Previous Q Flashcards
ethical reasons for why consent is important
• Legal requirement
• Respect patient autonomy
• Respect for persons
• Establishes relationships of trust with patient
• Benefits patient
-More realistic expectations (feels they are in control)
-More co-operation (they will fast before surgery)
Longitudinal/Cohort study
- Used to see if those with a certain characteristic, who don’t have disease develop it more frequently than those who dont have characteristic
- Divided into two groups – Those who have characteristics vs don’t
- When measuring exposure status of subjects they must be free of disease
- Can have a Prospective or Retrospective Cohort study
Prospective cohort study
- population studied for presence of fixed or modifiable exposure
- followed up + incidence of disease in exposed individuals compared with incidence of those who are not exposed
Retrospective cohort study
- past medical records to identify population + obtain data on previous exposures
- incidence of disease in exposed individuals compared with incidence in those not exposed
- cheaper + less time consuming
Advantages of Longitudinal/Cohort studies
- No recall bias as don’t rely on subjects memory
- Exposure measured before causality so less bias + increased reliability in causality
- More than 1 disease can be measured for any one exposure
- Can calculate incidence rates
- Can calculate relative risk!
- Potential to give more info leading to a nested case-control study
Disadvantages of Longitudinal/Cohort studies
- Expensive + time consuming
- Collection of data may alter behaviour (observer effect)
- Need to ensure definition of exposure or disease is consistent
- Losses by follow up may introduce selection bias (patients who are healthy leave)
- Unsuitable for low incidence diseases
Descriptive studies
Describe prevalence (number of cases in a population at a given time) of disease + how it varies over time, place by place, by characteristics
Advantages of descriptive studies:
- Identify trends to allow for further research/hypothesis – suggest clues to cause of disease
- Allow to see burden of disease (impact of disease – financial, mortality impact, community impact)
Disadvantages of descriptive studies:
- Don’t provide sufficient evidence to infer causality, as they’re mostly retrospective
- Dont account for many details such as confounders etc
Cross sectional studies:
- Measure prevalence of a disease (via medical records, questionnaires, census)
- Carried out by collecting data (characteristic + disease status) at one point in time to see if subjects with certain exposures/characteristics have higher disease prevalence
- Descriptive (aiming to assess burden of disease)
- Analytical (aim to explain observed pattern of disease by examining its relationship with possible aetiological factors)
Advantages of cross sectional studies:
- Common diseases
- Cheap + quick
- Gives estimates of prevalence of disease
Disadvantages of Cross sectional studies:
- Unable to measure incidence
- Unsuitable for rare diseases, as you’ll need large sample
- Need to ensure you avoid selection bias
- Exposure/characteristics may change in time or disease progression
- Measure both exposure/characteristics + disease status at one point in time so you don’t know what came first – Reverse causality (info on exposure preceding disease is unknown)
Analytical studies
examine associations between presence of diseases in individuals + populations with potential causative factors
Advantages of analytical studies:
- Gives equal info on both controls (free of disease) as cases (those with disease)
- Gives greater clues to causality than descriptive studies
Disadvantages of analytical studies:
•Unable to infer causality due to possible confounders/unknown variables
Case control study
- Subjects divided into 2 groups – those who have disease + those who don’t
- Identify cases + controls then measure prevalence of a particular exposure.
- See if cases had a characteristic more frequent than controls
- If exposure more common in cases than controls, it may be a risk factor, if less common then protective factor
- Can work out ‘odds ratio’ which is an estimate of ‘relative risk’
Advantages of case control studies
- Cheap and quick to do
- Efficient for rare diseases or diseases with low incidence
- Can investigate a range of risk factors for one disease
- Can work out the odds ratio – which is even more accurate in rare diseases and can be interchanged with relative risk
Disadvantages of case control studies
- Selection + information bias eg recall bias as exposure measured after disease develops
- Can’t calculate relative risk since no cases of incidence
- Unsuitable for exposures/characteristics that are rare
- Unsuitable for diseases with several main exposures/risk factors
- Need to ensure data collection not influenced by knowledge of exposure to prevent measurement bias
- Disease may affect the exposure (eg diabetes + blood glucose) - reverse causal relationship
Why not include people with CVD or hypertension in a study to find out if people develop hypertension over 7 years?
Avoid reverse causality
What does it mean to have randomisation?
Equal chance of being put in the control or intervention group
calculate cumulative incidence
Cumulative incidence= (number of new cases during period)/(size of population intially at risk)
eg 28 out of 1000 people develop a condition over a 2 year period the cumulative incidence = 28/1000 = 2.8%
Nested case-control study
- insert case-control study into cohort study
- subset of controls compared to incidence cases
- cases of cohort study become controls of nested case-control study
- controls selected for each case from that case’s matched risk set, matching on factors of age, gender etc to reduce confounding
- Carried out when exposure of interest difficult or expensive to obtain + rare outcome, utilizing data from a large cohort study helps reduce time and cost
Interventional (experimental) studies:
- All randomised control trials (RCTs), or uncontrolled trial – where everybody gets treatment
- Intervention administered to evaluate its efficacy + safety
- Tries to establish direct causation, by seeing if adding/removing a certain factor has a direct effect on developing/preventing a disease
- Does altering/removing characteristic reduce probability of developing disease?
