Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 511: Cardiac index is defined as:

A. Stroke volume/m 2/BSA
B. Cardiac output per minute per unit body surface area (Correct Answer)
C. Systolic pressure/m 2 BSA
D. End diastolic volume

Explanation: **Explanation:** **Cardiac Index (CI)** is a hemodynamic parameter that relates the Cardiac Output (CO) to an individual's body size, specifically their **Body Surface Area (BSA)**. Since a larger person requires more blood flow than a smaller person, the absolute Cardiac Output (L/min) is not a standardized measure of heart performance across different patients. By dividing CO by BSA, we get a standardized value that allows for accurate comparison between individuals of different sizes. * **Formula:** $CI = \frac{\text{Cardiac Output}}{\text{Body Surface Area}}$ * **Normal Range:** Approximately **2.5 to 4.2 L/min/m²**. **Analysis of Incorrect Options:** * **Option A:** Stroke volume per $m^2$ BSA is known as the **Stroke Index**. While related, it measures the volume per beat rather than the total output per minute. * **Option C:** Systolic pressure is a measure of force/tension in the arteries, not a measure of flow or volume relative to body size. * **Option D:** End Diastolic Volume (EDV) is the volume of blood in the ventricles at the end of filling; it is a measure of **Preload**, not an index of output. **High-Yield Clinical Pearls for NEET-PG:** * **Significance:** CI is a more accurate indicator of whether the heart is meeting the body's metabolic demands than Cardiac Output alone. * **Cardiogenic Shock:** A CI of **< 2.2 L/min/m²** in the presence of elevated pulmonary capillary wedge pressure is a diagnostic hallmark of cardiogenic shock. * **BSA Calculation:** Most commonly calculated using the **Mosteller formula** or the **DuBois formula** in clinical practice.

Question 512: A patient presents with a right-to-left shunt. The oxygen content in the arterial and venous blood is 18 ml/100 ml and 14 ml/100 ml, respectively. The oxygen content at the pulmonary capillary is 20 ml/100 ml. What is the percentage of shunting of cardiac output?

A. 23%
B. 33% (Correct Answer)
C. 43%
D. 53%

Explanation: ### Explanation **1. Understanding the Shunt Equation** The percentage of cardiac output that is shunted (bypassing oxygenation in the lungs) is calculated using the **Berggren Shunt Equation**: $$Qs/Qt = (CcO₂ - CaO₂) / (CcO₂ - CvO₂)$$ Where: * **Qs:** Shunted blood flow * **Qt:** Total cardiac output * **CcO₂:** Oxygen content of pulmonary capillary blood (ideal) = **20 ml/100 ml** * **CaO₂:** Oxygen content of arterial blood = **18 ml/100 ml** * **CvO₂:** Oxygen content of mixed venous blood = **14 ml/100 ml** **Calculation:** * Numerator (CcO₂ - CaO₂): 20 - 18 = **2** * Denominator (CcO₂ - CvO₂): 20 - 14 = **6** * Ratio: 2 / 6 = **1/3** * Percentage: 1/3 × 100 = **33.33%** **2. Analysis of Options** * **Option B (33%) is Correct:** This matches the mathematical derivation of the shunt fraction. * **Options A, C, and D (23%, 43%, 53%) are Incorrect:** These values result from calculation errors, such as incorrectly swapping the arterial and venous values or using the wrong denominator (e.g., using CaO₂ - CvO₂ as the denominator). **3. Clinical Pearls & High-Yield Facts** * **Physiological Shunt:** In healthy individuals, a small shunt (1–2%) exists due to the **Thebesian veins** (draining the myocardium into the left ventricle) and **bronchial veins** (draining into pulmonary veins). * **Right-to-Left Shunt:** Characterized by blood bypassing ventilated alveoli, leading to **hypoxemia** that is typically **refractory to supplemental oxygen** (unlike V/Q mismatch). * **Clinical Examples:** Cyanotic congenital heart diseases (e.g., Tetralogy of Fallot) or pulmonary conditions like ARDS where alveoli are collapsed or filled with fluid. * **Key NEET-PG Concept:** If the shunt fraction exceeds 30%, hypoxemia becomes severe and usually requires mechanical intervention rather than just increasing FiO₂.

