Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 581: Which of the following is NOT a component of the jugular venous pulse (JVP)?

A. A wave is bigger than the V wave
B. The C wave is called the Dicrotic notch (Correct Answer)
C. The X wave is seen during ventricular systole
D. The Y descent is seen during ventricular diastole

Explanation: The Jugular Venous Pulse (JVP) reflects pressure changes in the right atrium. Understanding its waveforms is crucial for NEET-PG. ### **Why Option B is Correct (The Incorrect Statement)** The **C wave** in the JVP is caused by the bulging of the tricuspid valve into the right atrium during early ventricular contraction (isovolumetric contraction). In contrast, the **Dicrotic notch** (incisura) is a feature of the **Arterial Pressure Waveform**, representing the closure of the aortic valve. These are two distinct physiological events in different systems. ### **Analysis of Other Options** * **Option A:** In a normal JVP, the **'a' wave** (atrial contraction) is the tallest wave, followed by the 'v' wave (venous filling). * **Option B (X-descent):** This occurs due to atrial relaxation and the downward pulling of the tricuspid annulus during **ventricular systole**. * **Option D (Y-descent):** This represents the rapid emptying of the right atrium into the right ventricle following the opening of the tricuspid valve during **ventricular diastole**. ### **High-Yield Clinical Pearls for NEET-PG** * **Giant 'a' waves:** Seen in Tricuspid Stenosis, Pulmonary Hypertension, and Pulmonary Stenosis. * **Cannon 'a' waves:** Seen in AV dissociation (Complete Heart Block) or Ventricular Tachycardia (atria contract against a closed tricuspid valve). * **Absent 'a' wave:** Pathognomonic for **Atrial Fibrillation**. * **Prominent 'v' wave:** Seen in Tricuspid Regurgitation (Lancisi’s sign). * **Friedreich’s Sign:** A steep 'y' descent seen in Constrictive Pericarditis.

Question 582: The AH interval on an ECG represents conduction through which pathway?

A. The His-Purkinje system
B. The AV node to the bundle of His (Correct Answer)
C. The Purkinje system to ventricular fibers
D. The ventricular fibers

Explanation: ### Explanation The **AH interval** is a measurement obtained during an **Electrophysiology Study (EPS)** using an intracardiac electrogram. It represents the time taken for the electrical impulse to travel from the low right atrium (A) to the Bundle of His (H). **1. Why the correct answer is right:** The AH interval primarily reflects **conduction through the AV node**. It is measured from the onset of the atrial deflection (A) to the first rapid deflection of the His bundle electrogram (H). Because the AV node is the site of physiological delay in the cardiac conduction system, the AH interval is the most significant component of this measurement. It is highly sensitive to autonomic tone and medications (like beta-blockers or calcium channel blockers). **2. Why the incorrect options are wrong:** * **Option A & C:** The **HV interval** (His to Ventricle) represents conduction through the **His-Purkinje system**. It is measured from the His bundle deflection to the onset of ventricular depolarization (V). * **Option D:** Conduction through the **ventricular fibers** is represented by the **QRS complex** on a surface ECG or the ventricular deflection (V) on an intracardiac electrogram. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Normal AH Interval:** 50–120 ms. * **Normal HV Interval:** 35–55 ms. * **Vagal Stimulation:** Increases the AH interval (slows AV conduction) but has no effect on the HV interval. * **Atropine:** Decreases the AH interval. * **Clinical Significance:** A prolonged AH interval indicates **supra-Hisian block** (AV nodal disease), whereas a prolonged HV interval indicates **infra-Hisian block** (distal conduction system disease), which carries a higher risk of progressing to complete heart block.

Question 583: What is the primary benefit of the biconcave shape of RBCs?

A. Increasing flexibility
B. Increasing surface area
C. Carrying more Haemoglobin
D. Facilitating passage through narrow capillaries (Correct Answer)

Explanation: **Explanation:** The biconcave shape of the Red Blood Cell (RBC) is a specialized evolutionary adaptation that provides an **extraordinarily high surface-area-to-volume ratio**. This geometric configuration allows for significant **deformability**. **Why Option D is Correct:** The average diameter of an RBC is approximately **7.5 µm**, whereas the smallest capillaries can be as narrow as **3–5 µm**. The biconcave shape allows the RBC to fold, twist, and "deform" without rupturing its membrane. This flexibility is the primary physiological requirement for the cell to navigate the microvasculature and the narrow slits of the splenic sinusoids. **Analysis of Incorrect Options:** * **A. Increasing flexibility:** While the shape *enables* flexibility, "facilitating passage through capillaries" is the functional *benefit* and the primary physiological purpose. Flexibility is the means; capillary transit is the end. * **B. Increasing surface area:** The shape does increase surface area (optimizing gas exchange), but this is secondary to the mechanical necessity of surviving microcirculation. * **C. Carrying more Haemoglobin:** A biconcave shape actually provides *less* volume for hemoglobin compared to a sphere of the same surface area. Spherocytes (seen in Hereditary Spherocytosis) are more "packed" but are pathologically fragile. **High-Yield NEET-PG Pearls:** * **Spectrin and Ankyrin:** These peripheral membrane proteins maintain the biconcave shape. Mutations here lead to **Hereditary Spherocytosis**, where cells become spherical, lose deformability, and are destroyed in the spleen. * **Rouleaux Formation:** The biconcave shape allows RBCs to stack like coins in slow-moving blood, a phenomenon reflected in the **ESR (Erythrocyte Sedimentation Rate)**. * **Mean Corpuscular Volume (MCV):** Normal range is **80–100 fL**. Changes in volume often precede changes in shape.

