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Physiology - Hayley > Instrumentation CA1 > Flashcards

Instrumentation CA1 Flashcards

1
Q

Transducer +3 clinical examples

A

Anything that converts one electrical source to another electrical source

Electrodes
Piezoelectric crystal
Spirometer

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2
Q

Filters

A

Mitigate any unwanted frequencies

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3
Q

Amplifiers

A

Electric bio signals are very small, so amplifiers increase the signal but is also used for filtration

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4
Q

Signal digitisation

A

electric bio signals are analogue and will need to be converted into digital form using an analogue to digital converter

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5
Q

When assessing the usefullness of a device, what two peramiters do we take into account

A

Specificity and Sensitivity

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6
Q

In what cases to we want a high specificity and in what cases do we want a high sensitivity

A

Want high sensitivity when screening for a disease
High specificity when confirming a disease

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7
Q

When assessing the quality of the medical devices the performance if determine by what 4 values

A

accuracy, resolution, precision, reproducibility

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8
Q

ROC curve
- what does it plot
- where on the graph would a device be deemed an acceptable classifier

A

ROC curve asseses the ability of the binary classifier. Plots sensitivity vs specificity

Anything above the positive slanted line is acceptable

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9
Q

What are the 4 rules in classifying non-invasive devices

A
  1. either do not touch the patient or contact only intact skin (I)
  2. intended for channelling or storing blood, body liquids, cells or tissues, liquids or gases for the purpose of eventual infusion into the body (I)
    • unless using with blood/body fluids (II1)
    • unless connected to a active device class IIa or higher (IIa)
    • unless bloodbags
  3. modifying the biological or chemical composition of human tissues, or cells, blood, other body liquids, or other liquids intended for implantation or administration into the body (IIb)
    • unless only filtration, centrifugation or exchange of gas or heart (IIa)
    • consisting of a substance intended to be used in vitro in direct contact with human cells (embryo) (III)
  4. In contact with injured skin or mucous membrane (or invasive device) (IIa)
    • unless as a mechanical barrier, compression or absorption (I)
    • unless intended for wounds which breach dermis and heal only by secondary intent (IIb)
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10
Q

Qualities of class 1 device

A

mostly non-sterile and non-invasive
e.g blood pressure machine, stethoscope, reusable surgical instruments

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11
Q

qualities of class IIa devices

A

short term, non-invasive devices intended for channelling or storing blood, body liquids for eventual administration into the body
If they are principally intended to manage the microenvironment of the cell
e.g ultrasound, diagnostic software

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12
Q

Qualities of class IIb devices

A

long term, intended to be used principally for injuring the skkin which can breach the dermis

e.g equipment used for intraoperative monitoring, ionizing radiation
intended to administer medicinal product by means of a delivery system

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13
Q

qualities of class 3 device

A

critical for patients life

e.g pacemaker, stent

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14
Q

What is not the responsibility of the regulatory bodies in medical device standardisation

A

designing specific safety tests that medical devices must pass

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15
Q

What are the two independent testing agencies

A

ISO and IEC

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16
Q

What are the 4 levels of risk severity

A
  1. Minor - recoverable
  2. Major - very slow to recover or permanent
  3. Critical - immediate or prolonged treatment
  4. Fatal - may result in death
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17
Q

What two components is risk made up of

A

Probability and consequence

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18
Q

What is requirement for hardware failures

A

A medical device must be safe in the case of a single fault
2 independent failures should not harm the patient
Therefore equipment must be designed so that the combination of the first and second failures cannot cause a hazard

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19
Q

What are the two primary principles behind software verification

A
  1. describe the exact function the software is supposed to perform
  2. device a very specific test to verify that the software works s designed
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20
Q

Resolution

A

The smallest differential value that can be measured

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21
Q

An electric shock of 80-600uA is likely to cause what to happen in a body

A

Ventricular Fibrillation

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22
Q

What is the difference in the travel path between macro and micro electric shocks

A

Macro - only a small amount of the current flows through the heart
Micro - introduced directly into the body via a high conducting avenue with a direct conduction path to the heart

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23
Q

What two parameters depend how bad an electric shock is

A

skin resistance and spatial distribution

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24
Q

How do you protect someone after having a macro shock

A

isolate patient from any grounded surface and all current sources.

