Cardiovascular System Practice Questions

Q: A patient has a blood pressure of 130/80 mmHg, a cardiac output of 5000 ml, and a heart rate of 70 beats per minute. Calculate the volume of blood pumped with each beat.

70 ml. **Explanation** The correct answer is **70 ml**. This question tests the fundamental physiological relationship between Cardiac Output (CO), Heart Rate (HR), and Stroke Volume (SV). **1. Why the Correct Answer is Right:** The volume of blood pumped with each beat is defined as the **Stroke Volume (SV)**. The relationship is expressed by the formula: * **Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)** * Rearranging for SV: **SV = CO / HR** * Calculation: $5000\text{ ml/min} \div 70\text{ beats/min} \approx 71.4\text{ ml}$ * Rounding to the nearest option gives **70 ml**, which is the standard physiological average for a healthy adult. **2. Why the Incorrect Options are Wrong:** * **B (110 ml):** This value is closer to the **End-Diastolic Volume (EDV)**, which is the total volume in the ventricle before contraction, not the amount ejected. * **C (50 ml):** This represents a reduced stroke volume, often seen in heart failure or tachyarrhythmias where filling time is compromised. * **D (90 ml):** While possible in athletes or during exercise (due to increased contractility), it does not fit the mathematical parameters provided in the question. **3. NEET-PG High-Yield Clinical Pearls:** * **Pulse Pressure:** In this patient, it is $130 - 80 = 50\text{ mmHg}$. Pulse pressure is directly proportional to stroke volume and inversely proportional to aortic compliance. * **Ejection Fraction (EF):** $EF = (SV / EDV) \times 100$. Normal range is 55–70%. * **Fick’s Principle:** Remember that CO can also be calculated as $\text{Oxygen consumption} / (\text{Arterial } O_2 \text{ content} - \text{Venous } O_2 \text{ content})$. * **Preload & Afterload:** Stroke volume is increased by preload (Frank-Starling law) and contractility, but decreased by excessive afterload.

Q: All are cardiovascular effects of parasympathetic stimulation except?

Increased automaticity. **Explanation:** The parasympathetic nervous system (PNS) influences the heart primarily through the **Vagus nerve (Cranial Nerve X)**, which releases **Acetylcholine (ACh)**. ACh acts on **M2 muscarinic receptors**, leading to inhibitory effects on cardiac tissue. **Why "Increased Automaticity" is the correct answer:** Parasympathetic stimulation **decreases automaticity**, particularly in the SA node. It does this by increasing K+ conductance (hyperpolarization) and decreasing the slope of Phase 4 spontaneous depolarization. Therefore, "Increased automaticity" is the opposite of what the PNS does; increased automaticity is a hallmark of **sympathetic** (adrenergic) stimulation. **Analysis of Incorrect Options:** * **Decreased heart rate (Negative Chronotropy):** ACh slows the firing rate of the SA node by hyperpolarizing the resting membrane potential. This is a classic PNS effect. * **Decreased conduction (Negative Dromotropy):** Vagal stimulation significantly slows conduction through the AV node by increasing the PR interval. This can lead to a physiological heart block in cases of high vagal tone. * **Increased refractive period:** By slowing the recovery of ion channels and slowing conduction velocity (especially in the AV node), the PNS increases the effective refractory period (ERP), protecting the ventricles from rapid atrial rates. **High-Yield Clinical Pearls for NEET-PG:** * **Vagal Escape:** If the vagus nerve is overstimulated, the heart may stop, but a latent pacemaker (like the Purkinje fibers) will eventually take over. * **Ventricular Effect:** Parasympathetic innervation to the ventricles is sparse compared to the atria; thus, its effect on ventricular contractility (Inotropy) is minimal. * **Atropine:** A muscarinic antagonist used to treat symptomatic bradycardia by blocking these parasympathetic effects.

Q: Cardiac output depends on all of the following except?

