Cardiovascular System Practice Questions

Q: Cardiac output is measured by all methods EXCEPT?

Oscillometry. **Explanation:** **1. Why Oscillometry is the correct answer:** Oscillometry is a technique used primarily for the measurement of **Blood Pressure**, not Cardiac Output (CO). It works by detecting the magnitude of oscillations caused by blood flow against an automated inflating/deflating cuff. While it provides systolic, diastolic, and mean arterial pressures, it does not directly measure the volume of blood pumped by the heart per minute. **2. Analysis of Incorrect Options:** * **Doppler (Option A):** This is a non-invasive method using ultrasound. By measuring the flow velocity of blood across the aortic or pulmonary valve and multiplying it by the cross-sectional area of the vessel, CO can be calculated (CO = Stroke Volume × Heart Rate). * **Thermo-dilution (Option B):** This is the **clinical gold standard** for measuring CO. It involves injecting a cold saline bolus via a Swan-Ganz catheter and measuring the temperature change downstream. The rate of temperature change is inversely proportional to the CO (based on the Stewart-Hamilton equation). * **Fick’s Principle (Option D):** This is the **theoretical gold standard**. It states that the uptake of a substance (usually Oxygen) by an organ is equal to the product of the blood flow to that organ and the arteriovenous concentration difference of that substance. Formula: $CO = \text{O}_2 \text{ consumption} / (\text{Arterial } \text{O}_2 - \text{Mixed Venous } \text{O}_2)$. **Clinical Pearls for NEET-PG:** * **Indicator Dilution Method:** Uses substances like Indocyanine green; it is the precursor concept to thermo-dilution. * **Echocardiography:** The most common non-invasive bedside method to estimate CO/Ejection Fraction. * **Mixed Venous Blood:** For Fick's principle, mixed venous blood must be sampled from the **Pulmonary Artery** to ensure proper mixing.

Q: All of the following are physiological effects of the manoeuvre shown below except?

Increased stroke volume. ***Increased stroke volume*** - During the **Valsalva manoeuvre**, increased **intrathoracic pressure** compresses the venous system, reducing **venous return** and **preload**. - This leads to **decreased stroke volume** due to reduced left ventricular filling, making this the exception among the listed effects. *Fall in BP* - The **decreased venous return** and reduced **stroke volume** during the manoeuvre result in a significant **drop in blood pressure**. - This occurs particularly during **phase 2** of the Valsalva manoeuvre when cardiac output is compromised. *Rise in HR* - The fall in blood pressure triggers **baroreceptor-mediated reflexes** that increase **sympathetic activity**. - This compensatory mechanism leads to **tachycardia** to maintain cardiac output despite reduced stroke volume. *Decreased venous return* - Increased **intrathoracic pressure** compresses the **inferior vena cava** and other venous structures. - This mechanical compression significantly reduces the **venous return** to the right heart, decreasing preload.

Q: What is the normal cardiac index in an adult?

3.2 L/min/m2. ### Explanation **1. Understanding the Correct Answer (C):** Cardiac Index (CI) is a hemodynamic parameter that relates the Cardiac Output (CO) to a person’s Body Surface Area (BSA). This provides a more accurate assessment of cardiac performance than CO alone, as it accounts for the individual's body size. * **Formula:** $CI = \frac{\text{Cardiac Output}}{\text{Body Surface Area}}$ * In a healthy adult, the average Cardiac Output is approximately **5 L/min** and the average BSA is **1.7 m²**. * Calculation: $5 / 1.7 \approx 2.9 \text{ to } 3.2 \text{ L/min/m}^2$. * The standard physiological range is **2.5 to 4.2 L/min/m²**, making **3.2 L/min/m²** the most accurate representative value among the options. **2. Analysis of Incorrect Options:** * **Option A (5.9 L/min/m²):** This value is significantly higher than normal. Such a high index would indicate a hyperdynamic state (e.g., severe thyrotoxicosis, sepsis, or strenuous exercise). * **Option B (2.3 L/min/m²):** This is below the normal threshold. A CI less than **2.2 L/min/m²** is a clinical marker for **cardiogenic shock** or significant heart failure. * **Option D (4.6 L/min/m²):** While closer to the upper limit, it is generally considered above the average resting baseline for a healthy adult. **3. NEET-PG High-Yield Pearls:** * **Peak Age:** Cardiac Index is highest at age 10 (approx. 4 L/min/m²) and gradually declines with age. * **Clinical Significance:** CI is vital in the ICU setting to differentiate types of shock. * **BSA Calculation:** Most commonly calculated using the **Mosteller formula** or **DuBois formula**. * **Key Value:** A CI $< 2.2 \text{ L/min/m}^2$ in the presence of high pulmonary capillary wedge pressure (PCWP) defines cardiogenic shock.

Q: Closing of the mitral valve begins at which point?