Question 513: The Bezold-Jarish reflex response is characterized by which of the following?

A. Tachycardia
B. Bradycardia (Correct Answer)
C. Hypertension
D. None of the above

Explanation: The **Bezold-Jarisch Reflex (BJR)** is a cardio-inhibitory reflex originating from sensory receptors (chemoreceptors and mechanoreceptors) located in the ventricular walls, particularly the inferoposterior wall of the left ventricle. ### **Mechanism of the Correct Answer** The reflex is triggered by chemical stimuli (e.g., serotonin, alkaloids, or contrast media) or mechanical stimuli (e.g., severe hypovolemia). These stimuli activate non-myelinated **C-fibers**, which transmit signals via the **Vagus nerve** to the Nucleus Tractus Solitarius (NTS) in the medulla. This results in a massive increase in parasympathetic (vagal) outflow and a decrease in sympathetic tone, leading to the classic triad of: 1. **Bradycardia** (due to SA node inhibition) 2. **Hypotension** (due to peripheral vasodilation) 3. **Apnea** (brief respiratory inhibition) ### **Why Other Options are Incorrect** * **A. Tachycardia:** This is the opposite of the BJR. Tachycardia is typically seen in the *Bainbridge reflex* (response to increased atrial stretch/volume) or the *Baroreceptor reflex* in response to hypotension. * **C. Hypertension:** The BJR causes profound vasodilation and a drop in cardiac output, leading to **hypotension**, not hypertension. ### **High-Yield Clinical Pearls for NEET-PG** * **Myocardial Infarction:** The BJR is most commonly seen in **Inferior Wall MI** because the receptors are concentrated in the inferior/posterior wall. This explains why these patients often present with bradycardia. * **Spinal Anesthesia:** BJR is a common cause of sudden bradycardia and collapse after spinal anesthesia due to decreased venous return (hypovolemia triggering the reflex). * **Contrast Agents:** Coronary angiography can trigger this reflex, leading to transient bradycardia. * **Key Distinction:** Remember **B**ezold-Jarisch = **B**radycardia; **B**ainbridge = **B**oost in heart rate (Tachycardia).

Question 514: Which of the following statements about the vasomotor centre is true?

A. Independent of hypothalamic inputs
B. Influenced by baroreceptor signals but not by chemoreceptors
C. Acts along with the cardiovagal centre to maintain blood pressure (Correct Answer)
D. Essentially silent during sleep

Explanation: The **Vasomotor Centre (VMC)**, located in the reticular formation of the medulla oblongata, is the primary neural regulator of blood pressure. ### **Explanation of the Correct Answer** **Option C** is correct because blood pressure regulation is a coordinated effort between the **VMC** (which controls sympathetic outflow to the heart and blood vessels) and the **Cardiovagal Centre** (Nucleus Ambiguus and Dorsal Motor Nucleus of Vagus, which control parasympathetic outflow). To maintain homeostasis, these centers act reciprocally: for instance, when BP rises, the VMC is inhibited (vasodilation) while the cardiovagal center is stimulated (bradycardia). ### **Analysis of Incorrect Options** * **Option A:** The VMC is **highly dependent** on higher centers. The hypothalamus (especially the posterior and lateral nuclei) sends potent excitatory or inhibitory signals to the VMC during stress, exercise, and temperature changes. * **Option B:** The VMC receives inputs from **both** baroreceptors (detecting pressure changes) and chemoreceptors (detecting hypoxia, hypercapnia, and acidosis). Chemoreceptors stimulate the VMC to increase BP during respiratory distress. * **Option D:** The VMC is **never silent**. It maintains a continuous state of partial contraction in blood vessels known as **vasomotor tone**. While its activity decreases during sleep, it remains active to prevent circulatory collapse. ### **High-Yield Facts for NEET-PG** * **Components of VMC:** It consists of the **RVLM** (Rostral Ventrolateral Medulla - Pressor area), **CVLM** (Caudal Ventrolateral Medulla - Depressor area), and the **NTS** (Nucleus Tractus Solitarius - Sensory area). * **Neurotransmitter:** The RVLM uses **Glutamate** to excite sympathetic preganglionic neurons. * **Cushing Reflex:** A clinical manifestation where increased intracranial pressure leads to VMC stimulation, resulting in hypertension and reflex bradycardia.

