Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 451: Cardiac output is decreased by?

A. Increased heart rate
B. Decreased heart rate (Correct Answer)
C. Increased stroke volume
D. None of the above

Explanation: **Explanation:** The fundamental physiological equation for Cardiac Output (CO) is: **Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)** **1. Why "Decreased heart rate" is correct:** Cardiac output is directly proportional to both heart rate and stroke volume. When the heart rate decreases (bradycardia), the number of times the heart pumps blood per minute reduces. Unless there is a massive compensatory increase in stroke volume, a decrease in heart rate will lead to a direct reduction in the total volume of blood ejected by the heart per minute. **2. Why the other options are incorrect:** * **A. Increased heart rate:** According to the formula, an increase in heart rate typically increases cardiac output (up to a physiological limit). However, at extremely high rates (tachyarrhythmias), CO may eventually fall because the diastolic filling time becomes too short. * **C. Increased stroke volume:** Stroke volume is the amount of blood pumped per beat. Increasing SV (via increased contractility or preload) directly increases the cardiac output. **High-Yield Clinical Pearls for NEET-PG:** * **Normal Range:** Average resting CO is approximately **5 L/min**. * **Cardiac Index:** CO adjusted for body surface area (Normal: 2.5–4 L/min/m²). * **The Limit of HR:** While increasing HR increases CO, if HR exceeds **160–180 bpm**, CO actually starts to decrease because the **ventricular filling time (diastole)** is severely compromised, leading to a drop in stroke volume. * **Factors increasing CO:** Anxiety, pregnancy, hyperthyroidism, and anemia (due to decreased viscosity). * **Factors decreasing CO:** Hemorrhage, shock, and heart failure.

Question 452: What is the normal pulmonary artery pressure?

A. 120/80 mm Hg
B. 25/0 mm Hg
C. 120/0 mm Hg
D. 25/8 mm Hg (Correct Answer)

Explanation: ### Explanation The correct answer is **D. 25/8 mm Hg**. **1. Understanding Pulmonary Artery Pressure (PAP):** The pulmonary circulation is a **low-pressure, low-resistance system** compared to the systemic circulation. This is because the right ventricle (RV) only needs to pump blood to the lungs, which are in close proximity to the heart. * **Systolic PAP (25 mm Hg):** Reflects the pressure generated by the RV during contraction. * **Diastolic PAP (8 mm Hg):** Reflects the pressure in the pulmonary artery while the RV is filling. * **Mean PAP:** Usually ranges between **10–20 mm Hg** (Average: 15 mm Hg). **2. Analysis of Incorrect Options:** * **A. 120/80 mm Hg:** This represents normal **Systemic Arterial Pressure**. The systemic circuit requires higher pressure to overcome high resistance and perfuse the entire body. * **B. 25/0 mm Hg:** This represents **Right Ventricular Pressure**. While the systolic pressure matches the pulmonary artery, the diastolic pressure in the ventricle drops to near zero during filling, whereas the pulmonary artery maintains a baseline pressure (8 mm Hg) due to the closure of the pulmonary valve. * **C. 120/0 mm Hg:** This represents **Left Ventricular Pressure**. The LV generates high systolic pressure to match the aorta but drops to zero during diastole to allow for filling. **3. High-Yield Clinical Pearls for NEET-PG:** * **Pulmonary Hypertension:** Defined clinically as a **Mean PAP >20 mm Hg** at rest (updated from the previous >25 mm Hg threshold). * **PCWP (Pulmonary Capillary Wedge Pressure):** Normal is **6–12 mm Hg**. It is a proxy for Left Atrial Pressure and is measured using a Swan-Ganz catheter. * **West Zones of the Lung:** Blood flow in the lungs is unevenly distributed due to gravity, influenced by the relationship between PAP, Pulmonary Venous Pressure, and Alveolar Pressure.

Question 453: Which type of blood vessel primarily regulates blood flow into capillary beds?

