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Question 1
Incorrect
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Of the following, which option best describes the muscle type that has the fastest twitch response to stimulation?
Your Answer: Cardiac muscle
Correct Answer: Type IIb skeletal muscle
Explanation:Human skeletal muscle is composed of a heterogeneous collection of muscle fibre types which differ histologically, biochemically and physiologically.
It can be biochemically classified into 2 groups. This is based on muscle fibre myosin ATPase histochemistry. These are:
Type 1 (slow twitch): Muscle fibres depend upon aerobic glycolytic metabolism and aerobic oxidative metabolism. They are rich in mitochondria, have a good blood supply, rich in myoglobin and are resistant to fatigue.
Type II (fast twitch): Muscle fibres are sub-divided into:
Type IIa – relies on aerobic/oxidative metabolism
Type IIb – relies on anaerobic/glycolytic metabolism.Fast twitch muscle fibres produce short bursts of power but are more easily fatigued.
Cardiac and smooth muscle twitches are relatively slow compared with skeletal muscle.
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This question is part of the following fields:
- Physiology
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Question 2
Correct
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Suppose the afterload and myocardial contractility remain unchanged, which of the following factors in the pressure-volume loop indicates an increase in the preload of the left ventricle?
Your Answer: Increased end-diastolic volume
Explanation:If the afterload and myocardiac contractility remains unchanged, an increase in the preload can be attributed to an increase in end-diastolic volume.
Preload can be defined as the initial stretching of the cardiac myocytes prior to contraction. Preload, therefore, is related to muscle sarcomere length. Because sarcomere length cannot be determined in the intact heart, other indices of preload are used such as ventricular end-diastolic volume or pressure. When venous return to the heart is increased, the end-diastolic pressure and volume of the ventricles are increased, which stretches the sarcomeres, thereby increasing their preload.
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This question is part of the following fields:
- Basic Physics
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Question 3
Correct
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Which of the following antihypertensive drugs is an alpha-blocker?
Your Answer: Doxazosin
Explanation:Doxazosin is selective alpha 1 blocker (it causes less tachycardia than a non-selective alpha-blocker) and is the drug of choice for a patient with hypertension and benign hyperplasia of the prostate (BHP).
The major adverse effect of an alpha-blocker is first-dose hypotension.
Atenolol and Labetalol are beta blockers. It works by relaxing blood vessels and slowing heart rate to improve blood flow and decrease blood pressure.
Clonidine is an α2A-adrenergic agonist used to treat high blood pressure, ADHD, drug withdrawal (alcohol, opioids, or nicotine), menopausal flushing, diarrhea, spasticity, and certain pain conditions.
Methyldopa is a centrally-acting alpha-2 adrenergic agonist used to manage hypertension alone or in combination with hydrochlorothiazide, and to treat hypertensive crises.
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This question is part of the following fields:
- Pharmacology
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Question 4
Correct
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Sugammadex binds to certain drugs that affect neuromuscular function during anaesthesia in a stereospecific, non-covalent, and irreversible manner.
It has the greatest impact on the activity of which of the following drugs?Your Answer: Vecuronium
Explanation:Sugammadex is a modified cyclodextrin that works as an aminosteroid neuromuscular blocking (nmb) reversal agent. By encapsulating each molecule in the plasma, it rapidly reverses rocuronium and, to a lesser extent, vecuronium-induced neuromuscular blockade. Consequently, a  concentration gradient favours the movement of these nmb agents away from the neuromuscular junction. Pancuronium-induced neuromuscular blockade at low levels has also been reversed.
By inhibiting voltage-dependent calcium channels at the neuromuscular junction, antibiotics in the aminoglycoside group potentiate neuromuscular blocking agents. This can be reversed by giving calcium but not neostigmine or sugammadex.
Sugammadex will not reverse the effects of mivacurium, which belongs to the benzylisoquinolinium class of drugs.
A phase II or desensitisation block occurs when the motor end-plate becomes less sensitive to acetylcholine as a result of an overdose or repeated administration of suxamethonium. The use of neostigmine has been shown to be effective in reversing this weakness.
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This question is part of the following fields:
- Pharmacology
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Question 5
Correct
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A 47-year-old woman presented with chief complaints of dysuria, urinary frequency, and malaise. On urine culture and sensitivity testing, E.coli was detected with resistance to ampicillin.
What is the mechanism of resistance to ampicillin?Your Answer: Beta-lactamase production
Explanation:Ampicillin belongs to the family of penicillin. Resistance to this group of drugs is due to ?-lactamase production which opens the ?-lactam ring and inactivates Penicillin G and some closely related congeners. The majority of Staphylococci and some strains of gonococci, B. subtilis, E. coli, and a few other bacteria produce penicillinase.
