ECE 405 Final Exam Qualitative Notes

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77 Terms

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Classification of Devices (3 types)
Diagnostic, Therapeutic, Assistive
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Examples of diagnostic devices
temperature, blood pressure, ECG
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Examples of therapeutic devices
defibrillators, electrocautery, radiation therapy
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Examples of assistive devices
artificial limbs, cochlear implants
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Sensor (definition)
a device that converts an environmental condition into an electrical signal
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Actuator (definition)
a device that converts a control signal (usually electrical) into mechanical action (motion)
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Resistive Temperature Devices (RTDs) (definition)– materials whose resistance changes in accordance with temperature, have a positive temperature coefficient
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Thermistors (definition)
semiconductor materials, negative temperature coefficient
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Thermocouples (definition)
pair of dissimilar metals joined at one end, so when there is a temperature difference between the joined ends and the open ends, a thermal EMF is generated and measured at the open ends
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Temperature transducers (3 types)
Thermoresistor, thermocouple, thermistor
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Pros and Cons of temperature transducers
Thermoresistor (linear, low cost, but low temperature coefficient, i.e. low sensitivity), thermocouple (ultra small but low sensitivity), thermistor (high sensitivity, small, but non-linear)
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Other methods of temperature transduction (4 types)
infrared radiation, liquid crystals, MRI, ultrasound thermometry
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Radiation thermometry
relationship between surface temperature and radiant power, non-contact temperature measurement
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What is measured in radiation thermometry
total radiant power (area under the curve)
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Pros and Cons of LCD Thermograph
low cost (pro), poor sensitivity and requires contact (cons)
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Glaucoma
raised intraocular pressure that causes vision disturbances and ultimately blindness
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Bed sores
ulcers that develop because of excessive pressures applied to skin for extended period
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Maximum sustained skin pressure
40 mmHg (only exception is the soles of the feet)
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Intraocular pressure measurement
tonometer uses indentation and flattening to measure pressure in eye by using a puff of air
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Laplace’s Law
pressure differential of cylinder (vessel): T/r pressure differential of sphere: 2T/r where T is tension in the wall/barrier
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Imbert Fick Law
if the wall of a sphere is locally flattened, the pressure is force/area
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Direct methods to measure blood pressure
intravascular: fiber optic, fluid filled catheter extravascular: strain gauge
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Indirect methods to measure blood pressure
auscultation, oscillometry, tonometry
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Auscultation
indirect method to measure blood pressure using Korotkoff method (pressure cuff and stethoscope)
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Oscillometry
indirect method to measure blood pressure in cuff
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Tonometry
indirect method to measure blood pressure by measuring the pressure required to flatten the vessel wall
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Kortokoff method
blood pressure decrease, hear faint tapping sounds (kortokoff sounds) heart at systolic pressure, sounds become muffled at diastolic pressure
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Ventricles during systole
contract
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Ventricles during diastole
relaxed and full
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Pathway of blood through the heart
from the body, into heart via vena cava, right atrium, tricuspid valve, right ventricle, pulmonary artery, lungs, pulmonary veins, left atrium, bicuspid valve, left ventricle, aorta, delivered to the body
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Poiseuille’s Law
relates pressure differential and flow rate to the viscosity and tube size (gives resistance formula)
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Fick’s first law
JD = -D*dC/dx where JD is the diffusion flux, and D is the diffusion coefficient
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Osmotic pressure
water molecules will want to diffuse across concentration gradient, pressure created due to concentration gradient across a membrane
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Osmolarity
concentrations of dissociate particles
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Van’t Hoff Equation
pi=RT([C1]-[C2])
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Causes of Biologic Charge Separation
positive/negative ions, diffusion, mobility coefficients, semipermeable membranes
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Passive membrane channel properties
nongated channels, responsible for resting membrane potentials, ion specific, bidirectional
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Active membrane channel properties
voltage gated channels, responsible for action potentials, ion specific, bidirectional
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Nodes of Ranvier
regions of axon not insulated by myelin, allows for generation of rapid electrical impulse along the axon (called saltatory conduction)
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Automaticity (definition)
