Cardiovascular System Practice Questions

Q: Long-acting calcium channel blockers act during which phase of the action potential?

Phase 2. **Explanation:** The correct answer is **Phase 2 (Plateau Phase)**. In the cardiac action potential of non-pacemaker cells (ventricular myocytes), **Phase 2** is characterized by a "plateau." This phase occurs due to a delicate balance between the inward movement of **Calcium ions (Ca²⁺)** through **L-type calcium channels** and the outward movement of Potassium ions (K⁺). Calcium channel blockers (CCBs), such as Verapamil, Diltiazem, and Amlodipine, specifically inhibit these L-type channels. By reducing the inward calcium current during this phase, CCBs shorten the plateau duration and decrease cardiac contractility (negative inotropy). **Analysis of Incorrect Options:** * **Phase 0 (Depolarization):** In ventricular cells, this is driven by the rapid influx of **Sodium (Na⁺)** via fast voltage-gated Na⁺ channels. (Note: CCBs do act on Phase 0 in *pacemaker* cells, but standard CCB pharmacology questions refer to the ventricular plateau). * **Phase 1 (Early Repolarization):** This brief phase is caused by the inactivation of Na⁺ channels and the transient outward flow of **K⁺ ions**. * **Phase 3 (Rapid Repolarization):** This phase is dominated by the massive efflux of **K⁺ ions** through delayed rectifier channels, bringing the membrane potential back to resting levels. **Clinical Pearls for NEET-PG:** * **Class IV Antiarrhythmics:** CCBs (Verapamil/Diltiazem) are classified here; they primarily slow conduction through the AV node by affecting the calcium-dependent upstroke in nodal tissue. * **Dihydropyridines (e.g., Amlodipine):** These are "long-acting" and more selective for vascular smooth muscle, used primarily for hypertension. * **Contractility:** Because Phase 2 provides the calcium necessary for **Calcium-Induced Calcium Release (CICR)** from the sarcoplasmic reticulum, CCBs significantly impact the force of contraction.

Q: The fourth heart sound is caused by:

Ventricular filling. ### Explanation **Correct Answer: C. Ventricular filling** The **fourth heart sound (S4)**, also known as the "atrial gallop," occurs during the late phase of ventricular diastole. It is caused by the **atrial kick**, where the atria contract to force the final 20–30% of blood into a stiff or non-compliant ventricle. This sudden surge of blood causes vibrations in the ventricular walls, papillary muscles, and chordae tendineae. Because it occurs just before the first heart sound (S1), it is described as having a "presystolic" rhythm. **Analysis of Incorrect Options:** * **Option A (Closure of semilunar valves):** This produces the **second heart sound (S2)**, marking the beginning of diastole. * **Option B (Vibrations during systole):** Heart sounds are primarily associated with valve closures or filling phases. While S1 occurs at the start of systole, S4 is strictly a diastolic event. * **Option D (Closure of AV valves):** This produces the **first heart sound (S1)**, marking the beginning of ventricular systole. **High-Yield Clinical Pearls for NEET-PG:** * **Pathological Significance:** S4 is almost always pathological (unlike S3, which can be physiological in young adults/athletes). It indicates **decreased ventricular compliance** (stiffness). * **Common Causes:** Left ventricular hypertrophy (due to systemic hypertension or aortic stenosis), ischemic heart disease, and hypertrophic cardiomyopathy (HCM). * **Auscultation:** Best heard with the **bell** of the stethoscope at the apex in the left lateral decubitus position. * **The "Tennessee" Rhythm:** S4-S1-S2 creates a cadence similar to the word "Ten-nes-see." * **Absent in Atrial Fibrillation:** Since S4 requires active atrial contraction, it **cannot** occur in patients with atrial fibrillation.

Q: What is the basal cardiac output in an adult?

5 litres. **Explanation:** **Cardiac Output (CO)** is defined as the volume of blood pumped by each ventricle per minute. It is the product of **Stroke Volume (SV)** and **Heart Rate (HR)** ($CO = SV \times HR$). 1. **Why 5 Litres is Correct:** In a healthy adult at rest (basal state), the average stroke volume is approximately **70 mL** and the average heart rate is **72 beats per minute**. Calculation: $70\text{ mL} \times 72\text{ bpm} \approx 5,040\text{ mL/min}$ or roughly **5 L/min**. This value represents the standard physiological baseline required to meet the metabolic demands of the body's tissues at rest. 2. **Why Other Options are Incorrect:** * **A (7.5 L):** This is higher than the basal rate and may be seen during mild exertion or in hyperdynamic states (e.g., pregnancy or hyperthyroidism). * **C & D (12 L and 10 L):** These values are significantly higher than resting levels. While the heart can reach these outputs during moderate to heavy exercise (the maximum CO can reach 20–25 L/min in athletes), they do not represent the "basal" state. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Index (CI):** Since CO varies with body size, the Cardiac Index is a more accurate clinical parameter. It is $CO \div \text{Body Surface Area}$. Normal range: **2.5 to 4.2 L/min/m²**. * **Distribution:** At rest, the **Liver (27%)** and **Kidneys (22%)** receive the highest percentage of cardiac output, while the heart itself (coronary circulation) receives about 5%. * **Fick’s Principle:** The gold standard for measuring CO. $CO = \text{Oxygen consumption} \div (\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content})$.

