Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 341: In which of the following conditions is the first heart sound loud?

A. Mitral regurgitation
B. Pregnancy
C. Anemia
D. Mitral stenosis (Correct Answer)

Explanation: **Explanation:** The **First Heart Sound (S1)** is primarily produced by the closure of the Atrioventricular (AV) valves (Mitral and Tricuspid) at the onset of ventricular systole. The intensity of S1 depends on the position of the leaflets at the start of systole and the rate of pressure rise in the ventricle. **Why Mitral Stenosis (MS) causes a Loud S1:** In MS, the elevated left atrial pressure keeps the mitral valve leaflets wide open throughout diastole. When ventricular systole begins, the leaflets must travel a greater distance to close, slamming shut with increased force. Additionally, in early MS, the leaflets remain pliable but thickened, creating a "snapping" sound upon closure. **Analysis of Incorrect Options:** * **Mitral Regurgitation (MR):** S1 is typically **soft or absent**. The leaflets often fail to coapt properly due to structural damage or calcification, leading to an inadequate "seal" and reduced sound intensity. * **Pregnancy & Anemia:** These are **hyperdynamic states**. While they can cause a loud S1 due to increased heart rate and contractility (shortened PR interval), **Mitral Stenosis** is the classic, definitive clinical condition associated with a "tapping" or loud S1 in exams. If multiple choices are present, MS is the most characteristic pathological cause. **High-Yield Clinical Pearls for NEET-PG:** * **Loud S1:** Mitral Stenosis, Short PR interval (Tachycardia, Wolff-Parkinson-White syndrome), and Hyperdynamic states. * **Soft S1:** Mitral Regurgitation, Long PR interval (First-degree heart block), and Heart Failure (reduced contractility). * **Variable S1:** Atrial Fibrillation and Complete Heart Block (due to varying AV valve positions). * **Key Sign in MS:** A loud S1, an Opening Snap, and a Mid-diastolic rumbling murmur.

Question 342: During ventricular systole, atrioventricular valves open and semilunar valves close. The statement is?

A. True
B. False (Correct Answer)
C. Partially true
D. Partially false

Explanation: ### Explanation **1. Why the statement is False:** Ventricular systole is the period of ventricular contraction. To ensure blood flows in the correct direction (from the ventricles into the great arteries), the pressure dynamics must change: * **AV Valves (Mitral and Tricuspid) Close:** As ventricular pressure rises above atrial pressure at the start of systole, the AV valves snap shut to prevent backflow (regurgitation) into the atria. This closure produces the **First Heart Sound (S1)**. * **Semilunar Valves (Aortic and Pulmonary) Open:** Once ventricular pressure exceeds the pressure in the aorta and pulmonary artery, these valves open to allow blood ejection. Therefore, the statement is exactly the opposite of physiological reality: during systole, AV valves are **closed** and semilunar valves are **open**. **2. Analysis of Incorrect Options:** * **Option A (True):** Incorrect because if AV valves were open during systole, blood would flow backward into the atria instead of the systemic/pulmonary circulation. * **Options C & D (Partially True/False):** These are distractors. In a normal cardiac cycle, the valve states are binary during the ejection phase of systole. There is no physiological phase where AV valves are open while semilunar valves are closed during systole. **3. High-Yield Clinical Pearls for NEET-PG:** * **Isovolumetric Contraction:** This is the earliest phase of systole where **all four valves are closed**. Pressure rises sharply, but volume remains constant. * **S1 vs. S2:** S1 (Lubb) marks the beginning of systole (AV closure); S2 (Dupp) marks the beginning of diastole (Semilunar closure). * **Pressure Gradient:** The Aortic valve opens when Left Ventricular pressure exceeds ~80 mmHg. * **Wiggers Diagram:** Always correlate valve movements with the pressure curves; the "c" wave in the atrial pressure tracing occurs due to the bulging of AV valves into the atria during isovolumetric contraction.

Question 343: Which of the following is an action of angiotensin II?

