Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 181: The Bezold-Jarisch reflex causes apnea followed by rapid breathing, hypotension, and bradycardia. Where are the receptors that produce this reflex located?

A. Lungs
B. Heart (Correct Answer)
C. Pleura
D. Brain

Explanation: ### Explanation The **Bezold-Jarisch reflex (BJR)** is a cardio-inhibitory reflex characterized by the triad of **bradycardia, hypotension, and apnea** (followed by tachypnea). **Why the Heart is Correct:** The receptors for this reflex are primarily **chemoreceptors and mechanoreceptors (C-fibers)** located in the ventricular walls, particularly the **inferior and posterior walls of the left ventricle**. These receptors are stimulated by chemical substances (e.g., serotonin, capsaicin, veratridine alkaloids) or mechanical triggers (e.g., severe hypovolemia or myocardial ischemia). The afferent pathway is via the **vagus nerve**, leading to increased parasympathetic outflow and decreased sympathetic activity. **Why Other Options are Incorrect:** * **Lungs:** While the lungs contain J-receptors (juxtacapillary receptors) that cause the **Hering-Breuer reflex** or rapid shallow breathing, they are not the primary site for the classic Bezold-Jarisch triad. * **Pleura:** The pleura contains sensory fibers that mediate pain and the "pleural shock" reflex (bradycardia/hypotension during pleural aspiration), but this is distinct from the BJR. * **Brain:** The brain (medulla) acts as the integrating center for these reflexes, but it does not house the initiating receptors. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Significance:** The BJR is often triggered during **Inferior Wall Myocardial Infarction (IWMI)** because the receptors are concentrated in the inferior wall. This explains why IWMI patients frequently present with bradycardia. * **Spinal Anesthesia:** BJR is a common cause of sudden bradycardia and hypotension following spinal anesthesia due to decreased venous return (empty heart syndrome). * **Key Triad:** Remember the "3 H's" (though technically it's **Bradycardia, Hypotension, and Apnea**). * **Afferent/Efferent:** Both are mediated by the **Vagus nerve** (Cranial Nerve X).

Question 182: Compensatory mechanisms during acute hemorrhage include:

A. Decreased cerebral and coronary blood flow
B. Decreased myocardial contractility
C. Renal and splanchnic vasodilation
D. Increased respiratory rate (Correct Answer)

Explanation: **Explanation:** Acute hemorrhage leads to a sudden decrease in blood volume (hypovolemia), triggering a series of compensatory mechanisms aimed at maintaining mean arterial pressure (MAP) and vital organ perfusion. **Why Option D is Correct:** The reduction in blood volume leads to decreased oxygen delivery to tissues and a drop in blood pressure. This triggers the **peripheral chemoreceptors** (carotid and aortic bodies) due to stagnant hypoxia and acidosis (lactic acid buildup from anaerobic metabolism). These receptors signal the medullary respiratory centers to **increase the respiratory rate and depth** (hyperpnea). This "respiratory pump" also aids venous return by increasing negative intrathoracic pressure. **Why the Other Options are Incorrect:** * **A & C:** During hemorrhage, the **Baroreceptor Reflex** triggers massive sympathetic outflow. This causes **selective vasoconstriction** in "non-essential" beds (renal, splanchnic, and cutaneous) to divert blood to "essential" organs. Therefore, renal/splanchnic vasodilation is incorrect. Conversely, **cerebral and coronary blood flow are preserved** (not decreased) through autoregulation and sympathetic-mediated shunting. * **B:** Sympathetic stimulation increases levels of circulating catecholamines, which act on $\beta_1$ receptors to **increase myocardial contractility** (positive inotropy) and heart rate (positive chronotropy) to maintain cardiac output. **High-Yield NEET-PG Pearls:** * **The "Gold Standard" Response:** The earliest sign of compensation in acute hemorrhage is usually **tachycardia**. * **CNS Ischemic Response:** This is the "last ditch stand" for BP control, occurring only when MAP falls below 60 mmHg. * **Fluid Shift:** The "Capillary Fluid Shift" mechanism moves fluid from the interstitial space into the intravascular compartment to restore volume (autoinfusion). * **Hormonal Response:** Activation of the Renin-Angiotensin-Aldosterone System (RAAS) and ADH (Vasopressin) release occurs to conserve water and salt.

