Cardiovascular System — MCQs

Cardiovascular System Indian Medical PG Practice Questions and MCQs

Question 431: Turbulence of blood flow increases when:

A. Viscosity decreases
B. Diameter of blood vessel decreases (Correct Answer)
C. Density decreases
D. Arteries are straight

Explanation: The concept of blood flow turbulence is governed by **Reynolds Number ($Re$)**, a dimensionless value used to predict whether flow is laminar or turbulent. The formula is: $$Re = \frac{\rho \cdot D \cdot v}{\eta}$$ *(Where $\rho$ = density, $D$ = diameter, $v$ = velocity, and $\eta$ = viscosity)* ### Why Option B is Correct While the formula suggests $Re$ is directly proportional to diameter ($D$), in the cardiovascular system, a **decrease in diameter** (like in stenosis) causes a disproportionate **increase in velocity ($v$)**. Because velocity increases to the fourth power relative to the radius change (Law of Continuity), the net effect is a significant rise in Reynolds Number. When $Re$ exceeds **2000–3000**, flow becomes turbulent. ### Why Other Options are Wrong * **A. Viscosity decreases:** According to the formula, viscosity ($\eta$) is in the denominator. A decrease in viscosity (e.g., severe anemia) actually **increases** the Reynolds Number and the likelihood of turbulence. * **C. Density decreases:** Density ($\rho$) is in the numerator. A decrease in density would **decrease** the Reynolds Number, making flow more laminar. * **D. Arteries are straight:** Turbulence is more likely to occur at **bends, branches, or bifurcations** (e.g., the carotid bulb). Straight vessels promote smooth, laminar flow. ### NEET-PG High-Yield Pearls * **Murmurs and Bruits:** Turbulence creates audible vibrations. In the heart, these are **murmurs**; in peripheral vessels (like a stenosed renal artery), they are **bruits**. * **Anemia & Turbulence:** In severe anemia, reduced RBC count decreases blood viscosity, leading to a "hyperdynamic state" and functional systolic murmurs. * **Critical Velocity:** The velocity at which laminar flow converts to turbulent flow is called critical velocity.

Question 432: A pilot in a Sukhoi aircraft is experiencing negative G. Which of the following physiological events will manifest in such a situation?

A. The hydrostatic pressure in veins of the lower limb increases.
B. The cardiac output decreases.
C. Blackout occurs.
D. The cerebral arterial pressure rises. (Correct Answer)

Explanation: **Explanation:** In aviation physiology, **Negative G (-Gz)** occurs when acceleration is directed from the feet toward the head (e.g., during a nose-dive or outside loop). This causes a massive shift of blood volume toward the upper body and head. **1. Why the Correct Answer is Right:** In -Gz, the inertial force pushes blood into the head. This results in a significant increase in **cerebral arterial and venous pressure**. To protect the brain, the baroreceptor reflex is triggered, leading to intense bradycardia and peripheral vasodilation; however, the mechanical force of the G-load still keeps the cephalic pressures high. **2. Analysis of Incorrect Options:** * **Option A:** Hydrostatic pressure in the lower limbs **decreases** because blood is forced away from the legs toward the head. (Increased pressure in lower limbs is seen in Positive G). * **Option B:** Cardiac output initially **increases** (or remains stable) due to the massive increase in venous return from the lower body to the heart. * **Option C:** **"Red-out"** occurs, not blackout. Red-out happens because the high pressure forces blood into the retinal capillaries and causes the lower eyelid to be pushed upward, covering the field of vision with a red tint. **Blackout** (loss of vision) is a feature of **Positive G (+Gz)** due to retinal ischemia. **3. Clinical Pearls for NEET-PG:** * **Positive G (+Gz):** Blood moves Head → Feet. Results in: Foot edema, decreased venous return, and **Blackout** (Vision loss) followed by **G-LOC** (G-induced Loss of Consciousness). * **Negative G (-Gz):** Blood moves Feet → Head. Results in: Facial congestion, **Red-out**, and risk of cerebral hemorrhage. * **Tolerance:** The human body is much less tolerant of Negative G (-3 to -4 G) compared to Positive G (+5 to +9 G). * **G-suit:** Designed to prevent blood pooling in the legs during **Positive G**; it is not effective against Negative G.