Resistance to cephalosporins is due to changes in penicillin-binding proteins.
Resistance to macrolides are due to post-transcriptional methylation of 23s bacterial ribosomal RNA
Resistance to fluoroquinolones is due to mutations in DNA gyrase.
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This question is part of the following fields:
- Pharmacology
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Question 6
Correct
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One of the commonest risks associated with a retrobulbar block for ophthalmic surgery is the injury to orbital structures within the tendinous ring.
The structure which passes through the superior orbital fissure and tendinous ring to enter the orbit is?Your Answer: Superior division of oculomotor nerve
Explanation:From superior to inferior, the following structures enter the orbit through the superior orbital fissure:
1. Lacrimal nerve
2. Frontal nerve
3. Superior ophthalmic vein
4. Trochlear nerve
5. Superior division of the oculomotor nerve*
6. Nasociliary nerve*
7. Inferior division of the oculomotor nerve*
8. Abducent nerve*
9. Inferior ophthalmic vein.The superior and inferior division of the oculomotor nerve, nasociliary nerve, and abducent nerve are within the tendinous ring.
The common origin of the four rectus muscles is the tendinous ring (also known as the annulus of Zinn). The tendinous ring’s lateral portion straddles the superior orbital fissure, while the medial portion encloses the optic foramen, through which the optic nerve and ophthalmic artery pass.
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This question is part of the following fields:
- Pathophysiology
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Question 7
Correct
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A measuring system's response to change is complex, yet it can be mathematically modelled.
Which of the following terms best characterises a pressure transducer's responsiveness to blood pressure changes?
Your Answer: Dynamic second-order response
Explanation:The static-response defines how a measuring system behaves while it is in equilibrium (i.e. when the measured values are not changing). If the value being measured changes over time, the reaction of a measuring system will change as well which would be a dynamic response.
The dynamic response of a measuring system can be subdivided into zero-order, first-order and second-order responses:Zero-order:
Consider a thermometer that has been left in a room for a week. The thermometer will display the current ambient temperature when you enter the room.First-order:
Consider the use of a mercury thermometer to check a patient’s temperature. It is comprised of a mercury column that expands as it warms up. The scale’s initial temperature is room temperature, but when it’s placed under the patient’s tongue, the temperature readings rise until they reach body temperature.Second-order
Consider putting weights on a mechanical weighing scale. The weight as reported on the measuring dial, will wobble around the correct value at first until reaching equilibrium. An example of this is in clinical practice is the direct measurement of arterial pressure with a transducer. The value of the input fluctuates around a central point.Drift is the progressive deterioration of a measurement system’s precision. With time, the measurement deviates from the genuine, calibrated value. The graph between this measurement and the real value should, ideally, be linear (e.g. on the y-axis the measured end-tidal CO2 against true value of the end-tidal CO2). Drift is split into three types: zero-offset, gradient, and zonal drift.
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This question is part of the following fields:
- Anaesthesia Related Apparatus
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Question 8
Incorrect
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The diaphragm is a muscle that is relatively resistant to non-depolarizing neuromuscular blockade's effects.
When these muscle relaxants are used, which of the following peripheral nerve stimulator twitch patterns is best for monitoring the return of diaphragmatic function?Your Answer: Train-of-four stimulation
Correct Answer: Post-tetanic count stimulation
Explanation:Certain skeletal muscles are more resistant to the effects of neuromuscular blocking agents, both non-depolarizing and depolarizing. The diaphragm is the most resistant. The muscles of the larynx and the corrugator supercilii are less resistant. The abdominal, orbicularis oris, and limb peripheral muscles are the most sensitive muscles.
Twitch stimulation patterns:
Supramaximal single stimulus:
The frequency ranges from 1 Hz to 0.1 Hz (one every second to one every 10 seconds)
The response is proportional to the frequency of the event.
It has limited clinical utility because it only tells you whether or not a patient is paralysed (no information on degree of paralysis).Over the course of 0.5 seconds (2 Hz), four supramaximal stimulate were applied:
It is possible to see ‘fade’ and use it as a basis for evaluation.
This stimulation pattern is used to determine the degree of blockade (1-2 twitches is appropriate for abdominal surgery)
If the train of four (TOF) count is 1-2, reversal agents can be used in conjunction with medium-acting neuromuscular blocking agents.Ratio of TOF:
This is the ratio of the 4th twitch amplitude to the 1st twitch amplitude.