Question 183: What is the state at the end of ventricular diastole?

A. Atrial volume is more
B. Coronary flow is maximum (Correct Answer)
C. Flow in aorta drops
D. All of the above

Explanation: **Explanation:** The correct answer is **B. Coronary flow is maximum.** In the cardiac cycle, coronary blood flow to the left ventricle is unique because it occurs primarily during **diastole**. During systole, the contracting myocardium compresses the intramyocardial blood vessels (extravascular compression), significantly increasing resistance and reducing flow. As the heart relaxes during diastole, this compression is removed. **Why at the end of ventricular diastole?** Coronary perfusion pressure is the difference between aortic diastolic pressure and left ventricular end-diastolic pressure (LVEDP). At the end of diastole, the myocardium is at its most relaxed state, and the resistance from the muscle mass is at its absolute minimum. This allows for peak coronary blood flow just before the next isometric contraction begins. **Analysis of Incorrect Options:** * **A. Atrial volume is more:** At the end of ventricular diastole, the atria have just finished the "atrial kick" (atrial systole), emptying their contents into the ventricles. Therefore, atrial volume is at its **minimum**, while ventricular volume (EDV) is at its maximum. * **C. Flow in aorta drops:** While aortic pressure gradually declines during diastole, the "drop" in flow is not the defining characteristic of this phase compared to the physiological significance of coronary perfusion. **High-Yield Clinical Pearls for NEET-PG:** * **Left vs. Right Ventricle:** The left ventricle receives ~80% of its flow during diastole. However, the right ventricle, being a low-pressure system, receives significant flow during **both** systole and diastole. * **Tachycardia:** As heart rate increases, the duration of diastole shortens disproportionately. This reduces the time available for coronary perfusion, which is why tachycardia can precipitate ischemia in patients with CAD. * **Subendocardium:** This layer is most vulnerable to ischemia because it experiences the greatest extravascular compression during systole.

Question 184: The ECG of a 40-year-old male was recorded using standard bipolar limb leads. The sum of the voltage of the three standard leads was found to be 5 millivolts. What does this indicate?

A. A normal heart
B. Right ventricular hypertrophy
C. Left ventricular hypertrophy
D. Increased cardiac muscle mass (Correct Answer)

Explanation: ### Explanation **1. Understanding the Correct Answer: Increased Cardiac Muscle Mass** The voltage recorded on an ECG is directly proportional to the amount of electrical activity generated by the myocardium. According to **Einthoven’s Law**, in standard bipolar limb leads, the potential in Lead II is equal to the sum of the potentials in Lead I and Lead III ($II = I + III$). In a healthy adult, the combined voltage of the QRS complexes in the three standard leads typically ranges between **0.5 mV and 2.0 mV**. When the sum of these voltages exceeds **4.0 mV**, it is clinically defined as **High Voltage ECG**. This occurs because a larger muscle mass (hypertrophy) contains more muscle fibers, generating a stronger dipole and greater electrical potential during depolarization. Therefore, a sum of 5 mV indicates significantly increased cardiac muscle mass. **2. Why Other Options are Incorrect:** * **A. A normal heart:** The normal cumulative voltage is significantly lower (usually <2.0 mV). A value of 5 mV is pathological. * **B & C. Right/Left Ventricular Hypertrophy:** While these conditions *do* cause increased muscle mass, they are specific diagnoses that usually present with **axis deviation** (Right Axis Deviation for RVH, Left Axis Deviation for LVH) and specific lead patterns (e.g., tall R waves in V1 for RVH or V5/V6 for LVH). "Increased cardiac muscle mass" is the broader, more accurate physiological description of why the voltage is high across all standard leads. **3. High-Yield Clinical Pearls for NEET-PG:** * **Low Voltage ECG:** Defined when the sum of QRS voltages in leads I, II, and III is **less than 0.5 mV**. Common causes include **pericardial effusion** (fluid dampens signal), **emphysema** (air acts as an insulator), and **myxedema**. * **Einthoven’s Triangle:** An equilateral triangle with the heart at the center; the sides represent the three bipolar limb leads. * **Goldberger’s Leads:** Refers to the augmented unipolar limb leads (aVR, aVL, aVF).

