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Phys Meas Flashcards

0
Q

Describe accuracy

A

How close a measured value is to the true value. Small amount of bias. Associated with systematic error

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1
Q

Describe precision

A

How close measured values are to each other. Associate with random error

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2
Q

Is it better for tests to be precise or accurate?

A

Precise. As tests can easily be recalibrated to be accurate

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3
Q

What are some general challenges of physiological measurements?

A 
Safety and comfort
Invasive vs non-invasive
Access- scopes
Environment
Interference
Biological variability
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4
Q

What does success of physiological measurements depend on?

A 
Technologically viable
Diagnostic accuracy
Diagnostic impact- significant
Therapeutic impact
Patient outcome
Social impact
Cost-effectiveness
Environmental impact
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5
Q

Give some examples of systematic errors and which value they affect

A

Equipment, technique, operator dependent.

Affects ACCURACY

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6
Q

Give some examples of random errors and which value they affect

A

Equipment, environment, subject movement.

Affects PRECISION

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7
Q

Describe sensitivity and how it can be calculated

A

Ability to correctly identify a condition. If person has a disease, how likely it is they will test positive. TP/TP+FN

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8
Q

Describe specifity and how it can be calculated

A

Ability to correctly exclude a condition. If person does not have a disease, how likely it is they will test negative. TN/TN+FP

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9
Q

What is the significance of a low test threshold?

A

To left. Low FN high FP. Catches everyone that has it.

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10
Q

What is the significance of a high test threshold

A

To right. High FN low FP. Can lead to under treatment

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11
Q

What is an ROC curve?

A

Receiver-operating characteristic. Used to select best test threshold.
Better test = higher top left corner. Will have perfect sensitivity and specificity. Plots sensitivity vs 1-specificity.

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12
Q

What is PPV and is it affected by prevalence?

A

PPV= likelihood of positive test result being truly positive. Is affected by prevalence.

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13
Q

What is NPV and is it affected by prevalence?

A

Probability of negative result being truly negative. Not affected by prevalence.

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14
Q

Give 3 uses for pulmonary function tests

A

Diagnosis
Patient assessment- response to therapy, pre-surgical, assessment for compensation
Research purposes

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15
Q

Give some areas for investigation for pulmonary function tests

A 
Lung mechanics/ventilation
Gas mixing/transfer
Blood flow
Respiratory control 
Ciliary function
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16
Q

Gives three broad causes of airway obstruction

A

Excess mucus secretion
Loss of radial traction
Muscle constriction/inflammation/oedema

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17
Q

Which problems will be exacerbated in expiration?

A

Pressure positive in comparison to outside so exacerbates intrathoracic problems e.g copd, emphysema, cf

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18
Q

Which problems will be exacerbated in inspiration?

A

Pressure negative in comparison, exacerbates extra thoracic problems eg bilateral vocal cord paralysis

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19
Q

Describe optimum conditions for infant respiratory testing

A

Sedation if less than 18 months
Warm, quiet environment
Explain all to parents

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20
Q

Give 3 methods of calculating lung volume

A

Plethysmography
Helium dilution
Nitrogen washout

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21
Q

Describe the test of helium dilution

A 
Used to measure gas volume and FRC. 
V1C1= V2C2 so V2 = V1C1/C2
V1 = starting volume of spirometer
C1 = starting conc of helium
C2 = final conc of He 
FRC = V2 - volume of spirometer
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22
Q

Describe the nitrogen washout test

A

Measures dead space in lungs.
Patient breathes out to RV then exhales one breath of 100% oxygen.
Patient then exhales and volume and conc of nitrogen is measured.
Measure how long before patient breathes nitrogen and amount of time to breathe out all nitrogen.

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23
Q

How might you asses inflammation in the airways?

A

Induced sputum then culture- look for inflammatory cells, eosinophils
Bronchoalveolar lavage
Monitor exhaled NO

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24
Q

Describe the reasoning behind the use of reference values

A

Necessary for interpreting measurements
Gathered from population considering ethnicity/age/height/gender
Similar methodology must be used for result collection- equipment, procedure, analysis

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25
Q

Describe the principles of oximetry

A

2 LED’s positioned across from each other, over the finger. Oxy/deoxy Hb absorb different wavelengths so ratio of red:infrared absorption can be used to calculate relative amounts of the two types of haemoglobin thus calculate the saturation levels.

