Cardiovascular System — MCQs

A 50-year-old man has been experiencing fainting episodes for approximately 2 weeks. During these episodes, his ECG reveals a ventricular rate of 25 beats per minute and a P wave rate of 100 beats per minute. The episodes last about 30 seconds, after which a normal sinus rhythm spontaneously recurs. What is the most likely diagnosis?

Q255Easy

What is the first reactionary change to occur after vessel injury and haemorrhage?

Q256Easy

Cerebral blood flow is regulated by all except?

Q257Easy

In healthy individuals, what characteristic is the same for both pulmonary and systemic circulations?

Q258Easy

What is the resting membrane potential of myocytes?

Q259Easy

Low-pressure receptors that play a role in minimal aerial pressure changes due to volume changes are located in which of the following locations?

Q260Medium

Elevated systolic blood pressure in the right ventricle suggests stenosis of which valve?

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 251: Mary's law states the relationship of heart rate with which of the following parameters?

A. Cardiac output
B. Stroke volume
C. Arterial blood pressure (Correct Answer)
D. Presystolic volume

Explanation: ### Explanation **Mary’s Law** states that the heart rate is inversely proportional to the arterial blood pressure. This relationship is primarily mediated by the **baroreceptor reflex**. **1. Why Arterial Blood Pressure is Correct:** When arterial blood pressure rises, it stimulates baroreceptors located in the carotid sinus and aortic arch. These receptors send impulses to the nucleus tractus solitarius (NTS) in the medulla, leading to increased vagal (parasympathetic) tone and decreased sympathetic activity. This results in bradycardia (decreased heart rate) to bring the blood pressure back toward normal. Conversely, a drop in blood pressure triggers tachycardia. * **Formula:** Heart Rate $\propto$ 1 / Blood Pressure. **2. Why Other Options are Incorrect:** * **Cardiac Output (A) & Stroke Volume (B):** While heart rate is a component of the Cardiac Output formula ($CO = HR \times SV$), Mary’s Law specifically describes the reflex response to pressure changes, not the mathematical product of output. * **Presystolic Volume (D):** Also known as End-Diastolic Volume (EDV), this relates to **Frank-Starling’s Law**, which states that the force of ventricular contraction is proportional to the initial length of the muscle fibers (preload). **3. High-Yield Clinical Pearls for NEET-PG:** * **Exception to Mary’s Law:** The **Bainbridge Reflex**. An increase in right atrial pressure (due to increased venous return) causes an *increase* in heart rate to pump the excess blood forward, overriding Mary’s Law. * **Marey’s Law vs. Cushing’s Reflex:** In increased intracranial pressure (ICP), the body shows hypertension with bradycardia. The bradycardia here is a classic clinical manifestation of Marey’s Law in response to the systemic hypertension (Cushing’s Triad). * **Key Nerve Pathways:** Carotid sinus (Hering’s nerve/CN IX) and Aortic arch (Vagus nerve/CN X).

Question 252: Which protein is primarily responsible for binding hemoglobin?

A. Haptoglobin
B. Hemopexin
C. Albumin
D. Both Haptoglobin and Hemopexin (Correct Answer)

Explanation: **Explanation:** The correct answer is **Both Haptoglobin and Hemopexin** because the body utilizes a dual-scavenging system to prevent oxidative damage and iron loss during hemolysis. 1. **Haptoglobin:** This is the primary plasma protein that binds to **free hemoglobin (Hb) dimers**. The resulting Haptoglobin-Hb complex is too large to be filtered by the glomerulus, preventing hemoglobinuria and protecting the kidneys. The complex is rapidly cleared by the reticuloendothelial system (via CD163 receptors on macrophages). 2. **Hemopexin:** When haptoglobin is saturated (as seen in severe hemolysis), free hemoglobin is oxidized into **methemoglobin**, which dissociates into globin and **free heme**. Hemopexin is the specific transport protein that binds to this free heme, transporting it to the liver for degradation. **Why other options are incorrect:** * **Albumin:** While albumin can bind to heme to form **methemalbumin**, it is a non-specific, low-affinity carrier that acts only as a temporary reservoir when hemopexin levels are depleted. * **Options A and B alone:** While both are correct, they are incomplete on their own as both play vital, distinct roles in the clearance of hemoglobin and its breakdown products. **NEET-PG High-Yield Pearls:** * **Diagnostic Marker:** A **decreased serum haptoglobin level** is one of the most sensitive laboratory markers for **intravascular hemolysis**. * **Function:** The primary goal of these proteins is to prevent **iron loss** and avoid **reactive oxygen species (ROS)** formation caused by free iron. * **Acute Phase Reactant:** Haptoglobin is an acute-phase reactant; its levels may rise during inflammation, which can sometimes mask underlying hemolysis.

