Cardiovascular System — MCQs
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Cardiac output increases in exercise primarily by
The main danger with low tension alternating current is
Which of the following is the PRIMARY location for arterial baroreceptors involved in blood pressure regulation?
Maximum cross sectional area is seen in which of the following vessels?
Most common cause of death in electric AC current burns is
In hemorrhagic shock, hypotension occurs when blood loss is more than:
The Penaz technique:
During heavy exercise the cardiac output (CO) increases up to five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by
Maximum CO2 is seen in ?
Most potent cerebral vasodilator is
Cardiovascular System Indian Medical PG Practice Questions and MCQs
Question 761: Cardiac output increases in exercise primarily by
- A. Increase in heart rate
- B. Increase in preload
- C. Sympathetic stimulation (Correct Answer)
- D. Increase in afterload
Explanation: ***Sympathetic stimulation*** - With exercise, the **sympathetic nervous system** is activated, leading to increased release of **norepinephrine**, which acts on beta-1 adrenergic receptors in the heart. - This stimulation directly increases **heart rate** and **contractility**, both of which contribute to a significant rise in cardiac output. *Increase in heart rate* - While an **increase in heart rate** does contribute to increased cardiac output during exercise (CO = HR x SV), it is a *consequence* of sympathetic stimulation, not the primary mechanism itself. - Sympathetic input drives the sinus node to fire faster, thus increasing heart rate. *Increase in preload* - **Increased preload** can enhance stroke volume via the **Frank-Starling mechanism**, but it is generally *not* the sole or primary factor for the dramatic increase in cardiac output during intense exercise. - During exercise, sympathetic venoconstriction can increase venous return and thus preload, but this is also mediated by sympathetic activity. *Increase in afterload* - An **increase in afterload** (resistance against which the heart pumps) typically *decreases* stroke volume and, consequently, cardiac output. - Although the mean arterial pressure may rise during exercise, the overall systemic vascular resistance often decreases in active muscles due to vasodilation, preventing a significant increase in afterload that would impair output.
Question 762: The main danger with low tension alternating current is
- A. Cardiac arrest (Correct Answer)
- B. Renal failure
- C. Myoglobinuria
- D. Burns
Explanation: ***Cardiac arrest*** - Low-tension alternating current (AC) is particularly dangerous because it can induce **ventricular fibrillation** at relatively low current levels. - The alternating nature allows for sustained muscle contraction and higher likelihood of interfering with the heart's electrical rhythm, leading to **cardiac arrest**. *Renal failure* - While severe electrical injuries can cause **rhabdomyolysis** and subsequent acute renal failure, this is typically associated with higher voltage and extensive tissue damage, not the primary danger of low-tension AC. - The immediate and most frequent life-threatening consequence of low-tension AC is its effect on the **heart rhythm**. *Myoglobinuria* - **Myoglobinuria** results from severe muscle damage (rhabdomyolysis), which can occur with electrical injury. - This is a consequence of significant tissue destruction, which is less common with low-tension AC compared to the risk of **cardiac arrhythmias**. *Burns* - **Burns** are a common consequence of electrical shock, especially with high-tension currents or prolonged contact. - While low-tension AC can cause burns, particularly at the contact points, the most immediate life-threatening risk is the disruption of **cardiac electrical activity**.
Question 763: Which of the following is the PRIMARY location for arterial baroreceptors involved in blood pressure regulation?
- A. Carotid sinus (Correct Answer)
- B. Aortic arch
- C. Left auricle
- D. Crista terminalis
Explanation: ***Carotid sinus*** - The **carotid sinus** is the **primary and most clinically significant location** for arterial baroreceptors, containing a high density of mechanoreceptors sensitive to changes in arterial blood pressure. - These baroreceptors are strategically located at the **bifurcation of the common carotid artery** and are particularly sensitive to **rapid pressure fluctuations** during the cardiac cycle. - The carotid sinus baroreceptors provide **immediate feedback** for short-term blood pressure regulation via the **baroreceptor reflex**. - Clinically, the carotid sinus is accessible for examination and can be stimulated during **carotid sinus massage** to diagnose or treat certain arrhythmias. *Aortic arch* - The **aortic arch** also contains important arterial baroreceptors, making it the **second major site** for baroreceptor location. - However, in medical education and clinical contexts, the **carotid sinus** is emphasized as the primary or most representative location for studying baroreceptor function. - Aortic baroreceptors work in conjunction with carotid baroreceptors for blood pressure homeostasis. *Left auricle* - The **left atrium** (including the auricle region) contains **low-pressure baroreceptors** (volume receptors), which are functionally different from arterial baroreceptors. - These receptors sense **atrial stretch** and blood volume changes rather than arterial pressure, triggering responses like **atrial natriuretic peptide (ANP)** release. - They are involved in **long-term fluid balance** regulation, not the immediate arterial pressure regulation that defines classic baroreceptor function. *Crista terminalis* - The **crista terminalis** is an anatomical landmark in the **right atrium**, representing a muscular ridge that separates smooth and trabeculated portions. - While the atria contain volume receptors, the crista terminalis itself is **not a recognized site** for baroreceptor concentration. - It serves as an anatomical reference point and the origin site for pectinate muscles.
