Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 671: What ECG finding is characteristic of hypercalcemia?

A. Widened QT interval
B. Shortened QT interval (Correct Answer)
C. Prolonged PR interval
D. Tall T waves

Explanation: **Explanation:** **Correct Answer: B. Shortened QT interval** **Mechanism:** The QT interval represents the total duration of ventricular depolarization and repolarization. In **hypercalcemia**, the increased extracellular calcium concentration increases the influx of calcium during the plateau phase (Phase 2) of the cardiac action potential. This leads to an accelerated repolarization process, effectively shortening the duration of the action potential and, consequently, the **QT interval**. **Analysis of Incorrect Options:** * **A. Widened QT interval:** This is characteristic of **hypocalcemia**. Low serum calcium slows Phase 2 of the action potential, prolonging the ST segment and the overall QT interval. * **C. Prolonged PR interval:** While severe hypercalcemia can occasionally cause AV blocks, a prolonged PR interval is more classically associated with **hyperkalemia**, digoxin toxicity, or first-degree heart block. * **D. Tall T waves:** "Tent-shaped" or tall peaked T waves are the hallmark ECG finding of **hyperkalemia**, not calcium imbalances. **High-Yield Clinical Pearls for NEET-PG:** * **Hypercalcemia Mnemonic:** "Short QT, Short Temper" (referring to neuropsychiatric symptoms). * **Osborn Waves (J waves):** Though primarily seen in hypothermia, they can occasionally appear in severe hypercalcemia. * **Hypocalcemia:** Look for a prolonged ST segment leading to a prolonged QT interval. * **Digoxin Effect:** Can also cause a shortened QT interval and the classic "reverse tick" or "scooped" ST-segment depression.

Question 672: A 47-year-old man with type II diabetes reports for his 6-month checkup. His doctor prescribes a daily 30-minute routine of walking at a brisk pace. During aerobic exercise, blood flow remains relatively constant to which of the following organs?

A. Brain (Correct Answer)
B. Heart
C. Kidneys
D. Skeletal muscle

Explanation: ### Explanation **1. Why the Brain is Correct:** The brain is the most metabolically sensitive organ and requires a continuous, stable supply of oxygen and glucose. During aerobic exercise, **cerebral blood flow is kept relatively constant** (approx. 750 mL/min) through a process called **autoregulation**. This mechanism ensures that despite fluctuations in systemic arterial blood pressure and cardiac output, the cerebral resistance vessels (arterioles) constrict or dilate to maintain steady perfusion. While there may be minor regional shifts in blood flow to the motor cortex, the total global cerebral blood flow does not change significantly. **2. Why the Other Options are Incorrect:** * **Heart (B):** Myocardial blood flow **increases** significantly during exercise (up to 3–4 times) to meet the increased oxygen demand caused by elevated heart rate and contractility. * **Kidneys (C):** Renal blood flow **decreases** during exercise. Sympathetic nervous system activation causes vasoconstriction of renal arterioles to divert blood toward the active muscles. * **Skeletal Muscle (D):** This organ shows the **most dramatic increase** in blood flow. Through active hyperemia (buildup of local metabolites like $K^+$, adenosine, and $CO_2$), blood flow can increase up to 20-fold to support aerobic metabolism. **3. High-Yield NEET-PG Pearls:** * **Autoregulation Range:** Cerebral blood flow remains constant between a Mean Arterial Pressure (MAP) of **60 to 140 mmHg**. * **Splanchnic Circulation:** Like the kidneys, blood flow to the GI tract decreases during exercise due to sympathetic-mediated vasoconstriction. * **Skin Blood Flow:** Initially decreases (vasoconstriction), but eventually **increases** as body temperature rises to facilitate heat loss through thermoregulation. * **Key Concept:** During exercise, Cardiac Output (CO) is redistributed: "More to the heart and muscles, less to the viscera, and constant to the brain."

Question 673: Venous return to the heart during quiet standing is facilitated by all of the following factors, except?

