WEEK 6 (Bioelectromagnetism) Flashcards
What is the history of Bioelectromagnetism?
- First mentioned by ancient Egyptians who had problems catching an electric ray due to the powerful electric shock it would give them (450V)
- First medical application - electric ray was used to treat headaches and arthritis from I to XVII centuries
- Physicist Luigi Galvani first recorded BEM while dissecting a frog at a table where he was conducting static electricity experiments
Define Electromagnetics
Study of electric and magnetic phenomena caused by electric charges at rest or in motion
What are the sources of an electric field?
Positive and negative charges
Moving charges produce a ___________, which gives a magnetic field
current
What results in an electromagnetic field?
time varied electric and magnetic fields that are coupled
under certain conditions, what do time-dependent electromagnetic fields produce?
waves that radiate from source
Define Bioelectromagnetism
A discipline that examines the electric, electromagnetic and magnetic phenomena which arise in biological tissues
What does the bioelectromagnetism phenomena include?
- behaviour of excitable tissues
- magnetic field at and beyond the body
- response of excitable tissues to electric and magnetic fields
- intrinsic electric and magnetic properties of tissue
What are some examples of the application of Bioelectromagnetism?
- membrane potentials
- action potentials
- electric currents through nerves and muscles
- brain oscillations
- electromagnetic field of the heart
What is the difference between Bioengineering and Biomedical engineering?
Bioengineering is the application of engineering to the development of health care devices, analysis of biological systems and manufacturing of products based on advances in this technology
Biomedical engineering is the application of science and technology to biology and medicine
What is the difference between Biophysics and Medical physics?
Biophysics is the science that is concerned with the solution of biological problems in terms of the concepts of physics
Medical physics is a science based on physical problems in clinical medicine
What did Andre Marie Ampere do?
Ampere presented the first mathematical theory of electrodynamics and discovered the magnetic effect of electric currents
What did Michael Faraday do?
Discovered electromagnetic induction
What did James Clerk Maxwell do?
Maxwell presented his theory of electromagnetism
What did Heinrich Rudolf Hertz do?
Hertz demonstrated the electromagnetic wave propagation in a series of experiments in a period through 1887
What does the measurement of an electric or magnetic field refer to?
The electric or magnetic signals produced by the activity of living tissues
What happens in bioelectromagnetism?
the active tissues produce electromagnetic energy which is measured either electrically or magnetically within or outside the organism in which the source lies
this includes the magnetic field produced by magnetic material in the tissue
What is a voltage clamp?
A voltage clamp is a technique used in electrophysiology to measure and characterise electric currents in cells (particularly excitable tissue cells such as neurons)
Describe the technique used for voltage clamps
A very fine micro electrode is inserted into the cell with another electrode in contact with the fluid around the outside of the cell
What is the current clamp technique?
Similar to the voltage clamp, except that the electrode feedback mechanism is used to keep the current across the membrane constant while allowing the voltage to vary
Describe the patch clamp technique
Instead of poking a sharp, metal electrode through the cell membrane, the electrode is placed inside a micropipette (a very thin glass tube) filled with an electrolyte solution and the micropipette is placed against the cell membrane. Gentle suction is applied, forming a tight seal between the micropipette and the cell membrane.
What is the function of a transducer?
It “transforms” the energy commanding the biological phenomenon to be measured into another type of energy which can be registered, processed and displayed
What are the properties of electrodes?
- simplest transducers
- transform ionic currents (usually present in biological media) into electronic currents which are registered, amplified, modified and displayed in the electronic device
What is the contact zone between the electrode and biological sample known as?
Electrode-electrolyte interface (EEI)
What are the properties of electrode-electrolyte interface?
- generates impedance (effective resistance)
- generates a direct current potential (half-cell potential)
- influences the instruments used to measure bioelectric potentials hence is widely studied in an effort to diminish it
What can electrodes be classified as?
Invasive and noninvasive
INVASIVE ELECTRODES: needle electrodes for percutaneous measurement of biopotentials & micro machined devices designed to pierce only the outer skin layer
NONINVASIVE ELECTRODES: metallic plates, discs, disposable foam-pad electrodes (ECG)
Why are micro needle electrodes important?
They can penetrate the outer skin layer without pain and greatly reduce impedance (resistance)
When was the first human electrodiagram recorded?
1887 with Lippmann’s capillary electrometer by Augustus D. Waller
This simple ECG revealed only two deflections indicating the ventricular events
What is the science behind the electrodiagram?
- cardiac muscle is a tissue specialised for complex periodic electrical activity and repetitive contraction
- certain parts of the myocardium (pacemaker cells) perform automatic electrical impulse generation
- conductive tissues are responsible for aligned impulse conduction towards the working muscle which is the main determinate of cardiac contractility
What is an ECG?
ECG (Electrocardiogram) is a graphic image of the sum of the electric currents generated in the heart. These currents spread over the tissue surrounding the heart and reach the surface of the body.
What can ECGs be recorded using?
Surface electrodes
What is the EEG (Electroencephalograph) and what is it used for?
The EEG (Electroencephalograph) is a test that records the electrical activity of the brain
It is used for monitoring and diagnosing epilepsy, sleep disorders, coma and brain-death
What are the 4 traditionally recognised EEG signal frequency types?
Alpha, Beta, Delta and Theta
What are the different deflections of the ECG?
P, Q, R, S and T
What is an electric shock?
Electric shock is defined as sudden violent response to electric current flow through any part of a person’s body. The amount of current determines effect of electric shock.
What are the effects of electric shock on a human body?
- paralysis of respiratory muscles
- ventricular fibrillation threshold
- cardiac standstill and internal organ damage
More than __% of body resistance to current flow is at the skin
99%
What are the ways that protective skin resistance is greatly reduced?
- significant physical skin damage (cuts, abrasions and burns)
- breakdown of skin at 500V or more
- rapid application of voltage to an area of skin
- immersion in water
What is the difference between voltage and current in regards to harming the human body?
Voltage is the force that pushes electric current through the body whereas the current determines physiological effects
(voltage still influences the outcome of an electric shock)
How does voltage influence the outcome of an electric shock?
- at 500V or more, high resistance in the outer layer of the skin breaks down
- cell membrane damage
What is the difference between direct current and alternating current?
Direct current you feel shock only when circuit is made or broken and in Alternating current you feel shock all the time voltage is applied
What are the properties of alternating current?
- changes amplitude and direction 50-60 times per second
- current passes easily
- tetanic muscle contraction
- loose of voluntary control of muscle contraction
- ventricular fibrillation (if current is enough)
What is total body resistance equal to?
internal body resistance plus twice skin resistances
What is the effect of lightning on the body?
- typically flashes over the surface of the body
- wet skin and very brief nature of the pulses of electricity encourage the current to travel on the surface of the body
- blast effect may rupture eardrums and injure internal organs
- intense light can result in cataracts
How is immersion contact fatal?
- immersion into water decreases skin resistance
- increase in contact area causes voltage to all submerged parts of the body
- electric current may enter through mucous membranes (mouth and throat)
What are the mechanisms of death in electric shock drowning?
- electrical stimulation of the heart causing ventricular fibrillation
- tetanic contraction (effective paralysis) of the muscles of respiration
- loss of muscle control of the extremities
What is the direction of the electric field through the cell membrane?
It’s always directed in the direction that a +be test charge would be pushed or pulled if placed in the space surrounding the source charge