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26
Q

State the acceptable limits of oximetry in adults/paeds

A

Adults HR: 55-140 sats: 85-100%

Paeds HR: higher . Sats: same

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27
Q

How many spirometry readings are needed for acceptability?

A

3

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28
Q

What does Plethysmography measure?

A

TGV, FRC and airway resistance

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29
Q

Describe the process of measuring Plethysmography

A

Patient sits in airtight chamber and breathes through pneumochromatograph
Patient breathes normally, then device is shuttered.
Patient make respiratory effort against the shutter
Alveolar pressure measured directly from mouthpiece
Change in thoracic volume measured indirectly from cabin pressure
Use Boyles Law

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30
Q

What is Boyles Law?

A

Pressure is inversely proportional to volume

V = deltaVP/deltaP

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31
Q

Describe testing for exercise induced asthma

A

Measure FEV1 before and after exercise. If less than 70% to begin then abandon test.
Use treadmill or corridor to exercise patient
Run for 6 mins- 3 to achieve target HR and 3 to maintain
Target is 80% of maximum, max = 230-age
Positive test is greater than 15% reduction in FEV after exercise.
Give bronchodilator and measure spirometry again.
Advise patient to take bronchodilator before exercising.

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32
Q

Which pre-analytical factors will affect measurements?

A 
Age 
Circadian rhythm
Menstrual cycle 
Food intake
Time after injury
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33
Q

How can clinical value of phys meas tests be improved?

A

Use combination of tests
Use sequential tests to show trends
Dynamic function tests- use of stressor spot measure variable not present at basal level
Venous sampling to love a hot spot

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34
Q

What is the normal distribution of values around the reference range?

A

95% values within reference range
5% healthy samples out side range, 2.5% above and below
Reference range is normally mean +-2SD

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35
Q

In order for measurement to be significant the change must be greater than the combined effects of biological and analytical variation. How is this calculated?

A

root(SDA2+SDB2)

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36
Q

What is standard deviation?

A

Root of variance. Spread of data around the mean

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37
Q

How is prevalence worked out?

A

TP/TP+FP

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38
Q

Describe how chemical pathology can be used to make a diagnosis

A

Diabetes
Hyoerlipidaemia
Phaeochromocytoma
Hormonal abnormalities

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39
Q

Describe how chemical pathology can be used to confirm a diagnosis

A

Renal failure
Liver failure
MI
Hormonal abnormalities

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40
Q

Describe how chemical pathology can be used to monitor disease

A 
Routine biochemistry UE LFT bone profile 
Tumour marker AFP CEA PSA
Screening CH PKU Down's syndrome
Hormone assays
Therapeutic drug monitoring , gentamicin
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41
Q

Describe which markers will be raised in different types of jaundice

A

Obstructive ALP
Hepatocellular ALT
Mixed both elevated

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42
Q

Discuss ALP

A

Produced in bone liver placenta intestines

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43
Q

Discuss ALT

A

Produced in liver muscle. Raised in hepatocellular damage eg drugs, TB

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44
Q

Discuss AST

A

Liver or muscle

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45
Q

Discuss gamma-GT

A

Specific to liver

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46
Q

Discuss amylase

A

Increased = increased risk of pancreatitis. Also raised in any acute abod pain eg appendicitis, ectopic pregnancy, bowel obstruction, acute MI, ovarian cyst

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47
Q

Discuss how chemical pathology may be used in diabetes

A

HBA1C greater than 6.5%

Fasting plasma glucose greater than 7mmol/l

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48
Q

Discuss how chemical pathology may be used in hypothyroidism

A

High lipids and CK

Determine cause by measuring TSH

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49
Q

Discuss how chemical pathology may be used in hypocortisolism

A

synacthen 200mg IV. Should see rise in cortisol when measuring after 30mins. Should be greater than 550

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50
Q

Discuss how chemical pathology may be used in hypercortisolism

A

Use high or lose dose dexamethasone suppression test. Distinguish disease vs syndrome. Pituitary cause = disease

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51
Q

Discuss how chemical pathology may be used in polyuria

A

Deprive patient of water. Give patient water and ADH. Monitor.
Compare plasma and urine osmolarity. Normally should see decreased plasma and increased urine osmolarities. Water is retained.
Abnormal could be result of diabetes insipidus.
Nephrogenic; kidney doesn’t respond to ADH so no change in urine osmolarity
Neurogenic: pituitary not producing causes fall in urine osmolarity