Question 253: Cardiac output increases by which of the following mechanisms?

A. Standing from a lying down position
B. Expiration
C. Increased cardiac contractility (Correct Answer)
D. Parasympathetic stimulation

Explanation: **Explanation:** **Cardiac Output (CO)** is the product of **Stroke Volume (SV)** and **Heart Rate (HR)** ($CO = SV \times HR$). Any factor that increases either of these variables will increase cardiac output. **Why Option C is Correct:** **Increased cardiac contractility** (positive inotropy) directly increases the Stroke Volume. According to the Frank-Starling mechanism and sympathetic influence, a more forceful contraction allows the heart to eject a larger fraction of its end-diastolic volume (increased Ejection Fraction), thereby increasing the total Cardiac Output. **Analysis of Incorrect Options:** * **A. Standing from a lying down position:** Upon standing, gravity causes venous pooling in the lower limbs. This leads to a **decrease in venous return**, which reduces preload and subsequently decreases cardiac output (the basis for orthostatic hypotension). * **B. Expiration:** During expiration, intrathoracic pressure increases. This compresses the vena cava, **decreasing venous return** to the right atrium, which leads to a transient decrease in cardiac output. (Conversely, inspiration increases CO via the respiratory pump). * **D. Parasympathetic stimulation:** The vagus nerve (parasympathetic) primarily acts on the SA and AV nodes to **decrease heart rate** (negative chronotropy). A decrease in heart rate leads to a decrease in cardiac output. **High-Yield Clinical Pearls for NEET-PG:** * **Determinants of CO:** Preload, Afterload, Contractility, and Heart Rate. * **Fick’s Principle:** The gold standard for measuring CO ($CO = \text{Oxygen consumption} / [\text{Arterial } O_2 - \text{Venous } O_2]$). * **Bainbridge Reflex:** An increase in right atrial pressure (increased preload) leads to an increase in heart rate to pump the excess blood, thus increasing CO. * **Metabolic Demand:** CO is directly proportional to the body's oxygen consumption; it increases during exercise, pregnancy, and hyperthyroidism.

Question 254: A 50-year-old man has been experiencing fainting episodes for approximately 2 weeks. During these episodes, his ECG reveals a ventricular rate of 25 beats per minute and a P wave rate of 100 beats per minute. The episodes last about 30 seconds, after which a normal sinus rhythm spontaneously recurs. What is the most likely diagnosis?

A. First-degree atrioventricular block
B. Second-degree atrioventricular block
C. Third-degree atrioventricular block
D. Stokes-Adams syndrome (Correct Answer)

Explanation: ### Explanation **Correct Answer: D. Stokes-Adams Syndrome** **1. Why it is correct:** The clinical presentation describes a classic case of **Stokes-Adams syndrome** (or Adams-Stokes attacks). This syndrome occurs when there is a sudden, periodic transition from a normal rhythm to a high-grade or complete atrioventricular (AV) block. * **The Mechanism:** When complete heart block occurs, the ventricles stop contracting for several seconds (ventricular standstill) before a distal pacemaker (like the Bundle of His or Purkinje fibers) takes over. * **The Symptoms:** During this "lag time," cerebral ischemia occurs due to lack of cardiac output, leading to fainting (syncope). The ECG findings of a P wave rate (100 bpm) being significantly higher than and dissociated from the ventricular rate (25 bpm) confirm **Third-degree AV block**, which is the underlying cause of the syndrome. **2. Why the other options are incorrect:** * **A. First-degree AV block:** Characterized only by a prolonged PR interval (>0.20s). Every P wave is followed by a QRS complex; it does not cause a drop in ventricular rate or syncope. * **B. Second-degree AV block:** Some P waves fail to conduct to the ventricles (Mobitz I or II). While it can cause bradycardia, it typically doesn't present with the sudden, transient 30-second "standstill" and spontaneous recovery described here. * **C. Third-degree AV block:** While this is the *rhythm* shown on the ECG, "Stokes-Adams syndrome" is the most appropriate *clinical diagnosis* for the episodic nature of the fainting spells followed by spontaneous recovery of sinus rhythm. **3. NEET-PG High-Yield Pearls:** * **Overdrive Suppression:** The delay in the ventricular escape rhythm is due to the fact that the Purkinje fibers were previously suppressed by the faster SA node. * **Duration:** If the ventricular standstill lasts longer than 15–30 seconds, it can lead to permanent brain damage or death. * **Treatment:** The definitive management for recurrent Stokes-Adams attacks is the implantation of a **permanent pacemaker**.