A. ***Point A*** - Point A marks the **beginning of ventricular systole** when **left ventricular pressure** first exceeds **left atrial pressure**, causing the **mitral valve** to close. - This corresponds to the start of **isovolumetric contraction** phase, where ventricular pressure rises rapidly with all valves closed. *Point B* - Point B typically represents **aortic valve opening** when left ventricular pressure exceeds aortic pressure. - At this point, the mitral valve is already **fully closed** and ventricular ejection begins. *Point C* - Point C usually corresponds to **peak systole** during the ejection phase when ventricular pressure is at its maximum. - The mitral valve remains **closed throughout systole** and does not begin closing at this point. *Point D* - Point D represents **aortic valve closure** at the end of systole when ventricular pressure falls below aortic pressure. - This marks the beginning of **diastole**, but mitral valve closure occurred much earlier at point A.

Q: Cushing's phenomenon is characterized by which of the following combinations?

High blood pressure and low heart rate. **Explanation:** **Cushing’s phenomenon** (or Cushing’s reflex) is a physiological response to **increased intracranial pressure (ICP)**. It is a classic high-yield topic in NEET-PG, representing the body’s attempt to maintain cerebral perfusion. **1. Why Option D is Correct:** When ICP rises (due to tumors, hemorrhage, or edema), it compresses cerebral blood vessels, leading to **cerebral ischemia**. To counteract this, the vasomotor center in the medulla triggers a massive sympathetic discharge. This causes a significant increase in systemic arterial blood pressure (**Hypertension**) to "push" blood into the brain against the high ICP. The sudden rise in blood pressure is sensed by baroreceptors in the carotid sinus and aortic arch, which triggers a compensatory parasympathetic (vagal) response, resulting in a decreased heart rate (**Bradycardia**). **2. Why Other Options are Incorrect:** * **Option A & B:** High heart rates (Tachycardia) are not part of the reflex; the baroreceptor reflex ensures bradycardia occurs in response to the hypertension. * **Option C:** Low blood pressure would further compromise cerebral blood flow, leading to brain death; the body’s reflex is specifically designed to raise pressure. **3. Clinical Pearls for NEET-PG:** * **Cushing’s Triad:** This is the clinical manifestation of the reflex and consists of: 1. **Hypertension** (specifically widened pulse pressure) 2. **Bradycardia** 3. **Irregular Respiration** (Cheyne-Stokes or ataxic breathing due to brainstem compression). * **Significance:** The appearance of Cushing’s triad is a late sign of brain herniation and is a neurosurgical emergency. * **Contrast:** It is the physiological opposite of **Shock**, where you typically see low blood pressure and a high heart rate.

Q: Major portion of coronary blood flow occurs during which phase of the cardiac cycle?

Diastole. **Explanation:** The correct answer is **Diastole**. This is a fundamental concept in cardiovascular physiology, particularly regarding the left ventricle. **Why Diastole is Correct:** During **systole**, the high pressure generated by the contracting myocardium (ventricular wall) compresses the intramyocardial portions of the coronary arteries. This mechanical compression significantly increases coronary vascular resistance, nearly halting blood flow to the subendocardial layers. During **diastole**, the myocardium relaxes, the compressive forces are removed, and the aortic pressure remains high enough to drive blood into the coronary circulation. Therefore, the left ventricle receives approximately **70-80% of its blood supply during diastole.** **Why Other Options are Incorrect:** * **A. Systole:** While some flow occurs during systole (especially in the right ventricle where pressures are lower), it is significantly less than diastolic flow due to the "extravascular compression" effect. * **C & D:** Coronary blood flow is strictly regulated by the phases of the cardiac cycle and metabolic demands; it is neither unrelated nor randomly variable. **NEET-PG High-Yield Pearls:** 1. **Left vs. Right Ventricle:** Unlike the left ventricle, the **Right Ventricle** receives blood flow during **both systole and diastole** because the right ventricular systolic pressure is much lower than the aortic pressure, failing to compress the vessels completely. 2. **Tachycardia:** As heart rate increases, the duration of diastole shortens more than systole. This reduces the time available for coronary perfusion, which is why tachycardia can trigger ischemia in patients with coronary artery disease. 3. **Subendocardium:** This is the most vulnerable layer to ischemia because it experiences the greatest compressive forces during systole.

Q: Cardiac output changes are minimal during which of the following conditions?

