Cardiovascular System Practice Questions

Q: The chemoreceptor reflex involved in blood pressure regulation is stimulated by all of the following except:

Decreased blood pressure. **Explanation:** The chemoreceptor reflex is a peripheral mechanism primarily designed to regulate respiration, but it also plays a secondary role in cardiovascular homeostasis. **Why "Decreased Blood Pressure" is the correct answer:** Peripheral chemoreceptors (located in the **carotid and aortic bodies**) are **chemical sensors**, not pressure sensors. They are stimulated by changes in the chemical composition of arterial blood. While a massive drop in blood pressure (below 80 mmHg) can lead to stagnant hypoxia in the chemoreceptors, "decreased blood pressure" itself is the primary stimulus for **Baroreceptors**, not chemoreceptors. Baroreceptors respond to mechanical stretch, whereas chemoreceptors respond to chemical changes. **Analysis of Incorrect Options:** * **Hypoxia (Option A):** This is the most potent stimulus for peripheral chemoreceptors. A decrease in $PO_2$ (specifically below 60 mmHg) triggers an increase in sympathetic outflow to raise blood pressure and increase ventilation. * **Acidosis (Option B):** An increase in hydrogen ion concentration ($H^+$) or a decrease in pH directly stimulates the glomus cells in the carotid bodies. * **Hypercapnia (Option D):** An increase in $PCO_2$ acts both peripherally and centrally to stimulate the respiratory and vasomotor centers. **High-Yield NEET-PG Pearls:** * **Location:** Carotid bodies are located at the bifurcation of the common carotid artery (innervated by **CN IX**); Aortic bodies are in the aortic arch (innervated by **CN X**). * **Primary vs. Secondary:** The primary effect of chemoreceptor stimulation is an **increase in rate and depth of respiration**. The vasomotor effect (vasoconstriction) is a secondary response. * **Threshold:** The chemoreceptor reflex becomes significant in blood pressure regulation only when the Mean Arterial Pressure (MAP) falls below **80 mmHg**, acting as a "backup" system to the baroreceptor reflex.

Q: What is the formula for mean aerial pressure?

Diastolic BP + (Systolic BP - Diastolic BP) / 3. ### Explanation **1. Understanding the Correct Answer (Option B)** Mean Arterial Pressure (MAP) is the average arterial pressure throughout one entire cardiac cycle. The formula is: **MAP = Diastolic BP + 1/3 (Pulse Pressure)** *(Where Pulse Pressure = Systolic BP - Diastolic BP)* The reason we use **1/3** of the pulse pressure rather than a simple average is that the heart spends significantly more time in **diastole** (approx. 2/3 of the cardiac cycle) than in systole (approx. 1/3) at resting heart rates. Therefore, the MAP is weighted more heavily toward the diastolic pressure. **2. Analysis of Incorrect Options** * **Option A & C:** These use a divisor of 2, which would represent a simple arithmetic mean. This is incorrect because the cardiac cycle is not divided equally between systole and diastole. * **Option D:** This starts with Systolic BP and subtracts a fraction. While mathematically one could calculate MAP as *SBP - 2/3(PP)*, the formula provided in Option D is mathematically inconsistent with the physiological definition of MAP. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Organ Perfusion:** A MAP of **≥ 65 mmHg** is generally considered necessary to maintain adequate tissue perfusion to vital organs (especially the kidneys and brain). * **Effect of Tachycardia:** As heart rate increases, the duration of diastole shortens more than systole. Consequently, at very high heart rates, the MAP becomes closer to the arithmetic mean of SBP and DBP. * **Determinants:** MAP is determined by Cardiac Output (CO) and Total Peripheral Resistance (TPR): **MAP = CO × TPR**. * **Pulse Pressure:** Remember that Pulse Pressure is primarily determined by stroke volume and arterial compliance.

Q: Cerebral ischemia occurs when cerebral blood flow is less than which of the following values?

20 ml/100g/minute. **Explanation:** The normal Cerebral Blood Flow (CBF) in an adult is approximately **50–55 ml/100g/min**. The brain is highly sensitive to fluctuations in blood flow, and symptoms of ischemia manifest progressively as flow decreases. **Why Option B is Correct:** When CBF falls below **20 ml/100g/min**, electrical activity in the neurons begins to fail. This threshold marks the onset of **cerebral ischemia**, where the brain can no longer maintain normal functional activity, leading to clinical symptoms like aphasia or hemiparesis. This is often referred to as the "threshold of electrical failure." **Analysis of Incorrect Options:** * **Option A (10 ml/100g/min):** This is the threshold for **irreversible neuronal death (infarction)**. At this level, ionic pumps fail, leading to massive calcium influx and cell necrosis. The zone between 10 and 20 ml/100g/min is known as the **Ischemic Penumbra**—tissue that is functionally silent but potentially salvageable. * **Option C (40 ml/100g/min):** At this level, the brain is still relatively well-perfused. While it is below the average normal, autoregulatory mechanisms usually prevent clinical ischemia at this stage. * **Option D (50 ml/100g/min):** This represents the **normal physiological CBF**. No ischemia occurs at this value. **High-Yield Clinical Pearls for NEET-PG:** * **Cerebral Perfusion Pressure (CPP):** Calculated as Mean Arterial Pressure (MAP) minus Intracranial Pressure (ICP). Normal CPP is 70–90 mmHg. * **Autoregulation:** The brain maintains constant CBF as long as the MAP stays between **60 and 160 mmHg**. * **Critical Thresholds:** * Normal: 50 ml/100g/min * Ischemia (Electrical failure): <20 ml/100g/min * Infarction (Membrane failure): <10 ml/100g/min

Q: What is the formula for calculating ejection fraction?

