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65 Cards in this Set
- Front
- Back
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What is the difference caused by movement of electrons from one material to another?
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electrical potential
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What is it called when electrons move one direction and current moves the other direction?
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Electricity
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What are problems r/t static electricity and electrical potential?
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sparking, explosion, fire, sticking bobbins in gas flowmeters
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What law describes the force between 2 charged particles?
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Coulomb's law;
like charges repel; depends on distance - if double the distance the force b/w them is 1/4th |
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What has outer electrons or ions loosly bound and free to move?
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conductors
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What has electrons firmly bound?
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insulators
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What has intermediate conductivity; outer electrons are bound to atoms less firmly than insulator?
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semi-conductors (intermed b/w conductor and insulator)
(ex: thermistor - conductivity increases with temp - give a little energy the electron can escape and conduct electricity) |
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What kind of conduction is a thermister?
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semi-conductor;
when radiation falls on device, electrons absorb some energy and move thru material more freely |
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What is "a conductor with a current flowing thru it that can exert a force on another conductor carrying a current"?
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magnetism
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What results from minute electric currents in material?
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Magnetic field
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A changing magnetic field induces a flow of electrons in a conductor to produce ____?
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electric current
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What is the unit of magnetic flux called?
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weber (Wb)
unit of magnetic flux density is tesla (T) Earths magnetic field = 60 uT MRI = 0.2 - 4T |
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Magnetic fields and electric fields are intimately related; thus they are called ______.
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Electromagnetic field
When a magnetic field is changed - causes an electric field (and vice versa) |
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What is the principle of the transformer?
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Electromagnetic field. Have electricity coming into initial windings, then Fe core in middle (no connections) when produce electric current, creates magnetic field, which then causes electric flow on opposite side thru other windings
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How is flow of electrons in a battery?
current? |
from negative to positive
current from positive to neg |
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What is current flow of 6.24 x 10 (18th) electrons/sec?
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Ampere
measured by galvanometer |
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What is a unit of electrical potential difference?
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Voltage
the higher the voltage, the more work they can do |
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What is the resistance which will allow one ampere of current to flow under the influence of an electrical potential of one volt?
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Ohm
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What is the most important, basic law of electricity? It defines the relationship b/w the 3 fundamental electrical quantities which are?
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Ohm's law
current voltage resistance |
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V=IxR is Ohm's law; how do you equate these values to the human cv system?
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V=voltage=BP
I=electrical current=CO R=resistance=SVR |
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DC current comes from ____
AC current comes out of ___ |
DC - batteries
AC - wall |
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Steady flow of electrons, from a battery or generator?
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DC
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Repetitive flow reversals (sine wave) from an alternator
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AC current
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How do you figure out power of electric circuit?
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W=VxI
Watts=Voltagexcurrent(amps) W same as power |
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What is Root mean square (RMS)?
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describes the voltage of a/c current
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This device stores electric charge in a circuit
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capacitor
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What is the difference b/w resistance in series vs parallel?
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in series resistance adds up = old xmas lights
in paralel resistance decreases |
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What is the amount of electric charge accumulated by a 1 ampere current for 1 second?
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coulomb
C=Axseconds |
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What is capacitance equal to coulombs per volt?
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farad
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What does this measure?
E=VxQ |
Energy to move an electric charge (Q) thru a potential difference (V)
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What is a measure of the ability of an object to hold an electric charge?
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capacitance
(even if something isn't plugged in, it can hold electricity in capacitance and get shocked) |
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What is the process of generating electrical currents in a conductor by placing the conductor in a changing magnetic field?
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Inductance (or elecrtomagnetic inductance); it's what the transformer is all about
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What is the total opposition that a circuit presents to alternating current (Z)?
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Impedance
inductor - the higher the frequency the higher the impedance capacitor - the higher the frequency the lower the impedance resistor - non-frequency dependent resistance |
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What kind of impedance do you want in EKG electrodes?