- ‘control group’ to compare to (standard therapy/no treatment/placebo) + ‘intervention group’ (receives intervention)
- Double blinding avoids knowledge of treatment influencing whether to enter a patient into a trail (selection bias) or observers assessment of patients response (assessor bias)
- Randomisation
Advantages of experimental studies:
- Establish strong direct causation factor
- Determining possible cures/treats – marketing of new medications
- Compare new treatments with current/conventional treatments to determine which is better
- Randomisation removes any selection/allocation bias. It is where each individual has equal chance of being allocated to either control or interventional group + only systematic difference between people in each group is treatment receiving. Other possibly determinants of health outcome differ randomly between each group so effects are likely to cancel out.
Disadvantages of experimental studies:
- Expensive + time consuming
- Requires direct contact with patient
- Ensure disease definition is consistent
- Need to take appropriate measures to avoid bias (double blind, randomisation, standardisation etc)
- Unfeasible if intentionally expose individual to a risk factor
- Some patients get better without any intervention, and some get better due to the placebo effect – Not necessarily the treatment
- Need to ensure results observed are statistically significant (P<0.05) with suitable confidence intervals.
- If unable to double blind due to obvious intervention then assessor bias (assessment of intervention different than assessment of control)
Interpretation of Randomised control trial
- Intention to treat analysis of results – Compare all randomised to treatment with all randomised to control, it is important in real life, as not everybody will comply with treatment 100%
- On treatment analysis of results – Compare those who only received/complied with treatment with those who received control, this may introduce selection bias however.
Parallel groups of RCT
- Half allocated to control, half to treatment
- Where individuals in control + intervention group remain in those groups through the study
- Used when health outcome is irreversible eg Cure, remission or death, things like stroke, heart attack
- eg we separate into placebo and drug, the outcome being measured is stroke
Crossover groups of RCT
- Halfway through the study, individuals in control group switched with intervention group
- For reversible health outcomes (where effect of treatment can be reversed), like analgesics for chronic pain, drug to lower serum cholesterol
- Good for continuous data outcomes eg BP
Confounding variables
- Variable associated with exposure being investigated + variable must be independently associated with risk of developing outcome of interest/disease
- eg those who drink coffee more have higher rates of CHD however because those who drink coffee more also smoke more
RR
RR = risk in exposed/risk in unexposed
-Ratio of two risks (probability an individual will experience event/disease).
-Measured as a rate (number of outcomes per person time) ratio or a risk (outcomes) ratio.
-Reference/baseline/unexposed/control group is denominator.
-Gives the strength of association, a high RR means there is a stronger association.
-Found in longitudinal/cohort studies + RCTs because population is split into an exposed vs non-exposed group
-Not in a case control study as they’re split into disease and non-disease groups, so work out the odds ratio for CCS
eg Point estimate for RR= 0.75
SO risk of stroke in statin group is 0.75 times that in placebo group, or those in simvastatin group at 25% less risk of a stroke
Absolute excess risk = Risk in exposed persons – Risk in unexposed person
Confidence interval !!!!!!!!!!!
If looking at confidence interval of relative risk or odds ratio, then if 1 lies in interval statistically insignificant (P>0.05)
-If looking at differences between means or proportions and 1 lies within interval then statistically insignificant (P>0.05)
-Increasing population size will decrease confidence interval.
eg 95% CI for RR above is 0.66 – 0.85
SO 95% sure true relative risk (true value, if we studied the population) lays between these values so we are 95% sure Simvastatin will reduce stroke risk by at least 15% and at most 34%.
What cell does not express MCHI
erythrocytes
What cells express cd4+/CD8+?
t helper cells/ cytotoxic t cells
Dirty bomb explodes in air and particles get stuck up the nose. Size is 75 micrometer per particle, which mechanisms deal with it or does it just get stuck up the nose?
Ie nasal epithelium, alveolar macrophages, nasal hair etc
GFR equation – someone has the renal plasma clearance measured, how? Person has 2.5ml/min produced with urine conc. of 20mg/ml. Plasma glucose of about 0.5mg/ml.
Answer = 100 ml/min
Esptein barr virus
glandular fever
What organism causes thrush
candida albicans
M3 receptor
Gq/G11 pathway
Beta blockers act on which receptor in the ventricular myosites?
B1 to decrease HR
Guy has regurgitation and dysphagia, also has nausea and vomiting?
Achalasia
-Treatment triple therapy:
2 Antibiotics eg amoxicillin, metronidazole
PPI eg Omeprazole, lanzoprazole, rabeprazole :
inactive at neutral pH, irreversibly blocks H+/K+-ATPase pump to reduce basal + food-stimulated gastric acid secretion
Hypovoleamia due to a stab would leads to what?
Decreased capillary hydrostatic pressure leading to increase internal perfusion to maintain BP
Minute ventilation equation?
runner runs a race which takes him 20 seconds, he takes 4 breathes with each race, 1 breath takes in 1L, Minute ventilation = 12L
ABG sample o Acidosis o Low HCO3- o Low PaCO2 o What is going on?
Metabolic acidosis with resp compensation
Upon activation of a GPCR, what is a direct consequence?
GDP is replaced by a GTP molecule on the alpha subunit causing dissociation from the alpha and beta subunits
B1/b2/b3 receptors are linked what receptors?
Gs
A1 adreno receptor activation causes what?
Decrease in PIP2