Question 255: What is the first reactionary change to occur after vessel injury and haemorrhage?

A. Vasoconstriction (Correct Answer)
B. Bradycardia
C. Raised cortisol
D. Raised adrenaline

Explanation: **Explanation:** The correct answer is **Vasoconstriction (Option A)**. When a blood vessel is injured and hemorrhage occurs, the body’s immediate priority is to minimize blood loss and maintain perfusion pressure. This is achieved through **local myogenic contraction** and **sympathetic stimulation**. 1. **Local Myogenic Spasm:** Damage to the vascular wall causes direct trauma to smooth muscle cells, leading to immediate contraction. 2. **Humoral Factors:** Platelets at the site of injury release potent vasoconstrictors like **Thromboxane A2** and **Serotonin**. 3. **Sympathetic Reflex:** The drop in blood pressure triggers the baroreceptor reflex, leading to generalized vasoconstriction to increase Total Peripheral Resistance (TPR). **Why other options are incorrect:** * **Bradycardia (Option B):** Hemorrhage typically causes **tachycardia** (increased heart rate) as a compensatory mechanism to maintain Cardiac Output ($CO = HR \times SV$). Bradycardia only occurs in terminal stages (Stage IV shock) or via the Bezold-Jarisch reflex in specific scenarios. * **Raised Cortisol (Option C):** While cortisol increases as part of the stress response, it is a hormonal change that takes minutes to hours to peak, making it much slower than the near-instantaneous vascular response. * **Raised Adrenaline (Option D):** Catecholamine release is a rapid systemic response, but the **local myogenic vasoconstriction** occurs milliseconds after the physical trauma, preceding the systemic endocrine surge. **High-Yield Clinical Pearls for NEET-PG:** * **Hemostasis Sequence:** 1. Vascular Spasm (Vasoconstriction) $\rightarrow$ 2. Platelet Plug formation $\rightarrow$ 3. Coagulation (Fibrin clot). * **Baroreceptor Reflex:** This is the most important short-term mechanism for BP regulation during hemorrhage. * **Shock Index:** Heart Rate / Systolic BP (Normal: 0.5–0.7). An increase is an early indicator of significant blood loss.

Question 256: Cerebral blood flow is regulated by all except?

A. Blood pressure
B. PaCO2
C. Potassium ions (Correct Answer)
D. Cerebral metabolic rate

Explanation: **Explanation:** Cerebral blood flow (CBF) is tightly regulated to ensure a constant supply of oxygen and glucose to the brain. The correct answer is **Potassium ions**, as they are not a primary systemic regulator of CBF, although they may play minor roles in local neurovascular coupling. **1. Why Potassium ions (Option C) is the correct answer:** While local changes in extracellular $K^+$ can cause transient vasodilation, it is not considered a primary regulatory mechanism for global cerebral blood flow. In contrast, factors like $CO_2$, $O_2$, and Mean Arterial Pressure (MAP) have profound, well-documented effects on the entire cerebral vasculature. **2. Analysis of Incorrect Options:** * **Blood Pressure (Option A):** Through **Cerebral Autoregulation**, CBF remains constant despite changes in MAP between **60 and 140 mmHg**. Outside this range, CBF becomes pressure-dependent. * **$PaCO_2$ (Option B):** This is the **most potent physiological stimulus** for CBF. Hypercapnia (high $CO_2$) causes marked vasodilation, while hypocapnia (low $CO_2$) causes vasoconstriction. * **Cerebral Metabolic Rate (Option D):** CBF is directly proportional to metabolic activity (Metabolic Autoregulation). Increased neuronal activity leads to the release of metabolites like Adenosine, $H^+$, and Nitric Oxide, which increase local blood flow. **High-Yield Facts for NEET-PG:** * **Normal CBF:** 50 ml/100g/min (approx. 750 ml/min or 15% of Cardiac Output). * **$CO_2$ Sensitivity:** A 1 mmHg rise in $PaCO_2$ increases CBF by approximately 3-4%. * **Cushing’s Reflex:** A clinical triad of hypertension, bradycardia, and irregular respiration seen in increased intracranial pressure (ICP). * **Monro-Kellie Doctrine:** The sum of volumes of brain, CSF, and intracerebral blood is constant; an increase in one must be offset by a decrease in another.