Q: Cushing's reflex is characterized by all of the following EXCEPT:

Increased heart rate. **Explanation:** Cushing’s reflex (or the Cushing triad) is a physiological nervous system response to **increased intracranial pressure (ICP)**. It is a compensatory mechanism aimed at maintaining cerebral perfusion pressure (CPP). **1. Why "Increased heart rate" is the correct answer (The Exception):** In Cushing’s reflex, the heart rate **decreases (Bradycardia)**, it does not increase. When ICP rises, the brainstem experiences ischemia. The sympathetic nervous system initially triggers a massive pressor response to increase systemic blood pressure. This high blood pressure is sensed by baroreceptors in the carotid sinus and aortic arch, which then trigger a compensatory **parasympathetic (vagal) response**, leading to reflex bradycardia. **2. Analysis of Incorrect Options:** * **Increased systolic blood pressure:** This is a hallmark of the reflex. The body raises the Mean Arterial Pressure (MAP) to overcome the high ICP and force blood into the brain (CPP = MAP - ICP). This often results in a **widened pulse pressure**. * **Irregular respiration:** As the brainstem (specifically the medulla) becomes compressed or ischemic due to high ICP, the normal respiratory rhythm is disrupted, often leading to Cheyne-Stokes breathing or ataxic respirations. **Clinical Pearls for NEET-PG:** * **The Cushing Triad:** 1. Hypertension (with widened pulse pressure), 2. Bradycardia, 3. Irregular respirations. * **Significance:** It is a late sign of high ICP and suggests imminent **brain herniation**. * **Mechanism:** Ischemia of the vasomotor center in the medulla → Sympathetic surge (Hypertension) → Baroreceptor activation → Vagal stimulation (Bradycardia).

Q: What is the normal total delay of the cardiac impulse in the A-V node and bundle of His?

0.16 second. ### Explanation The total delay of the cardiac impulse from the S-A node to the ventricles is approximately **0.16 seconds**. This physiological delay is crucial as it allows the atria to contract and empty their blood into the ventricles before ventricular contraction begins, ensuring optimal cardiac output. **Breakdown of the 0.16-second delay:** 1. **S-A Node to A-V Node:** 0.03 seconds. 2. **A-V Node proper (Nodal delay):** 0.09 seconds. 3. **A-V Bundle (Bundle of His):** 0.04 seconds. *Total time from S-A node to the beginning of the Purkinje system = 0.16 seconds.* #### Analysis of Options: * **Option C (0.16s):** This is the correct standard value cited in Guyton and Hall Physiology. It represents the sum of the conduction time through the atria, the A-V node, and the penetrating portion of the A-V bundle. * **Option D (0.13s):** This represents the delay *within* the A-V node and bundle system alone (0.09 + 0.04), excluding the initial 0.03s travel time from the S-A node. * **Option B (0.18s) & Option A (0.22s):** These values exceed the normal physiological range. A delay of >0.20 seconds (PR interval) is clinically defined as a First-degree Heart Block. #### High-Yield Clinical Pearls for NEET-PG: * **Slowest Conduction:** The A-V node has the slowest conduction velocity (0.01–0.05 m/sec) due to smaller fiber size and fewer gap junctions. * **Fastest Conduction:** The Purkinje system has the fastest conduction velocity (1.5–4.0 m/sec), ensuring near-simultaneous ventricular contraction. * **PR Interval:** On an ECG, the 0.16s delay is reflected within the PR interval (Normal: 0.12–0.20s). * **One-way Valve:** The A-V bundle is the only physiological pathway for electrical impulses to travel from the atria to the ventricles.

Question 1

All of the following statements about myocardial oxygen demand is true, except?

Accepted Answer

Is negligible when heart is at rest

Answer

Correlates with heart rate

Answer

Is proportional to external cardiac work

Answer

Depends upon duration of systole

Question 2

Which of the following represents Laplace's law related to pressure and tension, or a deviation from it?

Accepted Answer

T = WP/R

Answer

P = T/r

Answer

P = 2T/r

Answer

T = Pr/W

Question 3

Long-acting calcium channel blockers act during which phase of the action potential?

Accepted Answer

Phase 2

Answer

Phase 0

Answer

Phase 1

Answer

Phase 3

Question 4

Which of the following statements regarding blood pressure measurement is incorrect?

Accepted Answer

The blood pressure cuff should be placed at a higher level than the heart.

Answer

The bladder of the blood pressure cuff should cover more than 80% of the arm circumference.

Answer

The patient should be in a resting position.

Answer

The cuff should be tied over the upper arm.

Question 5

The fourth heart sound is caused by:

Accepted Answer

Ventricular filling

Answer

Closure of the aortic and pulmonary valves

Answer

Vibrations in the ventricular wall during systole

Answer

Closure of the mitral and tricuspid valves

Question 6

What is the basal cardiac output in an adult?

Accepted Answer

5 litres

Answer

7.5 litres

Answer

12 litres

Answer

10 litres

Question 7

Cushing's reflex is characterized by all of the following EXCEPT:

Accepted Answer

Increased heart rate

Answer

Increased systolic blood pressure

Answer

Irregular respiration

Answer

None of the above

Question 8

What is the normal total delay of the cardiac impulse in the A-V node and bundle of His?

Accepted Answer

0.16 second

Answer

0.22 second

Answer

0.18 second

Answer

0.13 second

Question 9

If both carotids are occluded proximal to the carotid bifurcation, what physiological changes would occur?

Accepted Answer

Decreased blood pressure and increased heart rate

Answer

Increased blood pressure and decreased heart rate

Answer

Decreased blood pressure and decreased heart rate

Answer

Increased blood pressure and increased heart rate

Question 10

In a measurement of cardiac output using the Fick principle, the O2 concentrations of mixed venous and arterial blood are 16 and 20 ml/100 ml, respectively, and the O2 consumption is 300 ml/min. The cardiac output in liters/min is?

Accepted Answer

7.5

Answer

5

Answer

8

Answer

9

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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