Question 764: Maximum cross sectional area is seen in which of the following vessels?
- A. Arteries
- B. Capillaries (Correct Answer)
- C. Arterioles
- D. Veins
Explanation: ***Capillaries*** - While individual capillaries are very narrow, their **vast number** and extensive branching result in the largest total cross-sectional area in the circulatory system. - This large cross-sectional area is crucial for **slow blood flow**, allowing for efficient exchange of nutrients, oxygen, and waste products with tissues. *Arteries* - Arteries have a relatively **small total cross-sectional area** compared to capillaries due to their limited number, even though individual arteries are wide. - This smaller area contributes to the **high pressure** and rapid flow of blood from the heart. *Arterioles* - Arterioles are smaller than arteries but still represent a collectively **smaller cross-sectional area** than capillaries due to their branching pattern. - They primarily function in **regulating regional blood flow** and systemic blood pressure through vasoconstriction and vasodilation. *Veins* - Veins collectively have a **larger cross-sectional area than arteries**, but it is still significantly less than the total cross-sectional area of the capillary beds. - They serve as a **blood reservoir** and return deoxygenated blood to the heart at low pressure.
Question 765: Most common cause of death in electric AC current burns is
- A. Hemorrhagic stroke
- B. Cardiac arrest (Correct Answer)
- C. Septic shock
- D. Myoglobinuria leading to ARF
Explanation: ***Cardiac arrest*** - **Alternating current (AC)** is particularly lethal because it can induce **ventricular fibrillation** at relatively low voltages, directly disrupting the heart's electrical activity. - The constant muscle contraction and relaxation caused by AC current can lead to prolonged exposure to electricity and increased risk of **arrhythmias** and cardiac arrest. *Hemorrhagic stroke* - While electrical injuries can sometimes lead to cerebrovascular events, **hemorrhagic stroke** is not the most common immediate cause of death from AC burns. - Neurological complications are generally less immediate and frequent than direct cardiac effects in acute deaths from electric shock. *Septic shock* - **Septic shock** is a complication of severe burns, including electrical burns, but it typically occurs in the **later stages** as a result of infection. - It is not the most immediate or common cause of death following the initial electric shock. *Myoglobinuria leading to ARF* - **Myoglobinuria** and subsequent **acute renal failure (ARF)** can occur due to extensive muscle damage from electrical burns. - This is a significant complication of severe electrical injury but tends to develop in the **hours to days** following the injury, rather than being the most common immediate cause of death, which is typically cardiac.
Question 766: In hemorrhagic shock, hypotension occurs when blood loss is more than:
- A. More than 40%
- B. 15% - 30%
- C. 30% - 40% (Correct Answer)
- D. 10% - 15%
Explanation: ***30% - 40%*** - **Hypotension** in hemorrhagic shock typically manifests when the blood volume loss exceeds **30-40%**, corresponding to Class III hemorrhage. - At this stage, compensatory mechanisms begin to fail, leading to reduced cardiac output and a significant drop in **blood pressure**. *More than 40%* - A blood loss of **more than 40%** (Class IV hemorrhage) results in profound shock with marked **vital sign instability** and is often immediately life-threatening. - Hypotension is severe at this stage, but it usually begins to appear earlier, around the 30-40% mark. *15% - 30%* - A blood loss between **15% and 30%** (Class II hemorrhage) is typically associated with **tachycardia** and mild changes in vital signs, but usually *not* significant hypotension. - **Compensatory mechanisms** like vasoconstriction and increased heart rate are generally still effective in maintaining blood pressure. *10% - 15%* - A blood loss of **10% to 15%** (Class I hemorrhage) is usually well-tolerated with minimal symptoms. - At this level, the body's **compensatory mechanisms** are highly effective, and there is typically *no* change in blood pressure or heart rate.
Question 767: The Penaz technique:
- A. Requires a pneumatic cuff
- B. Is suitable in presence of peripheral vascular disease
- C. Is invasive
- D. Uses plethysmography (Correct Answer)
Explanation: ***Uses plethysmography*** - The **Penaz technique**, also known as **Finapres** or volume-clamp method, continuously measures blood pressure using **photoplethysmography** to detect arterial wall movements. - This method maintains a constant transmural pressure across the arterial wall, providing beat-to-beat pressure readings in a **non-invasive** manner. *Requires a pneumatic cuff* - While it uses a cuff-like device on the finger, this is a **small occluding cuff** used to maintain a constant arterial volume and not a standard pneumatic cuff for intermittent oscillometric measurements. - The cuff inflates and deflates to counterbalance arterial pressure, unlike the complete occlusion and slow deflation of a conventional cuff. *Is suitable in presence of peripheral vascular disease* - The Penaz technique relies on intact peripheral arteries to function accurately. **Peripheral vascular disease** can affect arterial compliance and blood flow, leading to **inaccurate readings**. - Its use may be limited in conditions that significantly alter peripheral arterial hemodynamics, such as severe atherosclerosis or Raynaud's phenomenon. *Is invasive* - The Penaz technique is a **non-invasive** method for continuous blood pressure monitoring, relying on external sensors applied to the finger. - **Invasive blood pressure monitoring** involves catheter insertion directly into an artery, which is a fundamentally different procedure.