Question 257: In healthy individuals, what characteristic is the same for both pulmonary and systemic circulations?

A. Mean pressure
B. Vascular resistance
C. Compliance
D. Flow per minute (Correct Answer)

Explanation: **Explanation:** The correct answer is **Flow per minute (Cardiac Output)**. In a healthy individual, the pulmonary and systemic circulations are arranged in **series**. According to the principle of continuity, the volume of blood pumped by the right ventricle into the lungs must equal the volume of blood pumped by the left ventricle into the systemic circulation over a given period. If they were not equal, blood would rapidly accumulate in either the lungs or the systemic tissues, leading to immediate circulatory collapse. Therefore, **Cardiac Output (CO) = Right Ventricular Output = Left Ventricular Output.** **Why other options are incorrect:** * **Mean Pressure:** The systemic circulation is a high-pressure system (Mean Arterial Pressure ~93 mmHg), whereas the pulmonary circulation is a low-pressure system (Mean Pulmonary Artery Pressure ~15 mmHg). This protects the delicate alveolar-capillary membrane. * **Vascular Resistance:** Systemic Vascular Resistance (SVR) is significantly higher (about 10 times) than Pulmonary Vascular Resistance (PVR). The right ventricle is thinner because it pumps against much lower resistance. * **Compliance:** The pulmonary vessels are much more compliant (distensible) than systemic arteries. This allows the pulmonary system to accommodate increases in stroke volume without a significant rise in pressure. **High-Yield Clinical Pearls for NEET-PG:** * **Formula:** $Q (Flow) = \Delta P / R$. Since Flow (Q) is constant in both systems but Pressure ($\Delta P$) is much lower in the lungs, it follows that Resistance ($R$) must also be much lower in the lungs. * **Exception:** In the fetus, the circulations are in **parallel** (due to shunts like the ductus arteriosus), meaning flow is not equal. * **Left-to-Right Shunts (e.g., ASD/VSD):** In these pathologies, pulmonary flow ($Qp$) becomes greater than systemic flow ($Qs$), breaking the "equal flow" rule.

Question 258: What is the resting membrane potential of myocytes?

A. -90 mV (Correct Answer)
B. -70 mV
C. -50 mV
D. -60 mV

Explanation: The Resting Membrane Potential (RMP) of a cell is the electrical potential difference across the plasma membrane when the cell is in a non-excited state. **1. Why -90 mV is Correct:** In ventricular myocytes, the RMP is approximately **-90 mV**. This value is primarily determined by the high resting permeability of the membrane to **Potassium (K+) ions** through inward rectifier K+ channels ($I_{K1}$). Since the Nernst potential for Potassium is roughly -94 mV, the RMP sits very close to this value. The Na+/K+ ATPase pump also contributes by maintaining the ionic gradients (pumping 3 Na+ out and 2 K+ in), ensuring the interior remains electronegative. **2. Analysis of Incorrect Options:** * **-70 mV:** This is the typical RMP for **large myelinated neurons**. While still negative, neurons have a slightly higher permeability to Sodium at rest compared to cardiac myocytes. * **-60 mV:** This is the approximate RMP (or "maximal diastolic potential") of the **SA Node and AV Node**. Nodal tissue is less negative because it lacks $I_{K1}$ channels, which allows for spontaneous depolarization (pacemaker activity). * **-50 mV:** This value is too positive for a healthy resting myocyte and would result in the inactivation of fast Sodium channels, leading to impaired conduction. **3. NEET-PG High-Yield Pearls:** * **Phase 4:** In the cardiac action potential, the RMP corresponds to Phase 4. * **Ion Conductance:** At rest, the membrane is 100 times more permeable to $K^+$ than to $Na^+$. * **Hyperkalemia:** An increase in extracellular $K^+$ makes the RMP less negative (depolarized), which paradoxically decreases excitability over time by inactivating $Na^+$ channels. * **Skeletal Muscle:** Also shares a similar RMP of approximately -80 to -90 mV.

