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stats and clinical sciences Flashcards

1
Q

what is epidemiology

A

study of disease in population
it specifically look at the patterns, associations and effects of the disease in a defined population

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2
Q

what is incidence?

A

the number of individuals that develop a condition (new cases) during a defined period of time in a defined population

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3
Q

What is prevalence?

A

The total number of individuals in a defined population that have a condition at or during a specific period of time

prevalence = incidence x average duration

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4
Q

what is point prevalence?

A

the total number of individuals in a defined population that has a condition at specific time point

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5
Q

what is period prevalence?

A

the proportion of a population which have a condition during a defined period of time

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6
Q

what is lifetime prevalence?

A

the proportion of a population that will experience the condition at some point during their lifetime.

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7
Q

what is the crude birth rate

A

the number of live births / mid-yeah population

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8
Q

what is crude death rate

A

The incidence of death from a specified condition or disease

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9
Q

what is sensitivity

A

the ability of a test to correctly identify those with a condition

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10
Q

what is specificity

A

the ability of a test to correctly identify those that do not have a condition

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11
Q

what is the positive predictive value ?

A

The probability that a subject with a positive test actually has the condition being tested for

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12
Q

What is number neaded to treat ?

A

the number of patients it is necessary to treat to stop an event or illness, i.e needing to treat 10 people with a statin to prevent one heart attack

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13
Q

what is a type one error?

A

Incorrectly rejecting the null hypothesis (saying a treatment or intervention works when it does not)

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14
Q

What is a type two error?

A

incorrectly accepting the null hypothesis (saying a treatment does not work when it does)

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15
Q

what are the different types of bias?

A

Information bias - results from systematic differences in the way data is obtained from the study groups - examples include observer bias, interviewer bias, recall bias, instrument bias

Reporter bias - occurs when people report particular events with an unconscious preference

selection bias - occurs when there is a systematic difference between the study participants verses those who did not participate or between those in the treatment group vs those in the control group

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16
Q

What is the difference between parametric and non-parametric?

A

Parametric tests are those that make assumptions about the parameters of the population distribution from which the sample is drawn. This is often the assumption that the population data are normally distributed. Non-parametric tests are “distribution-free” and, as such, can be used for non-Normal variables.

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17
Q

What are the statistical tests used for parametric data?

A

Student’s t-test - paired or unpaired
Pearson’s product-moment coefficient - correlation

paired data refers to data obtained from a single group of patients, e.g. Measurement before and after an intervention. Unpaired data comes from two different groups of patients, e.g. Comparing response to different interventions in two groups

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18
Q

what are the statistical tests used for non-parametric tests?

A

Non-parametric tests:

Mann-Whitney U test
compares ordinal, interval, or ratio scales of unpaired data

Wilcoxon signed-rank test
compares two sets of observations on a single sample, e.g. a ‘before’ and ‘after’ test on the same population following an intervention

chi-squared test
used to compare proportions or percentages e.g. compares the percentage of patients who improved following two different interventions

Spearman, Kendall rank - correlation

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19
Q

What are the phases of the cardiac action potential?

A

Phase 0 - rapid depolarisation - rapid sodium influx, these channels automatically deactivate after a few ms

1 - early repolarisation - efflux of potassium

2 - plateau - slow influx of calcium

3 - final dépolarisation - efflux of potassium

4 - restoration of ionic concentrations - resting potential is restored by Na+/K+ ATPase. There is slow entry of sodium into the cell decreasing the potential difference until the threshold potential is reached, triggering a new action potential

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20
Q

what is the conduction velocity in the different areas of the heart?

A

Atrial conduction - spreads along ordinary atrial myocardial fibres at 1m/sec
AV node conduction 0.05m/sec
Ventricular contraction - the Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles

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21
Q

What is the most important stimulator of the central chemoreceptors?