Question 515: Which cardiovascular parameter is the best indicator of vagal tone?

A. Heart rate (Correct Answer)
B. Stroke volume
C. Ejection fraction
D. Diastolic blood pressure

Explanation: ### Explanation **Why Heart Rate is the Correct Answer:** The **vagus nerve (Cranial Nerve X)** provides the primary parasympathetic innervation to the heart, specifically targeting the **Sinoatrial (SA) node**. Vagal stimulation releases acetylcholine, which acts on $M_2$ muscarinic receptors to decrease the rate of spontaneous depolarization (Phase 4) of pacemaker cells. In a resting state, the heart is under dominant "vagal tone," which keeps the resting heart rate (60–80 bpm) significantly lower than the intrinsic firing rate of the SA node (~100 bpm). Therefore, changes in heart rate are the most direct and sensitive clinical indicator of fluctuations in parasympathetic/vagal activity. **Analysis of Incorrect Options:** * **B. Stroke Volume:** This is primarily determined by preload (Frank-Starling law), afterload, and myocardial contractility. While the vagus nerve has a minor effect on atrial contractility, it has negligible direct influence on ventricular stroke volume compared to the sympathetic nervous system. * **C. Ejection Fraction:** This is a measure of systolic function and ventricular efficiency. It is largely governed by sympathetic drive and intrinsic myocardial health, rather than vagal tone. * **D. Diastolic Blood Pressure:** This is primarily determined by **Total Peripheral Resistance (TPR)** and the elasticity of the arteries. Since the vagus nerve does not innervate systemic blood vessels, it does not directly regulate diastolic pressure. **High-Yield Clinical Pearls for NEET-PG:** * **Respiratory Sinus Arrhythmia (RSA):** This is a physiological variation in heart rate caused by vagal modulation during respiration (HR increases during inspiration, decreases during expiration). It is a hallmark of a healthy vagal tone. * **Atropine:** A muscarinic antagonist used to treat symptomatic bradycardia by blocking vagal influence, thereby increasing the heart rate. * **Vagal Maneuvers:** Techniques like the Valsalva maneuver or carotid sinus massage increase vagal tone to terminate Supraventricular Tachycardia (SVT).

Question 516: What is the basis of Korotkoff sound?

A. Aortic valve closure
B. Production of heat sound
C. Turbulent blood flow (Correct Answer)
D. Aortic valve expansion

Explanation: **Explanation:** The **Korotkoff sounds** are the sounds heard through a stethoscope during the non-invasive measurement of blood pressure using a sphygmomanometer. **Why Turbulent Blood Flow is Correct:** Under normal conditions, blood flow in the arteries is **laminar** (silent and streamlined). When a blood pressure cuff is inflated above systolic pressure, the artery is occluded, and no flow occurs. As the cuff is slowly deflated, the pressure drops just below the systolic level, allowing blood to squirt through the partially compressed vessel at high velocity. This sudden change in vessel diameter and high velocity converts laminar flow into **turbulent flow**. The vibrations produced by this turbulence create the audible Korotkoff sounds. Once the cuff pressure falls below diastolic pressure, the artery remains fully open, laminar flow is restored, and the sounds disappear. **Analysis of Incorrect Options:** * **A & D (Aortic Valve Closure/Expansion):** These relate to the cardiac cycle and the production of the second heart sound ($S_2$), not the peripheral arterial sounds heard during BP measurement. * **B (Production of Heart Sound):** Heart sounds ($S_1, S_2, S_3, S_4$) are primarily caused by the closure of valves and the vibration of cardiac chambers, whereas Korotkoff sounds are vascular in origin. **High-Yield Clinical Pearls for NEET-PG:** * **Phase I:** First appearance of clear tapping sounds (corresponds to **Systolic BP**). * **Phase V:** Complete disappearance of sounds (corresponds to **Diastolic BP** in adults). * **Phase IV:** Muffling of sounds (used for Diastolic BP in children or hyperdynamic states like pregnancy/thyrotoxicosis). * **Auscultatory Gap:** A period of silence between Phase I and II; failure to recognize it can lead to underestimating systolic or overestimating diastolic pressure.