The ratio decreases with non-depolarising block and is inversely proportional to the degree of block, allowing objective measurement of residual neuromuscular blockade.
To achieve adequate reversal, the ratio (as measured by accelerography) must be between 0.7 and 0.9.Count of twitches after a tetanic experience(PTC):
50 Hz for 5 seconds, then a 3 second pause, followed by a single 1 Hz twitch stimulus.
When the TOF count is zero, this stimulation pattern is used to assess deep blockade (that is, in neurosurgery, microsurgery or ophthalmic surgery when even small movements of a patient will disturb the surgical field)
It gives an estimate of how long it will take for the response to return to single twitches, allowing assessment of blocks that are too deep for any other technique.
A palpable post-tetanic count (PTC) of 2 indicates no twitch response for about 20-30 minutes, and a PTC of 5 indicates no twitch response for about 10-15 minutes.This is without a doubt the best way to keep track of paralysis in patients who need to avoid diaphragmatic movement. It’s best to use drug infusions and aim for a PTC of 2. After a tetanic stimulus, acetylcholine is mobilised, causing post-tetanic potentiation.
Stimulation in Two Bursts:
750 milliseconds between two short bursts of 50 Hz
This stimulation pattern is used to assess small amounts of residual blockade manually (tactile). -
This question is part of the following fields:
- Clinical Measurement
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Question 9
Incorrect
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A 68-year-old man is to be operated.
Â
His past history is significant for a stroke, and some residual neurological deficit. The cranial nerves are examined clinically. He is unable to rotate his head to the left side when resistance is applied. Moreover, there is tongue wasting on the right side. There are no unusual sensory signs and symptoms.
The most likely reason for these clinical findings is?Your Answer: Damage to glossopharyngeal (IX) and vagus (X) nerves
Correct Answer: Damage to hypoglossal (XII) and spinal accessory (XI) nerves
Explanation:The upper five cervical segments of the spinal cord give rise to the XI cranial nerve. They connect with a few smaller branches before exiting the skull through the jugular foramen. The sternomastoid and trapezius muscles get their motor supply from the accessory root. Except for the palatoglossus, the hypoglossal nerve supplies motor supply to all tongue muscles.
The inability to shrug the shoulder on the affected side and rotate the head to the side against resistance is caused by damage to the spinal accessory nerve. This is due to the trapezius and sternomastoid muscles’ weakness.
The hypoglossal nerve is damaged, resulting in tongue wasting and inability to move from side to side.
The stylopharyngeus receives motor supply from the glossopharyngeal nerve. It also carries taste sensory fibres from the back third of the tongue, as well as the carotid sinus, carotid body, pharynx, and middle ear.
Motor supply to the larynx, pharynx, and palate; parasympathetic innervation to the heart, lung, and gut; and sensory fibres from the epiglottis and valleculae are all provided by the vagus nerve.
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This question is part of the following fields:
- Pathophysiology
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Question 10
Incorrect
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An experiment is designed to investigate that how three diets having different sugar content affect the body weight to a different level.
Which one of the following test will determine a statistically significant difference among the diets?Your Answer: Chi squared test
Correct Answer: ANOVA
Explanation:Chi-square test is used to determine the statistically significant different between categorical variables. It also determines the difference between expected frequencies and the observed frequencies.
Mann Whitney U test is used to determine the statistically significant different between two independent groups.
Wilcoxon’s test is the test of dependency. it determines the statistically significant difference between two dependent groups.
Student t-test is one of the most commonly used method to test the hypothesis. It determines the significant difference between the means of two different groups.
ANOVA (analysis of variance) is similar to student’s t-test.
ANOVA is a statistical method used to determines the statistically significant difference between the mean of more than two group. In this experiment as we are dealing with three different group, ANOVA is most suitable test to determine the difference between each groups.
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This question is part of the following fields:
- Statistical Methods
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Question 11
Incorrect
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About low molecular weight (LMW) heparin, Which of these is true?
Your Answer: Inactivates thrombin more readily than unfractionated heparin
Correct Answer: Is excreted in the urine
Explanation:Low molecular weight heparin (LMWH) creates a complex by binding to antithrombin. This complex binds with and inactivates factor Xa.
There is less risk of bleeding with LMWH because it binds less to platelets, endothelium and von Willebrand factor.
LMW binds Xa more readily. The shorter chains are less likely to bind both antithrombin and thrombin.
