Cardiovascular System Practice Questions

Q: In the context of hypoxia, the cardiovascular response to peripheral chemoreceptor stimulation can result in which of the following changes in heart rate?

Either bradycardia or tachycardia. ***Either bradycardia or tachycardia*** - Peripheral chemoreceptor stimulation by hypoxia produces **complex cardiovascular responses** that can result in either bradycardia or tachycardia depending on the circumstances. - **Direct chemoreceptor reflex**: Stimulation of carotid and aortic bodies causes **reflex bradycardia** via vagal activation (direct effect). - **Net clinical effect**: In most physiological conditions, the bradycardia is overridden by **compensatory tachycardia** due to: - Sympathetic nervous system activation - Hyperventilation-induced stretch receptor stimulation - Direct myocardial effects attempting to maintain oxygen delivery - The actual heart rate response depends on the **balance between vagal and sympathetic inputs**, making both responses possible. *Only bradycardia* - While isolated peripheral chemoreceptor stimulation can produce **reflex bradycardia**, this ignores the compensatory sympathetic activation that typically occurs during hypoxia. - In clinical hypoxia, bradycardia alone is uncommon unless other factors suppress sympathetic responses. *Neither bradycardia nor tachycardia* - This is incorrect because peripheral chemoreceptor stimulation **invariably affects heart rate** through autonomic pathways. - The cardiovascular system must respond to hypoxia to maintain oxygen delivery to tissues. *Only tachycardia* - While **tachycardia** is the more common net clinical response to hypoxia, the initial chemoreceptor reflex involves **vagal bradycardia**. - Stating "only tachycardia" ignores the direct chemoreceptor-vagal reflex pathway and the possibility of bradycardia in certain experimental or clinical conditions.

Q: QT shortening is associated with which electrolyte imbalance?

Hypercalcemia. ***Hypercalcemia*** - **Elevated calcium levels** lead to a shortened **plateau phase of the cardiac action potential**, which manifests as a **shortened QT interval** on an ECG. - This imbalance increases the risk of ventricular arrhythmias, although profound shortening can lead to **QRS widening** with further increase in calcium. *Hypokalemia* - **Low potassium** levels typically cause **QT prolongation**, usually due to prominent U waves and T wave flattening. - It does not cause QT shortening; instead, it is associated with an **increased risk of Torsades de Pointes**. *Hypocalcemia* - **Low calcium** levels cause **QT prolongation** by lengthening the **plateau phase of the cardiac action potential**, increasing the duration of ventricular repolarization. - ECG findings include prolonged ST segment and can increase the risk of arrhythmias, including Torsades de Pointes. *Hyperkalemia* - **High potassium** levels primarily cause **peaked T waves**, a **widened QRS complex**, and a **prolonged PR interval**, potentially leading to asystole or ventricular fibrillation. - It does not cause QT shortening; instead, severe hyperkalemia can lead to **loss of P waves** and a **sine wave pattern**.

Q: The organ with maximum blood flow in milliliters per kilogram per minute during resting is:

Kidneys. ***Kidneys*** - The kidneys receive a disproportionately large share of cardiac output, approximately **20-25%**, which is essential for their role in **filtering blood** and maintaining fluid and electrolyte balance. - When adjusted for organ weight, the kidneys have the highest blood flow per unit mass due to their high metabolic demands for active transport and regulatory functions. *Liver* - The liver receives significant blood flow, but a substantial portion is **venous blood** from the portal system, which is lower in oxygen and nutrient content. - While total blood flow to the liver is high, its actual arterial supply and overall perfusion density per kilogram is lower than that of the kidneys. *Brain* - The brain has high metabolic demands and receives a constant and significant blood supply, typically around **15% of cardiac output**, to ensure adequate oxygen and glucose delivery. - However, when normalized per unit of tissue mass, its blood flow is less than that of the kidneys, which have specialized functions requiring extremely high perfusion. *Lungs* - The lungs receive the entire cardiac output through the **pulmonary circulation** for gas exchange, but this refers to the total volume of blood passing through, not the nutritive arterial supply to the lung tissue itself. - The bronchial circulation, which supplies oxygenated blood to the lung tissue, is relatively small compared to other highly metabolic organs.