Question 517: During which stage of the cardiac cycle are all heart valves closed?

A. Systolic ejection
B. Isovolumetric relaxation
C. Isovolumetric contraction
D. None of the above (Correct Answer)

Explanation: ### Explanation The correct answer is **None of the above** because the question asks for "the stage" (singular), but in the cardiac cycle, there are actually **two distinct stages** during which all four heart valves (Mitral, Tricuspid, Aortic, and Pulmonary) are closed. #### 1. Why "None of the above" is correct: For a valve to be closed, the pressure in the chamber ahead must be higher than the pressure in the chamber behind. All valves are closed during: * **Isovolumetric Contraction:** Ventricular pressure rises above atrial pressure (closing AV valves) but remains below arterial pressure (semilunar valves stay closed). * **Isovolumetric Relaxation:** Ventricular pressure falls below arterial pressure (closing semilunar valves) but remains above atrial pressure (AV valves stay closed). Since both Options B and C are correct, selecting only one would be incomplete. In competitive exams like NEET-PG, if two options are equally valid and a "Both" option is missing, "None of the above" or the most comprehensive choice is sought. #### 2. Analysis of Incorrect Options: * **A. Systolic Ejection:** The semilunar valves (Aortic/Pulmonary) are **open** to allow blood to leave the ventricles. * **B & C (Individually):** While all valves are closed during these phases, neither phase alone represents "the" single stage. #### 3. High-Yield Clinical Pearls for NEET-PG: * **Volume Change:** During isovolumetric phases, the ventricular volume remains constant (hence "isovolumetric"), making them the steepest vertical lines on a Pressure-Volume loop. * **Heart Sounds:** * **S1** (Lubb) occurs at the beginning of Isovolumetric Contraction (closure of AV valves). * **S2** (Dupp) occurs at the beginning of Isovolumetric Relaxation (closure of Semilunar valves). * **Maximum Oxygen Consumption:** The heart consumes the most oxygen during **Isovolumetric Contraction** because it is generating high pressure against closed valves.

Question 518: Falsely prolonged QT interval may be a feature of which one of the following conditions?

A. Hypokalemia (Correct Answer)
B. Hyperkalemia
C. Hypocalcemia
D. Hypercalcemia

Explanation: ### Explanation The correct answer is **Hypokalemia**. #### 1. Why Hypokalemia is Correct The term **"falsely prolonged"** is the key to this question. In hypokalemia, the characteristic ECG finding is the appearance of prominent **U waves** (due to delayed repolarization of Purkinje fibers). As the U wave follows the T wave, it often merges with it or is mistaken for it. When measuring the QT interval, clinicians may inadvertently include the U wave in the measurement (measuring the **QU interval** instead), leading to a **pseudo-prolongation** or a "falsely prolonged" QT interval. #### 2. Analysis of Incorrect Options * **Hypocalcemia:** This causes **true prolongation** of the QT interval. It specifically lengthens the **ST segment** (Phase 2 of the action potential) because low extracellular calcium delays the closing of sodium channels or slows calcium entry. It is not "false." * **Hypercalcemia:** This causes **shortening** of the QT interval due to a shortened ST segment. * **Hyperkalemia:** This typically presents with tall, peaked T waves, a shortened QT interval, and eventually PR prolongation and QRS widening. #### 3. NEET-PG High-Yield Pearls * **Hypokalemia ECG Sequence:** T-wave flattening → ST depression → Prominent U waves → Apparent QT prolongation. * **Hypocalcemia vs. Hypokalemia:** If the question asks for "prolonged QT," both can be answers, but if it specifies "falsely" or "pseudo" prolongation, always choose **Hypokalemia**. * **Formula:** Remember that the QT interval must be corrected for heart rate using **Bazett’s Formula** ($QTc = QT / \sqrt{RR}$). * **Drug-Induced:** Class IA and Class III antiarrhythmics are common causes of true QT prolongation, which can lead to *Torsades de Pointes*.