A. Calf muscle contraction during standing
B. Valves in perforators
C. Sleeve of deep fascia
D. Gravitational increase in atrial pressure (Correct Answer)

Explanation: **Explanation:** Venous return from the lower limbs against gravity is a complex physiological process. The correct answer is **D (Gravitational increase in atrial pressure)** because gravity actually causes blood to pool in the lower extremities, which **decreases** venous return and subsequently **lowers** right atrial pressure. An increase in atrial pressure would act as a back-pressure, further hindering venous return rather than facilitating it. **Analysis of Options:** * **A. Calf muscle contraction:** Known as the "Peripheral Heart," the contraction of gastrocnemius and soleus muscles compresses deep veins, propelling blood upward toward the heart. * **B. Valves in perforators:** These one-way valves allow blood to flow from superficial to deep veins but prevent reflux. This ensures that the "muscle pump" effectively moves blood toward the heart without it leaking back into the superficial system. * **C. Sleeve of deep fascia:** The tough, inelastic deep fascia (fascia lata/cruris) acts as a rigid compartment. This limits the outward expansion of muscles during contraction, ensuring that the pressure generated is directed inward to compress the veins. **NEET-PG High-Yield Pearls:** * **The Muscle Pump:** During walking, the venous pressure at the ankle drops from ~90 mmHg (standing still) to ~20 mmHg due to the efficiency of the calf muscle pump. * **Respiratory Pump:** During inspiration, intrathoracic pressure becomes more negative, "sucking" blood into the right atrium, further facilitating venous return. * **Clinical Correlation:** Failure of the valves in the perforators leads to **Varicose Veins** and chronic venous insufficiency.

Question 674: Which neurotransmitter is released in response to a raised blood pressure?

A. Acetylcholine (Correct Answer)
B. Adrenaline
C. Dopamine
D. Nor-adrenaline

Explanation: ### Explanation **1. Why Acetylcholine is Correct:** When blood pressure rises, it triggers the **Baroreceptor Reflex**. High pressure stretches baroreceptors in the carotid sinus and aortic arch, sending signals to the Medulla Oblongata (NTS). This results in a compensatory increase in **Parasympathetic (Vagal) activity** and a decrease in Sympathetic activity. The postganglionic parasympathetic fibers (Vagus nerve) release **Acetylcholine (ACh)** at the Sinoatrial (SA) node. ACh binds to **M2 muscarinic receptors**, leading to a decrease in heart rate (bradycardia) and a subsequent drop in cardiac output to normalize blood pressure. **2. Why the Other Options are Incorrect:** * **B. Adrenaline & D. Nor-adrenaline:** These are the primary neurotransmitters of the **Sympathetic Nervous System**. They are released in response to *low* blood pressure (hypotension) or stress (fight-or-flight). They act on $\beta_1$ receptors to increase heart rate and contractility, and $\alpha_1$ receptors to cause vasoconstriction, which would further *increase* blood pressure. * **C. Dopamine:** While dopamine has cardiovascular effects (vasodilation at low doses, inotropic at medium doses), it is not the primary neurotransmitter involved in the acute baroreceptor reflex arc for lowering blood pressure. **3. Clinical Pearls & High-Yield Facts:** * **The Reflex Arc:** Afferent limb (CN IX from carotid sinus, CN X from aortic arch) $\rightarrow$ Center (NTS in Medulla) $\rightarrow$ Efferent limb (Vagus nerve). * **Marey’s Law:** States that heart rate is inversely proportional to blood pressure (mediated by the baroreceptor reflex). * **Bezold-Jarisch Reflex:** A similar parasympathetic response (bradycardia and hypotension) triggered by noxious stimuli in the ventricles. * **Key Receptor:** Acetylcholine acts on **M2 receptors** in the heart to open K+ channels, causing hyperpolarization.

Question 675: Which of the following statements about shunt vessels is true?

A. Shunt vessels are evenly distributed throughout the skin.
B. Shunt vessels play a role in nutrition.
C. Shunt vessels play a role in thermoregulation. (Correct Answer)
D. Shunt vessels have no autonomic nervous regulation.

