Exam 1- through EKG lecture 1 Flashcards
Circuit
collection of elements or elements and signals connected together for purposes of modifying input signals to obtain other desired signals or responses
Electric Current
flow of charges per unit time
Electric Voltage
potential difference measured between 2 points. Expression of potential energy required to move a charge of one coulomb from point A to point B
Ohm’s Law
V=IR
Ohm’s Law Corollary/Darcy’s Law
P(pressure)=Q(flow)R(resistance)
Voltage Analogs
Pressure P (dynes/cm2), temperature T (C), solute concentration C (mg/ml)
Current I(amperes) Analogs
Flow V (cm3/sec), Heat Flow q(Watts), solute flow Q(mg/min)
Frequency
1/Period(T)
Period
1/frequency (f)
Coulomb’s Law
F=k(q1xq2/d^2), The greater the distance between the charges, the weaker the force
Power
P=IV
Kirchhoff’s Voltage Law
The sum of the voltage variations around a loop is 0.
Kirchhoff’s Current Law
The sum of all currents that converge on a node will be 0.
Parallel Resistance
1/R= 1/R1 + 1/R2 + 1/R3…
Series Resistance
R= R1+R2+R3…
Transducer
Converts one form of energy to another form
Wheatstone Bridge
V=0 when R1xR4=R2xR3
Capacitance
“compliance”- the ratio of change in an electric charge in a system to the corresponding change in its electric potential
Parallel Capacitance
C=C1+C2+C3
Inductors - Inertance
Measure of the pressure gradient in a fluid required to cause a change in flow rate with time
Series Inductance
Added together
Parallel Inductance
same formula as parallel resistance
Most circulatory systems
are parallel systems
I=V/R
Q=P/R
Open Circuit
No current flow
Current (capacitor)
decreases as time increases due to charge buildup on capacitor
Time Constant (capacitor)
Equals Resistance x Capacitance (RC)
Voltage
across the capacitor increases as time increases due to charge buildup on the capacitor
Current (inductor)
increases as time increases due to diminished impediment from the inductor
Time constant (inductor)
inductance/resistance (L/R)
Capacitive Reactance
Xc=1/2pifC, inversely proportional to frequency
Inductive Reactance
Xl=2pifL , directly proportional to frequency
Impedance
sum of resistance, capacitive reactance, and inductive reactance taking the phase contribution of each into account (Z)
High Pass Filter
output component chosen to be resistor rather than capacitor
American Heart Association Bandwidth
0.05-100.0 Hz
RMS Amplitude (root mean square)
the amplitude a DC signal would need in order to provide the same average power=(.707)peak amplitude
Peak Amplitude
the maximum amplitude in either the positive or negative half cycle
Peak to Peak Amplitude
twice the peak amplitude, includes positive and negative maxima
Average Amplitude
average amplitude for either half cycle= (.637) peak amplitude
Ohm’s Law Corollaries
P=QR (hydraulic/hemodynamic systems), T=qR (thermal systems), C=QR (concentration systems)
Current (I)
Amount of charge carriers moving through a circuit or circuit element per time, measured in Amperes
Voltage (V)
measure of electrical pressure needed to force charge carriers through a circuit or circuit element. Difference in electrical pressure measured across any elements that impede or resist flow of the charge carriers (measured in volts)
Resistance (R)
measure of the amount of impediment a circuit element provides to the flow of charge carriers (measured in ohms)
Macroshock 1mA
threshold of perception
Macroshock 5mA
maximum harmless current
Macroshock 10-20 mA
“let go” current
Macroshock 50 mA
pain, fainting, mechanical injury, cannot let go current
Macroshock 100-300 mA
Vfib, respiration center remains intact
Macroshock 6000 mA
sustained ventricular contraction, defibrillation, burns if current density is high enough
Microshock 10 uA
recommended safe current limit for directly applied cardiac equipment
Microshock 50uA
maximum fault condition for cardiac equipment
Microshock 100uA
Ventricular fibrillation
Electric shock
awareness of or a reflex response to the passage of electric current through the body