Question 584: Atrial Natriuretic Peptide (ANP) causes what change?

A. Increase in blood volume (Correct Answer)
B. Increase in cardiac output
C. Increase in urine output
D. Decrease in renin secretion

Explanation: **Explanation** **Atrial Natriuretic Peptide (ANP)** is a hormone synthesized and secreted by the atrial myocytes in response to **atrial stretch** (hypervolemia). Its primary physiological role is to defend against fluid overload by promoting the excretion of sodium and water. **Why Option C is Correct:** ANP acts on the kidneys to increase the **Glomerular Filtration Rate (GFR)** by dilating afferent arterioles and constricting efferent arterioles. Simultaneously, it inhibits sodium reabsorption in the distal tubule and collecting ducts. This process, known as **natriuresis** (sodium loss) and **diuresis** (water loss), leads to a significant **increase in urine output**, thereby reducing total blood volume. **Analysis of Incorrect Options:** * **Option A:** ANP *decreases* blood volume. Its goal is to counteract hypertension and fluid retention. * **Option B:** By reducing blood volume and causing systemic vasodilation (decreasing preload and afterload), ANP generally leads to a decrease or stabilization of cardiac output, not an increase. * **Option D:** While ANP *does* inhibit renin secretion (as part of its antagonism of the RAAS system), the most direct and hallmark physiological "change" or effect it causes in the context of renal function is the promotion of urine output. *Note: In many standardized exams, if both are present, the primary effect on fluid balance (diuresis) is prioritized.* **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** ANP works via the **cGMP (Cyclic Guanosine Monophosphate)** second messenger system (guanylyl cyclase receptor). * **Antagonist:** ANP is the direct physiological antagonist to **Aldosterone** and **Angiotensin II**. * **BNP (Brain Natriuretic Peptide):** Secreted by ventricles; used clinically as a diagnostic marker for **Congestive Heart Failure (CHF)**. * **Neprilysin:** The enzyme that degrades ANP/BNP. Neprilysin inhibitors (e.g., Sacubitril) are now used in heart failure management to keep ANP levels high.

Question 585: Peripheral resistance is inversely proportional to which of the following?

A. Radius (Correct Answer)
B. Viscosity
C. Length
D. Elasticity of blood vessels

Explanation: ### Explanation The relationship between peripheral resistance and the physical properties of blood vessels is governed by **Poiseuille’s Law**. The formula for resistance ($R$) is: $$R = \frac{8 \eta L}{\pi r^4}$$ Where: * $\eta$ = Viscosity of blood * $L$ = Length of the vessel * $r$ = Radius of the vessel **Why Radius is Correct:** According to the formula, resistance is **inversely proportional to the fourth power of the radius** ($R \propto 1/r^4$). This means even a small decrease in the radius (vasoconstriction) leads to a massive increase in peripheral resistance. Because it is the only factor in the denominator, it is the correct inverse relationship. **Why Other Options are Incorrect:** * **B. Viscosity:** Resistance is **directly proportional** to viscosity. Conditions like polycythemia increase viscosity, thereby increasing resistance. * **C. Length:** Resistance is **定期 proportional** to the length of the vessel. While vessel length is constant in adults, increased body mass (e.g., obesity) increases total vessel length and resistance. * **D. Elasticity:** While elasticity affects vessel compliance and pulse pressure, it is not a primary variable in Poiseuille’s equation for calculating systemic vascular resistance. **High-Yield Clinical Pearls for NEET-PG:** * **Arterioles** are known as the primary **"Resistance Vessels"** of the body because they have the greatest ability to change their radius. * If the radius of a vessel is halved, the resistance increases by **16 times** ($2^4$). * **Critical Closing Pressure:** The internal pressure at which a small blood vessel collapses and flow ceases; it is heavily influenced by sympathetic tone and radius.

Question 586: Which of the following statements regarding Laplace's Law is not true?