A

a decrease in pH.
Central chemoreceptors, located in the medulla oblongata of the brain, are primarily sensitive to changes in the pH of cerebrospinal fluid. They respond to changes in hydrogen ion concentration resulting from alterations in arterial CO2 tension
An increase in arterial pCO2 leads to an increase in hydrogen ions and this a decrease in pH. This stimulates central chemoreceptors leading to an increased rate and depth of respiration to eliminate excess CO2 and restore blood pH to normal

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22
Q

what controls respiration?

A

central regulatory centres
central and peripheral chemoreceptors
pulmonary receptors

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23
Q

where are the central respiratory regulatory centres?

A

medullary respiratory centre
apneustic centre (lower pons)
pneumotaxic centre (upper pons)

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24
Q

where are the central and peripheral chemoreceptors?

A

central: raised [H+] in ECF stimulates respiration
peripheral: carotid + aortic bodies, respond to raised pCO2 & [H+], lesser extent low pO2

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25
What are the pulmonary receptors involved in respiratory control?
stretch receptors, lung distension causes slowing of respiratory rate (Hering-Bruer reflex) irritant receptor, leading to bronchoconstriction juxtacapillary receptors, stimulated by stretching of the microvasculature
26
What is the likelihood ratio for a positive test result?
How much the odds of the disease increase when a test is positive
27
how is absolute risk reduction calculated?
Absolute risk reduction = (Control event rate) - (Experimental event rate)
28
what are the two types of error when testing the null hypothesis?
Type I - the null hypothesis is rejected when its true Type II - the null hypothesis is accepted when it is false
29
how is power defined in medical statistics?
Power = 1 - the probability of a type II error
30
how do you calculate a liklihood ratio for a positive test result ?
Likelihood ratio for a positive test result = sensitivity / (1 - specificity)
31
how do you calculate likelihood ratio for a negative test result?
likelihood ratios for a negative test result = 1-sensitivity/specificity
32
what is the power of a study?
the probability of detecting a statistically significant difference
33
what are the properties of normal distribution?
symmetrical i.e. Mean = mode = median 68.3% of values lie within 1 SD of the mean 95.4% of values lie within 2 SD of the mean 99.7% of values lie within 3 SD of the mean
34
what are the levels of evidence?
Ia - evidence from meta-analysis of randomised controlled trials Ib - evidence from at least one randomised controlled trial IIa - evidence from at least one well-designed controlled trial which is not randomised IIb - evidence from at least one well-designed experimental trial III - evidence from case, correlation and comparative studies IV - evidence from a panel of experts
35
how are recommendations graded?
Grade A - based on evidence from at least one randomised controlled trial (i.e. Ia or Ib) Grade B - based on evidence from non-randomised controlled trials (i.e. IIa, IIb or III) Grade C - based on evidence from a panel of experts (i.e. IV)
36
what are the functions of vitamin D?
increases plasma calcium and plasma phosphate increases renal tubular reabsorption and gut absorption of calcium increases osteoclastic activity increases renal phosphate reabsorption
37
What kind of disorder is fragile X syndrome?
Fragile X syndrome is a trinucleotide repeat disorder.
38
what are the features of fragile X?
Features in males learning difficulties large low set ears, long thin face, high arched palate macroorchidism hypotonia autism is more common mitral valve prolapse Features in females (who have one fragile chromosome and one normal X chromosome) range from normal to mild
39
How is fragile X diagnosed?
can be made antenatally by chorionic villus sampling or amniocentesis analysis of the number of CGG repeats using restriction endonuclease digestion and Southern blot analysis
40
what are the subunits of trop and what do they bind to?