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25
Q

electric field force eququation

A

F = qE

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26
Q

What does Coulombs law state

A

As you move away from the electric field, the strength gets weaker
Electric force is inversely proportional to R (electric field gets really weak, really quickly as yo move away from it)

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27
Q

What does Gauss Law explain

A

Explains how there are negative and positive charges that interact with each other without touching through electric fields

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28
Q

What will the net force of the magnetic field be in a magnet

A

Always 0

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29
Q

What is the role of a battery

A

A battery chemically rips apart charge allowing them to then snap together again (creating energy)

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30
Q

How do we measure the strength of a battery

A

put a single charge into the electric field of the batter and measure the electric potential of that single charge using (W=qEd)

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31
Q

What direction is conventional current

A

Positives moving towards negative

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32
Q

What makes a good conductor (theory and examples)

A

Good conductors font allow many collision between charges

Gold, platinum, copper

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33
Q

Capacitor + equation

A

A device with the ability to store electrical charge

C=Q/V

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34
Q

What determines the quality of conductivity of a material

A

The number of electrons on the outer shell and how bounded they are to the atom

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35
Q

What is the frequency of AC and DC circuit

A

AC - 50Hz
DC - 0

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36
Q

Are medical devices AC or DC

A

Medical devices can often use a combination of bothAC and DC circuits and need to change to either between one another. An inverter converts DC to AC while a rectifier converts AC to DC

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37
Q

What do electrodes do

A

Conduct electricity through non-metallic mediums

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38
Q

What is reactance

A

The opposing force to current in AC circuit

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39
Q

What is a semiconductor and an example of one

A

A semiconductor has properties of a conductor and insulator

e.g silicone

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40
Q

What is dopping

A

This is the process of introducing foreign material to pure crystal form semiconductors that improves their conductivity

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41
Q

n-type vs p-type dopping

A

n-type: created by doping in extrinsic semiconductor with an element with an additional election
p-type: created by doping in extrinsic semiconductor with an element with notable fewer electrons

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42
Q

How does a semiconductor work

A

The free electrons from the n-type migrate to the p-type to donate their electrons. There is a region close to where the two sides meet called the depletion layer, where there is no charge as there are no free flowing electrons.
This depletion layer allows of current flow only in one direction (anode>cathode)

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43
Q

What is a photodiode and how does it effect a semiconductor

A

A photodiode is light sensitive conductor that produces current when it absorbs photons

the direction of the electric current in the diode forces the electrons to move towards the n-side and consequently the holes move towards the p-side. This results in an increase in the number of electrons on the n-side and hold on the p-side, a rise in the electromotive force is observed

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44
Q

What is an LED and how does it effect a semiconductor

A

A LED is a semiconductor that emits light when a voltage is applied

The electrons from the n-side gain enough energy to cross the junction and recombine with the p-side. The energy released when the free electrons from the n-side combine with the p-side is released in the form of light.

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45
Q

What sort of sensor measure blood oxygen saturation

A

Optical sensor

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46
Q

What does beer lamberts law explain

A

The measured absorbance for a single compound is directional proportional to the concentration of the compound and the length of the light path through the sample

47
Q

What is a thermistor

A

Semiconductor whose resistance varies with temperature

48
Q

What is the purpose of a bridge circuit

A

Used to convert a change in the impedance of a senor into a change in an output voltage

49
Q

What is Poissons ratio (v)

A

explains the relationship between longitudinal and lateral strain in material

50
Q

What does it mean if the Poissons ratio is positive

A

when the material is stretched it contracts in the perpendicular direction and when compressed it expands laterally

51
Q

Explain the movement of particles in a sound wave

A

Sound waves are longitudinal waves - the particles aren’t actually moving the whole length of the wave, they are instead oscillating left and right and passing their energy onto the particle next to it

52
Q

What is the net movement of particles in sound waves

A

0

53
Q

The speed at which a sound wave can travel at is dependant on what two factors

A

Temperature and medium

54
Q

How quick does sound waves travel though biological tissue

A

1540m/s

55
Q

What frequencies are used in ultrasound for imaging and therapeutic

A

Imaging - 2-18MHz
Thereputic - 0.8-2MHz

56
Q

What 3 things can occur to an ultrasound wave when it is emittied from the probe

A
  1. Continue through the tissue
  2. Reflect back to the probe
  3. Get abosorbed in the tissue
57
Q

How are high energy ultrasound waves made and what material is commonly used

A

Piezoelectric effect changes the shape of a piezoelectric material using an electrical potential or a voltage. This is usually ceramic.