A. T = Pr/W
B. P = 2T/r
C. P = T/r
D. P = T/w (Correct Answer)

Explanation: **Explanation:** Laplace’s Law describes the relationship between the transmural pressure, wall tension, and the radius of a hollow organ (like a blood vessel or cardiac chamber). In cardiovascular physiology, it is used to understand how the heart compensates for changes in pressure and volume. **Why Option D is the Correct (False) Statement:** The formula **P = T/w** is incorrect because pressure (P) is not simply tension divided by wall thickness. According to the modified Laplace Law for thick-walled structures (like the left ventricle), the relationship is expressed as **Wall Stress (σ) = Pr / 2w**. Pressure itself is determined by the tension and radius, not the thickness alone. **Analysis of Other Options:** * **Option B & C (P = 2T/r and P = T/r):** These are the standard forms of Laplace’s Law. **P = 2T/r** applies to spherical structures (like the cardiac ventricles or pulmonary alveoli), while **P = T/r** applies to cylindrical structures (like blood vessels). * **Option A (T = Pr/w):** This represents the formula for **Wall Stress (Tension per unit area)**. It shows that as the radius (r) or pressure (P) increases, the tension on the wall increases, but an increase in wall thickness (w) helps distribute and reduce that stress. **NEET-PG High-Yield Pearls:** 1. **Cardiac Hypertrophy:** In chronic hypertension (increased P), the heart undergoes concentric hypertrophy (increased thickness, w) to keep wall stress (T) constant. 2. **Aneurysms:** As a vessel dilates (increased r), the wall tension (T) required to withstand the same pressure increases, making the vessel more likely to rupture. 3. **Heart Failure:** In a dilated failing heart (increased r), the wall tension is significantly higher, requiring more myocardial oxygen consumption to generate the same systolic pressure.

Question 587: Ventricular muscle receives electrical impulses directly from which structure?

A. Purkinje system (Correct Answer)
B. Bundle of His
C. Right and Left bundle branches
D. AV node

Explanation: **Explanation:** The conduction of electrical impulses through the heart follows a specific hierarchical sequence to ensure coordinated ventricular contraction. The correct sequence is: **SA node → Internodal pathways → AV node → Bundle of His → Right and Left Bundle Branches → Purkinje fibers → Ventricular Myocardium.** **Why Purkinje system is correct:** The Purkinje fibers represent the terminal portion of the cardiac conduction system. They are specialized cells located just beneath the endocardium that penetrate the ventricular muscle. Because they are in direct physical contact with the contractile myocytes of the ventricles, they are the immediate structures that deliver the electrical impulse to the ventricular muscle to initiate systole. **Why other options are incorrect:** * **AV node:** Acts as a "gatekeeper," delaying the impulse to allow for atrial emptying. It is located in the interatrial septum, far from the ventricular muscle. * **Bundle of His:** This is the only electrical bridge between the atria and ventricles, but it passes through the fibrous skeleton and does not directly stimulate the myocardium. * **Right and Left bundle branches:** These are subdivisions of the Bundle of His that travel down the interventricular septum. While they carry the impulse toward the apex, they must first branch into the Purkinje network before the impulse can reach the ventricular myocytes. **High-Yield NEET-PG Pearls:** * **Velocity:** Purkinje fibers have the **fastest conduction velocity** in the heart (approx. 1.5–4.0 m/s), ensuring near-simultaneous contraction of the ventricles. * **Slowest Conduction:** Occurs at the **AV node** (approx. 0.01–0.05 m/s), known as the "AV nodal delay." * **Pacemaker Hierarchy:** If the SA node fails, the Purkinje system can act as a tertiary pacemaker with an intrinsic rate of **15–40 bpm**.

Question 588: What is the therapeutic plasma level of digoxin?

