Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 831: Where is the highest oxygen concentration present in fetal circulation

A. SVC
B. IVC (Correct Answer)
C. Right ventricle
D. Aorta

Explanation: ***Correct: IVC (Inferior Vena Cava)*** - The IVC has the **highest oxygen concentration (~67% saturation)** among the vessels listed in fetal circulation - It receives **oxygenated blood from the placenta** via the umbilical vein, which continues as the ductus venosus and drains into the IVC - This well-oxygenated blood is preferentially shunted through the **foramen ovale** to the left atrium, then to the left ventricle and ascending aorta to supply the brain and heart *Incorrect: SVC (Superior Vena Cava)* - Carries **deoxygenated blood** from the upper body with oxygen saturation of only ~40% - Returns systemic venous blood without placental oxygenation *Incorrect: Right Ventricle* - Contains **mixed blood** from both SVC (deoxygenated) and IVC (oxygenated) - Has intermediate oxygen saturation (~52%) lower than the IVC alone *Incorrect: Aorta* - The **descending aorta** receives poorly oxygenated blood (~58%) from the ductus arteriosus - Even the ascending aorta (~62%) has slightly lower saturation than the IVC - The question asks for the highest concentration, which is the IVC before mixing occurs

Question 832: Which of the following does NOT significantly contribute to the regulation of cerebral blood flow?

A. Arterial PCO2
B. Potassium ions (Correct Answer)
C. Blood pressure
D. None of the options

Explanation: ***Potassium ions*** - While potassium channels play a role in vascular smooth muscle function, extracellular **potassium ion concentration** does not significantly regulate overall cerebral blood flow within physiological ranges. - Changes in systemic potassium levels typically have more pronounced effects on cardiac and neuromuscular function compared to direct, significant regulation of cerebral vasculature. *Arterial PCO2* - **Arterial PCO2** is a potent regulator of cerebral blood flow; an increase in PCO2 leads to **vasodilation** and increased cerebral blood flow, while a decrease causes vasoconstriction. - This effect is mediated by changes in brain extracellular pH, which influences the tone of cerebral arterioles. *Blood pressure* - **Cerebral autoregulation** maintains stable cerebral blood flow despite changes in mean arterial blood pressure between approximately 60 and 150 mmHg. - Outside this range, very high or low **blood pressure** directly influences cerebral perfusion, making it a critical factor in cerebral blood flow regulation. *None of the options* - This option is incorrect because **potassium ions** do qualify as a factor that does NOT significantly contribute to cerebral blood flow regulation, making it the correct answer to this question.

Question 833: What is the effect of the Bainbridge reflex?

A. Bradycardia
B. Increased cardiac output
C. Decreased venous return
D. Increased heart rate (Correct Answer)

Explanation: ***Increased heart rate*** - The **Bainbridge reflex** produces an increase in heart rate (tachycardia). - This reflex is triggered by an increase in **venous return** and **atrial distension**, which stimulates stretch receptors in the atria, leading to increased heart rate. - The reflex helps prevent venous pooling and maintains efficient cardiac function. *Bradycardia* - **Bradycardia** (slow heart rate) is the opposite effect of the Bainbridge reflex. - Other reflexes like the **baroreceptor reflex** can cause bradycardia when arterial pressure increases. *Increased cardiac output* - While increased heart rate can contribute to **increased cardiac output**, this is a secondary consequence, not the primary effect of the reflex. - Cardiac output = Heart rate × Stroke volume, so the direct effect is on heart rate. *Decreased venous return* - The Bainbridge reflex does not cause decreased venous return. - Instead, the reflex is **triggered by increased** venous return and responds by increasing heart rate to accommodate the increased blood flow.

Question 834: In the context of the jugular venous pulse, the C wave is seen during which phase of the cardiac cycle?

A. Slow filling at end of diastole
B. End of systole
C. Start of diastole
D. Isovolumetric contraction (Correct Answer)

Explanation: ***Isovolumetric contraction*** - The **C wave** of the jugular venous pulse is caused by the bulging of the **tricuspid valve** into the right atrium during the **isovolumetric contraction** phase of the right ventricle. - This phase occurs just after the onset of ventricular contraction but before the pulmonary valve opens. *Slow filling at end of diastole* - This is not associated with the C wave. The slow filling phase of diastole (diastasis) occurs much earlier in the cardiac cycle. - The C wave occurs during early ventricular systole, specifically during isovolumetric contraction. *End of systole* - This period is typically associated with the **y descent**, as the tricuspid valve opens and atrial emptying occurs rapidly into the ventricle. - The C wave occurs at the beginning of systole, not at the end. *Start of diastole* - The start of diastole is characterized by the **opening of the tricuspid valve** and rapid ventricular filling, leading to the **y descent**. - The **C wave** specifically occurs during ventricular contraction (systole), not during the start of diastolic relaxation and filling.