A. Arteries
B. Arterioles (Correct Answer)
C. Venules
D. Capillaries

Explanation: **Explanation:** **Why Arterioles are the Correct Answer:** Arterioles are known as the **"resistance vessels"** of the circulatory system. They possess a thick layer of smooth muscle in their walls relative to their lumen size, which is richly innervated by sympathetic adrenergic fibers. By undergoing vasoconstriction or vasodilation, arterioles create the greatest proportion of **Total Peripheral Resistance (TPR)**. This allows them to act as "adjustable nozzles," precisely regulating the volume and pressure of blood entering the fragile capillary beds. According to **Poiseuille’s Law**, since resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$), even small changes in arteriolar diameter significantly impact blood flow. **Analysis of Incorrect Options:** * **Arteries:** These are "conduit vessels" designed to transport blood under high pressure. While they have elastic properties to dampen pulsatility (Windkessel effect), they are not the primary site of resistance. * **Venules:** These are "capacitance vessels" that collect blood from capillaries. Their primary role is returning blood to the heart and serving as a reservoir for blood volume. * **Capillaries:** These are "exchange vessels." They lack smooth muscle entirely, consisting only of a single layer of endothelial cells, making them incapable of active diameter regulation. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Maximum Pressure Drop:** The largest drop in mean arterial pressure occurs across the arterioles. * **Pre-capillary Sphincters:** These are functional rings of smooth muscle at the arteriolar-capillary junction that determine the *number* of capillaries perfused at any given time. * **Pharmacology Link:** Drugs like Calcium Channel Blockers (e.g., Amlodipine) primarily act on arterioles to reduce TPR and blood pressure.

Question 454: A patient undergoing blood pressure testing reports an abnormal feeling in their fingertips followed by involuntary spasm of the fingers. What is the likely diagnosis?

A. Hysterical spasms
B. Pressure spasm of muscles due to neuropraxia
C. Hypocalcemic tetany (Correct Answer)
D. Ischemic muscle spasms

Explanation: ### Explanation The clinical scenario describes **Trousseau’s sign**, a classic physical exam finding indicative of **latent tetany** due to **hypocalcemia**. **1. Why Hypocalcemic Tetany is Correct:** When a blood pressure cuff is inflated above the systolic pressure for 3 minutes, it induces local ischemia. In patients with low serum ionized calcium, this ischemia increases neuromuscular irritability. Calcium ions normally stabilize neuronal membranes by blocking sodium channels; when calcium is low, the threshold for depolarization decreases. The resulting hyperexcitability leads to the characteristic **carpopedal spasm** (flexion of the wrist and metacarpophalangeal joints, extension of interphalangeal joints, and adduction of the thumb). **2. Why Other Options are Incorrect:** * **Hysterical spasms:** These are psychogenic and typically do not follow a specific physiological trigger like cuff inflation or present with the classic "obstetrician's hand" posture. * **Pressure spasm/Neuropraxia:** While nerve compression can cause paresthesia, it does not typically cause the specific, reproducible carpopedal spasm seen in this maneuver. * **Ischemic muscle spasms:** While ischemia is the *trigger* for Trousseau’s sign, the underlying pathology is the electrolyte imbalance (hypocalcemia) causing nerve irritability, not primary muscle ischemia (which would present as claudication or pain). **3. NEET-PG High-Yield Pearls:** * **Trousseau’s Sign:** More sensitive and specific for hypocalcemia than **Chvostek’s sign** (twitching of facial muscles upon tapping the facial nerve). * **Mechanism:** Low extracellular $Ca^{2+}$ $\rightarrow$ increased permeability to $Na^+$ $\rightarrow$ progressive depolarization $\rightarrow$ repetitive firing of action potentials. * **Other Causes of Tetany:** Hypomagnesemia and Respiratory Alkalosis (e.g., hyperventilation, which decreases ionized calcium by increasing calcium binding to albumin). * **Treatment:** Acute symptomatic tetany is treated with **IV Calcium Gluconate (10%)**.

Question 455: Which of the following situations will lead to increased viscosity of blood?