Sleep. **Explanation:** **Correct Option: A (Sleep)** Cardiac output (CO) is defined as the volume of blood pumped by each ventricle per minute (CO = Stroke Volume × Heart Rate). During **sleep**, the body is in a state of basal metabolic demand. While there is a slight parasympathetic dominance leading to a minor decrease in heart rate and blood pressure, the overall change in cardiac output is considered **minimal or negligible** compared to other physiological or pathological states. The body maintains a steady basal level to support vital organ perfusion. **Analysis of Incorrect Options:** * **B. Transition from supine to standing:** This causes a significant **decrease** in venous return due to gravity-induced pooling of blood in the lower extremities (orthostasis). This leads to a transient but marked drop in stroke volume and cardiac output before compensatory baroreceptor reflexes kick in. * **C. Exercise:** This is the most potent physiological stimulus for **increasing** cardiac output. CO can increase from a resting 5 L/min to 20–25 L/min in healthy individuals (and up to 35 L/min in athletes) due to increased heart rate and contractility. * **D. Arrhythmias:** Pathological rhythms significantly alter CO. For example, **Tachyarrhythmias** shorten diastolic filling time, while **Bradyarrhythmias** reduce the frequency of ejection, both typically leading to a **decrease** in cardiac output. **High-Yield Facts for NEET-PG:** * **Cardiac Index:** Cardiac output per square meter of body surface area (Normal: 3.2 L/min/m²). * **Factors increasing CO:** Anxiety/Excitement (50-100%), Eating (30%), Pregnancy, and High Altitude. * **Factors decreasing CO:** Sitting/Standing from lying down (approx. 20-30% decrease), Myocardial Infarction, and Rapid Arrhythmias. * **Metabolic Link:** Cardiac output is directly proportional to the overall oxygen consumption of the body (Fick’s Principle).

Q: Which of the following describes the low-pressure receptors?

Stimulated by atrial systole and diastole. **Explanation:** **Low-pressure receptors**, also known as **Cardiopulmonary receptors** or **Volume receptors**, are located in the walls of the atria (at the junctions with the vena cava and pulmonary veins) and the pulmonary vasculature. **Why Option B is Correct:** These receptors are mechanoreceptors that respond to the **distension (stretch)** of the atrial walls. They are stimulated during both **atrial diastole** (when the atria fill with blood) and **atrial systole** (due to the contraction of the atrial muscle against the blood volume). Their primary function is to sense changes in "effective circulating volume" rather than systemic arterial pressure. **Analysis of Incorrect Options:** * **Option A:** Low-pressure receptors respond to **venous return** and blood volume, not directly to cardiac output. * **Options C & D:** These describe the triggers for **High-pressure baroreceptors**. High-pressure receptors are located in the **carotid sinus** and **aortic arch**; they are stimulated by left ventricular contraction (systolic surge) and changes in mean arterial/aortic pressure. **High-Yield NEET-PG Pearls:** 1. **Bainbridge Reflex:** Increased atrial stretch (increased venous return) triggers these receptors to increase heart rate to prevent blood pooling. 2. **Atrial Natriuretic Peptide (ANP):** Stimulation of these receptors leads to the release of ANP, causing vasodilation and natriuresis. 3. **Volume Regulation:** Activation of low-pressure receptors **inhibits ADH (Vasopressin)** release from the posterior pituitary, leading to increased water excretion (diuresis) to normalize blood volume.

Question 1

During inhibition of the SA node by vagal stimulation, which of the following occurs?

Accepted Answer

Acting on K+ channels resulting in K+ efflux

Answer

Acting on K+ channels resulting in K+ influx

Answer

Acting on Ca2+ channels resulting in K+ efflux

Answer

Acting on Ca2+ channels resulting in K+ influx

Question 2

Cardiac output is measured by all methods EXCEPT?

Accepted Answer

Oscillometry

Answer

Doppler

Answer

Thermo-dilution method

Answer

Fick's principle

Question 3

What is the primary function of lymphatic vessels?

Accepted Answer

To transport proteins from interstitial fluid back to the bloodstream

Answer

To increase oncotic pressure in the blood

Answer

To carry immunocompetent cells throughout the body

Answer

All of the above

Question 4

All of the following are physiological effects of the manoeuvre shown below except?

Accepted Answer

Increased stroke volume

Answer

Fall in BP

Answer

Rise in HR

Answer

Decreased venous return

Question 5

What is the normal cardiac index in an adult?

Accepted Answer

3.2 L/min/m2

Answer

5.9 L/min/m2

Answer

2.3 L/min/m2

Answer

4.6 L/min/m2

Question 6

Closing of the mitral valve begins at which point?

Accepted Answer

A

Answer

B

Answer

C

Answer

D

Question 7

Cushing's phenomenon is characterized by which of the following combinations?

Accepted Answer

High blood pressure and low heart rate

Answer

Low blood pressure and high heart rate

Answer

High blood pressure and high heart rate

Answer

Low blood pressure and low heart rate

Question 8

Major portion of coronary blood flow occurs during which phase of the cardiac cycle?

Accepted Answer

Diastole

Answer

Systole

Answer

Not related to phases

Answer

It is variable

Question 9

Cardiac output changes are minimal during which of the following conditions?

Accepted Answer

Sleep

Answer

Transition from a supine to a standing position

Answer

Exercise

Answer

Arrhythmias

Question 10

Which of the following describes the low-pressure receptors?

Accepted Answer

Stimulated by atrial systole and diastole

Answer

Affected by cardiac output

Answer

Stimulation by left ventricular contraction

Answer

Stimulated by aortic pressure

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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