Body surface area. **Explanation:** The fundamental equation for cardiac output is **Cardiac Output (CO) = Stroke Volume (SV) × Heart Rate (HR)**. **Why Body Surface Area (BSA) is the correct answer:** Cardiac output is an absolute measurement of the volume of blood pumped by the heart per minute (typically ~5 L/min). While CO is often *normalized* to a person's body size to allow for clinical comparison between individuals of different sizes—a parameter known as the **Cardiac Index (CI = CO/BSA)**—the actual generation of cardiac output itself does not depend on the body surface area. BSA is a scaling factor used for interpretation, not a physiological determinant of the heart's pumping capacity. **Analysis of incorrect options:** * **Cardiac Rate (HR):** As per the formula (CO = SV × HR), any change in heart rate directly impacts the cardiac output. * **Stroke Volume (SV):** This is the volume of blood ejected per beat. It is a primary determinant of CO. * **Cardiac Contractility:** This is a major determinant of Stroke Volume (along with preload and afterload). Increased contractility (inotropy) increases the ejection fraction and stroke volume, thereby increasing cardiac output. **High-Yield Clinical Pearls for NEET-PG:** * **Cardiac Index (CI):** Normal range is **2.5 to 4.0 L/min/m²**. It is a more accurate indicator of whether the CO is sufficient for an individual's metabolic needs. * **Fick’s Principle:** The gold standard for measuring CO. $CO = \text{Oxygen Consumption} / (\text{Arterial } O_2 \text{ content} - \text{Mixed Venous } O_2 \text{ content})$. * **Preload:** According to the **Frank-Starling Law**, increased preload increases SV and thus CO, up to a physiological limit.

Q: What is the main role of angiotensin II?

Increased TPR. **Explanation:** Angiotensin II (AT-II) is a potent octapeptide and a central component of the Renin-Angiotensin-Aldosterone System (RAAS). Its primary physiological role is to maintain blood pressure and fluid balance. **1. Why "Increased TPR" is correct:** Angiotensin II is one of the most powerful direct **vasoconstrictors** known. It acts on **AT1 receptors** located on vascular smooth muscle cells throughout the systemic circulation. By causing widespread arteriolar constriction, it significantly increases **Total Peripheral Resistance (TPR)**, which directly raises the Mean Arterial Pressure (MAP = CO × TPR). **2. Analysis of Incorrect Options:** * **B. Constriction of afferent renal arteriole:** AT-II preferentially constricts the **efferent arteriole** more than the afferent. This increases glomerular capillary hydrostatic pressure, thereby maintaining the Glomerular Filtration Rate (GFR) even when renal blood flow is low. * **C. Decreased release of aldosterone:** AT-II actually **stimulates** the zona glomerulosa of the adrenal cortex to release aldosterone, which promotes sodium and water retention. * **D. Diuresis:** AT-II is **anti-diuretic** and **anti-natriuretic**. It promotes water and salt retention both directly (by stimulating Na+/H+ exchange in the proximal tubule) and indirectly (via aldosterone and ADH release). **High-Yield Clinical Pearls for NEET-PG:** * **Receptor Specificity:** Most known cardiovascular effects (vasoconstriction, thirst, aldosterone release) are mediated via **AT1 receptors**. AT2 receptors generally mediate vasodilation and anti-proliferation. * **ACE Inhibitors/ARBs:** These are first-line antihypertensives because they block the production or action of AT-II, leading to decreased TPR. * **Thirst Center:** AT-II acts on the subfornical organ in the brain to stimulate the thirst mechanism.

Q: According to the Frank-Starling law, to what is the extent of preload proportional?