Burns
may be confused with pressure ischemia
Macroshock
intact skin
Microshock
vascular access, or myocardial lead wires
Path of current
worst path is through heart or brain
Current density
higher current densities may come from lower currents passing through smaller area
Frequency
worst frequency is between 50 and 60 hz
Small area of contact
electrical density burns
45 C
temperatures at or above this may cause skin injury
Class I
grounded
Class II
insulated
Class III
internal power source
Radiation
Inverse square law: If distance is doubled, the energy density is quartered
Type of laser used medically
Class 4
O2 index of flammability for Polyvinylchloride
0.263, mean time to ignition: 3.06s
O2 index of flammability for Silicone
0.189, mean time to ignition not tested
O2 index of flammability for Red Rubber
0.176, mean time to ignition 33s
CO2 Laser
any plastic or glass lens will work
Nd:YAG laser
requires green filter
Ar and Kr laser
requires amber/orange filter
KTP:Nd:YAG laser
requires red filter
Combustible gases
Halothane, Enflurane, Isoflurane, Ethers
Combustion supporting gases
O2, N2O, Air
Combustion squelching gases
N2, CO2, He
Ignition sources
Lasers, Hot filaments, sparks and arcs, gas compression
Rule of Arrhenius
the rate of a reaction is doubled when the temperature of the initial mixture is raised by 10 C.
Vigilance
Watchful, alert for danger
Alarms and Priorities
Low (advisory)- one or 2 slow pulses, may repeat, requires awareness
Medium (caution)- 3 faster pulses, may repeat, requires prompt response
High (warning)-Ten rapid pulses, repeated pattern of 5, requires immediate response
SpO2
Worst way to discover oxygen supply failure, since this drops last, may be up to 5 minutes after O2 supply failure starts
Measured Value
True Value +(Systemic Error + Random Error)
Systemic Errors
predictable and may be compensated by adding, subtracting or multiplying by a constant
Random Errors
Unpredictable, averaging repeated measurements tend to reduce or eliminate random errors
Accuracy
Closeness of agreement between the measured value and the true value (# correct/# total) x 100
Percent Error
((True-measured)/true) x 100
Percent Difference
((A-B)/((A+B)/2)) x 100
Precision
the degree of consistency between repeated measurements of the same quantity = (measured-mean)/mean
Reproducibility
the ability to maintain precision during long term use
Sensitivity
the likelihood that when an event occurs, it will be detected (hit rate). = hits/(hits + misses)
Specificity
the likelihood that when the situation is normal, no event will be indicated = correct rejections/(correct rejections + false alarms)
Bland-Altman test
used to ascertain whether measurement techniques are interchangeable
Drift
slow, low frequency component of the signal, lower frequency than the signal
Rise Time
the time that it takes for the instrument to get from 10% to 90% of the complete response
Noise
Unwanted signal that, depending upon the magnitude, may interfere with the measurement
The greater the rise of the original waveform
the greater the number of harmonics needed to reproduce that waveform
Fourier Analysis
A complex waveform can be resolved into the fundamental waveform and a series of harmonics
Magnitude of the System response
output amplitude/input amplitude
Phase of the system response
output phase-input phase
Horizontal resolution
Sampling rate
Vertical Resolution
discrimination between 2 different amplitudes
Sampling Theorem
for a limited bandwidth signal with the maximum frequency fmax, the equally spaced sampling frequency fs must be greater than twice the maximum frenquency fmax: fs>2*fmax
Aliasing
Under-sampling causes frequency components that are higher than half of the sampling frequency to overlap with the lower frequency components. As a result the higher frequency components roll into the reconstructed signal and cause distortion of the signal
Nyquist Sampling Rate
2 * fmax
Nyquist frequency
fmax, half of nyquist sampling rate