A. Fasting state
B. Hypoglycemia
C. Multiple myeloma (Correct Answer)
D. Amyloidogenesis

Explanation: **Explanation:** The viscosity of blood is primarily determined by two factors: the concentration of cellular elements (mainly the **hematocrit**) and the concentration of plasma proteins (mainly **fibrinogen and globulins**). **Why Multiple Myeloma is Correct:** Multiple Myeloma is a plasma cell dyscrasia characterized by the monoclonal proliferation of plasma cells, leading to the overproduction of monoclonal immunoglobulins (M-proteins). These large, bulky globulin molecules significantly increase the plasma protein content. According to the laws of fluid dynamics, an increase in large molecular weight proteins increases the internal friction of the fluid, leading to **Hyperviscosity Syndrome**. This can manifest clinically as visual disturbances, neurological symptoms, and mucosal bleeding. **Analysis of Incorrect Options:** * **Fasting state:** Short-term fasting does not significantly alter blood viscosity. While extreme dehydration (which can occur with prolonged fasting) might increase viscosity due to hemoconcentration, "fasting" typically implies a metabolic state that does not inherently raise protein or cell levels. * **Hypoglycemia:** Glucose is a small molecule. Changes in blood glucose levels have a negligible effect on the osmotic pressure and viscosity of blood compared to proteins and cells. * **Amyloidogenesis:** While amyloidosis involves protein deposition, these proteins are deposited **extracellularly in tissues** (like the heart, kidneys, or liver) rather than remaining soluble in the plasma. Therefore, it does not typically lead to increased blood viscosity. **High-Yield Pearls for NEET-PG:** * **Poiseuille’s Law:** Resistance to flow is directly proportional to viscosity ($\eta$). * **Fahraeus-Lindqvist Effect:** Viscosity decreases as blood flows through very small capillaries (diameter < 1.5mm) due to the alignment of RBCs in the center of the vessel (axial accumulation). * **Temperature:** Hypothermia increases blood viscosity. * **Polycythemia:** The most common cause of increased whole-blood viscosity due to elevated hematocrit.

Question 456: What happens to the slope of the pacemaker potential when vagal tone is increased?

A. Increased Na+ influx, increased slope
B. Decreased Na+ influx, decreased slope (Correct Answer)
C. Increased Na+ influx, decreased slope
D. Decreased Na+ influx, increased slope

Explanation: ### Explanation **1. Underlying Medical Concept** The pacemaker potential (Phase 4) in the SA node is primarily driven by the **Funny current ($I_f$)**, which involves the slow influx of **Na+** through HCN channels. When **vagal tone** (parasympathetic activity) increases, Acetylcholine is released. It binds to **$M_2$ receptors** in the SA node, leading to: * **Decreased cAMP levels:** This reduces the opening of HCN channels, leading to **decreased Na+ influx**. * **Activation of $K_{ACh}$ channels:** This causes K+ efflux, hyperpolarizing the cell. * **Result:** The rate of spontaneous depolarization slows down, meaning the **slope of the pacemaker potential decreases**. This increases the time required to reach the threshold, thereby decreasing the heart rate (negative chronotropy). **2. Analysis of Incorrect Options** * **Option A & D:** Increased vagal tone *decreases* the heart rate. An "increased slope" would mean reaching the threshold faster, which increases heart rate (sympathetic effect). * **Option C:** While a decreased slope is correct for vagal stimulation, it is caused by *decreased* Na+ influx, not increased. Increased Na+ influx would steepen the slope. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Sympathetic Stimulation:** Acts via $\beta_1$ receptors to increase cAMP, increasing $I_f$ (Na+ influx) and $I_{Ca}$ (Ca2+ influx), which **increases the slope**. * **Phase 0 in SA Node:** Unlike ventricular muscle (Na+ driven), the upstroke in pacemaker cells is due to **Ca2+ influx** (L-type channels). * **Resting Membrane Potential:** Pacemaker cells do not have a true "resting" potential; they have a "maximal diastolic potential" of approximately -60 mV. * **Vagal Escape:** If vagal stimulation is intense and prolonged, the ventricles may begin to beat at their own intrinsic rate (Purkinje fiber rhythm).

