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Question 1
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The arterial-venous oxygen (a-vO2) difference is the difference between the oxygen content of arterial blood (CaO2) and mixed-venous blood (CvO2).
At rest, which organ has the greatest a-vO2 difference?Your Answer: Heart
Explanation:At rest, the heart has the greatest a-vO2 difference, a high capillary to myocyte ratio, short diffusion distances, and a high mitochondrial density. The flow of blood through the coronary arteries is also tightly controlled. At rest, 70-80 percent of the oxygen available to the cardiac muscle is extracted, increasing to 90 percent during exercise.
The a-vO2 difference indicates the body’s or an individual organ’s ability to extract oxygen from the blood.
CaO2 is influenced by a number of factors, including Hb concentration, PaO2 and pulmonary diffusion capacity.
CvO2 is influenced by a number of factors, including capillary density, regional blood flow, heart, resting skeletal muscle, kidney, intestine and skin.
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This question is part of the following fields:
- Pathophysiology
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Question 2
Incorrect
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A 43-year old woman, presented to the emergency department. She has suffered trauma to her right orbital floor.
On examination, it is noted that her right eye is deviated upwards when compared to her left. She also has a deliberate tilt in her head to the left in an attempt to compensate for loss of intorsion.
This clinical sign is caused by damage to which of the following cranial nerves?Your Answer:
Correct Answer: Trochlear nerve
Explanation:The trochlear nerve (CN IV) is the fourth and smallest cranial nerve. It’s role is to provide somatic motor innervation of the superior oblique muscle which is responsible for oculomotion.
Injury to the trochlear nerve will result in vertical diplopia, which worsens when looking downwards or inwards. This diplopia presents as an upward deviation of the eye with a head tilt away from the site of the lesion.
The abducens nerve (CN VI) provides somatic motor innervation for the lateral rectus muscle which functions to abduct the eye. Injury to this nerve will cause diplopia and an inability to abduct the eye, causing the patient to have to rotate their head to look sideways.
The facial nerve (CN VII) provides sensory, motor and parasympathetic innervations. It’s motor aspect controls the muscles of facial expression. Damage will cause paralysis of facial expression.
The oculomotor nerve (CN III) provides motor and parasympathetic innervations. Its motor component controls most of the other extraocular muscles. Damage to it will result in ptosis, dilatation of the pupil and a down and out eye position.
The ophthalmic division of the trigeminal nerve (CN VI) is responsible for sensory innervation of skin, mucous membranes and sinuses of the upper face and scalp.
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This question is part of the following fields:
- Pathophysiology
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Question 3
Incorrect
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A 60-year-old male is being reviewed in the peri-operative assessment before total knee replacement. He had a history of a heart transplant 10 years back. His resting heart rate is 110 beats per minute. On examination, ECG showed sinus tachycardia.
Which of the following explains this tachycardia?Your Answer:
Correct Answer: Loss of parasympathetic innervation
Explanation:Normally, at rest vagal influence is dominant producing the heart rate of 60-80 beats per minute even if the intrinsic automaticity of Sinoatrial Node is 100-110 beats per minute.
The transplanted heart has no autonomic nervous supply. So, it will respond to endogenous and exogenous catecholamine. This loss of parasympathetic innervation is responsible for the tachycardia in this patient.
Hypokalaemia can cause myocardial excitability and potential for ventricular ectopic and supraventricular arrhythmias. Hypothyroidism is also unlikely to cause tachycardia in this patient.
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This question is part of the following fields:
- Pathophysiology
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Question 4
Incorrect
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Concerning drug dose and response, one of the following statements is correct?
Your Answer:
Correct Answer: Intrinsic activity determines maximal response
Explanation:Dose response curves are plotted as % response to drug against Logarithm of drug concentration. The graph is usually sigmoid shaped.
Any drug that has high affinity and high intrinsic activity is likely an agonist. A drug with high affinity but no intrinsic activity will act as an antagonist. Displacement of an agonist also depends on the relative concentrations of the two drugs at the receptor sites.
Maximal response may be achieved by activation of a small proportion of receptor sites.
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This question is part of the following fields:
- Pharmacology
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Question 5
Incorrect
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An intravenous infusion is started with a 500 mL bag of 0.18 percent N. saline and 4% dextrose.
Which of the following best describes its make-up?Your Answer:
Correct Answer: Osmolarity 284 mOsmol/L, sodium 15 mequivalents and glucose 20 g
Explanation:30 mmol Na+ and 30 mmol Cl- are found in 1 litre of 0.18 percent N. saline with 4% dextrose. Percent (percent) refers to the number of grammes of a compound per 100 mL, so a litre of 4 percent dextrose solution contains 40 grammes.
As a result, a 500 mL bag of 1/5th N. saline and 4% dextrose contains approximately 15 mequivalents of sodium and 20 g of glucose. It is hypotonic due to its osmolarity of 284.
Because of the risk of hyponatraemia, it is no longer considered the crystalloid of choice for fluid maintenance in children.
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This question is part of the following fields:
- Physiology
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Question 6
Incorrect
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Which of the given statements is true about standard error of the mean?