Question 185: Maximum blood flow per 100 gm of tissue is observed in which organ?

A. Brain
B. Heart
C. Kidney (Correct Answer)
D. Liver

Explanation: **Explanation:** The correct answer is **Kidney**. In cardiovascular physiology, it is crucial to distinguish between **total blood flow** (cardiac output) and **blood flow per unit mass** (tissue perfusion). 1. **Why Kidney is Correct:** The kidneys receive approximately 20–25% of the total cardiac output (about 1100–1200 ml/min). When normalized for weight, the kidneys receive roughly **360–400 ml/min per 100g** of tissue. This high flow rate is not primarily for metabolic demand, but to maintain a high Glomerular Filtration Rate (GFR) for effective waste excretion and electrolyte balance. 2. **Analysis of Incorrect Options:** * **Liver:** While the liver receives the largest *total* blood flow (~1500 ml/min), its large mass results in a lower perfusion rate of approximately **95 ml/min per 100g**. * **Heart:** The coronary blood flow is roughly **70–80 ml/min per 100g**. While the heart has the highest oxygen extraction ratio, its flow per unit mass is lower than the kidney. * **Brain:** The brain receives about 15% of cardiac output, translating to roughly **50–54 ml/min per 100g**. **High-Yield NEET-PG Pearls:** * **Highest total blood flow:** Liver (1500 ml/min). * **Highest blood flow per 100g:** Carotid Body (~2000 ml/min/100g). *Note: If Carotid Body is an option, it is the absolute highest; among major organs, Kidney is the answer.* * **Highest oxygen extraction (A-V O2 difference):** Heart (extracts ~75% of delivered oxygen). * **Organ most sensitive to hypoxia:** Brain.

Question 186: Cyanosis is seen in all types of hypoxia except?

A. Hypoxic hypoxia
B. Stagnant hypoxia
C. Anemic hypoxia (Correct Answer)
D. High altitude

Explanation: **Explanation:** The fundamental requirement for the clinical manifestation of **cyanosis** is the presence of at least **5 g/dL of deoxygenated (reduced) hemoglobin** in the capillaries. **Why Anemic Hypoxia is the correct answer:** In anemic hypoxia, the total hemoglobin concentration is significantly reduced. For example, if a patient’s total hemoglobin is 8 g/dL, reaching a level of 5 g/dL of reduced hemoglobin would mean more than 60% of their hemoglobin is deoxygenated. Such a state is often incompatible with life or occurs only at extremely low oxygen saturations. Therefore, patients with severe anemia may be dangerously hypoxic (pale) but will not appear cyanotic because they simply do not have enough total hemoglobin to produce the required 5 g/dL of the reduced form. **Analysis of Incorrect Options:** * **Hypoxic Hypoxia:** Caused by low arterial $PO_2$ (e.g., COPD, shunts). Since total hemoglobin is usually normal or high (polycythemia), reaching 5 g/dL of reduced hemoglobin is easy, making cyanosis a hallmark feature. * **Stagnant Hypoxia:** Occurs due to slow blood flow (e.g., heart failure, shock). Increased extraction of oxygen by tissues leads to a high concentration of reduced hemoglobin in the stagnant capillary bed, causing peripheral cyanosis. * **High Altitude:** This is a form of hypoxic hypoxia. The low atmospheric $PO_2$ leads to inadequate oxygenation of normal hemoglobin levels, frequently resulting in cyanosis. **High-Yield NEET-PG Pearls:** * **Histotoxic Hypoxia:** Cyanosis is also **absent** here (e.g., Cyanide poisoning) because tissues cannot utilize oxygen; venous blood remains highly oxygenated (cherry-red appearance). * **Polycythemia:** Patients develop cyanosis very easily because their baseline hemoglobin is high. * **Carbon Monoxide Poisoning:** Does NOT cause cyanosis; it causes a characteristic **cherry-red skin** discoloration due to carboxyhemoglobin.

