Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 541: Which of the following is expected to increase in response to hemorrhage?

A. Arteriolar dilation in skeletal muscle
B. Sympathetic activity (Correct Answer)
C. Sodium excretion
D. Water excretion

Explanation: **Explanation:** Hemorrhage leads to a decrease in blood volume (hypovolemia), which causes a drop in mean arterial pressure (MAP). This triggers the **Baroreceptor Reflex**, the body’s primary short-term compensatory mechanism. **Why Sympathetic Activity Increases:** Decreased stretch of baroreceptors in the carotid sinus and aortic arch leads to a reduction in their firing rate to the medulla. This results in: 1. **Increased sympathetic outflow:** Leading to tachycardia (increased HR), increased myocardial contractility, and peripheral vasoconstriction. 2. **Decreased parasympathetic (vagal) tone.** These changes aim to restore cardiac output and systemic vascular resistance to maintain perfusion to vital organs. **Analysis of Incorrect Options:** * **A. Arteriolar dilation in skeletal muscle:** In response to hemorrhage, sympathetic stimulation causes **vasoconstriction** (via $\alpha_1$ receptors) in non-essential beds like skeletal muscle and skin to divert blood to the brain and heart. * **C & D. Sodium and Water excretion:** Hemorrhage activates the **Renin-Angiotensin-Aldosterone System (RAAS)** and stimulates **ADH (Vasopressin)** release. These hormones act on the kidneys to increase sodium and water **reabsorption** (decreasing excretion) to restore intravascular volume. **NEET-PG High-Yield Pearls:** * **Earliest sign of compensated shock:** Tachycardia. * **The "Goldman’s Rule":** In hemorrhage, the body prioritizes MAP over local tissue perfusion. * **Bainbridge Reflex vs. Baroreceptor Reflex:** While baroreceptors increase HR during hypotension, the Bainbridge reflex increases HR in response to increased venous return (atrial stretch). In hemorrhage, the Baroreceptor reflex dominates. * **Key Hormone:** Angiotensin II is a potent vasoconstrictor and also stimulates the thirst center in the hypothalamus.

Question 542: The shift of the oxygen dissociation curve to the left is facilitated by all except?

A. Decrease in pH (Correct Answer)
B. Fetal hemoglobin
C. Decrease in 2,3 DPG
D. Decrease in temperature

Explanation: The **Oxygen-Hemoglobin Dissociation Curve** represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. ### **Why "Decrease in pH" is the Correct Answer** A **decrease in pH** (acidosis) indicates an increase in $H^+$ ion concentration. This stabilizes the "Tense" (T) state of hemoglobin, reducing its affinity for oxygen and causing the curve to shift to the **RIGHT**. This is known as the **Bohr Effect**. A right shift facilitates oxygen unloading to tissues, which is the opposite of what the question asks. ### **Analysis of Incorrect Options (Left Shift Factors)** A **Left Shift** indicates an increased affinity of hemoglobin for oxygen (holding onto $O_2$ more tightly). * **Fetal Hemoglobin (HbF):** HbF lacks the ability to bind effectively with 2,3-DPG. This results in a higher affinity for $O_2$ compared to adult hemoglobin (HbA), shifting the curve to the **left** to ensure oxygen uptake from the placenta. * **Decrease in 2,3-DPG:** 2,3-Bisphosphoglycerate normally stabilizes the T-state. Its absence or decrease shifts the curve to the **left**. * **Decrease in Temperature:** Lower temperatures stabilize the bond between oxygen and hemoglobin, increasing affinity and shifting the curve to the **left**. ### **High-Yield NEET-PG Pearls** * **Mnemonic for Right Shift (CADET, face Right!):** * **C** – $CO_2$ increase * **A** – Acidosis (Decrease in pH) * **D** – 2,3-**D**PG increase * **E** – Exercise * **T** – Temperature increase * **P50 Value:** The $PO_2$ at which Hb is 50% saturated. Normal is **26.6 mmHg**. A **Right shift** increases P50; a **Left shift** decreases P50. * **Carbon Monoxide (CO):** Causes a **Left shift** and a downward shift (decreases oxygen-carrying capacity).