There is need for monitoring in renal impairment because LMHW is excreted in the urine (and partly by hepatic metabolism)
LMWH have been shown to be as efficacious as unfractionated heparin. It is also safer and have improved inpatient stay and reduced hospital cost.
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This question is part of the following fields:
- Pharmacology
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Question 12
Incorrect
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A controlled retrospective study's level of evidence is?
Your Answer: Level 5
Correct Answer: Level 3
Explanation:Level 1 – High-quality randomised controlled trial with statistically significant difference or no statistically significant difference but narrow confidence intervals (prospective controlled)
Level 2 – Prospective comparative study (prospective uncontrolled)
Level 3 – Case-control study, retrospective comparative study (retrospective controlled)
Level 4 – Case series (retrospective uncontrolled)
Level 5 – Expert opinion.
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This question is part of the following fields:
- Statistical Methods
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Question 13
Incorrect
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In the fetal circulation, the cerebral and coronary circulations are preferentially supplied by oxygen-rich blood over other organs. This is possible because of which phenomenon?
Your Answer: The ductus venosus allows 60% of well oxygenated blood from the placenta to bypass the liver into the inferior vena cava
Correct Answer: Well oxygenated blood from the inferior vena cava is preferentially streamed across the patent foramen ovale
Explanation:During fetal development, blood oxygenated by the placenta flows to the foetus through the umbilical vein, bypasses the fetal liver through the ductus venosus, and returns to the fetal heart through the inferior vena cava.
Blood returning from the inferior vena cava then enters the right atrium and is preferentially shunted to the left atrium through the patent foramen ovale. Blood in the left atrium is then pumped from the left ventricle to the aorta. The oxygenated blood ejected through the ascending aorta is preferentially directed to the fetal coronary and cerebral circulations.
Deoxygenated blood returns from the superior vena cava to the right atrium and ventricle to be pumped into the pulmonary artery. Fetal pulmonary vascular resistance (PVR), however, is higher than fetal systemic vascular resistance (SVR); this forces deoxygenated blood to mostly bypass the fetal lungs. This poorly oxygenated blood enters the aorta through the patent ductus arteriosus and mixes with the well-oxygenated blood in the descending aorta. The mixed blood in the descending aorta then returns to the placenta for oxygenation through the two umbilical arteries.
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This question is part of the following fields:
- Physiology
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Question 14
Incorrect
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A 61-year-old woman, present to her general practitioner. She complains of a severe lancinating pain in her forehead that only last a few seconds, possibly triggered by washing her face, occurring over the previous six weeks.
On examination, she is normal with no other signs or symptoms.
Which nerve is the most likely cause of her pain?Your Answer:
Correct Answer: Sensory branches of the ophthalmic division of the trigeminal nerve
Explanation:Her symptoms are suggestive of trigeminal neuralgia which is a short, sudden, severe sharp unilateral pain in the facial region. The pain often follows the sensory distribution of the trigeminal nerve (CN V).
The trigeminal nerve gives rise to 3 sensory and 1 motor nuclei. Neuralgia can arise from any of the 3 sensory divisions.
The ophthalmic division gives rise to 3 further sensory branches, which are the frontal, lacrimal and nasociliary.
The frontal branch of the ophthalmic division of the trigeminal nerve is responsible for the innervation of the area in question.
The superior alveolar dental, zygomatic and sphenopalatine nerves are all branches arising from the maxillary division of the trigeminal nerve.
The mandibular division of the trigeminal nerve provides sensory and motor innervation. The sensory innervation is carried out by the auriculotemporal nerve which supplies the lower third of the face, while the motor fibres are responsible for controlling the muscles of mastication.
The somatic sensory branches of the vagus nerve are responsible for sensory innervation of the external acoustic meatus and tympanic membrane.
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This question is part of the following fields:
- Pathophysiology
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Question 15
Incorrect
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Regarding tracheal tubes, which of the following statements are true?
Your Answer:
Correct Answer: Uncuffed RAE tubes have two Murphy eyes
Explanation:Tracheal tubes are made of either disposable plastic or reusable red rubber.
The tube size refers to the internal diameter (ID) in mm which is marked on the outside of the tube (some manufacturers mark the external diameter on the outside).
Plastic tubes have a radiopaque line spanning the entire length of the tube, which allows their position to be identified on x-rays. The bevel located at the end of the tube is left-facing and oval in shape, which improves the view of the vocal cords during intubation.
Oxford tubes are L-shaped and have a bevel that faces posteriorly. They have thick walls that increase the external diameter, making for a wider internal diameter.