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52
Q

Discuss how chemical pathology may be used in growth hormone deficiency

A

If baby has hypoglycaemia measure cortisol GH and insulin levels.
Infuse insulin in a stress test- both GH and cortisol should rise. NB: glucose must fall below 2.2 for effective results

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53
Q

Discuss how chemical pathology may be used in hyperpituitarism

A

If high GH then acromegaly and gigantism
OGTT, give glucose to healthy patient and GH should follow
Symptoms: headaches, visual field defects, hypertension, facial changes

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54
Q

Give some uses for vascular ultrasound

A

Carotid arteries, transcribing Doppler, AAA, ABPI, peripheral

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55
Q

Describe ABPI

A

Use Doppler and sphygmomanometer. Measure brachial and posterior tibial/dorsalis pedis pulses and compare, ankle/brachial
Greater than 1 is normal, less than 1 abnormal. Although in diabetics vessels may calcify leading to incompressibility of vessels and a result of greater than 1.

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56
Q

Describe amplitude

A

Height Of sound waves

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57
Q

Describe frequency

A

Number of sound waves per second measured in hertz

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58
Q

Which mediums does sound move through fastest?

A

Solid, liquid, air. Also affected by temperature and density

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59
Q

Describe the basics of ultrasound

A

Uses a transducer lined with piezoelectric crystals that change shape when a voltage is applied. Pulsatilla waves of ultrasound are fired into the body and will be reflected back. The extent and speed at which they are reflected back depends on the depth of structures, the barriers to reflection and the tissues they hit.

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60
Q

Discuss the use of different probes in ultrasound

A

Different probes have different advantages- depth penetration vs quality/resolution of image.
Flat/linear: high frequency high resolution poor penetration
Rounded: lower frequency, lower resolution good penetration- used for abdo

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61
Q

How can ultrasound images be balanced?

A

Using gain controls

Deeper structures give a weaker signal producing an unbalanced image. Gain controls boost intensity of returning signal

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62
Q

Describe the Doppler effect

A

Sound moving towards an object has a higher frequency than sound moving away.
Fd= 2 v ft cos theta / c

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63
Q

Give 4 types of Doppler

A

Colour (darker equals lower velocity of blood)
Spectral
Blue
Continuous wave

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64
Q

Describe an aliasing artefact in Doppler ultrasound

A

If speed if sampling is low then blood appears to be going backwards. Fix by increasing frequency of sampling

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65
Q

Give some specific clinical indications for use of ultrasound

A 
Carotid stenosis- carotid endarterectomy
Peripheral claudication
Critical ischaemia
Rest pain
Investigation of stenosis 
AAA
TIA
DVT
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66
Q

What are advantages of ultrasound over angiography

A

Cheaper, less risk, no radiation, less invasive

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67
Q

When would an AAA cause concern?

A

Greater than 5.5cm

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68
Q

How would ultrasound help to detect a DVT?

A

Veins are incompressible

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69
Q

What are nerve conduction studies used for?

A

Evaluate function/ability of electrical conduction of motor and sensory nerves of the body

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70
Q

What do nerve conduction studies detect?

A

Electrical and chemical changes, and conduction velocity of nerves. Affected by axon diameter and myelination

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71
Q

What can nerve conduction studies tell us?

A

Localisation of problem
Severity of problem
Pathophysiology of problem
Disease course

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72
Q

Describe the structure of motor neurones

A

All myelinated, muscle control

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73
Q

Describe the structure of sensory neurones

A

Myelinated - touch
Partially myelinated- cold and pain
Unmyelinated - heat and pain

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74
Q

Describe the structure of autonomic neurones

A

Thinly or Unmyelinated

Heart rate, bp, gut/git function, sweating

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75
Q

What 3 things are measured in nerve conduction studies?

A

Phase cancellation
Dispersion- may be a sign some fibres are damaged
Compound nerve AP- sum of APs of different fibres in entire nerve

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76
Q

How do nerve conduction studies work?

A

Stimulator sends impulses to nerves
Electrodes placed in muscle
EMG machine records electrical response (velocity and amplitude)

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77
Q

What is latency?

A

Time take for impulse to travel from stimulation site to recording site

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78
Q

How do you work out velocity?

A

Distance/time

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79
Q

Discuss nerve conduction tests with motor neurones

A

Start current at 0 and gradually increase until supramaximal value is reached. Do not increase further as is painful for patient and has no additional benefit.