Question 433: Which of the following factors is NOT involved in the intrinsic pathway of coagulation?

A. Factor VII (Correct Answer)
B. Factor VIII
C. Factor IX
D. Factor XII

Explanation: The coagulation cascade is divided into the Intrinsic, Extrinsic, and Common pathways. Understanding which factors belong to each is a high-yield requirement for NEET-PG. ### **Explanation** **Factor VII** is the correct answer because it is the primary component of the **Extrinsic Pathway**. The extrinsic pathway is triggered by "Tissue Factor" (Factor III) following vascular injury, which then activates Factor VII to form the TF-VIIa complex. **Why the other options are incorrect:** The **Intrinsic Pathway** (Contact Activation Pathway) involves factors that are present within the circulating blood. It is triggered when blood comes into contact with collagen or a negatively charged surface. * **Factor XII (Hageman factor):** The starting point of the intrinsic pathway. * **Factor XI:** Activated by Factor XIIa. * **Factor IX (Christmas factor):** Activated by Factor XIa. * **Factor VIII (Anti-hemophilic factor):** Acts as a cofactor for Factor IXa to activate the common pathway. ### **High-Yield Clinical Pearls** * **Memory Aid:** To remember the Intrinsic Pathway factors, think **"TENET"** (Twelve, Eleven, Nine, Eight, Ten). Note that Factor X is where the pathways merge into the **Common Pathway** (Factors X, V, II, I). * **Laboratory Correlation:** * **PT (Prothrombin Time)** measures the **Extrinsic** and Common pathways (specifically Factor VII). * **aPTT (activated Partial Thromboplastin Time)** measures the **Intrinsic** and Common pathways. * **Vitamin K Dependent Factors:** Factors II, VII, IX, and X (Remember: **1972**). Factor VII has the shortest half-life among these.

Question 434: Blood pressure is defined as the product of which of the following?

A. Systolic pressure and pulse
B. Diastolic pressure and pulse rate
C. Pulse pressure and pulse rate
D. Cardiac output and peripheral resistance (Correct Answer)

Explanation: **Explanation** **1. Why Option D is Correct:** The fundamental hemodynamic equation for blood pressure is derived from Ohm’s Law ($V = I \times R$), where Pressure ($P$) is the product of Flow ($Q$) and Resistance ($R$). In the cardiovascular system, this translates to: **Mean Arterial Pressure (MAP) = Cardiac Output (CO) × Total Peripheral Resistance (TPR)** * **Cardiac Output:** Represents the volume of blood pumped by the heart per minute. It primarily determines the systolic blood pressure. * **Peripheral Resistance:** Primarily determined by the diameter of the arterioles (resistance vessels). It is the chief determinant of diastolic blood pressure. **2. Why Other Options are Incorrect:** * **Options A & B:** Systolic and Diastolic pressures are *components* of blood pressure, not factors that multiply to define it. Pulse rate is a component of Cardiac Output ($CO = Stroke\ Volume \times Heart\ Rate$), but it is not the sole determinant of BP. * **Option C:** Pulse pressure is the difference between systolic and diastolic pressure ($SBP - DBP$). Multiplying it by pulse rate does not yield a physiological measurement for blood pressure. **3. NEET-PG Clinical Pearls & High-Yield Facts:** * **Poiseuille’s Law:** Resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). This means small changes in arteriolar diameter lead to massive changes in BP. * **MAP Calculation:** $MAP = DBP + 1/3\ (Pulse\ Pressure)$. This is a frequent numerical MCQ topic. * **Determinants:** Systolic BP is mainly affected by **Stroke Volume** and **Aortic Compliance**, while Diastolic BP is mainly affected by **TPR** and **Heart Rate**. * **Baroreceptor Reflex:** This is the primary short-term regulator of BP, sensing changes in "stretch" in the carotid sinus and aortic arch.

Question 435: Which of the following is FALSE regarding the funny current in the heart?