Explanation: ### Explanation **Correct Answer: C. Shunt vessels play a role in thermoregulation.** **Concept:** Shunt vessels, also known as **Arteriovenous (AV) Anastomoses**, are direct communications between arterioles and venules that bypass the capillary bed. Their primary physiological role is **thermoregulation**. When the body needs to dissipate heat, these shunts dilate, allowing a massive volume of warm blood to flow into the superficial venous plexuses of the skin, facilitating heat loss via radiation and convection. Conversely, in cold environments, sympathetic vasoconstriction closes these shunts to conserve core body heat. **Analysis of Incorrect Options:** * **A. Evenly distributed:** This is incorrect. AV anastomoses are highly localized. they are found predominantly in the **"apical" skin areas**—fingertips, toes, palms, soles, lips, and ears—where heat loss is most efficient. * **B. Role in nutrition:** This is incorrect. Because shunt vessels bypass the capillaries, no exchange of gases, nutrients, or waste products occurs. Their function is purely hemodynamic and thermal, not metabolic. * **D. No autonomic regulation:** This is incorrect. Shunt vessels are richly innervated by **sympathetic adrenergic fibers**. They are highly sensitive to catecholamines and are controlled by the hypothalamus (the body's thermostat). **High-Yield NEET-PG Pearls:** * **Glomus Body:** A specialized type of AV anastomosis found in the fingertips and under nails; it is encapsulated and highly sensitive to temperature changes. * **Triple Response of Lewis:** While related to skin blood flow, remember that the "flare" is mediated by an axon reflex, whereas shunt vessel regulation is centrally mediated via the sympathetic nervous system. * **Key Location:** The most abundant site for these shunts is the **fingertips**.

Question 676: Which blood pressure regulatory system functions as a buffer system?

A. Baroreceptor (Correct Answer)
B. Chemoreceptor
C. Kidney
D. CNS ischemic response

Explanation: **Explanation:** The **Baroreceptor reflex** is known as the **"Pressure Buffer System"** because it opposes both increases and decreases in arterial pressure, thereby reducing daily pressure variability. 1. **Why Baroreceptor is correct:** Located in the carotid sinus and aortic arch, these stretch receptors respond rapidly (within seconds) to changes in mean arterial pressure. When BP rises, they increase firing to the nucleus tractus solitarius (NTS), leading to parasympathetic activation and sympathetic inhibition. This "buffers" the rise in pressure. Conversely, a drop in BP triggers a reflex increase in heart rate and peripheral resistance. Without this system, activities like standing up or coughing would cause extreme, dangerous fluctuations in blood pressure. 2. **Why other options are incorrect:** * **Chemoreceptors:** These primarily respond to low $O_2$, high $CO_2$, and low pH. They are more critical for respiratory control and only significantly impact BP when it falls below 80 mmHg. * **Kidney:** This is a **long-term** regulatory mechanism (Renin-Angiotensin-Aldosterone System). It is highly potent but takes hours to days to act, unlike the immediate "buffering" of baroreceptors. * **CNS Ischemic Response:** This is the "Last Ditch Stand" mechanism. It only activates when MAP falls below 60 mmHg (most intense at <20 mmHg) to prevent brain death. **High-Yield Clinical Pearls for NEET-PG:** * **Location:** Carotid sinus (via Glossopharyngeal nerve) and Aortic arch (via Vagus nerve). * **Resetting:** Baroreceptors "reset" to a higher baseline in chronic hypertension within 1-2 days, making them ineffective for long-term BP control. * **Cushing’s Triad:** A clinical manifestation of the CNS ischemic response due to increased intracranial pressure (Hypertension, Bradycardia, Irregular Respiration).

Question 677: The pacemaker potential is due to which of the following?