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high impedence (resistance) to protect from electric flow thru to pt
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This is a semiconductor device which only permits current to flow in one direction
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Diode
(alternator has diodes that make ac --> dc |
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What is the purpose of a fuse or circuit breaker?
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To protect against an excessive amount of current or flow.
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How does a ground fault interruptor work?
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the number of electrons should be exactly the same as the number of electrons flowing out...if not shuts off
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What produces a high frequency AC current that can cut or coagulate current?
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bovie (electrosurgical equipment)
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What does the pad do that is placed on the pt?
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Returns the electricity back to the bovie (not a grounding pad)
pad should be as close as practical to where bovie is working |
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What can pt burns be caused by?
(4) |
poor "ground" pad
d/c "ground" pad pt touching metal table EKG electrodes |
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Higher risk of burns with bovie in pts with?
3 things |
small x section of body parts
metallic implants implanted electromedical devices |
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What discharges 35A for 3ms to produce synchronous contraction of myocardium followed by refractory period?
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defibrillator
typical 5000V and 160 millicoulombs; 400J energy |
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What slows down the charge in the defibrillator which prevents burn to pt?
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inductor
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What is max output for defib?
external? internal? |
ex 360J
in 100J |
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Where is synchronized shock delivered?
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on R wave
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EKG interference can be from 2 things...
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capacitance coupling - capacitor allowing current to pass thru
inductive coupling - by other electrical stuff in OR |
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How is signal to noise ratio reduced?
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By averaging repetitive waveforms
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What are the electrical hazards for patiens in the OR?
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Burns
macroshock - intact skin microshock - thru catheters or lead wires |
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What frequency has the greatest risk of shock?
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low (60 Hz)
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what is threshold of potential (current)?
max harmless? "let go" current? pain, fainting, mechanical injury? V fib |
1mA - threshold of perc
5mA - max harmless 10-20mA - "let go" before sustained muscle contraction 50mA - pain, poss fainting 100-300mA - v fib |
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What 3 things make electric currents passing thru body dangerous?
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1.path - thru heart or brain
2.current density - higher density may come from low current thru small area 3.worst freq 50-60Hz |
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A power station supplies electricity at ____ voltage to a ____, where voltage is reduced by a _____.
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High
substation transformer |
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The current passes from the substation to the hospital on 2 wires --
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live
neutral --connected to earth at substation |
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If you touch the live wire in the hospital what happens?
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the current goes thru your body and thru the earth back to the substation
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Is it good to stand in a puddle of saline holding a faulty apparatus with a broken ground wire?
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LOL
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What is Class I equipment?
Class II? Class III? |
I - all user accessible parts are grounded (3 prong)
II - all user accessible parts are double insulated (2 prong) III - internally powered -- battery |
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What are shock risks with grounded equipment?
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1.if ground fault risk of electrocution is high
2.space blankets - never use in OR 3.pt electrodes can provide path to ground if electrosx equipment is faulty 4.leakage current - capacitive and inductive coupline can result in shock danger |
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What can cause v fib with less than one volt (150 uA)?
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Microshock from central line, PA cath, temp internal pacer, esophageal steth
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What make microshock worse?
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low frequency AC
small cross section (high density) contact with ventricular wall (swan) |
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What is it that supplies isolated power to the OR so it's not coming directly from Turkey Pt?
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Isolation transformers
Line isolation monitors |
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Leakage standards for electrodes in direct contact with heart
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Type CF (cardiac floating) - leakage must be <50 uA with one fault
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Leakage standards for general monitoring circuit
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Type B or BP -
Leakage <500uA with one fault |
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What is voltage and pulse duration of temporary pacer normally?
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<4V and pulse duration <1ms
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Why must you find out whether your patient is pacer dependent?
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interference from bovie may cause pacer to stop firing...oops
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What are 2 saftey hazards r/t IVF?
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can conduct electricity into pt
spilled can cause hazards in equipment |