Question 543: Which of the following vessels has the function of capacitance?

A. Arteriole
B. Capillary
C. Vein (Correct Answer)
D. Artery

Explanation: **Explanation:** The correct answer is **Vein**. In the cardiovascular system, vessels are classified based on their primary physiological function. **1. Why Veins are Capacitance Vessels:** Capacitance refers to the ability of a vessel to accommodate a large volume of blood with a relatively small increase in pressure. Veins have thin, highly distensible walls with high compliance. At any given time, approximately **60-70% of the total blood volume** resides in the venous system, acting as a reservoir. This "capacitance" allows the body to adjust venous return to the heart by mobilizing this stored blood through sympathetic stimulation (venoconstriction). **2. Why the other options are incorrect:** * **Arterioles (Resistance Vessels):** These possess thick smooth muscle layers and are the primary site of peripheral resistance. They regulate blood flow into capillaries and determine arterial blood pressure. * **Capillaries (Exchange Vessels):** These have the thinnest walls (single layer of endothelium) and the largest total cross-sectional area, optimized for the diffusion of gases, nutrients, and waste. * **Arteries (Distribution/Windkessel Vessels):** Large arteries like the aorta are elastic; they dampen the pulsatile output of the heart to maintain continuous flow during diastole. **High-Yield NEET-PG Pearls:** * **Compliance Formula:** $C = V/P$. Veins are roughly **24 times** more compliant than arteries. * **Velocity of Flow:** Is lowest in the capillaries (due to the highest total cross-sectional area), facilitating exchange. * **Stressed vs. Unstressed Volume:** Blood in the arteries is "stressed volume" (high pressure), while blood in the veins is "unstressed volume" (low pressure).

Question 544: Which of the following groups of contrast agents may be safely injected intrathecally?

A. Water-soluble ionic monomers
B. Water-soluble non-ionic monomers (Correct Answer)
C. Water-soluble ionic dimers
D. Oil-based iodinated contrasts

Explanation: **Explanation:** The safety of a contrast agent for intrathecal injection (myelography) is primarily determined by its **neurotoxicity**, which is directly linked to its **osmolality** and **ionic charge**. **1. Why Water-soluble non-ionic monomers are correct:** Non-ionic monomers (e.g., **Iohexol, Iopamidol**) do not dissociate into ions in solution. This results in lower osmolality compared to ionic agents. Because they lack an electrical charge and are closer to the osmolality of cerebrospinal fluid (CSF), they do not interfere with the electrical potential of neuronal membranes. This significantly reduces the risk of neurotoxic complications such as seizures, arachnoiditis, or meningeal irritation. **2. Why the other options are incorrect:** * **Water-soluble ionic monomers (A) & dimers (C):** These agents dissociate into cations (sodium/meglumine) and anions. The high ionic charge and hyperosmolality are highly neurotoxic; they can trigger massive neuronal depolarization, leading to severe convulsions and even death if injected intrathecally. * **Oil-based iodinated contrasts (D):** (e.g., Ethiodol, Pantopaque) These were used historically but are now obsolete for myelography. They are not resorbed by the body, require manual removal, and carry a high risk of causing chronic adhesive arachnoiditis. **Clinical Pearls for NEET-PG:** * **Iohexol (Omnipaque)** is the most commonly used non-ionic agent for myelography. * **Osmolality Rule:** The lower the osmolality and the lower the ionicity, the safer the contrast for the CNS. * **Contraindication:** Never use **Ionic** contrast (like Diatrizoate/Urografin) for myelography; it is considered a "never event" due to fatal neurotoxicity. * **Non-ionic Dimers:** While even lower in osmolality (e.g., Iodixanol), non-ionic monomers remain the standard for intrathecal use due to established safety profiles.

Question 545: Which of the following causes an increase in conduction velocity of impulse through the heart?