58
Q

Direct vs Converse piezoelectric ultrasound waves

A

Direct - forcing piezoelectric material to compress there is a voltage coming out of it (converting mechanical input into electrical)
Converse - a voltage input into the piezoelectric material is converted into mechanical energy

59
Q

Explain transmission in ultrasound

A

Probe delivers high voltage pulse to the tip of the probe where piezoelectric material is stored, causing this material to change shape quickly. This fast change in shape when held against the tissue causes the tissue to vibrate and transfer sound waves though the tissue

60
Q

Explain reception in ultrasound

A

the sound waves come back from the tissue to the peizoelelctric material, causing the material to vibrate causing a small voltage signal to come out of the

61
Q

What electrical device is an ultrasound probe considered

A

A transducer

62
Q

Describe A mode ultrasound and what it primarily meaures

A

This only measures the amplitude of the sound waves as they return back to the probe.
This gives us information on the distance between tissue planes but not much else.

63
Q

In B-mode ultrasound what determines the vertical and horizontal position of the image

A

Vertical - related to the time for each echo to return back to the transducer. Further down the screen, deeper the surface.
Horizontal - based on the position of the transducer probe

64
Q

In B-mode ultrasound what determines the brightness of the image

A

The brighter the image the higher the amplitude of the returning sound wave. This means the image tends to get darker as the depth of the location increases

65
Q

With a lower frequency B-mode ultrasound what resolution would we expect and to what depth can these waves travel

A

Lower frequency sound waves will give a lover resolution but the energy can travel deeper and can image deeper tissues

66
Q

Describe M-mode ultrasound and what it shows

A

This plots a perpendicular image to that of B-mode ultrasound.
Shows the movement in a particular slice over time

67
Q

What do the different colours in Doppler ultrasound represent

A

Red - fluid travelling towards the probe
Blue - fluid travelling away from prob

68
Q

In Ultrasound, posterior shadowing usually looks like what, and what can cause it

A

Represented as a really dark region in the picture

Caused my material close to the probe that is very reflective so all the energy is reflecting back and not reaching the shadow area.

Same would occur is material close to the probe what extremally absorptive and there was no energy left to reach the deeper regions

69
Q

In Ultrasound, Posterior enhancements/amplification usually looks like what, and what can cause it

A

Look like bright spots

Caused by tissue not absorbing the expected amount of energy at a particular depth (e.g if there was a fluid filled cyst the energy would flow right through it and the tissue behind the cyst would be bright)

70
Q

In Ultrasound, reverbertations usually looks like what, and what can cause it

A

Look like lots of little white horizontal lines

These are usually due to reflections inside the piece of material inside the body (e.g a metal pin).

Can also be due to different tissue densities throughout the body

71
Q

What is the thermal index in ultrasound

A

It tells us the amount of time the ultrasound can be used at a particular energy before it s dangerous

72
Q

What does it mean if a tissue has a low Wdeg

A

It is very easily heated up and damaged

73
Q

What do biosensors do

A

Convert biological signals into an output signal (usually voltage)

74
Q

What do electrodes measure

A

potential difference between two points

75
Q

What causes the body to have an electrical potential difference

A

active transport of ions across the cellular membrane during major changes in potential difference of cells

76
Q

What is the difference from polerised to non-polerized elelctrodes

A

Polerized elelctordes - have current flowing through them that will charge the electrode-electrode interface causing polerisation

Non-polerized - the potential will not change from its equilibirum through the elelctrode

77
Q

The potential that the elelctrode develops is dependent on what

A

The Cl- concentration in the electrode

78
Q

Explain the conductivity of the different layers of the skin

A

Dermis/subcutaneous layer - resistor
Epidermis - semipermeable to ionic current

79
Q

What are two biopotentials in the heart

A

Pace maker potentials and myocardial action potentials

80
Q

What are pacemaker potentials in the heart and when do they occur

A

During diastole, pacemaker cells exhibit slow spontaneous depolarisation known as pacemaker potential

81
Q

What channels drive pacemaker potentials and myocardial action potentials reciprocally

A

Pacemaker potentials - voltage gates Ca2+
Myocardial Action Potentials - voltage gates Na+ channels

82
Q

Explain the direction of propagation of action potentials in the brain and which direction EEG is able to measure better

A

In the sulcus there is vertical propagation
In the gyrus there is horizontal propagation

EEG measure perpendicular AP’s best, so these tend to be those in the sulcus

83
Q

What are 3 brain biopotentials

A

Post synaptic potentials, axonal action potentials, saltatory conduction

84
Q

Where do post synaptic potentials occur

A

In the dendrites and cell bodies of the postsynaptic neuron

85
Q

What is the role of EPSP’s and what is their threshold for activation

A

EPSP’s depolarise the membrane towards threshold.

