Phys Meas Flashcards
(211 cards)
0
Q
Describe accuracy
A
How close a measured value is to the true value. Small amount of bias. Associated with systematic error
1
Q
Describe precision
A
How close measured values are to each other. Associate with random error
2
Q
Is it better for tests to be precise or accurate?
A
Precise. As tests can easily be recalibrated to be accurate
3
Q
What are some general challenges of physiological measurements?
A
Safety and comfort Invasive vs non-invasive Access- scopes Environment Interference Biological variability
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
5
Q
Give some examples of systematic errors and which value they affect
A
Equipment, technique, operator dependent.
Affects ACCURACY
6
Q
Give some examples of random errors and which value they affect
A
Equipment, environment, subject movement.
Affects PRECISION
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
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
9
Q
What is the significance of a low test threshold?
A
To left. Low FN high FP. Catches everyone that has it.
10
Q
What is the significance of a high test threshold
A
To right. High FN low FP. Can lead to under treatment
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.
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.
13
Q
What is NPV and is it affected by prevalence?
A
Probability of negative result being truly negative. Not affected by prevalence.
14
Q
Give 3 uses for pulmonary function tests
A
Diagnosis
Patient assessment- response to therapy, pre-surgical, assessment for compensation
Research purposes
15
Q
Give some areas for investigation for pulmonary function tests
A
Lung mechanics/ventilation Gas mixing/transfer Blood flow Respiratory control Ciliary function
16
Q
Gives three broad causes of airway obstruction
A
Excess mucus secretion
Loss of radial traction
Muscle constriction/inflammation/oedema
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
18
Q
Which problems will be exacerbated in inspiration?
A
Pressure negative in comparison, exacerbates extra thoracic problems eg bilateral vocal cord paralysis
19
Q
Describe optimum conditions for infant respiratory testing
A
Sedation if less than 18 months
Warm, quiet environment
Explain all to parents
20
Q
Give 3 methods of calculating lung volume
A
Plethysmography
Helium dilution
Nitrogen washout
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
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.
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
24
Describe the reasoning behind the use of reference values
Necessary for interpreting measurements
Gathered from population considering ethnicity/age/height/gender
Similar methodology must be used for result collection- equipment, procedure, analysis
25
Describe the principles of oximetry
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.
26
State the acceptable limits of oximetry in adults/paeds
Adults HR: 55-140 sats: 85-100%
| Paeds HR: higher . Sats: same
27
How many spirometry readings are needed for acceptability?
3
28
What does Plethysmography measure?
TGV, FRC and airway resistance
29
Describe the process of measuring Plethysmography
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
30
What is Boyles Law?
Pressure is inversely proportional to volume
| V = deltaVP/deltaP
31
Describe testing for exercise induced asthma
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.
32
Which pre-analytical factors will affect measurements?
```
Age
Circadian rhythm
Menstrual cycle
Food intake
Time after injury
```
33
How can clinical value of phys meas tests be improved?
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
34
What is the normal distribution of values around the reference range?
95% values within reference range
5% healthy samples out side range, 2.5% above and below
Reference range is normally mean +-2SD
35
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?
root(SDA2+SDB2)
36
What is standard deviation?
Root of variance. Spread of data around the mean
37
How is prevalence worked out?
TP/TP+FP
38
Describe how chemical pathology can be used to make a diagnosis
Diabetes
Hyoerlipidaemia
Phaeochromocytoma
Hormonal abnormalities
39
Describe how chemical pathology can be used to confirm a diagnosis
Renal failure
Liver failure
MI
Hormonal abnormalities
40
Describe how chemical pathology can be used to monitor disease
```
Routine biochemistry UE LFT bone profile
Tumour marker AFP CEA PSA
Screening CH PKU Down's syndrome
Hormone assays
Therapeutic drug monitoring , gentamicin
```
41
Describe which markers will be raised in different types of jaundice
Obstructive ALP
Hepatocellular ALT
Mixed both elevated
42
Discuss ALP
Produced in bone liver placenta intestines
43
Discuss ALT
Produced in liver muscle. Raised in hepatocellular damage eg drugs, TB
44
Discuss AST
Liver or muscle
45
Discuss gamma-GT
Specific to liver
46
Discuss amylase
Increased = increased risk of pancreatitis. Also raised in any acute abod pain eg appendicitis, ectopic pregnancy, bowel obstruction, acute MI, ovarian cyst
47
Discuss how chemical pathology may be used in diabetes
HBA1C greater than 6.5%
| Fasting plasma glucose greater than 7mmol/l
48
Discuss how chemical pathology may be used in hypothyroidism
High lipids and CK
| Determine cause by measuring TSH
49
Discuss how chemical pathology may be used in hypocortisolism
synacthen 200mg IV. Should see rise in cortisol when measuring after 30mins. Should be greater than 550
50
Discuss how chemical pathology may be used in hypercortisolism
Use high or lose dose dexamethasone suppression test. Distinguish disease vs syndrome. Pituitary cause = disease
51
Discuss how chemical pathology may be used in polyuria
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
52
Discuss how chemical pathology may be used in growth hormone deficiency
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
53
Discuss how chemical pathology may be used in hyperpituitarism
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
54
Give some uses for vascular ultrasound
Carotid arteries, transcribing Doppler, AAA, ABPI, peripheral
55
Describe ABPI
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.