A. Vagal stimulation
B. Parasympathetic stimulation
C. Sympathetic stimulation (Correct Answer)
D. All of the above

Explanation: **Explanation:** The conduction velocity of the cardiac impulse is primarily regulated by the autonomic nervous system. This property of the heart is known as **Dromotropy**. **1. Why Sympathetic Stimulation is Correct:** Sympathetic stimulation (via the release of Norepinephrine acting on **$\beta_1$ receptors**) increases conduction velocity (Positive Dromotropy). This occurs because it increases the rate of rise of the action potential (Phase 0) and increases the excitability of the conducting tissues, particularly at the **AV node**. By increasing the permeability to $Ca^{2+}$ and $Na^+$, it shortens the AV nodal delay, allowing the impulse to travel faster from the atria to the ventricles. **2. Why Other Options are Incorrect:** * **Vagal/Parasympathetic Stimulation (Options A & B):** These are essentially the same. Vagal fibers release Acetylcholine (ACh), which acts on **$M_2$ receptors**. This increases $K^+$ conductance (hyperpolarization) and decreases $Ca^{2+}$ conductance. This leads to a **decrease** in conduction velocity (Negative Dromotropy), primarily at the SA and AV nodes. In extreme cases, strong vagal stimulation can lead to a transient heart block. **High-Yield Clinical Pearls for NEET-PG:** * **Dromotropy:** Refers to conduction velocity. * **Inotropy:** Refers to contractility. * **Chronotropy:** Refers to heart rate. * **Bathmotropy:** Refers to excitability. * **AV Node Delay:** The slowest conduction velocity in the heart (approx. 0.01–0.05 m/s) occurs at the AV node to allow for ventricular filling. * **Purkinje System:** Possesses the **fastest** conduction velocity (approx. 1.5–4.0 m/s) to ensure near-simultaneous ventricular contraction.

Question 546: Right axis deviation is seen in:

A. Lying down position
B. Thin and tall individuals (Correct Answer)
C. Obese persons
D. At the end of peak expiration

Explanation: The electrical axis of the heart is primarily determined by its anatomical orientation within the thoracic cavity. **Explanation of the Correct Answer:** **B. Thin and tall individuals:** In ectomorphic (thin and tall) individuals, the diaphragm sits lower in the chest. This causes the heart to hang more vertically (a "vertical heart"). Since the electrical depolarization follows the anatomical long axis, the mean QRS vector shifts downward and to the right, resulting in **Right Axis Deviation (RAD)**. **Explanation of Incorrect Options:** * **A. Lying down position:** When a person lies supine, the abdominal contents push the diaphragm upward. This pushes the apex of the heart upward and to the left, leading to a more horizontal orientation or **Left Axis Deviation (LAD)**. * **C. Obese persons:** In obesity, increased intra-abdominal pressure and fat displacement push the diaphragm cranially. This rotates the heart transversely, causing **Left Axis Deviation (LAD)**. * **D. At the end of peak expiration:** During expiration, the diaphragm rises. This elevates the heart and rotates it to the left, resulting in **Left Axis Deviation (LAD)**. (Conversely, deep inspiration causes RAD). **High-Yield Clinical Pearls for NEET-PG:** * **Normal QRS Axis:** -30° to +90°. * **RAD (>+90°):** Seen in Right Ventricular Hypertrophy (RVH), Left Posterior Hemiblock (LPH), Pulmonary Embolism, and COPD. * **LAD (<-30°):** Seen in Left Ventricular Hypertrophy (LVH), Left Anterior Hemiblock (LAH), and Ascites/Pregnancy. * **Mnemonic:** **REACH** (Right Expiration—Wait, no): Remember **"Left Leaves, Right Reaches."** In LAD, QRS complexes in Lead I and Lead aVF point away from each other; in RAD, they point toward each other.

Question 547: Which of the following statements is TRUE regarding hemorrhage?

A. Pulse pressure decreases. (Correct Answer)
B. Hematocrit ratio increases.
C. Stroke volume and heart rate increase.
D. The number of impulses traveling in the sinus nerves increases.