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80
Q

Discuss nerve conduction tests with sensory neurones

A

Record from purely sensory part of nerve. Use 2 electrodes, one recording and one as a reference. Latency is time from stimulus to SNAP

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81
Q

Describe some problems with nerve conduction tests

A 
Patient discomfort
Neuropathy with age
Patient factors- movement, temperature, oedema
Problems with equipment
Electrical interference 
Very sensitive test
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82
Q

Describe EMG (electromyography)

A

Records electrical activity of skeletal muscle upon contraction
Activated muscles cells generate AP recorded with needle electrode or surface electrode. Needles are intramuscular and disposable.

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83
Q

Describe favours affecting EMG measurements

A

Insertion potential- fibres damaged by insertion of electrode causes spontaneous AP’s. Should clear up but may require relocation.
NB: at rest muscle should be electrically silent.
Spontaneous activity of Denervated fibres
Composition of motor units
Abnormality of fibres

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84
Q

Describe some abnormalities found with EMG

A

Nerve damage- some fibres/neurones taken up by other motor units producing abnormally large APs. Sound of machine demonstrates strength of contractions.
Muscle damage: reduced duration of motor unit AP, reduced amplitude

85
Q

Describe some Problems associated with EMG

A 
Operator dependent
Technical problems/ equipment
Interference
Inaccurate needle placement
Risk of haematoma
Painful and invasive
86
Q

Describe EEG - electroencephalography

A

Records electrical activity within the brain.
Has good temporal resolution but poor spatial.
Measures sum of all APs within proximity of recording electrode
Measures voltage fluctuations resulting from ionic current flows within neurones
Some patterns can be physiologically characteristic eg wakefulness vs sleeping

87
Q

Describe how EEG May be recorded

A

On scalp, dural/subdural (attached to dura mater), depth (deep brain stimulation)

Suitable for paeds as electrodes can be made into a cap

88
Q

Describe the labelling of EEG electrodes

A

Right side is even
Left side is odd
Z is midline
T is temporal, O occipital, F frontal etc

89
Q

give some causes of altered rhythms in EEG

A

Age, sleep, lesions, encephalopathy,

90
Q

Which rhythm will be seen on the EEG of a normal awake adult

A

Alpha
Eyes closed
Posterior region

91
Q

What things would you look at when assessing EEG

A

Frequency, amplitude, quantity, morphology, variability, topography, phase relationships, reactants

92
Q

Give some clinical indications for EEG

A

Epilepsy- distinguish type and give prognosis
Localise site of origin of seizure
Evoked potentials

93
Q

Give some advantages of EEG

A

Cheap, portable, non-harmful, suitable for paeds, good temporal resolution, useful for distinguishing types of epilepsy

94
Q

Give some disadvantages of EEG

A

Poor spatial resolution, staff must be experts, alterations with age and wakefulness

95
Q

Give some technical problems involved with EEG

A

Biological artefacts- blinking, muscle movements
Environmental- interference
Misplacement/disconnection of leads
Patient cooperation

96
Q

Give the 3 different states of brain activity

A

Wakefulness
Non-REM sleep
REM sleep

97
Q

Describe wakefulness

A

Cortex active, motor system capable

98
Q

Describe non-REM sleep

A 
Normally enter sleep through it
Cortex inactive, motor system capable
Slow rolling eye movements
Low frequency high amplitude EEG 
4 stages
99
Q

Describe REM sleep

A

Cortex active, motor system incapable. Loss of tone prevents acting out of dreams. Normally leave sleep through this. Rapid eye movements. High frequency low amplitude EEG.

100
Q

State the 5 different types of sleep disorder

A 
DIMS
DOES
Parasomnias
Circadian rhythm disturbances
Sleep problems with chronic/systemic disease
101
Q

Give examples of DIMS

A 
Acute or chronic insomnias
Depression, early waking
Poor sleep hygiene 
Drug induced
Fatal familial insomnia
102
Q

Give examples of DOES

A 
Restless limbs, limb twitching, periodic limb movement
Sleep apnoea, obstructive or central
Narcolepsy
Cerebral injury
Long or short sleepers
103
Q

What are parasomias?