End-diastolic volume. ### Explanation **The Core Concept: Frank-Starling Law** The Frank-Starling Law of the heart states that the force of ventricular contraction is directly proportional to the initial length of the cardiac muscle fibers. In clinical physiology, the **End-Diastolic Volume (EDV)** serves as the primary measure of this "initial length" or **Preload**. As the ventricle fills with more blood during diastole, the myocardial fibers are stretched; this stretch optimizes the overlap between actin and myosin filaments, leading to an increased force of contraction and a higher stroke volume. **Analysis of Options:** * **B. End-diastolic volume (Correct):** This represents the volume of blood in the ventricles just before systole begins. It is the gold-standard physiological parameter for preload. * **A. Increase in heart rate:** While an increase in heart rate can increase cardiac output, it is not the basis of the Frank-Starling mechanism. In fact, excessive tachycardia can decrease preload by shortening diastolic filling time. * **C. End-systolic volume:** This is the volume remaining in the ventricle *after* contraction. It reflects afterload and contractility rather than the initial stretch (preload). * **D. Ejection systolic volume:** This is a distractor term; the volume ejected is the "Stroke Volume," which is the *result* of the Frank-Starling mechanism, not the measure of preload itself. **NEET-PG High-Yield Pearls:** * **Preload** is synonymous with **End-Diastolic Fiber Length** or **EDV**. * **Afterload** is the resistance the heart must pump against (represented by Mean Arterial Pressure). * The Frank-Starling curve shifts **upward and to the left** with positive inotropic agents (e.g., Digoxin, Adrenaline) and **downward** in heart failure. * The mechanism is "intrinsic" to the heart and does not require nerve input (it occurs in denervated, transplanted hearts).

Q: Endothelium-derived relaxing factor is:

Nitric oxide. **Explanation:** **Endothelium-derived relaxing factor (EDRF)** is a potent endogenous vasodilator produced by vascular endothelial cells. In 1987, researchers (Furchgott and Ignarro) identified that EDRF is actually **Nitric Oxide (NO)**. 1. **Why Nitric Oxide is Correct:** NO is synthesized from the amino acid **L-arginine** by the enzyme **Nitric Oxide Synthase (NOS)**. Once released, it diffuses into the underlying vascular smooth muscle cells and activates the enzyme **soluble Guanylyl Cyclase (sGC)**. This increases levels of **cyclic GMP (cGMP)**, which leads to dephosphorylation of myosin light chains, resulting in smooth muscle relaxation and vasodilation. 2. **Why Other Options are Incorrect:** * **Angiotensin (II):** A potent **vasoconstrictor** and a key component of the Renin-Angiotensin-Aldosterone System (RAAS). * **Serotonin (5-HT):** Generally acts as a **vasoconstrictor** in damaged blood vessels to assist in hemostasis, though its effects can vary by receptor subtype. * **Norepinephrine:** Acts on $\alpha_1$-adrenergic receptors to cause systemic **vasoconstriction**. **High-Yield Clinical Pearls for NEET-PG:** * **Stimuli for NO release:** Shear stress (blood flow), Acetylcholine, Bradykinin, and Histamine. * **Mechanism:** NO $\rightarrow$ $\uparrow$ cGMP $\rightarrow$ Vasodilation (Remember: Sildenafil/Viagra inhibits PDE-5, preventing cGMP breakdown). * **Nitroglycerin:** Acts by being converted into Nitric Oxide, providing rapid relief in Angina Pectoris. * **Septic Shock:** Overproduction of NO by inducible NOS (iNOS) leads to the characteristic massive vasodilation and hypotension.

Q: What is the effect of sympathetic stimulation?