A. Fast Na+ channel
B. Decrease in K+ permeability (Correct Answer)
C. Slow Ca++ channel
D. Rapid repolarization

Explanation: ### Explanation The **pacemaker potential** (also known as the prepotential or Phase 4) is the slow, spontaneous depolarization of the SA node that brings the membrane potential to the threshold. Unlike ventricular myocytes, pacemaker cells do not have a stable resting membrane potential. **1. Why "Decrease in K+ permeability" is correct:** The pacemaker potential is a multi-ionic process. The initial phase is triggered by the opening of **HCN channels** (Funny current, $I_f$), allowing $Na^+$ influx. However, a critical contributing factor is the **progressive decrease in $K^+$ efflux (permeability)**. As the cell repolarizes from the previous action potential, $K^+$ channels begin to close. Since $K^+$ normally maintains the negative resting potential, its decreased permeability prevents positive charges from leaving the cell, causing the membrane potential to drift toward a more positive (depolarized) state. **2. Why other options are incorrect:** * **A. Fast $Na^+$ channel:** These are responsible for the rapid depolarization (Phase 0) in **atrial/ventricular myocytes**. Pacemaker cells lack functional fast $Na^+$ channels; their Phase 0 is mediated by $Ca^{2+}$. * **C. Slow $Ca^{2+}$ channel (L-type):** These channels are responsible for the **Phase 0 (depolarization phase)** of the pacemaker action potential, not the prepotential itself. (Note: *T-type* $Ca^{2+}$ channels contribute to the *latter* part of the prepotential). * **D. Rapid repolarization:** This refers to Phase 3, caused by $K^+$ efflux, which makes the membrane potential more negative, moving it *away* from the threshold. **Clinical Pearls & High-Yield Facts:** * **SA Node:** The primary pacemaker because it has the steepest prepotential slope. * **Autonomic Influence:** Sympathetic stimulation increases the slope (increases $I_f$ and $Ca^{2+}$ current), while Parasympathetic stimulation (ACh) decreases the slope and hyperpolarizes the cell by increasing $K^+$ permeability. * **Ivabradine:** A drug that specifically blocks the $I_f$ (Funny current) to reduce heart rate without affecting contractility.

Question 678: Heart rate increases with one of the following?

A. Stimulation of trigeminal nerve pain receptor
B. Increased intracranial tension
C. Decreased stimulation of baroreceptors (Correct Answer)
D. Increased parasympathetic stimulation

Explanation: ### Explanation **Correct Option: C. Decreased stimulation of baroreceptors** The baroreceptor reflex is a homeostatic mechanism that maintains blood pressure. Baroreceptors (located in the carotid sinus and aortic arch) are **stretch receptors**. * When blood pressure falls, there is **decreased stimulation** (less stretch) of these receptors. * This leads to a decrease in inhibitory signals sent via the Glossopharyngeal (IX) and Vagus (X) nerves to the Medullary Vasomotor Center. * The result is a compensatory **increase in sympathetic outflow** and a decrease in parasympathetic tone, leading to an **increase in heart rate (tachycardia)** and peripheral vasoconstriction. **Analysis of Incorrect Options:** * **A. Stimulation of trigeminal nerve pain receptor:** Intense stimulation of trigeminal pain receptors (e.g., during ocular surgery or nasal procedures) often triggers the **Oculocardiac reflex**, which causes profound **bradycardia** (decreased heart rate). * **B. Increased intracranial tension (ICT):** High ICT leads to the **Cushing Reflex**, characterized by the triad of hypertension, irregular respiration, and **reflex bradycardia**. * **D. Increased parasympathetic stimulation:** The Vagus nerve (parasympathetic) releases Acetylcholine at the SA node, which increases K+ conductance and hyperpolarizes the cell, thereby **decreasing the heart rate**. **High-Yield Clinical Pearls for NEET-PG:** * **Marey’s Law:** States that heart rate is inversely proportional to blood pressure (mediated by the baroreceptor reflex). * **Bainbridge Reflex:** Unlike the baroreceptor reflex, an increase in right atrial pressure (venous return) causes an **increase** in heart rate to pump the excess blood forward. * **Carotid Sinus Hypersensitivity:** Minor pressure on the neck can trigger excessive baroreceptor firing, leading to sudden bradycardia and syncope.

Question 679: Which of the following is NOT a cause of a rightward shift of the oxyhemoglobin dissociation curve?