A

Abnormal actions/movements in sleep eg walking or eating

104
Q

Give some examples of circadian rhythm disturbances

A 
Jet lag
Delayed sleep phase syndrome
Advanced sleep phase syndrome
Non-entrained circadian rhythm 
Long sleepers
105
Q

Describe narcolepsy

A

Associated with loss of hypocretin secretion
Breakdown of normal barrier between sleep and awake
Sometimes familial usually spontaneous

106
Q

What are the symptoms of narcolepsy?

A

Excessive daytime sleepiness- irresistible attacks partially relieved by napping
Sleep paralysis for minutes or seconds on waking up, eye/resp not affected
Hallucinations, vivid horrible dreams immediately on falling asleep
Cataplexy- muscle weakness often brought about by laughter or excitement
Disturbed night time sleep

107
Q

Describe OSA

A

100% loss of air for more than 10 seconds

108
Q

Give symptoms of OSA

A

Daytime sleepiness
Unrefreshing sleep
Nocturia (ANP release due to RA stretching)
Snoring
Obesity/metabolic syndrome
Crowded oropharynx (large tonsils and uvular, large tongue)
Mood changes

109
Q

What is hypopnoea?

A

Greater than 50% loss of airflow for more than 10 secs

110
Q

Give some diagnostics for OSA

A

LSAT
ODI
Frequency of events
TAL

111
Q

Give some differential diagnoses for snoring

A

OSA
Simple snoring
Upper airway resistance syndrome
Catahternea- moaning in sleep

112
Q

Give the 4 assessments of sleep

A

Duration
Quality
Architecture
Associated phenomena

113
Q

How would you asses duration of sleep?

A

Use a diary- time to bed time to sleep, often underestimates sleep
Actigraphy- usually on wrist. Measure for 6 weeks. Movement is awake, little or no movement means sleep
Polysmography- gold standard. Measure all aspects using resp, cvs, video, electrophysiology

114
Q

How would you assess wakefulness?

A

Questionnaire- likelihood of falling asleep in common situations, work out score. Epworth/Stamford.
Multiple sleep latency- give 5x20min opportunities to fall asleep
Multiple wakefulness- give 5x20min opportunities to stay awake. Good for judging up intended sleepiness
Vigilance testing- ask to press button every 3 secs when light flashes. 4 x 40 mins. Osler test. More than 21 seconds unresponsive is sleep

115
Q

Describe the use of subjective techniques in audiology testing

A

Gold standard. Subject provides response to stimulus. Measures perception but requires patient cooperation.

116
Q

Describe the use of objective techniques in audiology testing

A

Recordings made of physiological responses to stimulus, without need for conscious patient acknowledgement.

117
Q

Describe the anatomy of the outer ear

A

Localises sound and funnels into ear canal
Enables distinguishing between left/right and front/behind
As sound moves through cartilaginous canal it raises intensity of speech compared to other sounds

118
Q

Describe the anatomy of the middle ear

A

Sound waves cause tympanic membrane to vibrate. 3 ossicles transmit sound vibrations to fenestra ovalis to inner ear. Inside the cochlea sound waves change to nerve impulses.
Eustachian tube joins middle ear to nasopharynx

119
Q

Where would you find perilymph

A

Between by and membranous labyrinths, out 2 chambers

120
Q

Where would you find endolymph

A

Fluid filling membranous labyrinth of ear, middle or inner ear chambers.

121
Q

Explain how APs fire in the cochlea?

A

Vibrations of hair cells in cochlea causes movement to open and close a hole, allowing fluid to move down a gradient and allow APs to fire. They fire from vibration of the basilar membrane.

122
Q

Give some problems of the outer ear/ ear canal

A 
Atresia
Blockage of Eustachian tube, glue ear
Haematoma
Malformation
Impacted wax
Otitis externa
Trauma
Tumours (osteomas are benign)
Foreign bodies
Tympanic perforation
123
Q

Give some problems of the middle ear

A 
Acute or chronic otitis media
Cholesteatoma (epithelial overgrowth)
Tympanosclerosis
Otosclerosis
Ossicle fracture
Tympanic perforation
124
Q

Give some examples of cochlear dysfunction

A 
Menieres
Meningitis
Congenital
Presbyacusis, loss with age starting at higher frequency
Ototoxicity, aminoglycosides
Noise induced damage
Anoxia
Infection
125
Q

Describe Ménière’s disease

A

Increased endolymph causes a feeling of full ears. Sufferers have vertigo,tinnitus, ringing, balance problems

126
Q

In hearing loss give some causes of neural dysfunction

A

Vestibular schwannoma
Acoustic neuroma
Psychogenic, trauma

127
Q

Describe conductive hearing loss

A

Stops conduction of sound to cochlea. Sound is quiet and not distorted and responds well to amplification. Patients speak quietly.

