wire
what is Joules law?
E= I^2Rt
ie the heat (E=energy) produced in a conductor is directly proportional to the square of the current, the resistance of the conductor and the time of exposure
what are the 3 terminals of domestic electric supplies?
Live
Neutral
Earth
what is a fuse?
-a safety device used in electrical circuits to protect against overcurrent conditions.
- thin piece of wire or metal strip that is designed to melt or break when the current flowing through it exceeds a predetermined level, thereby interrupting the circuit and preventing damage to electrical components or appliances.