Question 835: In hypovolemic shock there is -

A. Efferent arteriolar constriction
B. Increased blood flow to kidney
C. Decreased cardiac output (Correct Answer)
D. Afferent arteriolar constriction

Explanation: ***Decreased cardiac output*** - **Hypovolemic shock** is fundamentally defined by **decreased circulating blood volume**, which leads to **decreased venous return** to the heart. - According to the **Frank-Starling mechanism**, decreased venous return leads to **decreased preload**, which results in **decreased stroke volume** and consequently **decreased cardiac output**. - This is the **primary hemodynamic characteristic** of hypovolemic shock and is present in ALL cases. - Decreased cardiac output triggers all the compensatory mechanisms seen in hypovolemic shock, including sympathetic activation and RAAS activation. *Afferent arteriolar constriction* - While afferent arteriolar constriction does occur in hypovolemic shock due to **sympathetic activation**, it is a **compensatory response** rather than the primary feature. - The predominant effect at the kidney level is actually a combination of both afferent and efferent arteriolar changes. - This occurs secondary to the decreased cardiac output. *Efferent arteriolar constriction* - **Efferent arteriolar constriction** is mediated primarily by **angiotensin II** and is actually MORE prominent than afferent constriction. - This helps **maintain glomerular filtration rate (GFR)** despite reduced renal blood flow by increasing glomerular hydrostatic pressure. - However, this is also a compensatory response, not the primary feature of hypovolemic shock. *Increased blood flow to kidney* - This is incorrect as hypovolemic shock causes **decreased renal blood flow**. - Blood is redistributed away from the kidneys to vital organs like the heart and brain through compensatory vasoconstriction.

Question 836: Cardiac output in pregnancy shows significant increase from which week of gestation

A. 25 weeks
B. 35 weeks
C. 5 weeks
D. 15 weeks (Correct Answer)

Explanation: ***15 weeks*** - Cardiac output shows a **significant and clinically measurable increase around 10-15 weeks of gestation**, which continues to rise, peaking between **20-28 weeks**. - This rise is primarily due to an increase in both **stroke volume** (increased by 25-30%) and **heart rate** (increased by 10-15 bpm) to meet the metabolic demands of the growing fetus and placenta. - By 15 weeks, cardiac output has typically increased by approximately **20-30% above pre-pregnancy levels**. *5 weeks* - While cardiac output does begin to rise very early in pregnancy (as early as 5-8 weeks), the increase at this stage is **subtle and not yet significant**. - At 5 weeks, the **placental circulation is still in early development**, and the hemodynamic changes are just beginning. - The question asks about **significant increase**, which is not yet established at 5 weeks. *25 weeks* - By 25 weeks, cardiac output has already completed its major rise and is at or near its **peak levels** (40-50% above baseline). - The **significant increase had already occurred** much earlier, around 10-15 weeks. - This timing represents the plateau phase rather than the initial significant increase. *35 weeks* - At 35 weeks, cardiac output remains elevated at near-peak levels but the **major increase happened much earlier** in pregnancy. - By this gestational age, the cardiovascular system has been adapted for months. - There may be minor positional variations (e.g., aortocaval compression in supine position) but no new significant increase occurs.

Question 837: What is the primary change in fetal circulation that occurs at birth?

A. Closure of the ductus venosus
B. Increased activity of the right ventricle
C. Closure of the foramen ovale (Correct Answer)
D. Closure of the patent ductus arteriosus

Explanation: ***Closure of the foramen ovale*** - The **foramen ovale** undergoes functional closure within minutes of birth, making it the **primary immediate circulatory change** - At birth, the first breath causes **dramatic decrease in pulmonary vascular resistance** and **increased pulmonary blood flow**, which raises **left atrial pressure** - Simultaneously, umbilical cord clamping **increases systemic vascular resistance** and **decreases right atrial pressure** (loss of placental return) - This **pressure gradient reversal** (left atrial pressure > right atrial pressure) causes the **septum primum** to be pushed against the **septum secundum**, achieving functional closure - This immediately separates the systemic and pulmonary circulations, which is the **most critical primary change** in transitioning from fetal to neonatal circulation *Closure of the patent ductus arteriosus* - The **ductus arteriosus** undergoes **functional closure over 10-15 hours** after birth, followed by **anatomical closure over 2-3 weeks** - Closure occurs due to increased arterial oxygen tension and decreased prostaglandin E2 levels, causing smooth muscle constriction - While important, this is a **secondary change** that occurs more gradually compared to the immediate foramen ovale closure *Closure of the ductus venosus* - The **ductus venosus** closes functionally within 3-7 days as umbilical venous flow ceases - This redirects portal blood through the liver but does not directly impact the critical pulmonary-systemic circulation separation *Increased activity of the right ventricle* - After birth, the **left ventricle** becomes dominant as it pumps against higher systemic vascular resistance - The right ventricle actually experiences **decreased afterload** due to falling pulmonary vascular resistance - This is a consequence of, not the primary change in, the circulatory transition

Question 838: What is the most common mechanism responsible for causing arrhythmias in the heart?

