Cardiovascular System Practice Questions

Q: At which point on the Pressure -Volume loop does the aortic valve open?

Point C. ***Point C*** - This represents the point of **isovolumetric contraction**, where the **left ventricular pressure** rises until it exceeds the **aortic diastolic pressure**. - Once the left ventricular pressure surpasses the aortic pressure, the **aortic valve opens**, initiating the period of **ventricular ejection**. *Point A* - This point marks the end of ventricular filling, where the **mitral valve closes**. - It signifies the beginning of **isovolumetric contraction**, where ventricular volume is at its maximum (**end-diastolic volume**). *Point B* - This represents the phase of **isovolumetric contraction** where ventricular pressure is still lower than the aortic pressure. - The heart is actively contracting, but **ventricular volume** remains constant because all valves are closed. *Point D* - This point marks the end of **ventricular ejection** and the closure of the **aortic valve**. - The remaining blood volume in the ventricle at this point represents the **end-systolic volume**.

Q: Reason for biphasic flow in right coronary artery?

Low pressure in right ventricle. ***Low pressure in right ventricle*** - The right coronary artery (RCA) supplies the right ventricle, which has a significantly lower wall pressure compared to the left ventricle, allowing for continuous myocardial perfusion throughout the cardiac cycle. - Because the **right ventricular (RV) systolic pressure** is low, mechanical compression of the coronary vessels is minimal during systole, resulting in a **biphasic flow pattern** with peaks in both systole and diastole. *Increased aortic pressure* - While higher aortic pressure generally increases coronary perfusion pressure across the entire heart, it does not specifically account for the unique **biphasic waveform** seen in the right coronary circulation. - The flow pattern is primarily determined by the **phasic intramyocardial pressure** variations rather than the absolute driving pressure provided by the aorta. *Increased right ventricular mass* - Hypertrophy of the right ventricle, such as in cases of **pulmonary hypertension**, would actually increase myocardial compressive forces and potentially attenuate or eliminate the systolic component of RCA flow. - Increased mass typically leads to higher localized resistance to flow, which would contradict the characteristic biphasic blood flow pattern observed in normal physiological states. *High pressure in right ventricle* - If the right ventricle were under high pressure, as seen in conditions like **pulmonary hypertension** or **pulmonary stenosis**, the RCA would experience profound systolic compression, often reducing or abolishing systolic flow. - High RV pressure would lead to a more **monophasic diastolic flow** pattern, similar to that observed in the left coronary artery, rather than the biphasic flow characteristic of low-pressure systems.

Q: A 28-year-old marathon runner undergoes maximal exercise testing. At peak exercise, her oxygen consumption reaches 3600 mL/min, cardiac output is 24 L/min, and arterial oxygen content is 200 mL O2/L blood. Apply the Fick equation to determine her mixed venous oxygen content at peak exercise.

50 mL O2/L blood. ***50 mL O2/L blood*** - According to the **Fick Principle**, oxygen consumption (VO2) equals cardiac output (CO) multiplied by the **arteriovenous oxygen difference** (CaO2 - CvO2); rearranging the formula gives **CvO2 = CaO2 - (VO2 / CO)**. - Calculating the values provided: **200 - (3600 / 24) = 200 - 150 = 50 mL O2/L**, illustrating the significantly increased **oxygen extraction** during peak exercise. *100 mL O2/L blood* - This value results from an incorrect calculation or an assumption of a smaller **arteriovenous oxygen difference** of only 100 mL/L. - At peak exercise in an athlete, the **tissues extract** more than 50% of the oxygen, making this value too high. *125 mL O2/L blood* - This value would imply a very narrow **a-v O2 difference** of 75 mL/L, which is more characteristic of moderate rather than maximal exercise. - It fails to account for the high **metabolic demand** and high VO2 (3600 mL/min) seen in a marathon runner. *75 mL O2/L blood* - This value suggests an oxygen extraction of 125 mL/L, which is lower than the **150 mL/L** actually occurring based on the provided data. - While closer to the correct physiological range, it does not satisfy the mathematical requirement of the **Fick equation** parameters provided. *150 mL O2/L blood* - This value represents the **arteriovenous oxygen difference** (VO2/CO) rather than the **mixed venous oxygen content**. - Selecting this option indicates a confusion between the amount of oxygen **extracted by tissues** and the amount remaining in the venous blood.