Subunits of troponin troponin C: binds to calcium ions troponin T: binds to tropomyosin, forming a troponin-tropomyosin complex troponin I: binds to actin to hold the troponin-tropomyosin complex in place
41
which tract are pain and temp carried in?
spinothalamic tract
42
where does the spinothalamic tract decussate?
At the level it enters at there fore a hemisection of the cord will result in contralateral loss of these functions.
43
which spinal tract are motor neurones carried in?
the corticospinal tract
44
what does the dorsal column medial lemniscus pathway carry?
fine touch, vibration and proprioception
45
what does the spinocerebellar tract carry?
cconeys proprioception
46
what are the features of Friedrich's ataxia?
Autosomal recessive - trinucleotide repeat disorder - GAA repeat in the X25 gene on chromosome 9. age 10-15 - gait ataxia, kyphoscoliosis Neurological features absent ankle jerks/extensor plantars cerebellar ataxia optic atrophy spinocerebellar tract degeneration Other features hypertrophic obstructive cardiomyopathy (90%, most common cause of death) diabetes mellitus (10-20%) high-arched palate
47
how does a CN6 palsy present?
diplopia could be a sign of brain mets The sixth cranial nerve (CN6) innervates the lateral rectus muscle which is responsible for moving the eye laterally. CN6 arises from the pons which sits on the clivus. Hence, a tumour involving the clivus would compress the CN6 causing its palsy. his leads to restricted lateral gaze which results in horizontal diplopia as seen in this patient.
48
What does a CN4 palsy cause?
vertical diplopia
49
what does a CN3 palsy cause?
CN3 palsy causes ptosis and involves four extraocular muscles
50
when do you see a barrelled chest?
in conditions such as emphysema
51
What is the Cushing reflex ?
Cushing's triad, compromised of widening pulse pressure, bradycardia and irregular breathing, is a late sign indicating impending brain herniation. Systolic hypertension occurs as a reflex to maintain cerebral perfusion pressure in the presence of raised intracranial pressure.
52
what is the cerebral perfusion pressure?
The cerebral perfusion pressure (CPP) is defined as being the net pressure gradient causing blood flow to the brain. The CPP is tightly autoregulated to maximise cerebral perfusion. A sharp rise in CPP may result in a rising ICP, a fall in CPP may result in cerebral ischaemia. It may be calculated by the following equation: CPP= Mean arterial pressure - Intra cranial pressure
53
What is Niacin? What are the consequences of Niacin deficiency?
Vitamin B 3 Niacin is a water soluble vitamin of the B complex group. It is a precursor to NAD+ and NADP+ and hence plays an essential metabolic role in cells. Biosynthesis Hartnup's disease: hereditary disorder which reduces absorption of tryptophan carcinoid syndrome: increased tryptophan metabolism to serotonin Consequences of niacin deficiency: pellagra: dermatitis, diarrhoea, dementia
54
What are the layers of the epidermis
Stratum corneum- Flat, dead, scale-like cells filled with keratin Continually shed Stratum lucidum- Clear layer - present in thick skin only Stratum granulosum- Cells form links with neighbours Stratum spinosum- Squamous cells begin keratin synthesis Thickest layer of epidermis Stratum germinativum The basement membrane - single layer of columnar epithelial cells Gives rise to keratinocytes Contains melanocytes
55
what are the risk factors for calcium oxalate renal stones?
Hypercalciuria Hyperoxaluria Hypocitraturia they are radio opaque
56
what leads to cystine renal stones?
Inherited recessive disorder of transmembrane cystine transport leading to decreased absorption of cystine from intestine and renal tubule Multiple stones may form Relatively radiodense because they contain sulphur
57
What causes uric acid renal stones?
Uric acid is a product of purine metabolism May precipitate when urinary pH low May be caused by diseases with extensive tissue breakdown e.g. malignancy More common in children with inborn errors of metabolism Radiolucent
58
what causes calcium phosphate stones?
May occur in renal tubular acidosis, high urinary pH increases supersaturation of urine with calcium and phosphate Renal tubular acidosis types 1 and 3 increase risk of stone formation (types 2 and 4 do not) Radio-opaque stones (composition similar to bone)