Explanation: **Explanation:** Hemorrhage leads to a reduction in total blood volume (hypovolemia), which triggers a sequence of compensatory and pathological changes in the cardiovascular system. **Why Option A is Correct:** Pulse pressure is the difference between systolic and diastolic blood pressure ($PP = SBP - DBP$). It is directly proportional to **Stroke Volume (SV)** and inversely proportional to arterial compliance. In hemorrhage, the decrease in venous return (preload) leads to a significant drop in SV (Frank-Starling law). This reduction in SV is the primary driver for the **decrease in pulse pressure**, making it one of the earliest signs of clinical shock. **Analysis of Incorrect Options:** * **Option B:** Hematocrit actually **decreases** (though not immediately). Following hemorrhage, the body initiates "capillary refill" where interstitial fluid shifts into the intravascular compartment to restore volume, hemodiluting the remaining red cells. * **Option C:** While Heart Rate (HR) increases (tachycardia) via the baroreceptor reflex to compensate for low BP, **Stroke Volume decreases** due to reduced filling pressure. * **Option D:** Sinus nerves (branches of the glossopharyngeal nerve) carry inhibitory impulses from the carotid sinus baroreceptors. In hemorrhage, the drop in MAP reduces the stretch on these receptors, leading to a **decrease in the firing rate** of sinus nerves to the medulla, which then triggers sympathetic outflow. **High-Yield Clinical Pearls for NEET-PG:** * **Baroreceptor Reflex:** The most rapid compensatory mechanism in acute hemorrhage. * **Class of Shock:** A decrease in pulse pressure is typically seen starting in Class II Hemorrhage (15-30% blood loss). * **Reverse Stress Relaxation:** A delayed compensatory mechanism where blood vessels constrict around the remaining volume to maintain pressure.

Question 548: In which type of blood vessel is the mean linear velocity of a red blood cell the lowest?

A. Aorta and large arteries
B. Arterioles
C. Capillaries (Correct Answer)
D. Small arteries

Explanation: **Explanation:** The velocity of blood flow is governed by the principle of continuity, which states that velocity ($V$) is inversely proportional to the **total cross-sectional area** ($A$) of the vascular bed ($V = Q/A$, where $Q$ is cardiac output). 1. **Why Capillaries are Correct:** Although an individual capillary has a tiny diameter, the human body contains billions of them. When arranged in parallel, their **total combined cross-sectional area** is the largest in the entire circulatory system (approximately 1000 times that of the aorta). Consequently, the velocity of blood flow reaches its minimum (approx. 0.03 cm/s) in the capillaries. This slow transit is physiologically essential to allow sufficient time for the exchange of gases, nutrients, and waste products between blood and tissues. 2. **Why Other Options are Incorrect:** * **Aorta and Large Arteries:** These have the smallest total cross-sectional area. Therefore, the mean linear velocity is **highest** here (approx. 20-40 cm/s) to ensure rapid distribution of blood. * **Arterioles and Small Arteries:** As blood moves from the aorta toward the periphery, the total cross-sectional area gradually increases. While velocity decreases in these vessels compared to the aorta, it remains significantly higher than in the capillaries. **NEET-PG High-Yield Pearls:** * **Velocity vs. Resistance:** Do not confuse velocity with resistance. The **arterioles** are the site of highest peripheral resistance and the greatest pressure drop, but the **capillaries** have the lowest velocity. * **Sequence of Velocity:** Aorta > Arteries > Arterioles > Venules > Veins > Capillaries (Lowest). * **Sequence of Cross-sectional Area:** Capillaries (Highest) > Venules > Arterioles > Veins > Arteries > Aorta (Lowest).

Question 549: Carotid baroreceptors are important in the regulation of arterial blood pressure. Which of the following statements best describes their function?

A. They are important in the rapid, short-term regulation of arterial blood pressure. (Correct Answer)
B. They do not fire until a pressure of approximately 100 mm Hg is reached.
C. They adapt over 1 to 2 weeks to the prevailing mean arterial pressure.
D. Their reflexive action decreases cerebral blood flow.