They have no individual threshold as they summate to

86
Q

What is saltatory conduction

A

The travel of an AP down an axon with myelin sheths

87
Q

What do EEG measure

A

electrical potential between dipole space (extracellular space)

88
Q

What 4 prerequisites are there to record energy of any network of neurons in EEG

A
  1. Neurons must be perpendicular to the scalp
  2. Dendrites must be parallel so their field potentials summate
  3. Activity must have synchronous structure
  4. Electrical activity produced by each neuron needs to have the same electrical sign
89
Q

What 4 things does the amplitude of a recorded potential in an EEG depend on

A
  1. Intensity of the electrical source
  2. Distance from the recording electrode
  3. Spatial orientation
  4. Electrical properties on the structure between the source and recording electrode
90
Q

What three factors would contribute to a EEG signal being very large

A
  1. Occur near the recording electrode
  2. Perpendicular to the recording electrode
  3. Generated by lots of neurons at once (highly synchronous)
91
Q

What does surface EMG provide information on

A

Global muscle function, particularly onset of muscle contraction

92
Q

What is the corneoretinal potential

A

biopotential located across the eye

93
Q

What bio potentials are found in the GI tract

A

Endogenous pacemaker cells of the intestine crease autonomic contraction of the intestinal smooth muscle

94
Q

Explain how pulse oximetry works

A

Deoxygenated HB absorbed more red light then oxygenated Hb.
LED emits red light and the photodiode on the other side detects how much red light passes through and converts this into voltage

95
Q

What is one factor that causes variation in blood oxygen saturation and how is this accounted for

A

On a heartbeat basis, small amounts of arterial blood is pumped into the veins, therefore the amount of light passing through the blood varies as a function of time.

This is accounted for by taking the ratio of the maximum and minimum detected intensities over the duration of a heartbeat

96
Q

What determines the sensitivity of the pulse oximeter

A

Sensitivity of the photodiode

97
Q

What does a piezorestrictive pressure sensor measure and how does it work

A

Measures physical displacement using a strain gauge. The strain gauge can be attached to a diaphragm which detects changes in pressure

98
Q

What 3 separate effects contribute to the change in resistance of a conductor

A
  1. the resistance of a conductor is proportional to it’s length (stretching increases resistance)
  2. As the conductor is stretched, its cross sectional area is reduced, which also increase the resistance
  3. The inherent resistivity of some material increases with stretched
99
Q

What is a gauge factor

A

Relative resistance change divided by the strain

100
Q

Venous occlusion plethysmography is an example of what sort of pressure sensor

A

Piezoretrictive pressure sensors

101
Q

What do piezoelectric sensors/transducers do

A

Generate voltage when a mechanical force is applied to one face of the sensor

102
Q

What are two examples of piexoelectric materials

A

PVDF and quartz

103
Q

What is an example of a piezoelectric sensor/tranducer used by a CMP

A

blood pressure monitors

104
Q

What do capacitive sensor/transducers measure and how

A

Measure pressure by detecting changes in electrical capacitance caused by movement of a diaphragm

105
Q

How does inductive transducers work

A

Connects a primary and two secondary coils to an input voltage source. The output voltage is the difference between the 2 secondary coils.

When the primary coil moves in one direction, the voltage in that direction increases and the voltage in the other direction decreases

106
Q

What equation is used to define a AC wave

A

Asin(2~ft)

107
Q

What is the term used for a capacitors ability to resist charge

A

Impendence

108
Q

What two factors can decrease the impendence of a capacitor

A

increase in frequency or capacitance

109
Q

What are the three passive components of a AC circuit

A

Resistor, capacitors, inductors

110
Q

What circuit attenuation mean

A

When the Vout is smaller then the Vin

111
Q

What is a passive circuit

A

Don’t contain components with a separate power supply and thus are not capable of providing gain in power

112
Q

In which direction does a silicone based diode have to be facing to be a ‘forward bias’ and ‘reversed bias’, respectfully

A

Forward bias - facing in away from the positive source
Reverse bias - facing towards the positive source (thick depletion layer, no flow)

113
Q

How does a NPN transistor work

A

If biased correctly, a small amount of current between the base and emitter aligns with a larger current flowing in the path of collector to emitter

Physiology - Hayley (9 decks)

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