Question 457: Increase in blood pressure occurs with?

A. Low potassium intake (Correct Answer)
B. Low calcium intake
C. Low sodium intake
D. Low chloride intake

Explanation: **Explanation:** The relationship between electrolyte intake and blood pressure is a high-yield topic in cardiovascular physiology. **Why Low Potassium Intake is Correct:** Potassium ($K^+$) plays a vital role in maintaining vascular tone and sodium balance. A **low potassium intake** leads to an increase in blood pressure through several mechanisms: 1. **Sodium Retention:** Low $K^+$ levels stimulate the kidneys to reabsorb more Sodium ($Na^+$), leading to water retention and increased plasma volume. 2. **Vasoconstriction:** Potassium normally promotes vasodilation by hyperpolarizing vascular smooth muscle cells. Deficiency leads to increased peripheral vascular resistance. 3. **RAAS Activation:** Low $K^+$ can trigger the Renin-Angiotensin-Aldosterone System (RAAS), further elevating blood pressure. **Analysis of Incorrect Options:** * **Low Sodium Intake:** Reducing sodium intake is a primary clinical intervention to *decrease* blood pressure, as it reduces extracellular fluid volume and sympathetic activity. * **Low Calcium Intake:** While chronic low calcium is associated with hypertension in some epidemiological studies, the physiological link is less direct than potassium. In acute settings, calcium channel blockers (which mimic "low calcium" action on vessels) are used to *lower* BP. * **Low Chloride Intake:** Chloride usually follows sodium. Low chloride intake is generally associated with a decrease in blood pressure or metabolic alkalosis, but it does not cause hypertension. **NEET-PG High-Yield Pearls:** * **DASH Diet:** Emphasizes high Potassium, Calcium, and Magnesium to lower BP. * **Na+/K+ Ratio:** The urinary sodium-to-potassium ratio is a stronger predictor of blood pressure than either nutrient alone. * **Hyperkalemia & ECG:** Remember that while low $K^+$ raises BP, *high* $K^+$ is cardiotoxic (Tall peaked T-waves).

Question 458: Which of the following is true about the S4 heart sound?

A. Can be heard by the unaided ear
B. Frequency is greater than 20 Hz
C. Heard during ventricular filling phase (Correct Answer)
D. Heard during ventricular ejection phase

Explanation: ### Explanation The **S4 heart sound** (atrial gallop) occurs during the **late phase of ventricular filling**, specifically during **atrial systole**. **1. Why Option C is Correct:** S4 is produced when the atria contract to force blood into a non-compliant or stiff ventricle. This occurs at the very end of diastole, just before S1. Since atrial contraction is the final component of the **ventricular filling phase**, S4 is inherently a filling sound. It represents the "atrial kick" vibrating against a resistant ventricular wall. **2. Why Other Options are Incorrect:** * **Option A:** Heart sounds, including S4, are generally low-frequency and low-intensity; they require a **stethoscope** (specifically the bell) for auscultation and cannot be heard by the unaided ear. * **Option B:** S4 is a **low-frequency sound**, typically falling **below 20 Hz**. The human ear is generally insensitive to frequencies below 20 Hz, which is why S4 is often difficult to hear and is better visualized on a phonocardiogram. * **Option D:** The ventricular ejection phase occurs during systole (between S1 and S2). S4 is a **presystolic/diastolic** sound, occurring before the valves even open for ejection. **3. High-Yield Clinical Pearls for NEET-PG:** * **Pathological Significance:** S4 is almost always pathological (unlike S3, which can be physiological in children/athletes). It indicates **reduced ventricular compliance** (e.g., Left Ventricular Hypertrophy, Systemic Hypertension, Aortic Stenosis, or Ischemic Heart Disease). * **The "Ten-nes-see" Rhythm:** S4-S1-S2 creates a cadence often described by this mnemonic. * **Absence in Atrial Fibrillation:** Since S4 requires active atrial contraction, it **disappears** in patients with Atrial Fibrillation. * **Best heard at:** The apex with the patient in the left lateral decubitus position using the **bell** of the stethoscope.