Q: Pressure-Volume loop of cardiac cycle is shown below. What does point C represent?

Aortic valve opens. ***Aortic valve opens*** - Point C represents the critical moment when the **left ventricular pressure** surpasses the **aortic pressure**, causing the aortic valve to open. - This event marks the beginning of the **ejection phase**, where blood is pumped from the left ventricle into the aorta. *Mitral valve opens* - The mitral valve opens at point A, signaling the start of **ventricular filling** as blood flows from the left atrium into the left ventricle. - At this point, the left ventricular pressure is at its lowest, and the volume begins to increase. *Mitral valve closes* - The mitral valve closes at point B, indicating the end of **ventricular filling** and the start of **isovolumetric contraction**. - This closure prevents backflow of blood into the left atrium as the ventricle begins to contract. *Aortic valve closes* - The aortic valve closes at point F, which signifies the end of **ejection** and the beginning of **isovolumetric relaxation**. - At this point, the left ventricular pressure falls below aortic pressure, and the ventricle begins to relax without changing volume.

Q: Hypotension in acute spinal injury is due to:

Loss of sympathetic tone. ***Loss of sympathetic tone*** - **Acute spinal cord injury** above T6 can interrupt the sympathetic outflow from the central nervous system. - This leads to unopposed **parasympathetic activity**, causing **vasodilation**, **bradycardia**, and resultant **hypotension**. *Loss of parasympathetic tone* - Loss of parasympathetic tone would typically result in **tachycardia** and potentially **hypertension**, as sympathetic activity would be unopposed. - This is not the primary mechanism for hypotension observed in acute spinal injury. *Orthostatic hypotension* - While patients with spinal cord injury can experience orthostatic hypotension, the initial acute hypotension is due to the fundamental physiological disruption of **autonomic control**. - **Orthostatic hypotension** specifically refers to a drop in blood pressure upon standing, which is a symptom that can persist, but not the direct cause of acute neurogenic shock. *Vasovagal attack* - A **vasovagal attack** is typically triggered by emotional stress or pain, leading to temporary reflex-mediated bradycardia and vasodilation. - It is not the underlying cause of sustained hypotension in the setting of acute spinal cord injury.

Q: The primary effect of vagal stimulation on the heart is

Decreased heart rate. ***Decreased heart rate*** - **Vagal stimulation** releases **acetylcholine**, which activates muscarinic receptors on the sinoatrial (SA) node, leading to a decrease in its firing rate and thus a slower heart rate. - This parasympathetic effect primarily targets the **SA node** and **AV node**, influencing chronotropy (heart rate) more significantly than inotropy (contractility). *Increased P-R interval in ECG* - While vagal stimulation does slow **AV node conduction**, increasing the P-R interval, this is a more specific electrophysiological effect rather than the primary overall physiological outcome of vagal stimulation on the heart. - The most direct and immediate consequence of vagal nerve activity is the slowing of the heart's rhythm, which manifests as a **decreased heart rate**. *Decreased force of heart contraction* - The **vagus nerve** has a relatively weak effect on ventricular contractility, as parasympathetic innervation is far less dense in the ventricles compared to the atria and nodal tissues. - Therefore, a significant **decrease in the force of contraction** is not a primary or direct result of typical vagal stimulation in a healthy heart. *Decreased cardiac output* - While a markedly decreased heart rate *could* lead to a decreased cardiac output (CO = HR x SV), this is not the most direct or immediate physiological effect of vagal stimulation. - The primary action is on the heart rate, and changes in cardiac output would be a **secondary consequence** depending on the extent of bradycardia and compensatory mechanisms.

Q: A shift of posture from supine to upright posture is associated with cardiovascular adjustments. Which of the following is NOT true in this context?