RAE (Ring, Adair, and Elwyn) tubes are preformed and can either be north or south facing and cuffed or uncuffed. The cuffed RAE tubes have one Murphy eye, whereas the uncuffed has two Murphy eyes. Uncuffed tubes are primarily used in paediatric anaesthesia and the two Murphy eyes ensure adequate ventilation- should the tube be too long.
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This question is part of the following fields:
- Anaesthesia Related Apparatus
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Question 16
Incorrect
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Which of the following statements is true regarding antibiotics?
Your Answer:
Correct Answer: Staphylococcus aureus colonises the nasopharynx in >20% of the general population
Explanation:Staphylococcus aureus colonizes the nasopharynx in >20% of the general population.
Methicillin-resistant Staphylococcus aureus (MRSA) is resistant to flucloxacillin.
Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.
All ?-lactam antibiotics like penicillin interfere with the synthesis of the bacterial cell walls. The ?-lactam antibiotics inhibit the transpeptidases so that cross-linking (which maintains the close-knit structure of the cell wall) does not take place
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This question is part of the following fields:
- Pharmacology
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Question 17
Incorrect
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It is safe to perform a central neuraxial block without an increased risk of developing a vertebral canal haematoma in?
Your Answer:
Correct Answer: A patient on clopidogrel 7 days after last dose
Explanation:The incidence of vertebral canal haematoma following neuraxial blockade was reported (third National Audit Project (NAP3)) as 0.85 per 100 000 (95% CI 0-1.8 per 100 000). The incidence following neuraxial blockade in coagulopathic patients is likely to be higher hence coagulopathy remains a relative contraindication for conducting a spinal or epidural. When indicate, risk and benefits are weighed, and it is only performed by experienced personnel in this case.
Acceptable time to perform a block after the last dose of rivaroxaban in a patient with a creatinine clearance of greater than 30mL/minute is 18 hours.
Acceptable time to perform a block after the last dose of subcutaneous LMWH as prophylaxis is 12 hours.
Acceptable time to perform a block after the last dose of subcutaneous UFH as prophylaxis is 4 hours.
Acceptable time to perform a block after the last dose of thrombolytic therapy (streptokinase or alteplase) is 10 days.
Clopidogrel should be stopped 7 days prior to surgery, particularly if a central neuraxial procedure is considered.
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This question is part of the following fields:
- Pathophysiology
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Question 18
Incorrect
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A chain smoker is interested in knowing how many years of his life would be lessened by smoking. You tell him explicitly that precise determination is impossible but you can tell him the proportion of people who died due to smoking. Which of the following epidemiological term is apt in this regard?
Your Answer:
Correct Answer: Attributable risk - the rate in the exposed group minus the rate in the unexposed group
Explanation:Attributable proportion is the proportion of disease that is caused due to exposure. It refers to the proportion of disease that would be eradicated from a particular population if the disease rate was diminished to match that of the unexposed group.
Risk ratio (relative risk) compares the probability of an event in an exposed (experimental) group to that of an event in the unexposed (control) group. Thus two are not the same.
The attributable risk is the rate of a disease in an exposed group to that of a group that has not been exposed to it i.e. how many deaths did the exposure cause.
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This question is part of the following fields:
- Statistical Methods
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Question 19
Incorrect
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A new study is being carried out on the measurement of a new cardiovascular disease biomarker, and its applications in preoperative screening. The data for this study is expected to be normally distributed.
Which of the following statements is true about normal distributions?Your Answer:
Correct Answer: The mean, median and mode are the same value
Explanation:The correct answer is the mean, median and mode of normally distributed data are the same value. This is as a result of the bell shaped curve which is equal on both sides.
The bell-shape indicates that values around the mean are more frequent in occurrence than the values farther away.
In a normal distribution:
1) +/- one standard deviation of the mean accounts for 68% of the data.
2) +/- two standard deviations of the mean accounts for 95% of the data.
3) +/- three standard deviations of the mean accounts for 99.7% of the data. -
This question is part of the following fields:
- Statistical Methods
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Question 20
Incorrect
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Which of the following statements is not true regarding Adrenaline?
Your Answer:
Correct Answer: Exerts its effect by decreasing intracellular calcium
Explanation:Noradrenaline also called norepinephrine belongs to the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter.
They have sympathomimetic effects acting via adrenoceptors (?1, ?2,?1, ?2, ?3) or dopamine receptors (D1, D2).
