Cardiovascular System Practice Questions

Q: A hospitalized patient has an ejection fraction of 0.4, a heart rate of 95 beats/min, and a cardiac output of 3.5 L/min. What is the patient's end-diastolic volume?

92 mL. ### Explanation To solve this problem, we must apply the fundamental relationships between Cardiac Output (CO), Heart Rate (HR), Stroke Volume (SV), and Ejection Fraction (EF). **Step 1: Calculate Stroke Volume (SV)** Cardiac Output is the product of Stroke Volume and Heart Rate ($CO = SV \times HR$). * $SV = \frac{CO}{HR}$ * $SV = \frac{3.5 \text{ L/min}}{95 \text{ beats/min}} = 0.0368 \text{ L}$ or approximately **36.8 mL**. **Step 2: Calculate End-Diastolic Volume (EDV)** Ejection Fraction is the fraction of the EDV that is ejected during one systole ($EF = \frac{SV}{EDV}$). * $EDV = \frac{SV}{EF}$ * $EDV = \frac{36.8 \text{ mL}}{0.4} = \mathbf{92 \text{ mL}}$. #### Analysis of Options: * **A (14 mL):** Incorrect. This value does not correlate with any standard physiological parameter in this context. * **B (37 mL):** Incorrect. This represents the **Stroke Volume (SV)**, not the EDV. * **C (55 mL):** Incorrect. This represents the **End-Systolic Volume (ESV)** ($EDV - SV = 92 - 37 = 55 \text{ mL}$). * **D (92 mL):** **Correct.** This is the total volume of blood in the ventricle at the end of diastole. #### Clinical Pearls for NEET-PG: 1. **Normal Values:** Normal EF is typically **55–70%**. An EF of 0.4 (40%) indicates reduced systolic function (e.g., Heart Failure with reduced Ejection Fraction - HFrEF). 2. **Preload:** EDV is the primary clinical surrogate for **Preload**. According to the Frank-Starling Law, an increase in EDV leads to an increase in SV (within physiological limits). 3. **Gold Standard:** While echocardiography is commonly used, **Cardiac MRI** is the gold standard for measuring ventricular volumes and EF.

Q: In systemic circulation, what proportion of the resistance to blood flow is offered by arterioles?

Arterioles. **Explanation:** The correct answer is **Arterioles** because they are the primary "resistance vessels" of the systemic circulation. **1. Why Arterioles are the correct answer:** According to **Poiseuille’s Law**, resistance is inversely proportional to the fourth power of the radius ($R \propto 1/r^4$). Arterioles have a small lumen and a thick layer of vascular smooth muscle. This allows them to undergo significant changes in diameter (vasoconstriction and vasodilation) in response to sympathetic stimulation and local metabolites. Consequently, the greatest drop in mean arterial pressure (from approx. 85 mmHg to 35 mmHg) occurs across the arteriolar network, accounting for nearly **50-70% of total peripheral resistance (TPR).** **2. Why other options are incorrect:** * **Small Arteries:** While they contribute to resistance, their muscular wall is less developed relative to their lumen size compared to arterioles. * **Capillaries:** Although an individual capillary has a very high resistance due to its tiny radius, the **total cross-sectional area** of the capillary bed is massive. Because they are arranged in **parallel**, the effective resistance offered by the entire capillary network is lower than that of the arterioles. * **Venules:** These are "capacitance vessels" rather than resistance vessels. They have thin walls and high compliance, serving primarily as a reservoir for blood volume. **High-Yield Clinical Pearls for NEET-PG:** * **Site of maximum resistance:** Arterioles. * **Site of maximum pressure drop:** Arterioles. * **Site of minimum flow velocity:** Capillaries (to allow for nutrient exchange). * **Site of maximum total cross-sectional area:** Capillaries. * **Major reservoir of blood volume:** Veins/Venules (~60-70% of total blood).

Q: What is true about the fourth heart sound?