A. It is a Na-K ATPase pump (Correct Answer)
B. They are responsible for diastolic depolarization
C. It is responsible for the spontaneous rhythm producing tissue of the heart
D. They are voltage-dependent channels only

Explanation: ### Explanation **1. Why Option A is the Correct (False) Statement:** The **funny current ($I_f$)** is not a pump; it is a **non-specific cation channel** (HCN channel - Hyperpolarization-activated Cyclic Nucleotide-gated channel). Unlike the Na-K ATPase, which requires ATP to move ions against their gradient, the funny current allows the passive influx of sodium ($Na^+$) and a minor efflux of potassium ($K^+$) down their electrochemical gradients. **2. Analysis of Other Options:** * **Option B (True):** The funny current is the primary driver of **Phase 4 (diastolic depolarization)** in pacemaker cells (SA and AV nodes). It slowly brings the membrane potential from the maximum diastolic potential toward the threshold. * **Option C (True):** Because $I_f$ initiates the spontaneous depolarization that leads to an action potential without external nerve stimulation, it is responsible for the **autorhythmicity** (automaticity) of the heart. * **Option D (True/Contextual):** While $I_f$ is modulated by cAMP (sympathetic/parasympathetic activity), it is fundamentally **voltage-gated**. Uniquely, it is activated by **hyperpolarization** (becoming more negative) rather than depolarization, which is why it was named "funny." **3. NEET-PG High-Yield Pearls:** * **Location:** Primarily found in the SA node, AV node, and Purkinje fibers. * **Activation:** It activates when the membrane potential reaches approximately **-60 mV** (at the end of repolarization). * **Clinical Correlation:** **Ivabradine** is a specific $I_f$ channel blocker used in heart failure and stable angina. It reduces heart rate without affecting myocardial contractility (negative chronotrope without being a negative inotrope). * **Ion Permeability:** It is more permeable to $Na^+$ than $K^+$, leading to net inward positive charge.

Question 436: Local control of blood flow is seen in all except which of the following?

A. Skin (Correct Answer)
B. Muscle
C. Splanchnic vessels
D. Cerebrum

Explanation: **Explanation:** The regulation of blood flow in the body is divided into **Local (Autoregulation)** and **Humoral/Neural (Extrinsic)** control. **Why Skin is the Correct Answer:** The primary function of cutaneous (skin) blood flow is **thermoregulation**, not the metabolic demands of the tissue itself. Therefore, skin blood flow is predominantly under **extrinsic neural control** via the sympathetic nervous system. When the body temperature rises, sympathetic tone decreases to allow vasodilation and heat loss. Because it lacks significant intrinsic metabolic autoregulation, it is the exception among the options provided. **Analysis of Incorrect Options:** * **B. Muscle:** During exercise, skeletal muscle blood flow is governed by **local metabolic factors** (e.g., increased $K^+$, $H^+$, lactate, and adenosine). This "active hyperemia" ensures oxygen delivery matches metabolic demand. * **C. Splanchnic vessels:** The gastrointestinal tract exhibits significant local control, especially postprandially (after meals), where metabolic products and GI hormones trigger local vasodilation to aid digestion. * **D. Cerebrum:** The brain has the most highly developed **autoregulation** mechanism. Cerebral blood flow remains constant despite fluctuations in mean arterial pressure (60–140 mmHg) and is exquisitely sensitive to local $PCO_2$ levels. **High-Yield Clinical Pearls for NEET-PG:** * **Most potent local vasodilator** in the brain: **$CO_2$** (via $H^+$ ions). * **Most potent local vasodilator** in skeletal muscle: **Adenosine** (during ischemia) and **$K^+$ ions** (during exercise). * **Organs with best autoregulation:** Brain, Kidney, and Heart. * **Organs with least autoregulation:** Skin.

Question 437: Which statement about the 'instantaneous mean vector' is true?