A. Increased hydrogen ions
B. Decreased CO2 (Correct Answer)
C. Increased temperature
D. Increased 2,3-bisphosphoglycerate (BPG)

Explanation: The oxyhemoglobin dissociation curve (ODC) represents the relationship between the partial pressure of oxygen ($PO_2$) and the percentage saturation of hemoglobin. A **rightward shift** indicates a decreased affinity of hemoglobin for oxygen, facilitating oxygen unloading to the tissues. ### Why "Decreased $CO_2$" is the Correct Answer A rightward shift is caused by factors that signal high metabolic activity in tissues. **Decreased $CO_2$** (hypocapnia) actually increases hemoglobin's affinity for oxygen, causing a **leftward shift**. This prevents oxygen from being released easily. Conversely, increased $CO_2$ causes a rightward shift (the **Bohr Effect**). ### Analysis of Incorrect Options (Causes of Rightward Shift) * **Increased Hydrogen Ions (Decreased pH):** An acidic environment (acidosis) reduces hemoglobin's affinity for $O_2$, shifting the curve to the right to provide more oxygen to metabolically active (acidic) tissues. * **Increased Temperature:** Hyperthermia (e.g., during exercise or fever) weakens the bond between hemoglobin and oxygen, shifting the curve to the right. * **Increased 2,3-BPG:** This byproduct of glycolysis binds to the beta chains of deoxyhemoglobin, stabilizing the "T" (Tense) state and promoting oxygen release (Right shift). ### NEET-PG High-Yield Pearls * **Mnemonic for Right Shift:** "**CADET**, face Right!" (**C**-$CO_2$ increase, **A**-Acid/H+ increase, **D**-2,3-DPG/BPG increase, **E**-Exercise, **T**-Temperature increase). * **Fetal Hemoglobin (HbF):** Causes a **Left shift** because it does not bind 2,3-BPG effectively, allowing the fetus to "pull" oxygen from maternal blood. * **P50 Value:** The $PO_2$ at which 50% of hemoglobin is saturated. A right shift **increases** the P50 (normal is ~26.7 mmHg).

Question 680: Following acute failure of the left ventricle, when does pulmonary edema generally begin to appear in relation to left atrial pressure?

A. 7 mm Hg
B. 15 mm Hg
C. 20 mm Hg (Correct Answer)
D. 30 mm Hg

Explanation: **Explanation:** The development of pulmonary edema in left ventricular failure is governed by **Starling’s Forces**. Under normal physiological conditions, the Left Atrial Pressure (LAP) is approximately **2–12 mm Hg**. Since there are no valves between the pulmonary veins and the left atrium, LAP is a direct reflection of Pulmonary Capillary Wedge Pressure (PCWP). **Why 20 mm Hg is correct:** Pulmonary edema occurs when the hydrostatic pressure in the pulmonary capillaries exceeds the **plasma colloid osmotic pressure** (which is approximately **25–28 mm Hg**). In acute left heart failure, as the left ventricle fails to pump, blood backs up into the left atrium and pulmonary circulation. When the LAP/PCWP rises above the "safety factor" threshold—typically **>20 mm Hg**—fluid begins to leak from the capillaries into the interstitial space and alveoli, leading to clinical pulmonary edema. **Analysis of Incorrect Options:** * **A (7 mm Hg):** This is within the normal range of LAP. At this pressure, Starling forces favor fluid remaining within the vessels. * **B (15 mm Hg):** While elevated (suggesting mild congestion), the lymphatic system can usually compensate for this slight increase in transudation, preventing overt edema. * **D (30 mm Hg):** While pulmonary edema is definitely present at 30 mm Hg, the question asks when it *begins* to appear. 20 mm Hg is the recognized threshold for the onset of transudation. **High-Yield Clinical Pearls for NEET-PG:** * **Safety Factor:** The difference between plasma colloid osmotic pressure and pulmonary capillary pressure is the "safety factor" against edema (approx. 21 mm Hg). * **Chronic vs. Acute:** In chronic mitral stenosis, LAP can rise to 40+ mm Hg without acute edema because the lymphatic drainage capacity increases over time. * **Chest X-ray:** Cephalization (upper lobe diversion) occurs at 12–18 mm Hg; Kerley B lines appear at 18–25 mm Hg; Alveolar edema (Bat-wing appearance) occurs at >25 mm Hg.

Practice by Chapter

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