Your Answer:
Correct Answer: Gets smaller as the sample size increases
Explanation:The standard error of the mean (SEM) is a measure of the spread expected for the mean of the observations – i.e. how ‘accurate’ the calculated sample mean is from the true population mean. The relationship between the standard error of the mean and the standard deviation is such that, for a given sample size, the standard error of the mean equals the standard deviation divided by the square root of the sample size.
SEM = SD / square root (n)
where SD = standard deviation and n = sample size
Therefore, the SEM gets smaller as the sample size (n) increases.
If we want to depict how widely scattered some measurements are, we use the standard deviation. For indicating the uncertainty around the estimate of the mean, we use the standard error of the mean. The standard error is most useful as a means of calculating a confidence interval. For a large sample, a 95% confidence interval is obtained as the values 1.96×SE either side of the mean.
A 95% confidence interval:
lower limit = mean – (1.96 * SEM)
upper limit = mean + (1.96 * SEM)
Results such as mean value are often presented along with a confidence interval. For example, in a study the mean height in a sample taken from a population is 183cm. You know that the standard error (SE) (the standard deviation of the mean) is 2cm. This gives a 95% confidence interval of 179-187cm (+/- 2 SE).
Hence, it would be wrong to say that confidence levels do not apply to standard error of the mean.
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This question is part of the following fields:
- Statistical Methods
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Question 7
Incorrect
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When combined with a general anaesthetic or central neuraxial block, which of the following medications used to treat dementia involves the risk of significant hypotension?
Your Answer:
Correct Answer: Risperidone
Explanation:Atypical antipsychotic drugs include risperidone and quetiapine. They not only inhibit dopamine receptors in the limbic system, but also histamine (H1) and alpha2 adrenoreceptors. When combined with general and/or central neuraxial block, this might result in severe hypotension.
Donepezil (Aricept) is an acetylcholinesterase (AChE) inhibitor that increases the neurotransmitter acetylcholine in the cerebral cortex and hippocampus in a reversible, non-competitive manner. It is used to reduce the advancement of Alzheimer’s disease symptoms (AD). Rivastigmine and galantamine are two more drugs that work in the same way.
Ginkgo Biloba contains anti-oxidant characteristics and is used to treat early-stage Alzheimer’s disease, vascular dementia, and peripheral vascular disease. It lowers platelet adhesiveness and decreases platelet activating factor (PAF) increasing the risk f bleeding, especially in individuals who are also taking anticoagulants and antiplatelet medication.
Memantine is an antagonist of the NMDA receptor. Synaptic plasticity, which is thought to be a critical component of learning and memory, can be inhibited at high doses. The use of ketamine is a relative contraindication since antagonism of this receptor can cause a dissociative state.
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This question is part of the following fields:
- Pharmacology
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Question 8
Incorrect
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A 54-year-old man weighing 70kg, underwent mesh repair for inguinal hernia under general anaesthesia. He was given intravenous co-amoxiclav (Augmentin) following which the patient developed widespread urticarial ras, became hypotensive (61/30 mmHg), and showed clinical signs of bronchospasm. Anaphylaxis is suspected in this patient.
Which one of the following is considered as best initial pharmacological treatment for this condition?Your Answer:
Correct Answer: Intravenous adrenaline 50 mcg
Explanation:The drug of choice for the treatment of anaphylaxis is adrenaline. It has an intravenous route of administration. Since the patient already has intravenous access, the intramuscular route is not appropriate.
Second-line pharmacological intervention includes the use of chlorpheniramine 10mg intravenous, Hydrocortisone 200mg.
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This question is part of the following fields:
- Pharmacology
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Question 9
Incorrect
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An 80-year-old man will be operated on for an arterial bypass procedure to treat claudication and foot ulceration. The anterior tibial artery will be the target for distal arterial anastomosis.
Which structure is NOT closely related to the anterior tibial artery?Your Answer:
Correct Answer: Tibialis posterior
Explanation:The anterior tibial artery originates from the distal border of the popliteus. In the posterior compartment, it passes between the heads of the tibialis posterior and the oval aperture of the interosseous membrane to reach the anterior compartment.
On entry into the anterior compartment, it runs medially along the deep peroneal nerve.
The upper third of the artery courses between the tibialis anterior and extensor digitorum longus muscles, while the middle third runs between the tibialis anterior and extensor hallucis longus muscles.At the ankle, the anterior tibial artery is located approximately midway between the malleoli. It continues on the dorsum of the foot, lateral to extensor hallucis longus, as the dorsalis pedis artery.
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This question is part of the following fields:
- Anatomy
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Question 10
Incorrect
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With regards to this state of matter which has a volume but no definite shape, particles are not tightly packed together. These are incompressible although there is free movement within the volume.
This statement best describes which one of the following states of matter?Your Answer:
Correct Answer: Liquid
Explanation:The solid state of matter has a definite volume and shape and particles are packed closely together and are incompressible. Within this tight lattice, there is enough thermal energy to produce vibration of particles.
Liquids however have a volume but no definite shape. These particles are less tightly packed together. Although there is free movement within the volume, they are incompressible.
Gases, however, have no finite shape or volume and particles are free to move rapidly in a state of random motion. They are compressible and are completely shaped by the space in which they are held. Vapours exist as a gas phase in equilibrium with identical liquid or solid matter below its boiling point.
The most prevalent state of matter in the universe is plasma which is formed by heating atoms to very high temperatures to form ions.
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This question is part of the following fields:
- Basic Physics
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