A. Systemic vasodilation (Correct Answer)
B. Systemic vasoconstriction
C. Renal vasodilation
D. Reabsorption of sodium ions in the proximal renal tubule

Explanation: **Explanation** Angiotensin II is a potent multifunctional hormone and a central component of the Renin-Angiotensin-Aldosterone System (RAAS). **Why Option B is Correct:** Angiotensin II acts primarily on **AT1 receptors** located on vascular smooth muscle cells. Its most immediate and potent effect is **systemic vasoconstriction** of the arterioles. This increases Total Peripheral Resistance (TPR), thereby rapidly elevating systemic blood pressure. **Analysis of Incorrect Options:** * **Option A & C:** Angiotensin II is a powerful **vasoconstrictor**, not a vasodilator. In the kidneys, it preferentially constricts the **efferent arterioles** more than the afferent arterioles to maintain Glomerular Filtration Rate (GFR) during states of low perfusion. * **Option D:** While Angiotensin II does promote sodium reabsorption, its primary direct action in the kidney is on the **Proximal Convoluted Tubule (PCT)** via the Na+/H+ exchanger. However, in the context of "classic" rapid systemic actions, vasoconstriction is its hallmark physiological effect. (Note: If the question asks for its effect on the adrenal cortex, it stimulates **Aldosterone** release, which acts on the Distal Tubule/Collecting Duct). **NEET-PG High-Yield Pearls:** * **Potency:** Angiotensin II is roughly 40-80 times more potent than Noradrenaline in raising blood pressure. * **Receptor Specificity:** Most known cardiovascular effects (vasoconstriction, aldosterone release, thirst) are mediated by **AT1 receptors**. AT2 receptors generally oppose these actions (vasodilation). * **ACE Inhibitors/ARBs:** These are first-line antihypertensives because they block the production or action of Angiotensin II, preventing systemic vasoconstriction. * **Dipsogenic Effect:** Angiotensin II acts on the subfornical organ in the brain to stimulate the **thirst center**.

Question 344: Coronary blood flow is regulated by which of the following mechanisms?

A. Sympathetic adrenergic system
B. Sympathetic cholinergic system
C. Local metabolic activity and reflexes (Correct Answer)
D. Parasympathetic system

Explanation: **Explanation:** The primary determinant of coronary blood flow is **local metabolic demand** (autoregulation). The heart is a highly aerobic organ with a high basal oxygen extraction rate (70-80%). Therefore, any increase in myocardial work must be met by an increase in blood flow rather than increased extraction. **1. Why the Correct Answer is Right:** When myocardial activity increases, local metabolites—most importantly **Adenosine**, but also $K^+$, $H^+$, $CO_2$, and lactate—accumulate. These act as potent vasodilators on the coronary arterioles. This "Active Hyperemia" ensures that blood supply matches the oxygen demand. Additionally, mechanical factors (reflexes) play a role, though metabolic control is the dominant force. **2. Why the Other Options are Wrong:** * **A & B (Sympathetic System):** While the heart has sympathetic innervation, its direct effect is weak. Sympathetic stimulation causes vasoconstriction (via $\alpha$-receptors), but this is immediately overridden by "functional sympatholysis"—where the increased heart rate and contractility produce metabolites that cause profound vasodilation. * **D (Parasympathetic System):** Vagal stimulation has a negligible direct effect on coronary vascular tone. **Clinical Pearls for NEET-PG:** * **Phasic Flow:** Coronary blood flow to the **Left Ventricle** is maximum during **Early Diastole** and minimum during Isovolumetric Contraction (due to mechanical compression of subendocardial vessels). * **Right Ventricle:** Flow is more uniform throughout the cardiac cycle because RV pressures are lower. * **Adenosine:** It is the most important local metabolic regulator of coronary blood flow. * **Coronary Steal Phenomenon:** Potent vasodilators (like Dipyridamole) can divert blood away from ischemic zones toward non-ischemic zones, worsening ischemia.

Question 345: Which of the following is a true statement about heart sounds S1 and S2?