Explanation: ### Explanation **1. Why Option A is Correct:** Carotid baroreceptors are high-pressure mechanoreceptors located in the carotid sinus. They are primarily responsible for **short-term, beat-to-beat regulation** of arterial blood pressure. When blood pressure changes suddenly (e.g., standing up), these receptors detect the stretch and send signals via the **Hering’s nerve (branch of Glossopharyngeal nerve)** to the Nucleus Tractus Solitarius (NTS) in the medulla. This triggers a rapid autonomic response to restore homeostasis within seconds. **2. Why the Other Options are Incorrect:** * **Option B:** Carotid baroreceptors are sensitive to pressures ranging from **60 to 180 mm Hg**. They start firing at around 60 mm Hg, with the maximal rate of change in firing occurring near the normal mean arterial pressure (approx. 95–100 mm Hg). * **Option C:** Baroreceptors are not effective for long-term regulation because they **"reset" or adapt** to a new baseline pressure within **1 to 2 days**, not weeks. Long-term regulation is primarily managed by the kidneys (Renin-Angiotensin-Aldosterone System). * **Option D:** The baroreceptor reflex aims to **maintain** adequate perfusion to vital organs. For example, if BP drops, the reflex causes vasoconstriction and increased heart rate to ensure cerebral blood flow remains stable. **3. High-Yield NEET-PG Pearls:** * **Location:** Carotid sinus (dilatation at the base of the internal carotid artery). * **Afferent Pathway:** Carotid sinus → Glossopharyngeal nerve (CN IX); Aortic arch → Vagus nerve (CN X). * **Sensitivity:** They are more sensitive to **pulsatile (changing) pressure** than to constant, steady pressure. * **Clinical Correlation:** **Carotid Sinus Hypersensitivity** can lead to syncope even with minor pressure on the neck (e.g., a tight collar) due to excessive vagal discharge.

Question 550: Which of the following events causes closure of the ductus arteriosus in a newborn?

A. Compression of the thorax during delivery
B. Compression of the pulmonary vessels during delivery
C. Fall in pulmonary arterial pressure (Correct Answer)
D. Fall in systemic arterial pressure

Explanation: ### Explanation **Correct Answer: C. Fall in pulmonary arterial pressure** **Underlying Medical Concept:** In fetal life, the lungs are collapsed and filled with fluid, leading to high pulmonary vascular resistance (PVR) and high pulmonary arterial pressure. This forces blood to bypass the lungs via the **ductus arteriosus (DA)** into the aorta. At birth, the first breath causes the lungs to expand and oxygenate. This leads to two critical changes: 1. **Vasodilation of pulmonary vessels:** This significantly decreases PVR and **falls the pulmonary arterial pressure**. 2. **Increased systemic resistance:** Clamping the umbilical cord increases systemic arterial pressure. As pulmonary pressure falls below systemic pressure, the flow through the DA reverses (left-to-right) and eventually ceases. The primary stimulus for the functional closure of the DA is the **increase in arterial oxygen tension (PaO₂)** and the **decrease in local prostaglandins (PGE2)**, but hemodynamically, it is the shift in pressure gradients (fall in pulmonary pressure) that facilitates this transition. **Analysis of Incorrect Options:** * **A & B:** Thoracic compression during delivery helps expel fetal lung fluid but does not directly cause the physiological closure of the ductus. * **D:** Systemic arterial pressure **rises** (not falls) at birth due to the loss of the low-resistance placental circulation. A fall in systemic pressure would actually favor continued right-to-left shunting. **High-Yield NEET-PG Pearls:** * **Functional Closure:** Occurs within 10–15 hours after birth due to smooth muscle contraction. * **Anatomical Closure:** Occurs by 2–3 weeks, forming the **ligamentum arteriosum**. * **Keep it open:** Prostaglandin E1 (Alprostadil) is used to maintain patency in ductal-dependent cyanotic heart diseases. * **Close it:** NSAIDs like **Indomethacin** or Ibuprofen (COX inhibitors) are used to treat Patent Ductus Arteriosus (PDA) by inhibiting prostaglandin synthesis.

Practice by Chapter

Cardiac Electrophysiology

Practice Questions

Cardiac Cycle

Practice Questions

Cardiac Output and Its Regulation

Practice Questions

Hemodynamics and Blood Flow

Practice Questions

Arterial System Physiology

Practice Questions

Microcirculation and Lymphatics

Practice Questions

Venous Return and Central Venous Pressure

Practice Questions

Cardiovascular Reflexes

Practice Questions

Regional Circulations

Practice Questions

Cardiovascular Responses to Exercise and Stress

Practice Questions

Want unlimited practice?

Get full access to all questions, explanations, and performance tracking.

Start For Free