Question 187: Which of the following is responsible for the Bezold-Jarisch reflex?

A. Serotonin (Correct Answer)
B. Histamine
C. Prostaglandin
D. Angiotensin

Explanation: ### Explanation The **Bezold-Jarisch Reflex (BJR)** is a cardioinhibitory reflex characterized by a triad of **bradycardia, hypotension, and apnea**. It is mediated by the stimulation of non-myelinated C-fiber vagal afferents located in the ventricles (chemoreceptors and mechanoreceptors). **Why Serotonin is Correct:** Serotonin (5-HT) is a potent chemical trigger for the BJR. It acts on **5-HT3 receptors** located on the vagal nerve endings in the heart. When these receptors are stimulated—often by exogenous administration or endogenous release (e.g., during myocardial ischemia)—it triggers a reflex increase in parasympathetic (vagal) tone and a decrease in sympathetic tone, leading to the characteristic triad. **Analysis of Incorrect Options:** * **B. Histamine:** While histamine can cause vasodilation and hypotension, it typically triggers a *reflex tachycardia* (via baroreceptors) rather than the bradycardia seen in BJR. * **C. Prostaglandin:** Prostaglandins are involved in inflammatory responses and ductal patency but do not serve as the primary chemical mediators for the BJR. * **D. Angiotensin:** Angiotensin II is a potent vasoconstrictor that increases blood pressure and does not trigger cardioinhibitory reflexes. **High-Yield Clinical Pearls for NEET-PG:** * **Receptors:** The reflex is mediated by **C-fiber sensory endings** in the left ventricle. * **Afferent/Efferent Path:** Both the afferent and efferent limbs of this reflex are carried by the **Vagus nerve**. * **Clinical Significance:** * **Myocardial Infarction:** BJR is often seen in **inferior wall MI** because the inferior wall has a high density of these vagal receptors. * **Anesthesia:** It can be triggered by spinal anesthesia or certain drugs like **Propofol**. * **Other Stimuli:** Besides serotonin, the reflex can be triggered by **veratridine alkaloids**, capsaicin, and certain contrast media.

Question 188: What is the approximate amount of blood in the heart?

A. 250-300 ml
B. 500-600 ml (Correct Answer)
C. 1-2 litre
D. 100-200 ml

Explanation: **Explanation:** The total blood volume in an average adult is approximately 5 liters. This volume is distributed throughout the circulatory system, with the heart acting as a reservoir for roughly **10–12%** of the total blood volume. Mathematically, 10-12% of 5000 ml equals **500–600 ml**, making Option B the correct choice. This volume includes the blood present in all four chambers (atria and ventricles) during the different phases of the cardiac cycle. **Analysis of Options:** * **Option A (250-300 ml):** This is an underestimate. While the End-Diastolic Volume (EDV) of both ventricles combined is roughly 240–280 ml, this figure ignores the blood volume present in the two atria. * **Option C (1-2 Litre):** This is too high. Such a volume would represent 20-40% of total blood volume, which would cause massive cardiac dilation and failure. The pulmonary circulation, not the heart, holds about 9-10% (approx. 500 ml). * **Option D (100-200 ml):** This is too low; it barely covers the stroke volume of a single heartbeat and does not account for the residual volume (ESV) or atrial filling. **High-Yield NEET-PG Pearls:** * **Distribution of Blood Volume:** * Systemic Veins (Reservoir): ~64% (Highest) * Systemic Arteries: ~13% * Pulmonary Circulation: ~9% * Heart: ~7–12% * Capillaries: ~5% * **End-Diastolic Volume (EDV):** Approximately 120 ml per ventricle. * **End-Systolic Volume (ESV):** Approximately 50 ml per ventricle. * **Stroke Volume (SV):** EDV - ESV = ~70 ml.