Vasoconstriction of skin and mucus membranes. The sympathetic nervous system (SNS) is the "fight or flight" system, designed to redirect blood flow to vital organs and prepare the body for physical exertion. ### **Explanation of the Correct Answer** **D. Vasoconstriction of skin and mucus membranes:** This occurs via the stimulation of **$\alpha_1$-adrenergic receptors**. During sympathetic activation, the body shunts blood away from non-essential peripheral areas (like the skin and mucosa) toward the skeletal muscles, heart, and brain. This is why a person may appear pale during a "fight or flight" response. ### **Analysis of Incorrect Options** * **A. Pupillary constriction:** This is a **parasympathetic** effect (miosis) mediated by $M_3$ receptors. Sympathetic stimulation causes **pupillary dilation (mydriasis)** via $\alpha_1$ receptors on the radial dilator pupillae muscle. * **B. Contraction of bladder detrusor:** This is a **parasympathetic** effect ($M_3$) to facilitate voiding. Sympathetic stimulation causes **relaxation** of the detrusor ($\beta_2/\beta_3$) and **contraction** of the internal sphincter ($\alpha_1$) to promote urinary retention. * **C. Bronchial smooth muscle contraction:** This is a **parasympathetic** effect ($M_3$). Sympathetic stimulation causes **bronchodilation** via **$\beta_2$ receptors** to increase airflow for oxygenation. ### **High-Yield NEET-PG Pearls** * **Dual Supply Exception:** Most blood vessels only have sympathetic innervation. Vasoconstriction is $\alpha_1$ mediated, while vasodilation in skeletal muscle is $\beta_2$ mediated. * **Sweat Glands:** Anatomically sympathetic but **cholinergic** (mediated by Acetylcholine acting on $M$ receptors). * **Mnemonic for SNS:** "Dilation" (Pupils, Bronchioles) and "Constriction" (Sphincters, Peripheral Vessels).

Q: Which scientific principle is the basis of the thermodilution method used in the measurement of cardiac output?

Stewart-Hamilton principle. ### Explanation **Correct Answer: C. Stewart-Hamilton principle** The **Stewart-Hamilton principle** is the foundation of the indicator-dilution method, of which **thermodilution** is a specific type. In this method, a known quantity of an indicator (cold saline) is injected into the right atrium. A thermistor at the tip of a Swan-Ganz catheter (positioned in the pulmonary artery) measures the change in temperature over time. The cardiac output is inversely proportional to the area under the temperature-time curve. Simply put: the faster the blood flows, the quicker the indicator is diluted and cleared. **Analysis of Incorrect Options:** * **A. Hagen-Poiseuille principle:** Describes the relationship between flow, pressure, and resistance in a laminar fluid system ($Q = \Delta P/R$). It explains how vessel diameter significantly impacts blood flow resistance but does not measure cardiac output. * **B. Bernoulli's principle:** States that an increase in the speed of a fluid occurs simultaneously with a decrease in pressure. In cardiology, it is used in echocardiography to calculate pressure gradients across stenotic valves. * **C. Universal gas equation ($PV=nRT$):** Relates pressure, volume, and temperature of an ideal gas; it has no direct application in measuring hemodynamic flow. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard:** While the **Fick Principle** (based on oxygen consumption) is the theoretical gold standard, **Thermodilution** is the most common clinical method used in ICUs. * **Site of Injection:** Cold saline is injected into the **Right Atrium**, and temperature change is sensed in the **Pulmonary Artery**. * **Inaccuracy:** Thermodilution can yield inaccurate results in patients with significant **tricuspid regurgitation** or intracardiac shunts.