128
Q

Describe test results in conductive hearing loss

A

Weber- localises to affected ear

Rinne- negative result, BC greater than AC

129
Q

Describe sensory/neural hearing loss

A

Sounds quiet and distorted. Amplification less effective. Patients speak loudly. could be due to neural dysfunction eg MS

130
Q

Describe test results in sensorineural hearing loss

A

Weber- sound localises to non-affected ear

Rinne- normal. Positive test, AC greater than BC

131
Q

Describe recruitment

A

Quiet sounds not heard, loud sounds sound normal or louder. Reduced range of hearing often of cochlear origin

132
Q

When taking an audiological history what must you ask a patient

A

Changes in hearing, hearing loss and is it gradual or spontaneous, in which ear
Otalgia
Ottorhoea
Tinnitus/vertigo

133
Q

How do you examine an ear?

A

Retract and lift ear to straighten canal. Examine canal and tympanic membrane. Should see triangle of light.
Check for blockage, could be wax or tumour

134
Q

Describe the use of a tuning fork in audiology testing

A

Assesses symmetry of hearing and can determine presence or absence of conductive loss. Air conduction is more efficient than bone conduction.

135
Q

What sort of test are tuning fork tests

A

Psychophysical

136
Q

Describe the Weber test

A

Tuning fork in centre of forehead.
If equal then normal or sensorineural loss
If localises to one side then conductive loss in that ear or sensorineural in other

137
Q

Describe the Rinne test

A

Tuning fork on mastoid process then in front of EAM
Positive is AC>BC normal or sensorineural loss
Negative is BC>AC conductive loss

138
Q

Give advantages of a tuning fork test

A

Cheap, easy, quick, minimal equipment, easy screening

139
Q

Give disadvantages of tuning fork tests

A

Does not quantify degree of loss, results influenced by technique. Must mask non-test ear

140
Q

Describe pure tone audiogram

A

Measures sensitivity to pure tones of different frequencies. Equipment and test are standardised.

141
Q

Adv of pure tone audiogram

A

Quantifiable
Standardised results
Differentiate type of loss
Shape of audiogram can provide info on underlying pathology

142
Q

Disadv of pure tone audiogram

A

Requires patient cooperation
Results influenced by technique
Susceptible to learning effects

143
Q

Sources of error of pure tone audiogram

A 
Environment or body noise
Learning effects
Fatigue
Tester technique
Tinnitus 
Patient motivation
Equipment calibration
144
Q

Describe speech audiometry

A

Measure ability to recognise speech, patient presented with word list and asked to repeat. Each word has 3 phenomes, for each phenome correct patient gets 1 point. Range of stimulus and intensity

145
Q

Give adv of speech audiometry

A

Physiologically relevant
Not cheatable
Determine type of loss

146
Q

Give disadvantages of speech audiometry

A

Not suitable for paeds or SEN
Not always available material
Dependent on cooperation

147
Q

Describe paediatric audiometry

A

Subjective assessment of paeds over 6 months. Uses sound field audiometry. Measures ability and allows early intervention
Distraction testing, cooperation testing, performance testing

148
Q

Describe the use of visual reinforcement in paediatric audiometry

A

Child sits on parents lap. Distractor in front, tester behind.
When sound made toy lights up. Child learns to look for toy her sound heard.

149
Q

Describe some sources of error in visual reinforcement in paediatric audiometry

A 
Olfactory cues
Auditory cues
Visual cues
Distractor technique, over or under stimulation
Rhythmic stimulation
150
Q

Describe tympanometry

A

Measure tympanic membrane motility or middle ear integrity, pure tone played into auditory canal. Intensity monitored while static pressure is applied and varied. Results expressed as compliance.

