bioelectricity, physiological response to electric current

Question 1

define static electricity

Answer 1

-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

Question 2

define current

Answer 2

the rate of flow of charge

Question 3

what are the units of current?

Answer 3

Amps

Question 4

what are Coulomb forces?

Answer 4

-type of force that exists between electrically charged objects
-the attractive / repulsive forces
-like charges repel and opposite charges attract

Question 5

what is earthing?

Answer 5

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.

Question 6

what can a build up of static electricity cause?

Answer 6

sparking - sudden discharge of electricity
- may have a visible flash of light
-can be dangerous in the presence of flammable gases eg oxygen

Question 7

what kind of conditions are electrostatic effects much more prominent in?

Answer 7

dry conditions w/ low humidity - since any moisture in the air can drain away excess charge through attachment to water molecules

Question 8

what are examples of precautions that should be taken against static discharge in a clinical setting?

Answer 8

-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

Question 9

describe conductors

Answer 9

-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

Question 10

describe insulators

Answer 10

-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

Question 11

why is the human body a reasonably good conductor?

Answer 11

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

Question 12

does a material with a high resistance have a low or high current flow & why?

Answer 12

• 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

Question 13

does a material with low resistance have a high or low current flow?

Answer 13

a high current flow, as there is minimal resistance to the movement of electric charge through the material

Question 14

what are the 2 types of electric currents that are distinguished by the direction of electric flow?

Answer 14

-unidirectional - d.c
-alternating a.c

Question 15

describe unidirectional current / d.c

Answer 15

-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

Question 16

describe alternating current / a.c

Answer 16

-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

Question 17

what unit is electrical resistance measured in?

Answer 17

Ohm

Question 18

define voltage

Answer 18

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

Question 19

describe ohms law

Answer 19

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

Question 20

describe the current flowing through wet skin (resistance = 1000 ohms) and dry skin (resistance = 100,000)?

Answer 20

-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

Question 21

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?

Answer 21

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

Question 22

what factors determine how the body will respond to electrical current ?

Answer 22

the magnitude of the current
-the duration of exposure to the current
-the path taken by the current

Question 23

what value of Hz is the human body most sensitive to?

Answer 23

10-60 Hz

Question 24

why are most physiological responses neuromuscular responses?

Answer 24

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

Question 25

what are the physiological effects of higher frequencies of current?

Answer 25

mostly thermal - due to the joule heating - this can be used clinically

Question 26

what is electrocautery?

Answer 26

-the sealing of open blood vessels for the control of bleeding
-uses high frequency currents to produce localised heating

Question 27

what is electrosurgery?

Answer 27

-surgery that involves devices for cutting through tissue using a hot tip
-frequencies of 500-600 kHz are most effective

Question 28

what kind of path can a current only flow through?

Answer 28

only through a closed path

Question 29

what is the purpose of the dispersive plate in electrosurgery?

Answer 29

serves as a crucial safety measure to complete the electrical circuit and safely return the electrical current to the electrosurgical generator.
-NB patient safety

Question 30

what would a typical delivery system (of electrotherapy) look like?

Answer 30

• 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

Question 31

what are examples of precautions that need to be taken when using devices in electrotherapy?

Answer 31

-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)

Question 32

why should the probe tip be moved rapidly?

Answer 32

as if you keep the probe tip in the same spot, the heat could damage the underlying tissue

Question 33

what are microshock hazards?

Answer 33

potential danger posed by small electric currents passing through the body

Question 34

define microshock

Answer 34

• 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

Question 35

what kind of patients are said ti be microshock sensitive?

Answer 35

patients with pacemakers, inserted catheters, any internally placed conductor

Question 36

what is the second condition for microshock risk?

Answer 36

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

Question 37

if a patient is isolated from the ground (ie not grounded), can a current flow?

Answer 37

no current will flow
- similar to a bird sitting on a high voltage wire

Question 38

what is Joules law?

Answer 38

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

Question 39

what are the 3 terminals of domestic electric supplies?

Answer 39

Live
Neutral
Earth

Question 40

what is a fuse?

Answer 40

-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.