Q: When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

5 mm Hg. ### Explanation The net movement of fluid across a capillary membrane is determined by **Starling’s Forces**. The Net Filtration Pressure (NFP) is calculated using the Starling equation: **NFP = (Forces favoring filtration) – (Forces opposing filtration)** **NFP = [ (Pc + πi) – (Pi + πc) ]** Where: * **Pc** (Capillary Hydrostatic Pressure) = 30 mm Hg (Favors filtration) * **πi** (Interstitial Oncotic Pressure) = 5 mm Hg (Favors filtration) * **Pi** (Interstitial Hydrostatic Pressure) = 5 mm Hg (Opposes filtration) * **πc** (Capillary Oncotic Pressure) = 25 mm Hg (Opposes filtration) **Calculation:** NFP = (30 + 5) – (5 + 25) NFP = 35 – 30 = **5 mm Hg** Since the result is positive, there is a net movement of fluid out of the capillary into the interstitial space. #### Analysis of Incorrect Options: * **B (10 mm Hg):** This error usually occurs if one forgets to subtract the interstitial hydrostatic pressure or incorrectly adds the oncotic pressures. * **C (15 mm Hg):** This result occurs if the interstitial oncotic pressure is ignored or if the hydrostatic pressures are subtracted incorrectly (30 - 15). * **D (20 mm Hg):** This value is obtained if only the difference between the two hydrostatic pressures (30 - 10) or two oncotic pressures is considered in isolation. #### High-Yield Clinical Pearls for NEET-PG: 1. **Edema Formation:** Edema occurs when NFP increases significantly, often due to increased $P_c$ (e.g., Heart Failure), decreased $\pi_c$ (e.g., Nephrotic Syndrome, Cirrhosis), or lymphatic obstruction. 2. **The "Safety Factor":** The lymphatic system can increase its flow up to 20-fold to compensate for increased filtration before clinical edema becomes apparent. 3. **Negative Interstitial Pressure:** In most loose subcutaneous tissues, the interstitial hydrostatic pressure ($P_i$) is actually slightly **sub-atmospheric (negative)**, which helps hold the tissues together.

Question 1

A patient has a blood pressure of 130/80 mmHg, a cardiac output of 5000 ml, and a heart rate of 70 beats per minute. Calculate the volume of blood pumped with each beat.

Accepted Answer

70 ml

Answer

110 ml

Answer

50 ml

Answer

90 ml

Question 2

All are cardiovascular effects of parasympathetic stimulation except?

Accepted Answer

Increased automaticity

Answer

Decreased heart rate

Answer

Decreased conduction

Answer

Increased refractive period

Question 3

In a patient with a transplanted heart, which of the following mechanisms contributes to the increase in cardiac output during exercise?

Accepted Answer

Circulating epinephrine released from the adrenal medulla

Answer

Reinnervation of the transplanted heart by the vagus nerve

Answer

Intrinsic contractile mechanisms of the transplanted heart

Answer

The Bainbridge reflex

Question 4

Cardiac output depends on all of the following except?

Accepted Answer

Body surface area

Answer

Cardiac rate

Answer

Stroke volume

Answer

Cardiac contractility

Question 5

What is the main role of angiotensin II?

Accepted Answer

Increased TPR

Answer

Constriction of afferent renal arteriole

Answer

Decreased release of aldosterone

Answer

Diuresis

Question 6

According to the Frank-Starling law, to what is the extent of preload proportional?

Accepted Answer

End-diastolic volume

Answer

Increase in heart rate

Answer

End-systolic volume

Answer

Ejection systolic volume

Question 7

Endothelium-derived relaxing factor is:

Accepted Answer

Nitric oxide

Answer

Angiotensin

Answer

Serotonin

Answer

Norepinephrine

Question 8

What is the effect of sympathetic stimulation?

Accepted Answer

Vasoconstriction of skin and mucus membranes

Answer

Pupillary constriction

Answer

Contraction of bladder detrusor

Answer

Bronchial smooth muscle contraction

Question 9

Which scientific principle is the basis of the thermodilution method used in the measurement of cardiac output?

Accepted Answer

Stewart-Hamilton principle

Answer

Hagen-Poiseuille principle

Answer

Bernoulli's principle

Answer

Universal gas equation

Question 10

When capillary hydrostatic pressure is 30 mm of Hg and interstitial hydrostatic pressure is 5 mm of Hg, and the colloid oncotic pressure of capillaries is 25 mm of Hg and the interstitium is 5 mm of Hg, what is the net filtration pressure?

Accepted Answer

5 mm Hg

Answer

10 mm Hg

Answer

15 mm Hg

Answer

20 mm Hg

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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