59
what causes struvite renal stones?
Stones formed from magnesium, ammonium and phosphate Occur as a result of urease producing bacteria (and are thus associated with chronic infections) Under the alkaline conditions produced, the crystals can precipitate Slightly radio-opaque
60
what is the usual outcome measures in a cohort study?
relative risk
61
what statistical test do you use for correlation?
Correlation parametric (normally distributed): Pearson's coefficient non-parametric: Spearman's coefficient
62
what is Tay-Sachs disease and how does it present?
It causes an accumulation of GM2 ganglioside within lysosomes. Typical presentation is by around 6 months of age. Key features include developmental delay/regression and a cherry-red spot on the macula.
63
what are the features of Fabry disease?
A. Features can be remembered with the mnemonic FABRY-C: Febrile episodes Angiokeratomas (in bathing trunk distribution), Alpha galactosidase A defect Burning - peripheral neuropathy of hands/feet Renal failure Young (premature) death Cardiovascular disease/corneal 'whorl' keratopathy (also occurs with amiodarone)
64
what kind of hormone is growth hormone?
an anabolic hormone
65
what is the source of growth hormone?
Anterior pituitary: Somatotrophs comprise 50% of the cells of the anterior pituitary gland
66
what is the function of growth hormone?
Postnatal growth and development Numerous actions on protein, carbohydrate and fat metabolism (including increasing lipolysis and gluconeogenesis)
67
what is the mechanism of action of growth hormone?
Mechanism of action acts on a transmembrane receptor for growth factor binding of GH to the receptor leads to receptor dimerization acts directly on tissues and also indirectly via insulin-like growth factor 1 (IGF-1), primarily secreted by the liver
68
what increases and decreases the secretion of growth hormone?
Increases secretion growth hormone releasing hormone (GHRH): released in pulses by the hypothalamus fasting exercise sleep (particularly delta sleep) Decreases secretion glucose somatostatin (itself increased by somatomedins, circulating insulin-like growth factors, IGF-1 and IGF-2)
69
what are the most common form of CNS tumour?
- 60% = Glioma and metastatic disease 20% = Meningioma 10% = Pituitary lesions
70
what is endothelin?
Endothelin is a potent, long-acting vasoconstrictor and bronchoconstrictor.
71
when is Endothelia secreted from?
It is secreted initially as a prohormone by the vascular endothelium and later converted to ET-1 by the action of endothelin converting enzyme. It acts via interaction with a G-protein linked to phospholipase C leading to calcium release.
72
what promotes and inhibits the release of endothelin ?
Promotes release angiotensin II ADH hypoxia mechanical shearing forces Inhibits release nitric oxide prostacyclin
73
what conditions are endothelin raised in?
primary pulmonary hypertension myocardial infarction heart failure acute kidney injury asthma
74
which part of an antibody do immune cells bind to?
Immune cells bind to the crystallising region (Fc) of immunoglobulins
75
what is IgG and what is its function?
monomer Enhance phagocytosis of bacteria and viruses * Fixes complement and passes to the fetal circulation * Most abundant isotype in blood serum
76
what is IgA
monomer/dimer IgA is the predominant immunoglobulin found in breast milk. It is also found in the secretions of digestive, respiratory and urogenital tracts and systems * Provides localized protection on mucous membranes * Most commonly produced immunoglobulin in the body (but blood serum concentrations lower than IgG.) * Transported across the interior of the cell via transcytosis
77
what is IgM and what is its shape and function?
Pentamer First immunoglobulins to be secreted in response to an infection * Fixes complement but does not pass to the fetal circulation * Anti-A, B blood antibodies (note how they cannot pass to the fetal circulation, which could of course result in haemolysis) Pentamer when secreted
78
What is the shape of IgD and what is its function ?
Monomer Role in immune system largely unknown * Involved in activation of B cells
79
What is IgE and what is its function ?