A. S1 has a higher frequency and longer duration than S2.
B. S2 has a higher frequency and longer duration than S1.
C. S1 has a higher frequency but shorter duration compared to S2.
D. S2 has a higher frequency but shorter duration compared to S1. (Correct Answer)

Explanation: ### Explanation The characteristics of heart sounds are determined by the tension of the valves and the velocity of blood flow during closure. **1. Why Option D is Correct:** * **S1 (First Heart Sound):** Caused by the closure of the Atrioventricular (Mitral and Tricuspid) valves. These valves are relatively "floppy," and the pressure gradient rises more slowly at the start of systole. This results in a **lower frequency** (lower pitch) and a **longer duration** (approx. 0.14 seconds). It is often described as "Lubb." * **S2 (Second Heart Sound):** Caused by the closure of the Semilunar (Aortic and Pulmonary) valves. These valves are more rigid and close rapidly due to the high elastic recoil of the arteries. This rapid closure and high tension create a **higher frequency** (higher pitch) and a **shorter duration** (approx. 0.11 seconds). It is described as "Dupp." **2. Why Other Options are Incorrect:** * **Options A & C:** Incorrect because S1 is characterized by a lower frequency (pitch) than S2. * **Option B:** Incorrect because while S2 does have a higher frequency, it is shorter in duration, not longer. **3. NEET-PG High-Yield Pearls:** * **S1** is best heard at the **Apex** (Mitral area). It marks the beginning of ventricular systole. * **S2** is best heard at the **Base** (2nd intercostal space). It marks the beginning of ventricular diastole. * **Physiological Splitting of S2:** During inspiration, S2 splits into A2 and P2 because increased venous return to the right heart delays the closure of the pulmonary valve. * **S3 (Ventricular Gallop):** Occurs during the rapid filling phase; normal in children/athletes but pathological (volume overload/HF) in adults. * **S4 (Atrial Gallop):** Occurs during atrial contraction; always pathological, indicating a stiff/non-compliant ventricle (e.g., LV hypertrophy).

Question 346: How long does it take for diastolic blood pressure to return to normal after standing up?

A. 15-30 seconds
B. 30-60 seconds (Correct Answer)
C. 60-90 seconds
D. 90-120 seconds

Explanation: **Explanation:** When an individual moves from a supine to a standing position, approximately 500–1000 mL of blood pools in the lower extremities due to gravity. This leads to a transient decrease in venous return, stroke volume, and cardiac output. **Why Option B is correct:** The sudden drop in blood pressure triggers the **Baroreceptor Reflex**. High-pressure baroreceptors in the carotid sinus and aortic arch detect the decrease in stretch and decrease their firing rate to the medulla. This results in increased sympathetic outflow and decreased parasympathetic activity. The resulting peripheral vasoconstriction (increasing Total Peripheral Resistance) and increased heart rate work to restore blood pressure. While the initial compensatory response begins within seconds, it typically takes **30–60 seconds** for the diastolic blood pressure to stabilize and return to its baseline or slightly above-baseline level. **Analysis of Incorrect Options:** * **Option A (15-30 seconds):** This is the timeframe for the *initial* compensatory heart rate increase and the start of the reflex, but it is usually too brief for the diastolic pressure to fully stabilize. * **Options C & D (60-120 seconds):** These durations are too long for a healthy physiological response. If blood pressure takes this long to recover, it may indicate autonomic dysfunction or significant hypovolemia. **Clinical Pearls for NEET-PG:** * **Orthostatic Hypotension:** Defined as a sustained reduction in systolic BP of at least **20 mmHg** or diastolic BP of at least **10 mmHg** within 3 minutes of standing. * **The 30:15 Ratio:** In a normal response to standing, the heart rate peaks at the 15th beat and slows down by the 30th beat. A ratio of <1.03 is suggestive of autonomic neuropathy (common in Diabetes Mellitus). * **Key Mediator:** The primary neurotransmitter involved in this rapid stabilization is **Norepinephrine**, acting on alpha-1 receptors to cause vasoconstriction.

Question 347: Which of the following conditions is characterized by the absence of P waves on an electrocardiogram?