It occurs at the end of the P wave in the ECG.. The **fourth heart sound (S4)**, also known as the atrial gallop, is a low-frequency sound occurring late in diastole, just before S1. ### **Explanation of the Correct Option** **A. It occurs at the end of the P wave in the ECG:** The P wave represents atrial depolarization, which triggers atrial contraction (atrial systole). S4 is produced by the vibration of the ventricular walls as blood is forcefully pushed into a stiff or non-compliant ventricle during atrial contraction. Therefore, S4 coincides with the end of the P wave and the PR interval on an ECG. ### **Why Other Options are Incorrect** * **B. End of the T wave:** The T wave represents ventricular repolarization. The end of the T wave marks the beginning of isovolumetric relaxation, not atrial contraction. * **C. Early rapid filling phase:** This phase occurs shortly after S2 and is associated with the **third heart sound (S3)**, not S4. S4 occurs during the *late* filling phase (atrial kick). * **D. Slow ejection phase:** This is a phase of ventricular systole. Heart sounds S3 and S4 are diastolic sounds. ### **High-Yield NEET-PG Pearls** * **Mechanism:** S4 is always pathological in adults (unlike S3, which can be physiological in young individuals). It indicates **decreased ventricular compliance**. * **Clinical Associations:** Commonly heard in **Left Ventricular Hypertrophy (LVH)**, Systemic Hypertension, Aortic Stenosis, and Ischemic Heart Disease. * **Absence:** S4 is **never heard in Atrial Fibrillation** because there is no coordinated atrial contraction to produce the sound. * **Best heard:** At the apex with the bell of the stethoscope in the left lateral decubitus position.

Q: Which of the following acts as a local vasodilator?

Carbon dioxide tension. **Explanation:** Local blood flow is primarily regulated by metabolic autoregulation. When tissues become metabolically active, they consume nutrients and produce metabolic byproducts that act as local vasodilators to increase blood flow and meet the increased demand. **Why Carbon Dioxide (CO₂) Tension is correct:** Increased CO₂ tension ($PCO_2$) is a potent local vasodilator, particularly in the cerebral and skeletal muscle circulation. As metabolic activity increases, CO₂ levels rise. This leads to a decrease in local pH (acidosis) and directly relaxes vascular smooth muscle cells, causing vasodilation to "wash out" the metabolic waste. **Analysis of Incorrect Options:** * **Oxygen Tension ($PO_2$):** High oxygen tension acts as a **vasoconstrictor** in most systemic tissues. Conversely, it is *low* oxygen tension (hypoxia) that acts as a vasodilator (except in the pulmonary circulation, where hypoxia causes vasoconstriction). * **pH:** A high pH (alkalosis) generally acts as a vasoconstrictor. It is a **low pH** (acidosis), often resulting from lactic acid or CO₂ accumulation, that functions as a local vasodilator. * **Option D:** This is a duplicate of the correct answer. **High-Yield Clinical Pearls for NEET-PG:** * **Most Potent Cerebral Vasodilator:** CO₂ tension is the most important factor regulating cerebral blood flow. Hyperventilation (which lowers $PCO_2$) is used clinically to cause cerebral vasoconstriction and reduce intracranial pressure. * **Other Local Vasodilators:** Adenosine (crucial in coronary circulation), $K^+$ ions, $H^+$ ions, Lactic acid, and Nitric Oxide (NO). * **The Pulmonary Exception:** While hypoxia causes vasodilation systemically, it causes **vasoconstriction** in the lungs (Hypoxic Pulmonary Vasoconstriction) to shunt blood away from poorly ventilated alveoli.

Q: What is true about fetal circulation?