Question 519: Which of the following vessels carries the maximum volume of blood?

A. Arteries
B. Veins (Correct Answer)
C. Aorta
D. Arterioles

Explanation: **Explanation:** The distribution of blood volume within the cardiovascular system is determined by the **compliance (distensibility)** of the vessels. **Why Veins are the Correct Answer:** Veins are known as **capacitance vessels**. Due to their thin, highly distensible walls and large luminal diameters, they can accommodate large volumes of blood at low pressures. At any given time, approximately **64% to 70%** of the total blood volume resides in the systemic venous system (veins, venules, and venous sinuses). This acts as a reservoir that can be mobilized to the heart during exercise or hemorrhage via sympathetic vasoconstriction. **Why Other Options are Incorrect:** * **Aorta:** While it is the largest artery, it serves as a high-pressure conduit. It contains only about **2%** of the total blood volume. * **Arteries:** Systemic arteries are "stress vessels" with thick, muscular walls designed to withstand high pressure. They hold only about **13-15%** of the total blood volume. * **Arterioles:** These are known as **resistance vessels**. Their primary role is to regulate peripheral resistance and blood flow; they contain a very small fraction (approx. **3%**) of the total volume. **High-Yield NEET-PG Pearls:** * **Maximum Volume:** Veins (Capacitance vessels). * **Maximum Resistance:** Arterioles (Resistance vessels). * **Maximum Total Cross-sectional Area:** Capillaries (where the velocity of blood flow is slowest). * **Maximum Pressure:** Aorta. * **Maximum Velocity of Flow:** Aorta.

Question 520: Traube-Hering waves are due to what phenomenon?

A. Fluctuation in blood pressure with respiration (Correct Answer)
B. Fluctuations in jugular venous pressure with respiration
C. Fluctuation in central venous pressure with respiration
D. Fluctuation in intracranial pressure with respiration

Explanation: **Explanation:** **Traube-Hering waves** are rhythmic fluctuations in arterial blood pressure that are synchronous with respiration. **Why Option A is correct:** The underlying mechanism involves the **irradiation of impulses** from the respiratory center in the medulla to the adjacent vasomotor center (VMC). During inspiration, the respiratory center stimulates the VMC, leading to vasoconstriction and a rise in blood pressure. Additionally, the mechanical effects of respiration (changes in intrathoracic pressure) affect venous return and stroke volume, further contributing to these rhythmic oscillations in systemic blood pressure. **Why other options are incorrect:** * **Options B & C:** While jugular venous pressure (JVP) and central venous pressure (CVP) do fluctuate with respiration (e.g., the inspiratory fall in JVP), these fluctuations are not termed Traube-Hering waves. JVP waves are categorized as *a, c,* and *v* waves. * **Option D:** Fluctuations in intracranial pressure (ICP) related to respiration or cardiac cycles exist but are distinct from the systemic arterial pressure oscillations described by Traube and Hering. **High-Yield NEET-PG Pearls:** 1. **Traube-Hering Waves:** Synchronous with **respiration** (BP fluctuations). 2. **Mayer Waves:** Slower oscillations in blood pressure that are **independent of respiration**. They are typically seen in states of hypotension or ischemia and are attributed to baroreceptor reflex oscillations. 3. **Mnemonic:** **T**raube-**H**ering = **T**horacic (Respiration); **M**ayer = **M**edullary (Vasomotor center rhythmicity). 4. In clinical practice, these waves are often observed in kymograph tracings or continuous arterial line monitoring.

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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