A. Atrial fibrillation (Correct Answer)
B. Congestive Cardiac Failure (CCF)
C. Atrial flutter
D. Paroxysmal Supraventricular Tachycardia (PSVT)

Explanation: ### Explanation **Correct Answer: A. Atrial Fibrillation** In **Atrial Fibrillation (AF)**, the normal organized electrical activity of the SA node is replaced by rapid, chaotic, and disorganized electrical impulses originating from multiple ectopic foci (often near the pulmonary veins). Because the atria do not contract as a single unit but rather "quiver," there is no coordinated atrial depolarization. Consequently, distinct **P waves are absent** on the ECG and are replaced by fine, irregular oscillations called **fibrillatory (f) waves**. The hallmark of AF is an "irregularly irregular" ventricular rhythm. **Analysis of Incorrect Options:** * **B. Congestive Cardiac Failure (CCF):** This is a clinical syndrome of pump failure. While CCF can lead to AF due to atrial stretch, it does not inherently cause the absence of P waves. The ECG may show signs of chamber hypertrophy or underlying ischemia, but P waves are typically present if the rhythm is sinus. * **C. Atrial Flutter:** This is characterized by a "re-entrant" circuit in the right atrium. Instead of absent P waves, it produces regular, rapid, and identical **"saw-tooth" waves** (F waves), usually at a rate of 250–350 bpm. * **D. PSVT:** This typically presents as a narrow-complex tachycardia. While P waves may be difficult to see because they are buried within or immediately follow the QRS complex (due to retrograde conduction), they are technically present or represented by pseudo-S or pseudo-R' waves. **High-Yield NEET-PG Pearls:** * **Atrial Fibrillation:** Look for the triad of **absent P waves**, **irregularly irregular R-R intervals**, and **variable pulse deficit**. * **Ashman Phenomenon:** A long R-R interval followed by a short R-R interval leading to an aberrantly conducted QRS (often RBBB morphology) in AF. * **Hyperkalemia:** Another critical condition where P waves may be absent (or flattened) along with tall tented T waves and widened QRS complexes.

Question 348: What is true regarding myocardial oxygen demand?

A. Inversely related to heart rate
B. Has a constant relation to external cardiac work
C. Directly proportional to the duration of systole (Correct Answer)
D. Is negligible at rest

Explanation: **Explanation:** Myocardial oxygen demand ($MVO_2$) is primarily determined by the energy required for ventricular contraction and the maintenance of wall tension. **Why Option C is Correct:** The duration of systole is a critical determinant of oxygen consumption. During systole, the heart performs its most energy-intensive work (isovolumetric contraction and ventricular ejection). The **Tension-Time Index (TTI)**, which is the area under the left ventricular pressure curve during systole, is a major correlate of $MVO_2$. Therefore, any increase in the duration of systole (e.g., in aortic stenosis) significantly increases oxygen demand. **Analysis of Incorrect Options:** * **Option A:** $MVO_2$ is **directly related** to heart rate. A higher heart rate increases the number of contractions per minute, leading to higher cumulative energy expenditure. * **Option B:** There is **no constant relation** to external work. The heart is "inefficient"; pressure work (overcoming afterload) consumes much more oxygen than volume work (cardiac output/stroke volume). This is why hypertensive patients have higher oxygen demands than athletes with high stroke volumes. * **Option D:** $MVO_2$ is **never negligible**. Even at rest, the heart has a high basal metabolic rate to maintain ionic gradients and internal basal metabolism, extracting 70-80% of oxygen from the blood (the highest extraction ratio in the body). **High-Yield NEET-PG Pearls:** 1. **Law of Laplace:** Wall Tension = (Pressure × Radius) / (2 × Wall Thickness). Increased wall tension is the #1 determinant of $MVO_2$. 2. **Oxygen Extraction:** Unlike other organs, the heart cannot increase oxygen extraction significantly during exercise (as it is already near maximum); it must increase **coronary blood flow** to meet demand. 3. **Most Energy Consuming Phase:** Isovolumetric contraction consumes the most oxygen relative to the work performed.