A. Re-entry (Correct Answer)
B. Early after depolarization
C. Late after depolarization
D. Automaticity

Explanation: ***Re-entry*** - **Re-entry** is the most common mechanism for arrhythmias and involves a re-excitation of cardiac tissue due to a circulating electrical impulse. - This requires at least two pathways with differing conduction velocities and refractory periods, creating a path for the impulse to re-excite an area after its normal refractory period has ended. *Early after depolarization* - **Early afterdepolarizations (EADs)** occur during phase 2 or 3 of the action potential when repolarization is incomplete, often due to prolonged action potential duration. - They are typically associated with conditions like **long QT syndrome** and can trigger polymorphic ventricular tachycardia, but are less common than re-entry. *Late after depolarization* - **Late afterdepolarizations (DADs)** occur during phase 4 of the action potential, after repolarization is complete, due to excessive intracellular calcium. - They are often seen in conditions like **digoxin toxicity** or **catecholaminergic polymorphic ventricular tachycardia**, but are not the most prevalent mechanism. *Automaticity* - **Abnormal automaticity** refers to pacemaker activity arising in non-pacemaker cells or an acceleration of normal pacemaker activity. - While it can cause arrhythmias such as accelerated idioventricular rhythm, re-entry is far more frequently implicated in the etiology of clinical arrhythmias.

Question 839: Aortic valve closure occurs in which part of cardiac cycle?

A. Beginning of isovolumetric contraction
B. During rapid ventricular filling
C. Beginning of ventricular ejection
D. Beginning of isovolumetric relaxation (Correct Answer)

Explanation: ***Beginning of isovolumetric relaxation*** - Aortic valve closure marks the end of **ventricular systole** and the start of **isovolumetric relaxation**, as blood ceases to be ejected and the ventricle begins to relax while remaining closed. - This event corresponds to the **second heart sound (S2)** and signifies the beginning of a period where ventricular volume remains constant, but pressure drops. *Beginning of isovolumetric contraction* - This phase begins with the closure of the **mitral and tricuspid valves** (first heart sound, S1), as ventricular pressure rises but volume remains constant before ejection. - The aortic valve is still closed at this point, as ventricular pressure is not yet high enough to open it. *Beginning of ventricular ejection* - This phase begins when the **aortic valve opens** as ventricular pressure exceeds aortic pressure, allowing blood to be ejected from the left ventricle. - Aortic valve closure occurs *after* ejection, not at its beginning. *During rapid ventricular filling* - Rapid ventricular filling occurs when the **mitral valve opens** (following isovolumetric relaxation), allowing blood to flow from the atria into the ventricles. - During this phase, the aortic valve is closed, but its closure happened earlier, at the beginning of isovolumetric relaxation.

Question 840: Which of the following factors is most commonly targeted therapeutically for blood pressure control?

A. Heart rate
B. Peripheral resistance (Correct Answer)
C. Cardiac output
D. Stroke volume

Explanation: ***Peripheral resistance*** - **Peripheral resistance** is primarily determined by the **arteriolar tone**, which can be effectively modulated by various antihypertensive medications. - Medications like **ACE inhibitors**, **ARBs**, **calcium channel blockers**, and **diuretics** all influence peripheral resistance to lower blood pressure. *Heart rate* - While heart rate contributes to **cardiac output** and thus blood pressure, it is not the most common primary target for hypertension management. - **Beta-blockers** reduce heart rate, but they are often used for specific indications beyond essential hypertension, such as angina or post-MI. *Cardiac output* - **Cardiac output** is a product of **heart rate** and **stroke volume**, and while it directly impacts blood pressure, directly targeting cardiac output as a whole is less common than modulating its individual components or peripheral resistance. - Many antihypertensive drugs reduce cardiac output as a secondary effect of reducing blood volume or heart rate, but directly reducing cardiac output is not the primary mechanism for the most common medications. *Stroke volume* - **Stroke volume** is influenced by **preload**, **afterload**, and **contractility**, and while it impacts cardiac output, it is generally less accessible for direct pharmacological manipulation in hypertension management compared to peripheral resistance. - **Diuretics** can indirectly reduce stroke volume by decreasing preload, but this is often considered a mechanism related to volume status rather than a direct myocardial effect.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Hemodynamics and Blood Flow

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Arterial System Physiology

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Microcirculation and Lymphatics

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Venous Return and Central Venous Pressure

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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