A. 0.1-0.3 ng/ml
B. 0.5-1.4 ng/ml (Correct Answer)
C. 1.2-2.0 ng/ml
D. More than 2.4 ng/ml

Explanation: **Explanation:** Digoxin is a cardiac glycoside used primarily in the management of congestive heart failure (CHF) and atrial fibrillation. It has a **narrow therapeutic index**, meaning the margin between a therapeutic dose and a toxic dose is very slim, necessitating precise plasma monitoring. 1. **Why Option B is Correct:** The established therapeutic range for digoxin is generally **0.5–2.0 ng/ml**. However, recent clinical guidelines (based on trials like the DIG trial) suggest that for patients with heart failure, the optimal range is lower, typically **0.5–0.9 ng/ml**, while for rate control in atrial fibrillation, levels up to **1.4–1.5 ng/ml** are acceptable. Option B (0.5-1.4 ng/ml) best represents this safe and effective clinical window. 2. **Analysis of Incorrect Options:** * **Option A (0.1-0.3 ng/ml):** These levels are sub-therapeutic and unlikely to provide significant inhibition of the Na+/K+ ATPase pump required for its inotropic effect. * **Option C (1.2-2.0 ng/ml):** While the upper limit of the traditional range was 2.0 ng/ml, levels above 1.5 ng/ml are increasingly associated with a higher risk of toxicity without additional benefit. * **Option D (>2.4 ng/ml):** This is well into the **toxic range**. Digoxin toxicity typically manifests at levels >2.0 ng/ml. **High-Yield Clinical Pearls for NEET-PG:** * **Mechanism:** Inhibits Na+/K+ ATPase pump $\rightarrow$ increased intracellular Na+ $\rightarrow$ decreased Na+/Ca2+ exchange $\rightarrow$ increased intracellular Ca2+ (**Positive Inotropy**). * **ECG Changes:** Characterized by the "reverse tick" sign or **Sagging ST-segment depression**. * **Toxicity Predisposition:** **Hypokalemia** (potassium competes with digoxin for the binding site), hypomagnesemia, and hypercalcemia. * **Antidote:** Digoxin-specific antibody fragments (**DigiFab**).

Question 589: What is the typical systolic blood pressure in the right ventricle?

A. 25 mmHg (Correct Answer)
B. 80 mmHg
C. 95 mmHg
D. 120 mmHg

Explanation: **Explanation:** The right ventricle (RV) is a low-pressure pump designed to propel deoxygenated blood into the pulmonary circulation. Unlike the left ventricle, which must overcome high systemic vascular resistance, the RV encounters the low resistance of the pulmonary vasculature. **1. Why 25 mmHg is Correct:** During ventricular systole, the right ventricle contracts to eject blood into the pulmonary artery. The normal range for **RV systolic pressure is 15–25 mmHg**, while the **RV diastolic pressure is 0–8 mmHg**. Therefore, 25 mmHg represents the typical upper limit of normal systolic pressure in the right heart. **2. Analysis of Incorrect Options:** * **80 mmHg (Option B):** This represents the typical **diastolic** blood pressure in the systemic circulation (Aorta/Left Ventricle during filling). * **95 mmHg (Option C):** This is close to the **Mean Arterial Pressure (MAP)** of the systemic circulation, calculated as $[(2 \times \text{diastolic}) + \text{systolic}] / 3$. * **120 mmHg (Option D):** This is the typical **systolic** blood pressure of the **Left Ventricle** and the Aorta. The left ventricle is significantly thicker because it must generate 5–6 times more pressure than the right ventricle to maintain systemic perfusion. **3. High-Yield NEET-PG Pearls:** * **Pulmonary Artery Pressure (PAP):** Normal is ~25/10 mmHg. Note that RV systolic pressure equals Pulmonary Artery systolic pressure in the absence of pulmonary valve stenosis. * **Pulmonary Hypertension:** Defined clinically when the mean pulmonary artery pressure is **>20 mmHg** at rest. * **RV vs. LV:** The RV is "volume-stressed," whereas the LV is "pressure-stressed." In conditions like Mitral Stenosis or COPD, the RV undergoes hypertrophy to compensate for increased pulmonary pressures (Cor Pulmonale).

Question 590: What is the lifespan of neutrophils?

A. 6 hours (Correct Answer)
B. 1 day
C. 7 days
D. 120 days

Explanation: **Explanation:** The lifespan of neutrophils is highly variable depending on their location, but for the purpose of medical examinations like NEET-PG, it is categorized into two phases: their time in the **circulating blood** and their time in the **tissues**. 1. **Why Option A is Correct:** In the peripheral blood, neutrophils have a very short half-life, typically circulating for only **6 to 10 hours**. After this brief period, they migrate into the tissues (diapedesis) or are removed by the spleen and liver. While they may survive for 2–5 days once they enter the tissues, the standard physiological answer for "lifespan" in a general context refers to their intravascular transit time. 2. **Why Other Options are Incorrect:** * **Option B (1 day):** While some newer studies suggest neutrophils might live longer under non-inflammatory conditions, "1 day" is not the classic textbook value used for standardized exams. * **Option C (7 days):** This is closer to the lifespan of **platelets** (8–12 days) or the maturation time in the bone marrow, but far exceeds the circulating life of a neutrophil. * **Option D (120 days):** This is the classic lifespan of **Red Blood Cells (RBCs)**. **High-Yield NEET-PG Pearls:** * **Granulopoiesis:** It takes about 14 days for a neutrophil to mature in the bone marrow before release. * **First Responders:** Neutrophils are the first cells to arrive at the site of acute inflammation. * **Left Shift:** An increase in immature neutrophils (band cells) in the blood indicates an active infection or "shift to the left." * **Death:** Neutrophils die via apoptosis and form the primary component of **pus**.

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