monomer Mediates type 1 hypersensitivity reactions * Synthesised by plasma cells * Binds to Fc receptors found on the surface of mast cells and basophils * Provides immunity to parasites such as helminths * Least abundant isotype in blood serum
80
how do you calculate the number needed to treat
1/absolute risk reduction
81
what conditions are associated with HLA-DR3
dermatitis herpetiformis Sjogren's syndrome primary biliary cirrhosis
82
what conditions are associated with HLA A3
haemochromatosis
83
what condition is associated with HLA-51?
Behcet's disease
84
what conditions are associated with HLA-B27?
ankylosing spondylitis reactive arthritis acute anterior uveitis psoriatic arthritis
85
what conditions are associated with HLA-DQ2/DQ8
coeliac
86
what conditions are associated with HLA DR2
narcolepsy Goodpasture's
87
what conditions are associated with HLA-DR4?
type 1 diabetes mellitus* rheumatoid arthritis - in particular the DRB1 gene (DRB1*04:01 and DRB1*04:04 hence the association with DR4)
88
what cancer is the general p53 associated with?
Common to many cancers, Li-Fraumeni syndrome
89
what cancer is APC gene associated with?
colorectal cancer
90
what cancer is BRAC1 and BRCA 2 associated with?
Breast and ovarian cancer In men, there is an increased risk of breast cancer and prostate cancer
91
what cancer is associated with NF1 gene?
Neurofibromatosis
92
What cancer is the gene Rb associated with?
retinoblastoma
93
what cancer is the gene WT1 associated with?
wilms tumour
94
which cancer is associated with Multiple tumor suppressor 1 (MTS-1, p16) associated with
melanoma
95
what is the difference between tumour suppressor genes and oncogenes?
Tumour suppressor genes - loss of function results in an increased risk of cancer Oncogenes - gain of function results in an increased risk of cancer
96
what are the histological features of diabetic nephropathy?
Diabetic nephropathy histological findings- Kimmelstiel-Wilson lesions, nodular glomerulosclerosis
97
what conditions are x-linked recessive?
Androgen insensitivity syndrome Becker muscular dystrophy Colour blindness Duchenne muscular dystrophy Fabry's disease G6PD deficiency Haemophilia A,B Hunter's disease Lesch-Nyhan syndrome Nephrogenic diabetes insipidus Ocular albinism Retinitis pigmentosa Wiskott-Aldrich syndrome
98
how Is variance calculated ?
Variance is a measure of the spread of scores away from the mean. Variance = square of standard deviation therefore the standard deviation is the square root of variance
99
what is the function of vitamin K
Vitamin K is a fat-soluble vitamin which acts as a cofactor in the carboxylation of clotting factors (II, VII, IX, X).
100
what is turners syndrome?
Turner's syndrome is a chromosomal disorder affecting around 1 in 2,500 females. It is caused by either the presence of only one sex chromosome (X) or a deletion of the short arm of one of the X chromosomes. Turner's syndrome is denoted as 45,XO or 45,X.
101
101
what are the features of turners syndrome?
short stature shield chest, widely spaced nipples webbed neck bicuspid aortic valve (15%), coarctation of the aorta (5-10%) an increased risk of aortic dilatation and dissection are the most serious long-term health problems for women with Turner's syndrome regular monitoring in adult life for these complications is an important component of care primary amenorrhoea cystic hygroma (often diagnosed prenatally) high-arched palate short fourth metacarpal multiple pigmented naevi lymphoedema in neonates (especially feet) gonadotrophin levels will be elevated hypothyroidism is much more common in Turner's horseshoe kidney: the most common renal abnormality in Turner's syndrome
102
what are the examples of adenosine diphosphate (ADP) receptor inhibitors ?
Clopidogrel Prasugrel Ticagrelor Ticlopidine
103
what is the mechanism of action of ADP receptor inhibitors ?
Adenosine diphosphate (ADP) is one of the main platelet activation factors, mediated by G-coupled receptors P2Y1 and P2Y12. The main target of ADP receptor inhibition is the P2Y12 receptor, as it is the one which leads to sustained platelet aggregation and stabilisation of the platelet plaque.
104
why may ticagrelor cause dyspnoea ?
due to the impaired clearance of adenosine
105
what PPI can not be used with clopidogrel?
omeprazole and eso

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