Cardiovascular Physiology — MCQs
Coronary blood flow is maximum during which phase of the cardiac cycle?
Pressure-Volume loop of cardiac cycle is shown below. What does point C represent?
All of the following arteries are common sites of occlusion by a thrombus except:
During exercise in physiological limits, what is the effect on end systolic volume?
Decreased CVP is seen in
Aortic valve closure corresponds to the beginning of which phase of the cardiac cycle?
The following data were obtained from a man weighing 70 kg: Aorta oxygen (O2) content is 20.0 vol%, femoral vein O2 content is 16 vol%, coronary sinus O2 content is 10 vol%, and pulmonary artery O2 content is 15 vol%. What is the cardiac output of this man, given a total body O2 consumption of 400 ml/min?
Which of the following best describes hypoxic pulmonary vasoconstriction?
Most sensitive method of monitoring cardiovascular ischemia in the perioperative period is -
Drug that does not cause cardiac depression:
Cardiovascular Physiology Indian Medical PG Practice Questions and MCQs
Question 1: Coronary blood flow is maximum during which phase of the cardiac cycle?
- A. 70 mL/min
- B. Maximum during diastole (Correct Answer)
- C. Adenosine increases it
- D. Less than skin
Explanation: ***Maximum during diastole*** [1] - During **diastole**, the ventricular myocardium **relaxes**, reducing extravascular compression on the intramural coronary arteries [1] - This allows **maximum coronary blood flow** to perfuse the myocardium (approximately 70-80% of total coronary flow occurs during diastole) [1] - During **systole**, strong ventricular contraction compresses coronary vessels, significantly **impeding blood flow** (especially in the subendocardium) [1] - The left coronary artery flow is almost completely interrupted during systole due to high intraventricular pressure [1] *70 mL/min* - This represents a numerical value for coronary blood flow but does not specify the **phase of the cardiac cycle** - Average resting coronary blood flow is approximately 225-250 mL/min (about 5% of cardiac output) *Adenosine increases it* - While adenosine is a potent **coronary vasodilator**, this describes a regulatory mechanism, not the **phase** when flow is naturally maximal *Less than skin* - This is a comparative statement about regional blood flow distribution, not the **timing during the cardiac cycle**
Question 2: Pressure-Volume loop of cardiac cycle is shown below. What does point C represent?
- A. Aortic valve closes
- B. Mitral valve closes
- C. Aortic valve opens (Correct Answer)
- D. Mitral valve opens
Explanation: ***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.
Question 3: All of the following arteries are common sites of occlusion by a thrombus except:
- A. Posterior interventricular
- B. Circumflex
- C. Marginal (Correct Answer)
- D. Anterior interventricular
Explanation: ***Marginal*** - The **marginal arteries** are typically small and supply a smaller portion of the right ventricle, making them less likely sites for **major clinical occlusion** compared to larger, more critical coronary vessels. - While occlusion can occur, it usually causes less extensive damage and is therefore **less common** as a primary site of acute thrombus-related myocardial infarction. *Posterior interventricular* - The **posterior interventricular artery (PDA)** is a major coronary artery, responsible for supplying the posterior walls of the ventricles and the posterior one-third of the interventricular septum. - Occlusion of the PDA, often a branch of the right coronary artery (RCA) or circumflex artery, can lead to **significant infarction** in these critical areas, making it a common site of thrombus formation. *Circumflex* - The **circumflex artery (Cx)** is a major branch of the left main coronary artery that supplies the left atrium and the posterior and lateral walls of the left ventricle. - Occlusion of the circumflex artery can result in **lateral or posterior myocardial infarction**, making it a frequent site for thrombus formation. *Anterior interventricular* - The **anterior interventricular artery (LAD)**, also known as the left anterior descending artery, is the most common site of coronary artery occlusion. - It supplies the anterior wall of the left ventricle and the anterior two-thirds of the interventricular septum, and its occlusion is often referred to as the **"widowmaker"** due to the extensive damage and high mortality associated with it.
Question 4: During exercise in physiological limits, what is the effect on end systolic volume?