Q: A 45-year-old sedentary man begins a supervised exercise program. After 8 weeks of training at 70% of his maximum heart rate for 30 minutes daily, his resting heart rate decreases from 80 to 65 beats per minute. His cardiac output at rest remains unchanged at 5 L/min. Apply your understanding of cardiovascular adaptations to determine what compensatory change occurred.

Increased stroke volume from 62.5 mL to 77 mL. ***Increased stroke volume from 62.5 mL to 77 mL*** - According to the formula **Cardiac Output (CO) = Heart Rate (HR) × Stroke Volume (SV)**, if CO is constant and HR decreases, the SV must increase to compensate. - Initial SV was **62.5 mL** (5000/80) and the post-training SV rose to **77 mL** (5000/65), reflecting common **aerobic training adaptations** like eccentric hypertrophy and increased vagal tone. *Decreased peripheral vascular resistance* - While long-term exercise can lower **Total Peripheral Resistance (TPR)** during exercise, it is not the primary factor maintaining a constant **resting cardiac output** when HR drops. - Changes in resistance primarily influence **mean arterial pressure** rather than the direct mathematical relationship between HR and SV in determining CO. *Increased venous capacitance* - Increased **venous capacitance** would actually lead to a decrease in **venous return** and stroke volume by pooling blood in the periphery. - Training typically improves **venous return** through mechanisms like increased blood volume, rather than increasing the storage capacity of the veins. *Decreased blood viscosity* - **Blood viscosity** is primarily determined by hematocrit levels and does not decrease as a standard compensatory mechanism to maintain **cardiac output** in athletes. - While plasma volume expands with training (which can slightly lower hematocrit), it does not explain the specific rise in **stroke volume** needed to balance a lower HR. *Increased myocardial contractility at rest* - While **stroke volume** increases, resting **contractility** (inotropic state) is generally not elevated in a resting state after endurance training. - The increase in SV at rest is primarily driven by **increased end-diastolic volume (preload)** and a longer filling time due to **bradycardia**.

Q: Sinus arrhythmia is due to?

Fluctuating parasympathetic response during respiration. **Explanation:** **Sinus Arrhythmia** is a normal physiological variation in heart rate characterized by an increase in heart rate during inspiration and a decrease during expiration. **1. Why Option C is Correct:** The primary mechanism is the **fluctuating parasympathetic (vagal) tone** synchronized with the respiratory cycle. * **During Inspiration:** Lung inflation triggers the **Bainbridge reflex** and inhibits the cardioinhibitory center (vagal tone decreases). This leads to an **increase** in heart rate. * **During Expiration:** Vagal tone increases, leading to a **decrease** in heart rate. This phenomenon is a sign of a healthy autonomic nervous system and is most prominent in children and young adults. **2. Why Other Options are Incorrect:** * **Option A:** Sinus node disease (Sick Sinus Syndrome) involves pathological bradycardia or tachy-brady syndrome, not the rhythmic physiological variation seen in sinus arrhythmia. * **Option B:** Sinus arrhythmia is mediated by the **parasympathetic** (vagus nerve) system, not an exaggerated sympathetic response. * **Option D:** This is factually incorrect; the heart rate **increases** during inspiration and **decreases** during expiration. **High-Yield Clinical Pearls for NEET-PG:** * **ECG Finding:** The P-P interval varies, but the P-wave morphology remains constant (since the impulse still originates from the SA node). * **Clinical Significance:** It is a **benign** finding. If sinus arrhythmia disappears, it may indicate autonomic neuropathy (e.g., in Diabetes Mellitus). * **Mnemonic:** **I**nspiration = **I**ncrease in heart rate.

Q: Which ECG lead represents the augmented unipolar limb lead that views the heart from the right shoulder?