A. Equal and same as the mean QRS vector
B. It is drawn through the center of the vector in a direction from base toward the apex
C. Summated vector of generated potential at a particular instant caused by inflowing septal depolarization (Correct Answer)
D. When a vector is exactly horizontal and directed toward the person's left side, the vector is said to extend in the direction of 0 degrees

Explanation: ### Explanation **1. Why Option C is Correct:** The **instantaneous mean vector** represents the net electrical potential generated by the heart at a specific, single moment in time during the cardiac cycle. It is the summated vector of all individual dipoles (depolarization or repolarization fronts) occurring simultaneously. For example, during the initial phase of ventricular depolarization, the "instantaneous" vector is directed downward and to the right due to **septal depolarization**. As the impulse spreads, these instantaneous vectors change direction and magnitude every millisecond. **2. Why the Other Options are Incorrect:** * **Option A:** The **Mean QRS Vector** is the average of all instantaneous vectors during the entire period of ventricular depolarization (usually around +59°). An instantaneous vector is only a "snapshot" and is rarely equal to the overall mean. * **Option B:** While the mean vector generally points from the base toward the apex, an instantaneous vector can point in any direction (e.g., toward the base during terminal depolarization of the Purkinje fibers). * **Option D:** This statement is a **factually true** definition of the 0-degree axis in the hexagonal reference system, but it does **not** define what an "instantaneous mean vector" is. It describes the coordinate system, not the physiological vector itself. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Vectorcardiogram:** A loop formed by connecting the heads of all instantaneous vectors. * **Normal Axis:** The Mean QRS vector normally lies between **-30° and +90°**. * **Left Axis Deviation (LAD):** Seen in Left Anterior Fascicular Block (LAFB), LVH, and inferior wall MI. * **Right Axis Deviation (RAD):** Seen in RVH, Left Posterior Fascicular Block (LPFB), and lateral wall MI. * **Sequence of Depolarization:** Septum (Left to Right) → Apex → Free walls → Base of the heart.

Question 438: All of the following factors normally increase the length of the ventricular cardiac muscle fibers except?

A. Increased venous tone
B. Increased total blood volume
C. Increased negative intrathoracic pressure
D. Lying to standing change in posture (Correct Answer)

Explanation: ### Explanation The length of ventricular cardiac muscle fibers is determined by the **End-Diastolic Volume (EDV)**, also known as **Preload**. According to the **Frank-Starling Law**, an increase in venous return leads to increased ventricular filling, which stretches the myocardial fibers. **Why Option D is Correct:** When a person moves from a **lying to a standing position**, gravity causes blood to pool in the highly distensible veins of the lower extremities (venous pooling). This significantly **decreases venous return** to the heart, leading to a decrease in EDV and, consequently, a **decrease** in the length of the ventricular muscle fibers. **Why the Other Options are Incorrect:** * **A. Increased venous tone:** Sympathetic stimulation causes venoconstriction, which decreases the capacitance of veins and pushes more blood toward the heart, increasing preload and fiber length. * **B. Increased total blood volume:** Conditions like IV fluid resuscitation or polycythemia increase the overall circulating volume, thereby increasing venous return and fiber stretch. * **C. Increased negative intrathoracic pressure:** During deep inspiration, the intrathoracic pressure becomes more negative. This creates a "suction effect" on the vena cava, drawing more blood into the right atrium and increasing ventricular fiber length. **High-Yield NEET-PG Pearls:** * **Frank-Starling Law:** States that the force of ventricular contraction is proportional to the initial length of the muscle fiber (within physiological limits). * **Preload vs. Afterload:** Preload is the degree of stretch (EDV); Afterload is the resistance the heart must pump against (MAP). * **Postural Hypotension:** The initial drop in BP upon standing is normally compensated by the **Baroreceptor Reflex**, which increases heart rate and peripheral resistance.

Question 439: Blood is flowing through a circuit with an inflow pressure of 100 mmHg and an outflow pressure of 10 mmHg. Each of the parallel circuits (R1, R2, R3, R4, and R5) has a resistance of 5 mmHg/mL/min. What is the blood flow across this circuit?