Rise in central venous pressure. ***Rise in central venous pressure*** - When a person moves from a supine to an upright posture, gravity causes **blood pooling in the lower extremities**, leading to a *decrease* in venous return to the heart, not a rise in central venous pressure. - A decrease in central venous pressure is an expected physiological response to orthostasis due to the aforementioned venous pooling. *Decrease in central venous pressure* - This statement is physiologically *true* because gravity causes blood to pool in the lower limbs, reducing venous return and subsequently lowering the central venous pressure. - The **baroreflex** responds to this fall, attempting to restore blood pressure. *Rise in heart rate* - This is a normal physiological response to orthostatic stress, mediated by the **baroreflex**, to maintain cardiac output and blood pressure against gravity. - The sympathetic nervous system increases **heart rate** and contractility to compensate for reduced venous return. *Decrease in cardiac output* - Upon standing, the initial reduction in venous return leads to a transient decrease in **stroke volume**, which, despite the compensatory rise in heart rate, often results in a net *decrease* in cardiac output. - This is a normal and expected cardiovascular adjustment as the body adapts to the upright position.

Q: What is the mean arterial pressure (MAP) for a person with an arterial blood pressure of 125/75 mm Hg?

The mean arterial pressure is 92 mm Hg. ***The mean arterial pressure is 92 mm Hg*** - **Mean arterial pressure (MAP)** is calculated using the formula: **MAP = Diastolic Pressure + 1/3 (Systolic Pressure - Diastolic Pressure)**. - Given a blood pressure of **125/75 mm Hg** (systolic/diastolic), MAP = 75 + 1/3 (125 - 75) = 75 + 1/3 (50) = 75 + 16.67 ≈ **91.67 mm Hg**, which rounds to 92 mm Hg. *The pulse pressure is 50 mm Hg* - **Pulse pressure** is the difference between **systolic and diastolic pressure**. - In this case, 125 mm Hg (systolic) - 75 mm Hg (diastolic) = **50 mm Hg**, which is accurate but not the MAP. *Diastolic pressure is 75 mm Hg* - The **diastolic pressure** is the lower number in a blood pressure reading, representing the pressure during cardiac relaxation. - For a blood pressure of 125/75 mm Hg, the **diastolic pressure is indeed 75 mm Hg**, but this is only one component of MAP. *Systolic pressure is 125 mm Hg* - The **systolic pressure** is the upper number in a blood pressure reading, representing the pressure during cardiac contraction. - For a blood pressure of 125/75 mm Hg, the **systolic pressure is indeed 125 mm Hg**, but this alone does not represent MAP.

Q: Below are two vessels shown. Assuming the pressure along both the vessels is the same and both of them follow linear flow pattern, what will be the amount of blood flow in vessel A compared to vessel B?

16 times. ***16 times*** - According to **Poiseuille's Law**, blood flow through a vessel is given by: Q = (π × ΔP × r⁴) / (8 × η × L) - Flow is **directly proportional to the fourth power of the radius** (Q ∝ r⁴) when pressure gradient, viscosity, and length remain constant - If vessel A has **twice the radius of vessel B** (r_A = 2r_B) and both have the same length and pressure gradient, then: - Q_A / Q_B = (r_A / r_B)⁴ = (2)⁴ = **16** - Therefore, blood flow in vessel A is **16 times greater** than in vessel B - This demonstrates the powerful effect of vessel radius on blood flow—a fundamental principle in cardiovascular physiology *8 times* - This would only be correct if flow were proportional to r³ (cube of radius), which is **not consistent with Poiseuille's Law** - Poiseuille's Law clearly states Q ∝ r⁴, not r³ - This is a common distractor that underestimates the impact of radius on flow *32 times* - This answer would be correct if vessel A had **twice the radius AND half the length** of vessel B - Since Q ∝ r⁴/L, if r_A = 2r_B and L_A = 0.5L_B: Q_A/Q_B = (2)⁴ × (1/0.5) = 16 × 2 = 32 - However, the question states both vessels have the same pressure along their length, implying equal lengths *4 times* - This would only be correct if flow were proportional to **r² (radius squared)**, which is incorrect - This might confuse students thinking about cross-sectional area (A ∝ r²), but **flow rate depends on r⁴**, not just the area - This represents a fundamental misunderstanding of Poiseuille's Law

Q: Which of the following equations correctly represents Poiseuille's Hagen law for fluid flow?