56
Describe amplitude
Height Of sound waves
57
Describe frequency
Number of sound waves per second measured in hertz
58
Which mediums does sound move through fastest?
Solid, liquid, air. Also affected by temperature and density
59
Describe the basics of ultrasound
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.
60
Discuss the use of different probes in ultrasound
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
61
How can ultrasound images be balanced?
Using gain controls
| Deeper structures give a weaker signal producing an unbalanced image. Gain controls boost intensity of returning signal
62
Describe the Doppler effect
Sound moving towards an object has a higher frequency than sound moving away.
Fd= 2 v ft cos theta / c
63
Give 4 types of Doppler
Colour (darker equals lower velocity of blood)
Spectral
Blue
Continuous wave
64
Describe an aliasing artefact in Doppler ultrasound
If speed if sampling is low then blood appears to be going backwards. Fix by increasing frequency of sampling
65
Give some specific clinical indications for use of ultrasound
```
Carotid stenosis- carotid endarterectomy
Peripheral claudication
Critical ischaemia
Rest pain
Investigation of stenosis
AAA
TIA
DVT
```
66
What are advantages of ultrasound over angiography
Cheaper, less risk, no radiation, less invasive
67
When would an AAA cause concern?
Greater than 5.5cm
68
How would ultrasound help to detect a DVT?
Veins are incompressible
69
What are nerve conduction studies used for?
Evaluate function/ability of electrical conduction of motor and sensory nerves of the body
70
What do nerve conduction studies detect?
Electrical and chemical changes, and conduction velocity of nerves. Affected by axon diameter and myelination
71
What can nerve conduction studies tell us?
Localisation of problem
Severity of problem
Pathophysiology of problem
Disease course
72
Describe the structure of motor neurones
All myelinated, muscle control
73
Describe the structure of sensory neurones
Myelinated - touch
Partially myelinated- cold and pain
Unmyelinated - heat and pain
74
Describe the structure of autonomic neurones
Thinly or Unmyelinated
| Heart rate, bp, gut/git function, sweating
75
What 3 things are measured in nerve conduction studies?
Phase cancellation
Dispersion- may be a sign some fibres are damaged
Compound nerve AP- sum of APs of different fibres in entire nerve
76
How do nerve conduction studies work?
Stimulator sends impulses to nerves
Electrodes placed in muscle
EMG machine records electrical response (velocity and amplitude)
77
What is latency?
Time take for impulse to travel from stimulation site to recording site
78
How do you work out velocity?
Distance/time
79
Discuss nerve conduction tests with motor neurones
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.
80
Discuss nerve conduction tests with sensory neurones
Record from purely sensory part of nerve. Use 2 electrodes, one recording and one as a reference. Latency is time from stimulus to SNAP
81
Describe some problems with nerve conduction tests
```
Patient discomfort
Neuropathy with age
Patient factors- movement, temperature, oedema
Problems with equipment
Electrical interference
Very sensitive test
```
82
Describe EMG (electromyography)
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.