A. 3.6 ml/min
B. 45 ml/min
C. 90 ml/min (Correct Answer)
D. 135 ml/min

Explanation: ### Explanation This question tests the application of **Ohm’s Law** to hemodynamics. To find the total blood flow ($Q$), we use the formula: $$Q = \frac{\Delta P}{R_{total}}$$ **1. Calculate the Pressure Gradient ($\Delta P$):** $\Delta P = \text{Inflow Pressure} - \text{Outflow Pressure} = 100\text{ mmHg} - 10\text{ mmHg} = 90\text{ mmHg}$. **2. Calculate the Total Resistance ($R_{total}$):** The circuit consists of 5 resistors in **parallel**. For identical resistors in parallel, the total resistance is the resistance of one divided by the number of resistors ($R/n$): $$R_{total} = \frac{5\text{ mmHg/mL/min}}{5} = 1\text{ mmHg/mL/min}$$ **3. Calculate Total Flow ($Q$):** $$Q = \frac{90\text{ mmHg}}{1\text{ mmHg/mL/min}} = 90\text{ mL/min}$$ --- ### Analysis of Options * **Option C (90 mL/min):** Correct. Derived by dividing the pressure gradient (90) by the equivalent parallel resistance (1). * **Option A (3.6 mL/min):** Incorrect. This occurs if you mistakenly treat the resistors as being in **series** ($R_{total} = 25$) and divide 90 by 25. * **Option B (45 mL/min):** Incorrect. This would occur if only two parallel resistors were accounted for or if the pressure gradient was miscalculated as 45. * **Option D (135 mL/min):** Incorrect. This does not correlate with standard physiological calculations for this circuit. --- ### Clinical Pearls & High-Yield Facts * **Parallel Arrangement:** Most organ systems in the body (renal, cerebral, coronary) are arranged in parallel. This ensures that: 1. Each organ receives blood at the same mean arterial pressure. 2. Adding an organ (resistor) in parallel **decreases** the total peripheral resistance (TPR). * **Series Arrangement:** Seen within a single organ (e.g., artery $\rightarrow$ arteriole $\rightarrow$ capillary). Adding a resistor in series **increases** total resistance. * **Key Determinant:** The **arteriole** is the primary site of resistance in the systemic circulation (the "stopcocks" of the circulation).

Question 440: Which of the following is true about stroke volume?

A. It decreases with an increase in heart rate. (Correct Answer)
B. It is determined by pre-diastolic volume.
C. It is determined by afterload.
D. It is equal to cardiac output.

Explanation: ### Explanation **Correct Option: A (It decreases with an increase in heart rate)** Stroke volume (SV) is the volume of blood pumped by the left ventricle per beat ($SV = EDV - ESV$). When the heart rate increases significantly (tachycardia), the duration of the cardiac cycle decreases. This reduction primarily affects **diastole**, the period when the ventricles fill with blood. Shorter diastolic filling time leads to a decreased **End-Diastolic Volume (EDV)**. According to the Frank-Starling Law, a lower EDV results in a reduced stroke volume. **Analysis of Incorrect Options:** * **B. It is determined by pre-diastolic volume:** This is a distractor term. SV is determined by **End-Diastolic Volume (EDV)** (preload), not "pre-diastolic" volume. * **C. It is determined by afterload:** While afterload *influences* SV (increased afterload decreases SV), the question asks for a "true statement" among the choices. Option A is a more fundamental physiological relationship in the context of the cardiac cycle. Furthermore, SV is determined by three factors: Preload, Afterload, and Contractility. * **D. It is equal to cardiac output:** This is mathematically incorrect. **Cardiac Output (CO) = Stroke Volume × Heart Rate**. SV is only one component of the total output per minute. **High-Yield Clinical Pearls for NEET-PG:** * **Frank-Starling Law:** Within physiological limits, the force of ventricular contraction is proportional to the initial length of the muscle fibers (EDV). * **Filling Time:** At heart rates above 170–180 bpm, SV drops so significantly that Cardiac Output may actually begin to fall despite the high rate. * **Ejection Fraction (EF):** $EF = (SV / EDV) \times 100$. Normal range is 55–70%. It is the most common clinical index of left ventricular function.

Practice by Chapter

Cardiac Electrophysiology

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Cardiac Cycle

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Cardiac Output and Its Regulation

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Cardiovascular Reflexes

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Regional Circulations

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Cardiovascular Responses to Exercise and Stress

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