The heart receives blood with high oxygen saturation.. ### Explanation **Correct Answer: D. The heart receives blood with high oxygen saturation.** In fetal circulation, the oxygenated blood from the placenta travels via the **umbilical vein** to the **Ductus Venosus**, bypassing the liver to enter the Inferior Vena Cava (IVC). Upon reaching the right atrium, a physiological mechanism called **"streaming"** occurs. The "crista dividens" (the lower edge of the septum secundum) directs this highly oxygenated IVC blood through the **Foramen Ovale** into the left atrium. From there, it enters the left ventricle and is pumped into the ascending aorta. Consequently, the **coronary arteries** and the **carotid arteries** (supplying the heart and brain) receive the most oxygenated blood available in the fetus (approx. 65-70% saturation). **Why other options are incorrect:** * **A:** Blood in the **SVC** is deoxygenated blood returning from the upper body (saturation ~40%), whereas the IVC carries oxygenated blood from the placenta. * **B:** In the fetus, the **Right Ventricular pressure is higher** than the Left Ventricular pressure. This is due to high pulmonary vascular resistance (collapsed lungs) and low systemic resistance (placenta). * **C:** The brain receives blood from the ascending aorta (via the brachiocephalic, carotid, and subclavian arteries), which is **highly oxygenated** due to the streaming effect mentioned above. **High-Yield NEET-PG Pearls:** 1. **Highest $PO_2$:** Found in the **Umbilical Vein** (approx. 30-35 mmHg; 80% saturation). 2. **Lowest $PO_2$:** Found in the **Umbilical Arteries** (returning to the placenta). 3. **Ductus Arteriosus:** Shunts deoxygenated blood from the pulmonary artery to the descending aorta (distal to the branching of head/neck vessels) to protect the lungs from fluid overload. 4. **Closure:** The Foramen Ovale closes functionally at birth due to increased left atrial pressure.

Question 1

Which of the following is true regarding cardiac oxygen demand?

Accepted Answer

Directly proportional to mean arterial pressure

Answer

Inversely proportional to heart rate

Answer

Inversely proportional to cardiac work

Answer

Has a constant relation to the external work done by the heart

Question 2

What is the primary role of the baroreceptor reflex?

Accepted Answer

It is primarily involved in short-term regulation of systemic blood pressure.

Answer

It leads to an increase in heart rate because of inhibition of the vagal cardiac motor neurons.

Answer

It inhibits neurons in the cardiovascular medullary nucleus.

Answer

It excites neurons in the rostral ventrolateral medulla.

Question 3

A hospitalized patient has an ejection fraction of 0.4, a heart rate of 95 beats/min, and a cardiac output of 3.5 L/min. What is the patient's end-diastolic volume?

Accepted Answer

92 mL

Answer

14 mL

Answer

37 mL

Answer

55 mL

Question 4

In systemic circulation, what proportion of the resistance to blood flow is offered by arterioles?

Accepted Answer

Arterioles

Answer

Small arteries

Answer

Capillaries

Answer

Venules

Question 5

A patient's systolic blood pressure (SBP) decreased by 10 mmHg upon standing, and the diastolic blood pressure (DBP) increased by only 8 mmHg. What was the net change in diastolic blood pressure?

Accepted Answer

-10 mmHg

Answer

+10 mmHg

Answer

-8 mmHg

Answer

+8 mmHg

Question 6

An arteriole with a damaged endothelial cell layer will not:

Accepted Answer

Dilate in response to adenosine diphosphate (ADP) or acetylcholine

Answer

Constrict when intravascular pressure is increased

Answer

Dilate when adenosine is applied to the vessel wall

Answer

Constrict in response to norepinephrine

Question 7

What is true about the fourth heart sound?

Accepted Answer

It occurs at the end of the P wave in the ECG.

Answer

It occurs at the end of the T wave in the ECG.

Answer

It occurs during the early rapid filling phase of ventricular diastole.

Answer

It occurs during the slow ejection phase of ventricular systole.

Question 8

Carotid sinus baroreceptors are most sensitive to which of the following?

Accepted Answer

Mean arterial pressure

Answer

Pulse pressure

Answer

Diastolic blood pressure

Answer

Systolic blood pressure

Question 9

Which of the following acts as a local vasodilator?

Accepted Answer

Carbon dioxide tension

Answer

Oxygen tension

Answer

pH

Question 10

What is true about fetal circulation?

Accepted Answer

The heart receives blood with high oxygen saturation.

Answer

Blood in the superior vena cava (SVC) has more oxygen saturation.

Answer

Pressure in the left ventricle is higher than in the right ventricle.

Answer

The brain receives blood with low oxygen saturation.

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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