Question 768: During heavy exercise the cardiac output (CO) increases up to five fold while pulmonary arterial pressure rises very little. This physiological ability of the pulmonary circulation is best explained by
- A. Large amount of smooth muscle in pulmonary arterioles
- B. Increase in the number of open capillaries (Correct Answer)
- C. Sympathetically mediated greater distensibility of pulmonary vessels
- D. Smaller surface area of pulmonary circulation
Explanation: ***Increase in the number of open capillaries*** - During heavy exercise, the significant increase in cardiac output is accommodated by the **recruitment of previously closed pulmonary capillaries**. - This recruitment, along with **distension of existing capillaries**, reduces overall pulmonary vascular resistance, allowing blood flow to increase without a substantial rise in pulmonary arterial pressure. *Large amount of smooth muscle in pulmonary arterioles* - While pulmonary arterioles do contain smooth muscle, their primary role is in **regulating regional blood flow** and response to hypoxia, not facilitating large increases in overall blood flow during exercise. - The pulmonary circulation is characterized by **low resistance** and high capacitance compared to the systemic circulation, meaning it has less smooth muscle tone at baseline. *Sympathetically mediated greater distensibility of pulmonary vessels* - The pulmonary vasculature has **limited sympathetic innervation** compared to systemic vessels, and sympathetic activity plays a minor role in its distensibility during exercise. - Changes in pulmonary vascular resistance during exercise are primarily due to **mechanical factors** (recruitment and distension) rather than neurogenic control. *Smaller surface area of pulmonary circulation* - The pulmonary circulation actually has a **vast capillary surface area** crucial for efficient gas exchange. - A smaller surface area would lead to **higher resistance** and a greater pressure increase for a given flow, which contradicts the observation during exercise.
Question 769: Maximum CO2 is seen in ?
- A. Left ventricle
- B. Left atrium
- C. Pulmonary artery (Correct Answer)
- D. Pulmonary vein
Explanation: ***Pulmonary artery*** - The pulmonary artery carries **deoxygenated blood** from the right ventricle to the lungs. - This blood has picked up carbon dioxide from systemic circulation, making the pulmonary artery the vessel with the **highest CO2 concentration** leaving the heart. *Left ventricle* - The left ventricle pumps **oxygenated blood** to the systemic circulation. - This blood has recently returned from the lungs, where **CO2 was offloaded**, resulting in a very low CO2 concentration. *Left atrium* - The left atrium receives **oxygenated blood** from the pulmonary veins. - Similar to the left ventricle, this blood has a **low CO2 concentration** after gas exchange in the lungs. *Pulmonary vein* - Pulmonary veins carry **oxygenated blood** from the lungs to the left atrium. - During its passage through the lungs, CO2 is **exhaled**, leading to a low CO2 concentration in the pulmonary vein.
Question 770: Most potent cerebral vasodilator is
- A. Nitroprusside
- B. Nitro-glycerine
- C. Hypercarbia (Correct Answer)
- D. Beta blocker
Explanation: ***Hypercarbia*** - **Hypercapnia** (increased arterial carbon dioxide tension, PaCO2) is the most potent physiological cerebral vasodilator. - An increase in PaCO2 directly causes cerebral arterioles to dilate, leading to a significant increase in **cerebral blood flow (CBF)** to help clear excess CO2. *Nitroprusside* - **Sodium nitroprusside** is a powerful systemic vasodilator that also affects cerebral vessels, but its primary action is not selectively cerebral. - Its effects on CBF are complex and can be inconsistent in comparison to CO2, and it carries risks like **cyanide toxicity**. *Nitroglycerin* - **Nitroglycerin** primarily causes venodilation and has some arterial vasodilating effects, mainly in vascular beds like the coronary arteries. - While it can cause some cerebral vasodilation, it is not as potent or direct in modulating CBF as CO2. *Beta blocker* - **Beta-blockers** (e.g., propranolol, metoprolol) are primarily used to reduce heart rate, blood pressure, and myocardial contractility. - They generally have **minimal or no direct vasodilatory effect** on cerebral blood vessels; some may even cause vasoconstriction.
Practice by Chapter
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Cardiac Cycle
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Cardiac Output and Its Regulation
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Venous Return and Central Venous Pressure
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Cardiovascular Reflexes
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Regional Circulations
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Cardiovascular Responses to Exercise and Stress
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