Stroke Volume (SV) / End-Diastolic Volume (EDV). **Explanation:** **Ejection Fraction (EF)** is a critical clinical index used to assess the pumping efficiency of the heart, specifically the ventricles. It represents the fraction of blood pumped out of the ventricle with each heartbeat relative to the total amount of blood available at the end of filling. **1. Why Option A is Correct:** The formula for EF is **Stroke Volume (SV) / End-Diastolic Volume (EDV)**. * **Stroke Volume (SV):** The volume of blood ejected per beat (EDV – ESV). * **End-Diastolic Volume (EDV):** The total volume of blood in the ventricle just before contraction. By dividing SV by EDV, we determine what percentage of the "full" ventricle was successfully ejected. It is usually expressed as a percentage (Normal range: 55%–70%). **2. Analysis of Incorrect Options:** * **Option B (EDV / SV):** This is the inverse of the correct formula and has no physiological significance. * **Option C (ESV / EDV):** This represents the "Residual Fraction"—the percentage of blood remaining in the heart after contraction. While mathematically related (EF = 1 - Residual Fraction), it is not the definition of Ejection Fraction. * **Option D:** (Duplicate of Option A). **3. Clinical Pearls for NEET-PG:** * **Gold Standard Measurement:** Transthoracic Echocardiography (ECHO) is the most common bedside tool, but **Cardiac MRI** is the gold standard for accurate volume assessment. * **Heart Failure Classification:** * **HFrEF (Reduced EF):** EF ≤ 40% (indicates systolic dysfunction). * **HFpEF (Preserved EF):** EF ≥ 50% (indicates diastolic dysfunction). * **Sympathetic Stimulation:** Increases contractility (Inotropy), which increases SV and subsequently increases the EF. * **Preload vs. Afterload:** EF is highly sensitive to afterload; an acute increase in systemic vascular resistance will decrease the EF.

Question 1

The chemoreceptor reflex involved in blood pressure regulation is stimulated by all of the following except:

Accepted Answer

Decreased blood pressure

Answer

Hypoxia

Answer

Acidosis

Answer

Hypercapnia

Question 2

Short term BP regulation is mediated by which of the following hormones?

Accepted Answer

Antidiuretic hormone (ADH)

Answer

Atrial natriuretic peptide (ANP)

Answer

Epinephrine

Answer

Aldosterone

Question 3

Regulation of coronary circulation is primarily controlled by which system?

Accepted Answer

All of the above

Answer

Autonomic nervous system

Answer

Auto-regulatory mechanisms

Answer

Chemical factors

Question 4

A 59-year-old woman with a 10-year history of type 2 diabetes mellitus presents with bilateral pitting edema of the ankles and feet. She also reports shortness of breath on exertion and orthopnea, using 3 pillows at night to sleep comfortably. A chest X-ray shows pulmonary venous congestion and interstitial edema. Which of the following physiologic mechanisms is most likely the immediate cause of the pulmonary edema?

Accepted Answer

Elevated pulmonary capillary pressure

Answer

Damage to endothelial cells

Answer

Damage to the epithelial lining of the alveoli

Answer

Low serum albumin

Question 5

What is the nongenomic effect of testosterone on vascular smooth muscle?

Accepted Answer

Vasodilation

Answer

Vasoconstriction

Answer

Increase in prostaglandins

Answer

Increase in estrogen receptors

Question 6

What is the formula for mean aerial pressure?

Accepted Answer

Diastolic BP + (Systolic BP - Diastolic BP) / 3

Answer

Diastolic BP + (Systolic BP - Diastolic BP) / 2

Answer

Systolic BP + (Diastolic BP - Systolic BP) / 2

Answer

Systolic BP + (Diastolic BP - Systolic BP) / 3

Question 7

Cerebral ischemia occurs when cerebral blood flow is less than which of the following values?

Accepted Answer

20 ml/100g/minute

Answer

10 ml/100g/minute

Answer

40 ml/100g/minute

Answer

50 ml/100g/minute

Question 8

Stimulation of the parasympathetic nerves to the normal heart can lead to complete inhibition of the SA node for several seconds. During that period, what cardiac electrical events would be observed?

Accepted Answer

There would be fewer P waves than T waves

Answer

P waves would become larger

Answer

There would be fewer T waves than QRS complexes

Answer

There would be fewer QRS complexes than P waves

Question 9

Right atrial distension leading to increased heart rate occurs in which reflex?

Accepted Answer

Bezold Jarisch reflex

Answer

Bainbridge reflex

Answer

J reflex

Answer

None of the above

Question 10

What is the formula for calculating ejection fraction?

Accepted Answer

Stroke Volume (SV) / End-Diastolic Volume (EDV)

Answer

End-Diastolic Volume (EDV) / Stroke Volume (SV)

Answer

End-Systolic Volume (ESV) / End-Diastolic Volume (EDV)

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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