Question 349: Flare response in triple response occurs due to?

A. Vasodilation due to release of secondary mediators (Correct Answer)
B. Chemotaxis and adhesion of leucocytes to vessel wall
C. Direct vessel injury
D. Increased permeability

Explanation: The **Triple Response of Lewis** is a physiological reaction of the skin to firm stroking or mechanical injury. It consists of three stages: the Red Reaction, the Flare, and the Wheal. ### **Explanation of the Correct Answer** **Option A** is correct because the **Flare** (the spreading redness beyond the initial line of injury) is mediated by the **Axon Reflex**. When the skin is injured, sensory nerve endings are stimulated. The impulse travels orthodromically toward the spinal cord but also **antidromically** (backward) along collateral branches of the same sensory nerve. This triggers the release of **secondary mediators**, primarily **Substance P** and **Calcitonin Gene-Related Peptide (CGRP)**. These potent vasodilators act on local arterioles, causing them to dilate and create the characteristic spreading flush. ### **Analysis of Incorrect Options** * **Option B:** Chemotaxis and leucocyte adhesion are features of the late-phase inflammatory response and cellular migration, not the acute vascular changes seen in the triple response. * **Option C:** Direct vessel injury causes the initial **Red Reaction** (Stage 1), which is a localized capillary dilation due to mechanical stimulation, independent of the nerve supply. * **Option D:** Increased permeability leads to the **Wheal** (Stage 3). This is localized edema caused by histamine release from mast cells, increasing capillary permeability and leading to exudation of fluid. ### **High-Yield NEET-PG Pearls** * **Sequence:** Red Reaction (Capillary dilation) → Flare (Arteriolar dilation via Axon Reflex) → Wheal (Exudation/Edema). * **Mediator for Wheal:** Histamine. * **Mediator for Flare:** Substance P / CGRP (Axon Reflex). * **Clinical Note:** If the sensory nerve to the skin area is severed and allowed to degenerate, the **Flare response will be absent**, while the Red Reaction and Wheal may still occur.

Question 350: What percentage of the total blood volume is contained within the splanchnic vessels and venules?

A. 10-20%
B. 20-30% (Correct Answer)
C. 40-50%
D. 60-70%

Explanation: ### Explanation **1. Understanding the Correct Answer (B: 20-30%)** The venous system acts as the primary **capacitance reservoir** of the body, holding approximately 64% of the total blood volume. Within this system, the **splanchnic circulation** (comprising the blood supply to the gastrointestinal tract, liver, spleen, and pancreas) is the most significant reservoir. Under resting conditions, the splanchnic vessels and venules contain roughly **20-30% of the total blood volume**. This high capacity is due to the high compliance of the splanchnic veins, which can mobilize large amounts of blood into the systemic circulation during stress or hemorrhage via sympathetic-mediated venoconstriction. **2. Analysis of Incorrect Options** * **Option A (10-20%):** This is too low for the splanchnic bed. This range more closely represents the volume found in the entire pulmonary circulation (approx. 9-10%) or the heart (approx. 7%). * **Option C (40-50%):** This is an overestimation for a single regional reservoir. While the entire venous system holds >60%, the splanchnic portion specifically does not exceed 30% at rest. * **Option D (60-70%):** This represents the **total systemic venous volume** (the "stressed" and "unstressed" volume combined), not just the splanchnic component. **3. NEET-PG High-Yield Pearls** * **The "Blood Reservoir" Concept:** The liver and spleen are the most important organs within the splanchnic bed for blood storage. In humans, the liver can provide an additional 250-500 mL of blood during hemorrhage. * **Distribution of Blood Volume:** * Systemic Veins/Venules: ~64% (Highest) * Systemic Arteries: ~13% * Pulmonary Circulation: ~9% * Capillaries: ~5% (Lowest volume, but highest cross-sectional area) * Heart: ~7% * **Clinical Correlation:** During hypovolemic shock, sympathetic stimulation causes constriction of these splanchnic venules (via $\alpha_1$ receptors), shifting blood to the "central" circulation to maintain perfusion to the brain and heart.

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