- A. ESV decreases (Correct Answer)
- B. ESV increases
- C. ESV first decreases and then increases
- D. ESV remains unchanged
Explanation: ***ESV decreases*** - During exercise, **sympathetic nervous system activity** increases, leading to enhanced cardiac contractility. - Improved contractility allows the heart to eject a greater percentage of its end-diastolic volume, resulting in a smaller **residual volume** in the ventricle after systole. *ESV increase* - An increase in ESV would indicate a **reduced ejection fraction** and poorer cardiac efficiency, which is contrary to the physiological adaptations during exercise. - This typically occurs in conditions of **heart failure** or myocardial dysfunction, not healthy exercise. *ESV first decrease and then increases* - While there are complex physiological responses during exercise, the primary and sustained effect on ESV within physiological limits is a **net decrease** due to increased contractility. - A subsequent increase would suggest a decline in cardiac function or the onset of fatigue beyond physiological limits. *ESV remain unchanged* - An unchanged ESV would imply no significant alteration in **cardiac contractility** or **ejection efficiency**, which is inconsistent with the cardiovascular demands and adaptations during exercise. - The body actively works to optimize cardiac output by increasing stroke volume, partly by reducing ESV during exercise.
Question 5: Decreased CVP is seen in
- A. PEEP
- B. Bacterial sepsis (Correct Answer)
- C. Heart failure
- D. Pneumothorax
Explanation: ***Bacterial sepsis*** - In **sepsis**, widespread **vasodilation** and increased capillary permeability lead to significant fluid redistribution out of the intravascular space [3]. - This results in a decrease in **venous return** and thus a lower **central venous pressure (CVP)** due to relative hypovolemia [2]. *Pneumothorax* - A **pneumothorax** causes increased intrathoracic pressure, compressing the great veins and heart. - This leads to **reduced venous return** and typically an *increase* in CVP, or at least a minimal change, due to obstructed outflow from the right atrium, not a decrease [2]. *PEEP* - **Positive end-expiratory pressure (PEEP)** increases intrathoracic pressure, which impedes venous return to the right atrium [2]. - This elevated pressure can artificially *increase* the measured CVP reading, and it does not typically cause a decrease in intrinsic CVP [2]. *Heart failure* - In **heart failure**, particularly right-sided heart failure or biventricular failure, the heart's pumping efficiency is reduced [1]. - This leads to **venous congestion** and an *increase* in CVP due to fluid overload and the inability of the right ventricle to effectively pump blood forward [2].
Question 6: Aortic valve closure corresponds to the beginning of which phase of the cardiac cycle?
- A. Systole
- B. Parasystole
- C. Isovolumetric contraction
- D. Isovolumetric relaxation (Correct Answer)
Explanation: ***Isovolumetric relaxation*** - **Aortic valve closure** marks the end of **ventricular ejection** and the beginning of **isovolumetric relaxation** as both the aortic and mitral valves are closed, and ventricular pressure drops without a change in volume. - This phase is vital for the heart to relax and prepare for filling, corresponding to the **second heart sound (S2)**. *Systole* - **Systole** refers to the **contraction phase** of the heart, encompassing both isovolumetric contraction and ventricular ejection. - Aortic valve closure signifies the end of the **ejection phase** of systole, not its beginning. *Parasystole* - **Parasystole** is an **arrhythmia** where an ectopic pacemaker competes with the normal sinus rhythm, leading to independent atrial or ventricular contractions. - It is a **pathological condition** and not a normal phase of the cardiac cycle. *Isovolumetric contraction* - **Isovolumetric contraction** occurs after the **mitral valve closes** and before the aortic valve opens, causing pressure to build in the ventricle. - This phase precedes **ventricular ejection** and is initiated by mitral valve closure, not aortic valve closure.
Question 7: The following data were obtained from a man weighing 70 kg: Aorta oxygen (O2) content is 20.0 vol%, femoral vein O2 content is 16 vol%, coronary sinus O2 content is 10 vol%, and pulmonary artery O2 content is 15 vol%. What is the cardiac output of this man, given a total body O2 consumption of 400 ml/min?
- A. 10 L/min
- B. 8 L/min (Correct Answer)
- C. 6 L/min
- D. 5 L/min
Explanation: ***8 L/min*** - The cardiac output is calculated using the **Fick principle**: CO = Total body O2 consumption / (Arterial O2 content - Mixed venous O2 content). - In this case, **Arterial O2 content is 20 vol%** and **Mixed venous O2 content (pulmonary artery) is 15 vol%**. So, CO = 400 ml/min / (20 vol% - 15 vol%) = 400 ml/min / 5 ml O2/100 ml blood = 400 / 0.05 = 8000 ml/min = **8 L/min**. *10 L/min* - This result would be obtained if the arteriovenous oxygen difference was smaller, specifically 4 vol% (400 / 0.04 = 10000 ml/min). - This calculation does not correctly use the given **mixed venous O2 content** from the pulmonary artery. *6 L/min* - This result would be obtained if the arteriovenous oxygen difference was larger, specifically 6.67 vol% (400 / 0.0667 ≈ 6000 ml/min). - This calculation misrepresents the **actual O2 extraction** from the arterial blood. *5 L/min* - This result would be obtained if the arteriovenous oxygen difference was 8 vol% (400 / 0.08 = 5000 ml/min). - This choice indicates an incorrect application of the **Fick principle** or misidentification of the relevant oxygen content values.