83
Describe favours affecting EMG measurements
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
84
Describe some abnormalities found with EMG
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
Describe some Problems associated with EMG
```
Operator dependent
Technical problems/ equipment
Interference
Inaccurate needle placement
Risk of haematoma
Painful and invasive
```
86
Describe EEG - electroencephalography
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
Describe how EEG May be recorded
On scalp, dural/subdural (attached to dura mater), depth (deep brain stimulation)
Suitable for paeds as electrodes can be made into a cap
88
Describe the labelling of EEG electrodes
Right side is even
Left side is odd
Z is midline
T is temporal, O occipital, F frontal etc
89
give some causes of altered rhythms in EEG
Age, sleep, lesions, encephalopathy,
90
Which rhythm will be seen on the EEG of a normal awake adult
Alpha
Eyes closed
Posterior region
91
What things would you look at when assessing EEG
Frequency, amplitude, quantity, morphology, variability, topography, phase relationships, reactants
92
Give some clinical indications for EEG
Epilepsy- distinguish type and give prognosis
Localise site of origin of seizure
Evoked potentials
93
Give some advantages of EEG
Cheap, portable, non-harmful, suitable for paeds, good temporal resolution, useful for distinguishing types of epilepsy
94
Give some disadvantages of EEG
Poor spatial resolution, staff must be experts, alterations with age and wakefulness
95
Give some technical problems involved with EEG
Biological artefacts- blinking, muscle movements
Environmental- interference
Misplacement/disconnection of leads
Patient cooperation
96
Give the 3 different states of brain activity
Wakefulness
Non-REM sleep
REM sleep
97
Describe wakefulness
Cortex active, motor system capable
98
Describe non-REM sleep
```
Normally enter sleep through it
Cortex inactive, motor system capable
Slow rolling eye movements
Low frequency high amplitude EEG
4 stages
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99
Describe REM sleep
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
State the 5 different types of sleep disorder
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DIMS
DOES
Parasomnias
Circadian rhythm disturbances
Sleep problems with chronic/systemic disease
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101
Give examples of DIMS
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Acute or chronic insomnias
Depression, early waking
Poor sleep hygiene
Drug induced
Fatal familial insomnia
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102
Give examples of DOES
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Restless limbs, limb twitching, periodic limb movement
Sleep apnoea, obstructive or central
Narcolepsy
Cerebral injury
Long or short sleepers
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103
What are parasomias?
Abnormal actions/movements in sleep eg walking or eating
104
Give some examples of circadian rhythm disturbances
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Jet lag
Delayed sleep phase syndrome
Advanced sleep phase syndrome
Non-entrained circadian rhythm
Long sleepers
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105
Describe narcolepsy
Associated with loss of hypocretin secretion
Breakdown of normal barrier between sleep and awake
Sometimes familial usually spontaneous
106
What are the symptoms of narcolepsy?
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
Describe OSA
100% loss of air for more than 10 seconds
108
Give symptoms of OSA
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
What is hypopnoea?
Greater than 50% loss of airflow for more than 10 secs
110
Give some diagnostics for OSA
LSAT
ODI
Frequency of events
TAL
111
Give some differential diagnoses for snoring
OSA
Simple snoring
Upper airway resistance syndrome
Catahternea- moaning in sleep
112
Give the 4 assessments of sleep
Duration
Quality
Architecture
Associated phenomena
113
How would you asses duration of sleep?
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
How would you assess wakefulness?
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
Describe the use of subjective techniques in audiology testing
Gold standard. Subject provides response to stimulus. Measures perception but requires patient cooperation.
116
Describe the use of objective techniques in audiology testing
Recordings made of physiological responses to stimulus, without need for conscious patient acknowledgement.
117
Describe the anatomy of the outer ear
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
Describe the anatomy of the middle ear
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
Where would you find perilymph
Between by and membranous labyrinths, out 2 chambers
120
Where would you find endolymph
Fluid filling membranous labyrinth of ear, middle or inner ear chambers.
121
Explain how APs fire in the cochlea?