May cause reflex bradycardia, reduce cardiac output and increase myocardial oxygen consumption
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This question is part of the following fields:
- Pharmacology
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Question 21
Incorrect
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All the following statements are false regarding gabapentin except:
Your Answer:
Correct Answer: Requires dose adjustment in renal disease
Explanation:Therapy with gabapentin requires dose adjustment with renal diseases. However, plasma monitoring of the drug is not necessary.
Gabapentin is not a liver enzyme inducer unlike other anticonvulsants like phenytoin and phenobarbitone
Gabapentin has not been shown to be associated with visual disturbances.
Gabapentin is used for add-on therapy in partial or generalized seizures and used in the management of chronic pain conditions but is of no use in petit mal.
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This question is part of the following fields:
- Pharmacology
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Question 22
Incorrect
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All of the following are responses to massive haemorrhage except which of the following?
Your Answer:
Correct Answer: Decreased cardiac output by increased direct parasympathetic stimulation
Explanation:With regards to compensatory response to blood loss, the following sequence of events take place:
1. Decrease in venous return, right atrial pressure and cardiac output
2. Baroreceptor reflexes (carotid sinus and aortic arch) are immediately activated
3. There is decreased afferent input to the cardiovascular centre in medulla. This inhibits parasympathetic reflexes and increases sympathetic response
4. This results in an increased cardiac output and increased SVR by direct sympathetic stimulation. There is increased circulating catecholamines and local tissue mediators (adenosine, potassium, NO2)
5. Fluid moves into the intravascular space as a result of decreased capillary hydrostatic pressure absorbing interstitial fluid.A slower response is mounted by the hypothalamus-pituitary-adrenal axis.
6. Reduced renal blood flow is sensed by the intra renal baroreceptors and this stimulates release of renin by the juxta-glomerular apparatus.
7. There is cleavage of circulating Angiotensinogen to Angiotensin I, which is converted to Angiotensin II in the lungs (by Angiotensin Converting Enzyme ACE)Angiotensin II is a powerful vasoconstrictor that sets off other endocrine pathways.
8. The adrenal cortex releases Aldosterone
9. There is antidiuretic hormone release from posterior pituitary (also in response to hypovolaemia being sensed by atrial stretch receptors)
10. This leads to sodium and water retention in the distal convoluted renal tubule to conserve fluid
Fluid conservation is also aided by an increased amount of cortisol which is secreted in response to the increase in circulating catecholamines and sympathetic stimulation. -
This question is part of the following fields:
- Physiology And Biochemistry
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Question 23
Incorrect
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A 55-year-old woman presents for transsphenoidal surgery following a diagnosis of pituitary macroadenoma.
Which of the following is the most common visual field defect caused by such lesions?Your Answer:
Correct Answer: Bitemporal hemianopia
Explanation:Pituitary tumours that compress the optic chiasma primarily affect the neurones that decussate at this location. Bitemporal hemianopia is caused by neurones that emerge from the nasal half of the retina and transmit the temporal half of the visual field.
The axons of ganglion cells in the retina form the optic nerve.
It exits the orbit through the optic foramen and projects to the thalamic lateral geniculate body. The optic chiasma forms above the sella turcica as the nasal fibres decussate along the way. The optic radiation travels from the lateral geniculate body to the occipital cortex.
Lesions at various points along this pathway cause the following visual field defects:
Scotoma implies partial retinal or optic nerve damage.
Monocular vision loss occurs when the optic nerve is completely damaged.
Pathology at the optic chiasma causes bitemporal hemianopia.
Cortical blindness with occipital cortex pathology and homonymous hemianopia with lesions compromising the optic radiation. -
This question is part of the following fields:
- Pathophysiology
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Question 24
Incorrect
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Which of the following causes a left shift of the haemoglobin dissociation curve?
Your Answer:
Correct Answer:
Explanation:With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.
Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain.
There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions.
The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.The oxygen dissociation curve (ODC) describes the relationship between the percentage of saturated haemoglobin and partial pressure of oxygen in the blood.
Of note, it is not affected by haemoglobin concentration.Chronic anaemia causes 2, 3 DPG levels to increase, hence shifting the curve to the right
Haldane effect – Causes the ODC to shift to the left. For a given oxygen tension there is increased saturation of Hb with oxygen i.e. Decreased oxygen delivery to tissues.
This can be caused by:
-HbF, methaemoglobin, carboxyhaemoglobin
-low [H+] (alkali)
-low pCO2
-ow 2,3-DPG
-ow temperatureBohr effect – causes the ODC to shifts to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues. This can be caused by:
– raised [H+] (acidic)
– raised pCO2
-raised 2,3-DPG
-raised temperature -
This question is part of the following fields:
- Physiology And Biochemistry
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Question 25
Incorrect
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A 33-year-old woman known to be hypothyroid and taking 150 mcg l-thyroxine daily is reviewed in the preoperative assessment clinic prior to a laparoscopic cholecystectomy.