F = (PA-PB) X 3.14 X r^4/8nl. ***F = (PA-PB) X 3.14 X r^4/8nl*** - This equation correctly represents Poiseuille's Hagen law, which describes the **volumetric flow rate** (F) of an incompressible fluid through a rigid cylindrical tube. - It shows that flow is directly proportional to the **pressure difference** ($P_A - P_B$) and the **fourth power of the radius** (r⁴), and inversely proportional to the fluid's **viscosity** (n) and the **length of the tube** (l). *F = (PA-PB) X 3.14 X r^3/8nl* - This option incorrectly uses **r³** instead of **r⁴** in the numerator. - Poiseuille's law explicitly states that the flow rate is proportional to the **fourth power of the radius**, highlighting the significant impact of vessel diameter on fluid flow. *F = (PA-PB) X 3.14 X r^4/8n* - This equation omits the **length of the tube (l)** from the denominator. - Flow rate is inversely proportional to the **length of the tube** because a longer tube implies greater resistance to flow. *F = (PA-PB) X 3.14 X r^2/8nl* - This option incorrectly uses **r²** instead of **r⁴** in the numerator. - The **fourth power dependence** on radius is a critical aspect of Poiseuille's law, demonstrating that even small changes in vessel radius have a large effect on flow.

Question 1

In the context of hypoxia, the cardiovascular response to peripheral chemoreceptor stimulation can result in which of the following changes in heart rate?

Accepted Answer

Either bradycardia or tachycardia

Answer

Only bradycardia

Answer

Neither bradycardia nor tachycardia

Answer

Only tachycardia

Question 2

QT shortening is associated with which electrolyte imbalance?

Accepted Answer

Hypercalcemia

Answer

Hypokalemia

Answer

Hypocalcemia

Answer

Hyperkalemia

Question 3

The organ with maximum blood flow in milliliters per kilogram per minute during resting is:

Accepted Answer

Kidneys

Answer

Brain

Answer

Lungs

Answer

Liver

Question 4

Pressure-Volume loop of cardiac cycle is shown below. What does point C represent?

Accepted Answer

Aortic valve opens

Answer

Aortic valve closes

Answer

Mitral valve closes

Answer

Mitral valve opens

Question 5

Hypotension in acute spinal injury is due to:

Accepted Answer

Loss of sympathetic tone

Answer

Loss of parasympathetic tone

Answer

Orthostatic hypotension

Answer

Vasovagal attack

Question 6

The primary effect of vagal stimulation on the heart is

Accepted Answer

Decreased heart rate

Answer

Increased P-R interval in ECG

Answer

Decreased force of heart contraction

Answer

Decreased cardiac output

Question 7

A shift of posture from supine to upright posture is associated with cardiovascular adjustments. Which of the following is NOT true in this context?

Accepted Answer

Rise in central venous pressure

Answer

Rise in heart rate

Answer

Decrease in cardiac output

Answer

Decrease in central venous pressure

Question 8

What is the mean arterial pressure (MAP) for a person with an arterial blood pressure of 125/75 mm Hg?

Accepted Answer

The mean arterial pressure is 92 mm Hg

Answer

The pulse pressure is 50 mm Hg

Answer

Diastolic pressure is 75 mm Hg

Answer

Systolic pressure is 125 mm Hg

Question 9

Below are two vessels shown. Assuming the pressure along both the vessels is the same and both of them follow linear flow pattern, what will be the amount of blood flow in vessel A compared to vessel B?

Accepted Answer

16 times

Answer

4 times

Answer

32 times

Answer

8 times

Question 10

Which of the following equations correctly represents Poiseuille's Hagen law for fluid flow?

Accepted Answer

F = (PA-PB) X 3.14 X r^4/8nl

Answer

F = (PA-PB) X 3.14 X r^3/8nl

Answer

F = (PA-PB) X 3.14 X r^4/8n

Answer

F = (PA-PB) X 3.14 X r^2/8nl

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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