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
Give some problems of the outer ear/ ear canal
```
Atresia
Blockage of Eustachian tube, glue ear
Haematoma
Malformation
Impacted wax
Otitis externa
Trauma
Tumours (osteomas are benign)
Foreign bodies
Tympanic perforation
```
123
Give some problems of the middle ear
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Acute or chronic otitis media
Cholesteatoma (epithelial overgrowth)
Tympanosclerosis
Otosclerosis
Ossicle fracture
Tympanic perforation
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124
Give some examples of cochlear dysfunction
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Menieres
Meningitis
Congenital
Presbyacusis, loss with age starting at higher frequency
Ototoxicity, aminoglycosides
Noise induced damage
Anoxia
Infection
```
125
Describe Ménière's disease
Increased endolymph causes a feeling of full ears. Sufferers have vertigo,tinnitus, ringing, balance problems
126
In hearing loss give some causes of neural dysfunction
Vestibular schwannoma
Acoustic neuroma
Psychogenic, trauma
127
Describe conductive hearing loss
Stops conduction of sound to cochlea. Sound is quiet and not distorted and responds well to amplification. Patients speak quietly.
128
Describe test results in conductive hearing loss
Weber- localises to affected ear
| Rinne- negative result, BC greater than AC
129
Describe sensory/neural hearing loss
Sounds quiet and distorted. Amplification less effective. Patients speak loudly. could be due to neural dysfunction eg MS
130
Describe test results in sensorineural hearing loss
Weber- sound localises to non-affected ear
| Rinne- normal. Positive test, AC greater than BC
131
Describe recruitment
Quiet sounds not heard, loud sounds sound normal or louder. Reduced range of hearing often of cochlear origin
132
When taking an audiological history what must you ask a patient
Changes in hearing, hearing loss and is it gradual or spontaneous, in which ear
Otalgia
Ottorhoea
Tinnitus/vertigo
133
How do you examine an ear?
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
Describe the use of a tuning fork in audiology testing
Assesses symmetry of hearing and can determine presence or absence of conductive loss. Air conduction is more efficient than bone conduction.
135
What sort of test are tuning fork tests
Psychophysical
136
Describe the Weber test
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
Describe the Rinne test
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
Give advantages of a tuning fork test
Cheap, easy, quick, minimal equipment, easy screening
139
Give disadvantages of tuning fork tests
Does not quantify degree of loss, results influenced by technique. Must mask non-test ear
140
Describe pure tone audiogram
Measures sensitivity to pure tones of different frequencies. Equipment and test are standardised.
141
Adv of pure tone audiogram
Quantifiable
Standardised results
Differentiate type of loss
Shape of audiogram can provide info on underlying pathology
142
Disadv of pure tone audiogram
Requires patient cooperation
Results influenced by technique
Susceptible to learning effects
143
Sources of error of pure tone audiogram
```
Environment or body noise
Learning effects
Fatigue
Tester technique
Tinnitus
Patient motivation
Equipment calibration
```
144
Describe speech audiometry
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
Give adv of speech audiometry
Physiologically relevant
Not cheatable
Determine type of loss
146
Give disadvantages of speech audiometry
Not suitable for paeds or SEN
Not always available material
Dependent on cooperation
147
Describe paediatric audiometry
Subjective assessment of paeds over 6 months. Uses sound field audiometry. Measures ability and allows early intervention
Distraction testing, cooperation testing, performance testing
148
Describe the use of visual reinforcement in paediatric audiometry
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
Describe some sources of error in visual reinforcement in paediatric audiometry
```
Olfactory cues
Auditory cues
Visual cues
Distractor technique, over or under stimulation
Rhythmic stimulation
```
150
Describe tympanometry
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
Give adv of tympanometry
Minimal cooperation
Quick
Simple
152
Give disadv of tympanometry
Not measure of hearing
| Probe must have airtight seal
153
Describe otoacoustic emissions
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
Give different types of otoacoustic emissions
TEOAE transient, stimulate then record
| DPOAE distortion product, stimulate and record simultaneously
155
Give adv of otoacoustic emissions
```
Non-invasive
Quick
Minimal cooperation
All ages
Reliable
```
156
Give disadv of otoacoustic emissions
Can't measure perception
Sensitive to outer or middle ear pathology
Response abolished with hearing loss
157
Describe electrocochleography
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
Give adv of electrocochleography
No patient response required
Response not affected by sleep or sedation
Intraoperative monitoring
159
Give disadv of electrocochleography
Can be invasive
Doesn't test perception
Reference data required
160
Describe auditory brainstem response
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
Describe differential amplification in auditory brainstem response
Cancels signals from distant origins
162
Describe signal filtering in auditory brainstem response
Removal of signals above and below a predetermined level
163
Give adv of auditory brainstem response
No cooperation or response
Patient can be sedated
Objective
164
Give disadv of auditory brainstem response
Sensitive to interference
| Subject must be relaxed or asleep
165
Describe cortical evoked responses
Measurement of EPs from non-specific cortical structures evoked by acoustic stimuli
Provides estimation of auditory sensitivity
166
Describe indications for use of cortical evoked responses
Medico legal patients
Patients with inconsistent results
Patients unable or unwilling to participate in subjective testing
167
Give disadv of cortical evoked responses
```
Large variability with results
Response affected by alertness
Not paeds suitable
Extensive test time
Not under sedation
```
168
What is Bayes theorem?