151
Q

Give adv of tympanometry

A

Minimal cooperation
Quick
Simple

152
Q

Give disadv of tympanometry

A

Not measure of hearing

Probe must have airtight seal

153
Q

Describe otoacoustic emissions

A

Stimulus sounds introduced into EAM and all sounds in canal are measured acoustically. Measures inner ear health
Normally cochlear echo should be detectible in ear canal
Compare frequency/content of stimulus and emission

154
Q

Give different types of otoacoustic emissions

A

TEOAE transient, stimulate then record

DPOAE distortion product, stimulate and record simultaneously

155
Q

Give adv of otoacoustic emissions

A 
Non-invasive
Quick
Minimal cooperation
All ages
Reliable
156
Q

Give disadv of otoacoustic emissions

A

Can’t measure perception
Sensitive to outer or middle ear pathology
Response abolished with hearing loss

157
Q

Describe electrocochleography

A

Assesses functional integrity of cochlea. Measure AP’s from cochlea or auditory nerve evoked by stimulation of cochlea. Signal detected by electrode in canal or drum. Stimuli may be acoustic clicks or brief tone bursts
Determine cochlear pathology eg Ménière’s disease

158
Q

Give adv of electrocochleography

A

No patient response required
Response not affected by sleep or sedation
Intraoperative monitoring

159
Q

Give disadv of electrocochleography

A

Can be invasive
Doesn’t test perception
Reference data required

160
Q

Describe auditory brainstem response

A

Measures APs originating in auditory nerve or brainstem
Pathways evoked by acoustic stimulation of cochlea. Test requires relaxed patient so infants often sedated.
Used in newborn screening and intraoperative monitoring

161
Q

Describe differential amplification in auditory brainstem response

A

Cancels signals from distant origins

162
Q

Describe signal filtering in auditory brainstem response

A

Removal of signals above and below a predetermined level

163
Q

Give adv of auditory brainstem response

A

No cooperation or response
Patient can be sedated
Objective

164
Q

Give disadv of auditory brainstem response

A

Sensitive to interference

Subject must be relaxed or asleep

165
Q

Describe cortical evoked responses

A

Measurement of EPs from non-specific cortical structures evoked by acoustic stimuli
Provides estimation of auditory sensitivity

166
Q

Describe indications for use of cortical evoked responses

A

Medico legal patients
Patients with inconsistent results
Patients unable or unwilling to participate in subjective testing

167
Q

Give disadv of cortical evoked responses

A 
Large variability with results
Response affected by alertness
Not paeds suitable
Extensive test time
Not under sedation
168
Q

What is Bayes theorem?

A

New OR = previous OR x likelihood OR

169
Q

What is probability

A

Value between 0 and 1. Degree of beliefs about a proposition

170
Q

How do you work out an odds ratio?

A

P(A) / (1-P(A))

171
Q

How do you work out a likelihood ratio?

A

P(E|H) / P(E|H’)

172
Q

Describe the use of nuclear medicine

A

Use is declining due to risks.
Tiny amounts of radioactive material incorporated into compounds/pharmaceuticals
Distribution in the body can be visualised
Material can be ingested or injected

173
Q

Describe scintigraphy

A

Produces 2D plain image

Use iodine for thyroid

174
Q

Describe SPECT

A

Single photon emission CT
Uses a gamma ray emitting radio pharmaceutical to produce a picture
Eg technetium in heart

175
Q

Describe PET

A

Positron emission tomography
B-particle emitting radiopharmaceutical. Particle decays to emit an electron and positron, a 3D picture is produced. Produces best functional picture.

176
Q

Describe use of 18FDG (PET)

A

Fluordeoxyglucose used in mets. Shows abnormal glucose metabolism, high in metastases.
But can give false positive or negative findings.

177
Q

What is SUV?

A

Standard uptake value. Inject standard amount of activity, PET camera measures activity per volume, expressed as SUV units.
Result greater than 2.5 is suspicious for malignancy

178
Q

What method might you use in optical imaging?

A

Image retina using OCT
Optical coherence tomogrpahy
Uses visible Iight

179
Q

What are good points of X-rays

A

Low radiation risk

CXR has best spatial resolution

180
Q

X-ray absorption depends on…

A 
Tube voltage (potential difference between anode and cathode)
Anode material (tungsten or molybdenum)
Atomic number (z) of absorbing matter
Low in water, high of bone
181
Q

How does CT scanning work and what does it measure

A

X-rays spinning around object received by detector on other side of object. Measures attenuation (gradual loss of intensity through medium, depends on material of medium).

182
Q

How many slices can CT image per second?

A

256

183
Q

What is the measurable value of CT?