She has required three increases in her thyroid replacement therapy in the last six months.
Her thyroid function tests are as follows:
TSH 11 (normal range 0.4-4mU/L)
T3 20 (normal range 9-25mU/L)
T4 6.2 (normal range 3.5-7.8mU/L)
What will explain this biochemical picture?Your Answer:
Correct Answer: Poor compliance with medication
Explanation:In patients with an intact hypothalamic-pituitary axis, serial TSH measurements are used to determine the adequacy of treatment with thyroid hormones . changes in TSH levels becoming apparent after approximately eight weeks of therapy with thyroid hormone replacement. Change in T3/T4 levels are seen before changes in TSH .
In patients taking thyroid replacement therapy, the most frequent reason for persistent elevation of serum TSH is poor compliance. Patients who do not regularly take their L-thyroxine try and catch up just before a visit to a clinician for blood test.
Tissue-level unresponsiveness to thyroid hormone is caused by mutation in the gene controlling a receptor for T3 and is rare.
Reduced responsiveness of target tissues to thyroid hormone aka resistance to thyroid hormones (rTH) occurs when there is a mutation in the thyroid hormone receptor ? gene. It is a rare autosomal dominant inherited syndrome of reduced end-organ responsiveness to thyroid hormone and has two types:
Generalised resistance (GrTH)
Pituitary resistance (PrTH)Patients with rTH have normal or slightly elevated serum thyroid stimulating hormone (TSH) level, elevated serum free thyroxine (FT4) and free triiodothyronine (FT3) concentrations.
Drugs that increase metabolism of thyroxine include:
Warfarin
Rifampin
Phenytoin
Phenobarbital
St John’s Wort
CarbamazepineThese drugs lower circulating thyroid hormones and would be associated with a raised TSH but low T3/T4.
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This question is part of the following fields:
- Pathophysiology
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Question 26
Incorrect
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Which statement best describes the bispectral index (BIS)?
Your Answer:
Correct Answer: It decreases during normal sleep
Explanation:The bispectral index (BIS) is one of several systems used in anaesthesiology as of 2003 to measure the effects of specific anaesthetic drugs on the brain and to track changes in the patient’s level of sedation or hypnosis. It is a complex mathematical algorithm that allows a computer inside an anaesthesia monitor to analyse data from a patient’s electroencephalogram (EEG) during surgery. It is a dimensionless number (0-100) that is a summative measurement of time domain, frequency domain and high order spectral parameters derived from electroencephalogram (EEG) signals.
Sleep and anaesthesia have similar behavioural characteristics but are physiologically different but BIS monitors can be used to measure sleep depth. With increasing sleep depth during slow-wave sleep, BIS levels decrease. This correlates with changes in regional cerebral blood flow when measured using positron emission tomography (PET).
BIS shows a dose-response relationship with the intravenous and volatile anaesthetic agents. Opioids produce a clinical change in the depth of sedation or analgesia but fail to produce significant changes in the BIS. Ketamine increases CMRO2 and EEG activity.
BIS is unable to predict movement in response to a surgical stimulus. Some of these are spinal reflexes and not perceived by the cerebral cortex.
BIS is used during cardiopulmonary bypass to measure depth of anaesthesia and an index of cerebral perfusion. However, it cannot predict subtle or significant cerebral damage.
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This question is part of the following fields:
- Physiology
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Question 27
Incorrect
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A 19-year-old woman presents to the emergency department. She complains of symptoms indicative of an acute exacerbation of known 'brittle' asthma. On history, she reveals her asthma is normally controlled using inhalers and she has never had an acute exacerbation requiring hospitalisation.
On her admission into the ICU, further examination and diagnostic investigations are conducted. Her readings are:
Physical state: Alert, anxious and non-cyanotic.
Respiratory rate: 30 breaths/min
Pulse: 120 beats/min
Blood pressure: 150/90 mmHg
SPO2: 95% on air
Auscultation: Quiet breath sounds at both lung bases
What is the next most important step of investigation?Your Answer:
Correct Answer: Peak expiratory flow rate
Explanation:Peak expiratory flow rate (PEFR) is the maximum speed of air flow generated during a single forced exhaled breath. It is most useful when expressed as a percentage of the best value obtained from the patient.