New OR = previous OR x likelihood OR
169
What is probability
Value between 0 and 1. Degree of beliefs about a proposition
170
How do you work out an odds ratio?
P(A) / (1-P(A))
171
How do you work out a likelihood ratio?
P(E|H) / P(E|H')
172
Describe the use of nuclear medicine
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
Describe scintigraphy
Produces 2D plain image
| Use iodine for thyroid
174
Describe SPECT
Single photon emission CT
Uses a gamma ray emitting radio pharmaceutical to produce a picture
Eg technetium in heart
175
Describe PET
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
Describe use of 18FDG (PET)
Fluordeoxyglucose used in mets. Shows abnormal glucose metabolism, high in metastases.
But can give false positive or negative findings.
177
What is SUV?
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
What method might you use in optical imaging?
Image retina using OCT
Optical coherence tomogrpahy
Uses visible Iight
179
What are good points of X-rays
Low radiation risk
| CXR has best spatial resolution
180
X-ray absorption depends on...
```
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
How does CT scanning work and what does it measure
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
How many slices can CT image per second?
256
183
What is the measurable value of CT?
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
What colours do different tissues appear on CT
Bone is white water is black
185
What is the difference between a pixel and a voxel
Pixel is 2D
| Voxel is 3D
186
What are advantages of a spiral or helical CT scanner
Faster, more powerful, better for operator/patient/taxpayer, easier use of contrast, thinner slices without extra time
187
Discuss the use on contrast in CT
Poor contrast of intrinsic tissue so contrast often used.
This enhances visibility of structures and pathology
Particularly useful with mets and stones
188
Give some different types of contrast used in CT
```
IV wait 55-60s
Intra arteial wait 20-30s
Positive iodinated
Negative fat or air
Oral
```
189
What are some side effects of contrast
Exacerbation of renal impairment
190
Discuss the use on contrast in the brain
Contrast broken down by BBB so contrast enters mets but not brain tissue
191
What are some patient related artefacts in CT
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Movement
Respiratory- diaphragm
Bowel peristalsis
Cardiac output
Delayed contrast bolts
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192
Describe the basis of MRI
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
What is the best property of MRI?
Has best contrast
194
What is a stochastic risk?
Risk/ chance of effect increases with exposure
195
What is a non-stochastic risk?
Severity of effect depends with dose but will occur over a certain threshold eg sunburn.
196
What is the best attribute of CXR
Best spatial resolution
197
What is the best attribute of PET
Best functional resolution
198
What is the best attribute of CT
Good compromise of all
199
What is the best attribute of ultrasound
Cheap, fast, safe, but quality is variable and operator dependent.
200
Describe investigations you would carry out on a 52 year old man admitted with chest pain
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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
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201
Briefly outline the formation and excretion of bilirubin
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
What tests would you carry out on a 7 year old boy presenting with asthma
EIA test
Spirometry
Vitalograph
Maybe helium dilution and nitrogen washout if severe
203
What is spatial resolution?
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
What is contrast resolution?
How well different tissues can be distinguished, based on attenuation and density.
Expressed as Hounsfield units
205
Which vessels normally have monophasic blood flow and why?
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
Which vessels normally have triphasic waveform recordings and why?
Peripheral lower limb vessels. Have elastic recoil
207
Give 4 factors you would consider when deciding whether or not to order a test for a patient
Acceptability to patient
Sensitivity and specificity of test
Cost of test
Whether it will change outcomes/ management
208
Describe the EEG montage and the information it allows us to obtain
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
List technical factors that can lead to artefacts in the recording of nerve conduction studies
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Movement
Interference
Oedema
Temperature
Equipment failure
Insertion potentials
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210
Which likelihood ratio is most significant, 0.1 1.2 or 10
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.