automatic nature of the heartbeat, heart will beat if myocardial cells remain alive
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Sinoatrial node
only region in heart that demonstrates spontaneous electrical activity, cells don’t maintain a resting membrane potential
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Pacemaker potential
slow spontaneous depolarization of the SA node during diastole, from -60 to -40 mV threshold
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Resting membrane potentials of myocardial cells
\-90 mV
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Conduction of Impulse from SA node
spreads quickly to the atria, slowly to the AV node, time delay between excitation of atria and ventricles, rapid spread in Purkinje fibers
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How does electrocardiogram work
action potentials spreads from atria to ventricles, voltage measured between these two will vary in a way that provides a picture of the electrical activity of the heart
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Two types of ECG leads
bipolar (record voltage between electrodes placed on wrists and legs) unipolar (record voltage between a single exploratory electrode and ground electrode built into the electrocardiograph)
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How many leads for a standard ECG
12 leads
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Distinct ECG waves (3 types)
P, QRS, T waves represent changes in potential between two regions (not action potentials)
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P-wave physical meaning
spread of atrial depolarization
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QRS-wave physical meaning
spread of depolarization into ventricles
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T-wave physical meaning
repolarization of ventricles
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Dipole model of the heart
superposition of dipole moments of each individual cardiac cell for a net dipole moment
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Einthoven’s Triangle
three limb leads form an equilateral triangle with dipole located at the center
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Augmented Terminal Reference Limb Leads (3 types)
aVR, aVL, and aVF
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12-lead electrocardiogram
3 standard leads, 6 precordial leads, 3 augmented leads (Wilson’s central terminal)
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Ideal properties of amplifier
infinite gain, infinite bandwidth, infinite input impedance, infinite CMRR, zero output impedance, zero noise
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4 rules of Op Amp
no current can enter the terminals, output voltage is gain times differential input voltage, V+=V- via virtual ground property, opamp needs two rail voltages to power it
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Comparator Op Amp Application
detection of QRS complex in ECG
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Voltage follower Op Amp Application
interfacing high impedance sensors such as microelectrodes or microphones
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Properties of instrumentation amplifier
differential amplification, very high gain, very high input resistance, common-mode rejection
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EEG (definition)
electroencephalography, uses 10-20 standard lead system, used to identify sources of brain activity
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Sources of noise when measuring biopotentials
power lines, other biopotentials, motion artifacts, electrode noise, circuit noise, common mode noise
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Power rating of electrical outlets
110V AC with respect to center tap
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Wall socket contacts (3 types)
Hot (black), Neutral (white), and Green (ground, center tap)
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Ground faults (definition)
short circuit between the hot conductor and ground, injects large currents into the grounding system
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Bioelectric Stimulation depends on
current density
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Macroshock
lightning, instruments, externally applied currents spread throughout the body via contact with skin (dry skin has high resistance, limits current flow through body)
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Microshock
implantable catheters leakage, internally applied current flows through the heart (low tissue impedance below the skin, takes less to do serious damage/kill)
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Grounding Philosophy 1
if every object is maintained at ground potential, subject can never have voltage drop across body (not foolproof, e.g. ground faults)
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Grounding Philosophy 2
eliminate use of grounds in system/environment, everything is at same potential
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Double insulation technique
enclose circuit/system in an insulating chasis which is grounded
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Ground fault circuit interpreters
use an electrical circuit to monitor current flow through hot and neutral wires of outlet, if there is a difference between the currents, it trips the circuit breaker and removes the power
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Transformer isolation
power supply and instrument are “connected” via transformers, not direct contact so power supply is isolated
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Optical isolation
used in simple circuit designs, electronic component that transfers electrical signals between two isolated circuits using light
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Piezoelectricity (definition)
piezoelectric materials generate an electric potential when mechanically strained or electric potential and cause physical deformation of the material
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Piezoelectric effect
converts mechanical energy (deformation of crystal) into electrical energy
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Inverse Piezoelectric Effect
converts electrical energy (electric potential) into mechanical energy (deformation of crystal)