aVR. **Explanation:** The correct answer is **aVR**. This question tests your understanding of the 12-lead ECG configuration and the spatial orientation of the limb leads. **1. Why aVR is correct:** The term **aVR** stands for **augmented Vector Right**. It is a unipolar limb lead where the positive electrode is placed on the right arm (shoulder). It views the heart’s electrical activity from the right superior perspective. Because the heart’s main depolarization vector (the QRS complex) normally travels downward and to the left (away from the right shoulder), the waves in aVR (P, QRS, and T) are characteristically **inverted** in a healthy heart. **2. Why the other options are incorrect:** * **aVL (augmented Vector Left):** This is a unipolar limb lead that views the heart from the **left shoulder**. It looks at the high lateral wall of the left ventricle. * **V1:** This is a **precordial (chest) lead** placed in the 4th intercostal space at the right sternal border. While it is on the right side of the chest, it is not a limb lead and views the septum/right ventricle, not the heart from the shoulder. * **V6:** This is a precordial lead placed in the 5th intercostal space at the mid-axillary line. It views the **lateral wall** of the left ventricle. **3. High-Yield Clinical Pearls for NEET-PG:** * **The "Forgotten Lead":** aVR is often ignored but is crucial for diagnosing **aVR elevation**, which can indicate Left Main Coronary Artery (LMCA) occlusion or proximal LAD disease. * **Dextrocardia/Lead Reversal:** If the P-wave and QRS are **upright** in aVR, consider limb lead reversal (most common) or dextrocardia. * **Einthoven’s Law:** Lead II = Lead I + Lead III. * **Augmented Leads:** aVR, aVL, and aVF use the center of the heart (Wilson’s Central Terminal) as the negative reference point.

Question 1

At which point on the Pressure -Volume loop does the aortic valve open?

Accepted Answer

Point C

Answer

Point A

Answer

Point B

Answer

Point D

Question 2

Reason for biphasic flow in right coronary artery?

Accepted Answer

Low pressure in right ventricle

Answer

Increased aortic pressure

Answer

Increased right ventricular mass

Answer

High pressure in right ventricle

Question 3

A 28-year-old marathon runner undergoes maximal exercise testing. At peak exercise, her oxygen consumption reaches 3600 mL/min, cardiac output is 24 L/min, and arterial oxygen content is 200 mL O2/L blood. Apply the Fick equation to determine her mixed venous oxygen content at peak exercise.

Accepted Answer

50 mL O2/L blood

Answer

100 mL O2/L blood

Answer

125 mL O2/L blood

Answer

75 mL O2/L blood

Answer

150 mL O2/L blood

Question 4

A 45-year-old sedentary man begins a supervised exercise program. After 8 weeks of training at 70% of his maximum heart rate for 30 minutes daily, his resting heart rate decreases from 80 to 65 beats per minute. His cardiac output at rest remains unchanged at 5 L/min. Apply your understanding of cardiovascular adaptations to determine what compensatory change occurred.

Accepted Answer

Increased stroke volume from 62.5 mL to 77 mL

Answer

Decreased peripheral vascular resistance

Answer

Increased venous capacitance

Answer

Decreased blood viscosity

Answer

Increased myocardial contractility at rest

Question 5

Why do mammals have a four-chambered heart while amphibians have a three-chambered heart?

Accepted Answer

Mammals require complete separation of oxygenated and deoxygenated blood for endothermy

Answer

Amphibians rely on cutaneous respiration primarily

Answer

Amphibians have lower metabolic rate due to aquatic lifestyle

Answer

Mammals have evolved from reptiles with incomplete septa

Question 6

A 45-year-old man with diabetes insipidus forgets to take his desmopressin for 24 hours. His serum sodium is 158 mEq/L and osmolality is 320 mOsm/kg. Despite severe hypernatremia, his blood pressure remains stable at 130/80 mmHg. Which mechanism best explains this?

Accepted Answer

Activation of RAAS maintaining blood volume through aldosterone

Answer

Compensatory increase in atrial natriuretic peptide

Answer

Shift of fluid from interstitial to intravascular compartment

Answer

Direct effect of hypernatremia on vascular smooth muscle tone

Question 7

How does the body compensate for prolonged standing to maintain cerebral perfusion?

Accepted Answer

Baroreceptor-mediated sympathetic activation and muscle pump mechanism

Answer

Decreased ADH secretion to reduce blood volume

Answer

Increased heart rate and peripheral vasoconstriction only

Answer

Parasympathetic activation to increase cardiac output

Question 8

Sinus arrhythmia is due to?

Accepted Answer

Fluctuating parasympathetic response during respiration

Answer

Sinus node disease

Answer

Exaggerated response to the sympathetic system

Answer

Decreased heart rate during inspiration

Question 9

Which ECG lead represents the augmented unipolar limb lead that views the heart from the right shoulder?

Accepted Answer

aVR

Answer

aVL

Answer

V1

Answer

V6

Question 10

Elevation of which of the following ions causes vasoconstriction?

Accepted Answer

Ca2+

Answer

Na+

Answer

K+

Answer

Mg2+

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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