Question 459: The dicrotic notch of the aortic pressure waveform is lost in which condition?

A. Aortic Stenosis (Correct Answer)
B. Aortic Regurgitation
C. Patent Ductus Arteriosus (PDA)
D. Arteriosclerosis

Explanation: ### Explanation The **dicrotic notch (incisura)** on the aortic pressure curve represents the brief interruption of blood flow caused by the **closure of the aortic valve** at the onset of ventricular diastole. **1. Why Aortic Stenosis (AS) is the Correct Answer:** In Aortic Stenosis, the aortic valve leaflets become thickened, calcified, and rigid. This structural damage prevents the sharp, snapping closure of the valve required to produce the dicrotic notch. Furthermore, the narrowed orifice leads to a slow, prolonged ejection of blood (pulsus tardus) and a lower peak pressure (pulsus parvus), resulting in a "smoothed out" pressure waveform where the dicrotic notch is typically **absent or significantly diminished**. **2. Analysis of Incorrect Options:** * **Aortic Regurgitation (AR):** Characterized by a "Water-hammer pulse." While the dicrotic notch may be small, the hallmark is a rapid upstroke and a rapid collapse. * **Patent Ductus Arteriosus (PDA):** Similar to AR, this creates a hyperdynamic circulation with a wide pulse pressure. The notch is usually present but may be shifted or less prominent due to the continuous runoff of blood into the pulmonary artery. * **Arteriosclerosis:** Hardening of the arteries actually makes the dicrotic notch **more prominent** and shifts it higher up on the waveform due to increased wave reflection and decreased arterial compliance. **3. NEET-PG High-Yield Pearls:** * **Anacrotic Notch:** Seen on the *ascending* limb of the pulse wave in Aortic Stenosis. * **Dicrotic Wave:** Do not confuse the *notch* (valve closure) with the *wave* (rebound of blood against the closed valve). * **Dicrotic Pulse (Double-peaked):** Seen in conditions with low cardiac output and high systemic vascular resistance (e.g., severe heart failure, dilated cardiomyopathy). * **Bisferiens Pulse:** Two systolic peaks; characteristic of AR combined with AS or Hypertrophic Obstructive Cardiomyopathy (HOCM).

Question 460: Memory cells do not undergo apoptosis due to the presence of which growth factor?

A. Platelet-derived growth factor
B. Nerve growth factor (Correct Answer)
C. Insulin-like growth factor
D. Fibroblast growth factor

Explanation: **Explanation:** The survival of memory B-cells and T-cells is a tightly regulated process essential for long-term immunity. While most effector lymphocytes undergo apoptosis following the clearance of an antigen, memory cells persist for years. **Why Nerve Growth Factor (NGF) is correct:** Recent immunological research has identified that **Nerve Growth Factor (NGF)** plays a non-neuronal role in the immune system. Memory B-cells express high-affinity NGF receptors (**TrkA**). The interaction between NGF and TrkA upregulates the anti-apoptotic protein **Bcl-2**, which inhibits the programmed cell death pathway. This allows memory cells to bypass the default apoptosis that occurs at the end of an immune response. **Analysis of Incorrect Options:** * **A. Platelet-derived growth factor (PDGF):** Primarily involved in connective tissue growth, angiogenesis, and wound healing by stimulating mesenchymal cells (fibroblasts and smooth muscle). * **C. Insulin-like growth factor (IGF):** Primarily mediates the effects of Growth Hormone, promoting systemic cell growth and skeletal development. * **D. Fibroblast growth factor (FGF):** Crucial for embryonic development, tissue repair, and hematopoiesis, but does not specifically regulate memory cell longevity. **NEET-PG High-Yield Pearls:** * **Bcl-2** is the "survival molecule"; its overexpression is also linked to Follicular Lymphoma (t:14,18). * **NGF** is a member of the neurotrophin family, which also includes Brain-Derived Neurotrophic Factor (BDNF). * Memory cells are characterized by being in the **G0 phase** of the cell cycle until re-exposure to an antigen.

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