Question 189: Which substance is present in both serum and plasma?

A. Fibrinogen
B. Factor VII (Correct Answer)
C. Factor V
D. Factor II

Explanation: **Explanation:** The fundamental difference between **plasma** and **serum** lies in the clotting process. Plasma is the liquid, cell-free part of blood treated with anticoagulants, containing all coagulation factors. Serum is the liquid remains of blood after it has been allowed to clot; therefore, it lacks the factors consumed during the formation of the fibrin clot. **Why Factor VII is the correct answer:** Coagulation factors are categorized based on whether they are consumed during clotting. **Factor VII (Stable Factor)** is a unique member of the Prothrombin complex that is **not consumed** during the clotting process. Consequently, it remains present in both plasma and serum. Other factors typically found in serum include Factors VII, IX, X, XI, and XII. **Analysis of Incorrect Options:** * **A. Fibrinogen (Factor I):** This is the precursor to fibrin. It is completely converted into a fibrin mesh during clot formation and is therefore absent in serum. * **C. Factor V (Labile Factor):** This is a cofactor consumed during the formation of the prothrombinase complex. It is absent in serum. * **D. Factor II (Prothrombin):** Prothrombin is converted into thrombin to facilitate clotting. Since it is consumed in this reaction, it is absent in serum. **High-Yield NEET-PG Pearls:** * **Formula:** Serum = Plasma – (Clotting Factors + Fibrinogen). * **Factors consumed during clotting (Absent in Serum):** I, II, V, VIII, and XIII. (Mnemonic: **1, 2, 5, 8, 13**). * **Factors present in Serum:** VII, IX, X, XI, XII. * **Clinical Note:** Serum is preferred for most serological tests and blood chemistry because the absence of fibrinogen prevents interference with the testing reagents.

Question 190: In hypovolemic shock, which of the following occurs EXCEPT?

A. Constriction of capacitance vessels
B. Constriction of arterioles in the skin
C. Decrease in cardiac output
D. Heart rate decreases (Correct Answer)

Explanation: **Explanation:** In hypovolemic shock, the primary pathology is a significant loss of blood or fluid volume, leading to decreased venous return and reduced stroke volume. To maintain mean arterial pressure (MAP), the body activates the **baroreceptor reflex**. **1. Why "Heart rate decreases" is the correct answer (The Exception):** When blood pressure drops, baroreceptors in the carotid sinus and aortic arch decrease their firing rate. This inhibits the nucleus tractus solitarius (NTS), leading to **increased sympathetic outflow** and decreased parasympathetic activity. The result is a **compensatory tachycardia** (increased heart rate) to maintain cardiac output ($CO = HR \times SV$). Therefore, a decrease in heart rate is physiologically incorrect in typical hypovolemic shock. **2. Analysis of Incorrect Options:** * **A. Constriction of capacitance vessels:** Sympathetic stimulation causes venoconstriction (constriction of veins/capacitance vessels). This shunts blood from the peripheral venous reservoir toward the heart to maintain preload. * **B. Constriction of arterioles in the skin:** Increased sympathetic activity causes alpha-1 mediated vasoconstriction in non-essential organs like the skin and kidneys to divert blood to the brain and heart. This explains why patients in shock present with "cold and clammy" skin. * **C. Decrease in cardiac output:** This is the hallmark of hypovolemic shock. The loss of circulating volume directly reduces stroke volume, which the body tries (but often fails) to fully compensate for via tachycardia. **Clinical Pearls for NEET-PG:** * **Bezold-Jarisch Reflex:** A rare exception where profound hypovolemia can cause *bradycardia* due to paradoxical activation of ventricular mechanoreceptors. * **Shock Index:** Heart Rate / Systolic BP. An index > 0.9 suggests significant blood loss. * **Urine Output:** The most sensitive clinical indicator of organ perfusion in shock management.

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