Forced expiratory volume over 1 second (FEV1) is a lung parameter measured using spirometry. It is the amount of air forced out of the lung in one exhaled breath. It is a more accurate measure of lung obstructions as it doesn’t rely on effort like PEFR
PEFR and FEV1 are usually similar, but become more different in asthmatic patients as airflow becomes increasingly obstructed.
Acute severe asthma is most often diagnosed on history taking and examinations:
Respiratory rate: >25 breaths/min
Heart rate: >110 beats/min
PEFR: 33 – 50% predicted (<200L/min)
Patient state: Unable to complete a sentence in a single breath.A chest x-ray is not routinely required, and is only indicated in specific circumstances, which are:
If a pneumomediastinum or pneumothorax is suspected
Possible life threatening asthma
Possible consolidation
Unresponsive asthma
If ventilation is required.An echocardiograph (ECG) is not necessary in this case
Routine haematological and biochemical investigations are not urgent in this case as any abnormalities they detect will be secondary to the patient’s presentation.
An arterial blood gas (ABG) will only be indicated if SPO2 was <92% or if patient presented with life threatening symptoms.
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This question is part of the following fields:
- Clinical Measurement
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Question 28
Incorrect
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Using a negative feedback loop, Haem production is controlled by which of these enzymes?
Your Answer:
Correct Answer: ALA synthetase
Explanation:Heme a exists in cytochrome a and heme c in cytochrome c; they are both involved in the process of oxidative phosphorylation. 5′-Aminolevulinic acid synthase (ALA-S) is the regulated enzyme for heme synthesis in the liver and erythroid cells.
There are two forms of ALA Synthase, ALAS1, and ALAS2.
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This question is part of the following fields:
- Physiology
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Question 29
Incorrect
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A 52-year-old patient is brought to ER with a chief complaint of chest pain for two hours. Chest pain was tightness in nature, located in the centre of the chest and radiate into the neck and left arm. The patient otherwise looks fit and well.
Just after admitting the patient, he suffered VF cardiac arrest and is immediately defibrillated with the return of spontaneous circulation (ROSC).
On clinical examination following was the finding:
BP: 82/45 mmHg
Heart rate: 120 beats/min
Oxygen saturation on air: 25%
Heart sounds: Normal
There is no sign of pulmonary oedema. The patient is anxious, cold, and clammy.
A 12 lead ECG was done which revealed a sinus rhythm of 120 with ST-segment depression and T wave inversion in leads II, III, and aVF. Which of the following is considered best for the initial treatment of the patient?Your Answer:
Correct Answer: Oral aspirin
Explanation:This is a classical case of unstable angina or NSTEMI (Non-ST-elevation myocardial infarction). As soon as the diagnosis of unstable angina or NSTEMI is made the initial treatment is Aspirin and antithrombin therapy.
Betablocker is known to reduce mortality from acute myocardial infarction by reducing oxygen demand. If there is no contraindication (heart block, bradycardia, hypotension, severe left ventricular dysfunction, and asthma), a beta-blocker should be given early. This patient has hypotension and therefore metoprolol is contraindicated.
If three doses of nitroglycerine tablets or Nitrolingual sprays and intravenous beta-blockers too cannot relieve the symptoms intravenous Glyceryl Trinitrate (GTN) should be considered provided that there is no hypotension. But in this case, the patient is hypotensive, and therefore, it is contraindicated.
If the symptoms are not relieved after three serial doses of nitroglycerine or if symptoms recur despite adequate anti-anginal treatment morphine sulphate is indicated.
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This question is part of the following fields:
- Pathophysiology
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Question 30
Incorrect
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Which oral hypoglycaemic agent has no effect on insulin sensitivity or secretion?
Your Answer:
Correct Answer: Alpha glucosidase inhibitors
Explanation:Because alpha glucosidase inhibitors slow starch digestion in the small intestine, glucose from a meal enters the bloodstream more slowly and can be matched more effectively by an impaired insulin response or sensitivity, glucose from a meal enters the bloodstream more slowly and can be matched more effectively by an impaired insulin response or sensitivity.
Biguanides decrease hepatic glucose output while increasing glucose uptake in peripheral cells.
The meglitinides are secretagogues that act on a different site of the KATP receptors.
Insulin secretion is stimulated by sulphonylureas, which stimulate insulin secretion from pancreatic beta cells. The KATP channels are inhibited by these substances.
Insulin-sensitive genes are influenced by thiazolidinediones, which increase the production of mRNAs for insulin-dependent enzymes. As a result, the cells make better use of glucose.
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This question is part of the following fields:
- Pharmacology
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