A

Hounsfield unit. Represents transformation from original linear attenuation to one where air is -1000 water is 0 and metal is +1000

Change in one Hounsfield unit is 0.1% attenuation coefficient

Allows comparison of CT values obtained
Different body tissues have different HU values

184
Q

What colours do different tissues appear on CT

A

Bone is white water is black

185
Q

What is the difference between a pixel and a voxel

A

Pixel is 2D

Voxel is 3D

186
Q

What are advantages of a spiral or helical CT scanner

A

Faster, more powerful, better for operator/patient/taxpayer, easier use of contrast, thinner slices without extra time

187
Q

Discuss the use on contrast in CT

A

Poor contrast of intrinsic tissue so contrast often used.
This enhances visibility of structures and pathology
Particularly useful with mets and stones

188
Q

Give some different types of contrast used in CT

A 
IV wait 55-60s
Intra arteial wait 20-30s
Positive iodinated
Negative fat or air
Oral
189
Q

What are some side effects of contrast

A

Exacerbation of renal impairment

190
Q

Discuss the use on contrast in the brain

A

Contrast broken down by BBB so contrast enters mets but not brain tissue

191
Q

What are some patient related artefacts in CT

A 
Movement
Respiratory- diaphragm 
Bowel peristalsis
Cardiac output 
Delayed contrast bolts
192
Q

Describe the basis of MRI

A

Atom has a nucleus with orbiting atoms
Nucleus has protons and neutrons with spin
Spinning charge gives a magnetic field
Some atoms, hydrogen, are paramagnetic ie only magnetised in presence of magnetic field
Therefore patient must be magnetised for imaging
Superconducting magnet lines up nuclei to point in the same direction

193
Q

What is the best property of MRI?

A

Has best contrast

194
Q

What is a stochastic risk?

A

Risk/ chance of effect increases with exposure

195
Q

What is a non-stochastic risk?

A

Severity of effect depends with dose but will occur over a certain threshold eg sunburn.

196
Q

What is the best attribute of CXR

A

Best spatial resolution

197
Q

What is the best attribute of PET

A

Best functional resolution

198
Q

What is the best attribute of CT

A

Good compromise of all

199
Q

What is the best attribute of ultrasound

A

Cheap, fast, safe, but quality is variable and operator dependent.

200
Q

Describe investigations you would carry out on a 52 year old man admitted with chest pain

A 
U+E to check electrolytes such as K+
Glucose
Cardiac enzymes, troponin I and creatine kinase
Repeat 3 hours after
Then perform ECG and Echo
201
Q

Briefly outline the formation and excretion of bilirubin

A

Haemolysis of rbc’s produces bilirubin
It is conjugated in the liver by gluconryl transferase
It is then excreted in urine as urobilinogen
Bilirubin is also added to bile in the gut and excreted in faeces

202
Q

What tests would you carry out on a 7 year old boy presenting with asthma

A

EIA test
Spirometry
Vitalograph
Maybe helium dilution and nitrogen washout if severe

203
Q

What is spatial resolution?

A

The physical size of pixels that make up the ct image

It is determined by the physical size of the detectors surrounding the patient

204
Q

What is contrast resolution?

A

How well different tissues can be distinguished, based on attenuation and density.
Expressed as Hounsfield units

205
Q

Which vessels normally have monophasic blood flow and why?

A

Carotid and renal arteries as they need to remain patent at all times for continuous flow and do not have much elastic recoil
Low resistance and low pulsatility

206
Q

Which vessels normally have triphasic waveform recordings and why?

A

Peripheral lower limb vessels. Have elastic recoil

207
Q

Give 4 factors you would consider when deciding whether or not to order a test for a patient

A

Acceptability to patient
Sensitivity and specificity of test
Cost of test
Whether it will change outcomes/ management

208
Q

Describe the EEG montage and the information it allows us to obtain

A

Electrode are placed either on the scalp, dura or deep brain.
Even number are right side, odd are left and z is in midline. Letters correspond to areas of the head.
Measures electrical activity in the brain recording APS from neurones local to the electrode

209
Q

List technical factors that can lead to artefacts in the recording of nerve conduction studies

A 
Movement
Interference
Oedema
Temperature
Equipment failure
Insertion potentials
210
Q

Which likelihood ratio is most significant, 0.1 1.2 or 10

A

Tests with likelihood ratio close to 1 do not provide any useful information since they barely modify the previous OR.
High likelihood ratio will significantly alter the posterior probability so add useful info to the diagnostic process.

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