Question 259: Low-pressure receptors that play a role in minimal aerial pressure changes due to volume changes are located in which of the following locations?

A. Left Atrium
B. Right Atrium
C. Pulmonary arteries
D. All of the above (Correct Answer)

Explanation: ### Explanation **Concept: Low-Pressure Baroreceptors (Volume Receptors)** In the cardiovascular system, receptors are categorized into high-pressure and low-pressure systems. While high-pressure baroreceptors (Carotid sinus and Aortic arch) monitor arterial blood pressure, **low-pressure receptors** (also known as **volume receptors**) are located in the "distensible" parts of the circulation. These receptors detect changes in blood volume rather than systemic arterial pressure. **Why "All of the Above" is Correct:** Low-pressure receptors are strategically located in areas that can accommodate large changes in volume with minimal changes in pressure. These include: 1. **Atria (Both Left and Right):** Specifically at the junction of the vena cavae with the right atrium and the pulmonary veins with the left atrium. 2. **Pulmonary Vasculature:** Including the pulmonary arteries and the pulmonary trunk. 3. **Ventricles:** To a lesser extent. When these receptors are stretched due to increased volume, they trigger the **Bainbridge Reflex** (increasing heart rate) and inhibit the release of ADH (Vasopressin), leading to increased diuresis to normalize blood volume. **Analysis of Options:** * **A & B (Atria):** The atria are the primary sites for volume sensing. Stretching of atrial receptors leads to the release of **Atrial Natriuretic Peptide (ANP)**, which promotes sodium and water excretion. * **C (Pulmonary Arteries):** The pulmonary circuit is a low-pressure system. Receptors here monitor the volume entering the left heart, ensuring the "low-pressure" side of the circulation is not overloaded. **High-Yield Clinical Pearls for NEET-PG:** * **Bainbridge Reflex vs. Baroreceptor Reflex:** Increased atrial stretch (volume) *increases* heart rate via the Bainbridge reflex, whereas increased arterial stretch (pressure) *decreases* heart rate via the baroreceptor reflex. * **ANP & BNP:** These are "volume-regulating" hormones. ANP is released from the atria, while BNP (Brain Natriuretic Peptide) is released from the ventricles in response to volume/pressure overload (useful marker for Heart Failure). * **Location Summary:** High pressure = Aortic arch & Carotid sinus; Low pressure = Atria & Pulmonary vessels.

Question 260: Elevated systolic blood pressure in the right ventricle suggests stenosis of which valve?

A. Aortic
B. Mitral
C. Pulmonary (Correct Answer)
D. Tricuspid

Explanation: ### Explanation **Correct Option: C. Pulmonary** **Mechanism:** The right ventricle (RV) pumps deoxygenated blood into the pulmonary artery through the pulmonary valve. In **Pulmonary Stenosis**, the valve orifice is narrowed, creating significant resistance to blood outflow. To maintain stroke volume and overcome this obstruction, the RV must generate much higher pressures during systole. This leads to **concentric right ventricular hypertrophy** and elevated systolic pressure within the RV chamber. **Analysis of Incorrect Options:** * **A. Aortic Valve:** Stenosis here increases systolic pressure in the **left ventricle**, as it must work harder to pump blood into the systemic circulation. * **B. Mitral Valve:** Stenosis of the mitral valve restricts flow from the left atrium to the left ventricle. This leads to elevated **left atrial pressure** and pulmonary venous congestion, but does not directly cause primary elevation of RV systolic pressure (though chronic cases may lead to secondary pulmonary hypertension). * **C. Tricuspid Valve:** Stenosis here restricts flow from the right atrium to the right ventricle. This would actually result in **decreased** filling and potentially lower pressures in the right ventricle, while increasing pressure in the **right atrium**. **High-Yield Facts for NEET-PG:** * **Normal RV Pressure:** Typically 15–25 mmHg (systolic) / 0–8 mmHg (diastolic). In severe pulmonary stenosis, systolic pressure can exceed 100 mmHg. * **Clinical Sign:** Pulmonary stenosis typically presents with an **ejection systolic murmur** best heard at the left second intercostal space, often preceded by a systolic click. * **Bernoulli Equation:** In the echo lab, the pressure gradient across the stenotic valve is calculated as $\Delta P = 4v^2$ (where $v$ is peak velocity). * **EKG Findings:** Right axis deviation and tall R-waves in V1-V2 are characteristic of the resulting RV hypertrophy.

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