Question 8: Which of the following best describes hypoxic pulmonary vasoconstriction?
- A. Reversible pulmonary vasoconstriction due to hypoxia (Correct Answer)
- B. Irreversible pulmonary vasoconstriction due to hypoxia
- C. Redirects blood to well-ventilated areas
- D. Occurs immediately in response to hypoxia
Explanation: ***Reversible pulmonary vasoconstriction due to hypoxia*** - Hypoxic pulmonary vasoconstriction (HPV) is a physiological response in which **pulmonary arterioles constrict** in areas of the lung with low oxygen levels. - This mechanism is **reversible**, meaning that when oxygen levels improve, the constricted vessels will dilate again. - The underlying mechanism involves hypoxia-induced inhibition of voltage-gated K⁺ channels in pulmonary arterial smooth muscle, leading to membrane depolarization, Ca²⁺ influx, and smooth muscle contraction. *Irreversible pulmonary vasoconstriction due to hypoxia* - This statement is incorrect because HPV is fundamentally a **reversible process**, designed to adapt to transient changes in alveolar oxygen. - Irreversible vasoconstriction typically occurs in chronic hypoxia, leading to **pulmonary hypertension** and structural remodeling (vascular remodeling with medial hypertrophy), which is a pathological state rather than the acute physiological response of HPV. *Redirects blood to well-ventilated areas* - While this is the **physiological purpose** and overall effect of hypoxic pulmonary vasoconstriction, it describes the functional outcome rather than what HPV fundamentally is. - The redirection of blood flow is the **consequence** of vasoconstriction in hypoxic areas, which optimizes ventilation-perfusion matching. *Occurs immediately in response to hypoxia* - While HPV does begin rapidly in response to hypoxia (within seconds to minutes), this describes the **timing characteristic** rather than what HPV is. - This statement is also somewhat imprecise, as the response involves intracellular signaling pathways that take time to manifest fully, though the onset is relatively quick compared to other vascular responses.
Question 9: Most sensitive method of monitoring cardiovascular ischemia in the perioperative period is -
- A. NIBP
- B. ECG
- C. Pulse oximeter
- D. TEE (Correct Answer)
Explanation: ***TEE*** - **Transesophageal echocardiography (TEE)** is the most sensitive method for detecting perioperative myocardial ischemia because it can visualize **regional wall motion abnormalities** and changes in **ventricular function** much earlier than ECG. - **Ischemia** directly impairs the contractility of the affected myocardium, leading to subtle changes in wall motion that TEE can identify. *NIBP* - **Non-invasive blood pressure (NIBP)** monitoring can detect **hemodynamic changes** (like hypotension or hypertension) that may precede or accompany ischemia. - However, these changes are **non-specific** and occur relatively late, making NIBP a less sensitive indicator of early ischemia. *ECG* - **Electrocardiography (ECG)** monitors the electrical activity of the heart and can detect **ST-segment changes** indicative of ischemia. - While useful, ECG changes may appear later than wall motion abnormalities, and **silent ischemia** can be missed if the leads are not optimally placed or if the ischemia does not produce significant electrical changes. *Pulse oximeter* - A **pulse oximeter** measures **oxygen saturation** in the peripheral blood. - It is primarily used to assess **respiratory function** and tissue oxygenation, and it does not directly monitor myocardial ischemia or cardiac function.
Question 10: Drug that does not cause cardiac depression:
- A. Thiopentone
- B. Ketamine
- C. Propofol
- D. Etomidate (Correct Answer)
Explanation: ***Etomidate*** - Etomidate is known for its **cardiovascular stability**, making it a preferred induction agent in patients with **compromised cardiac function**. - It maintains **myocardial contractility** and does not typically cause a significant drop in blood pressure. *Thiopentone* - Thiopentone causes **dose-dependent myocardial depression** and peripheral vasodilation. - This can lead to a significant **decrease in blood pressure** and cardiac output, especially in hypovolemic patients. *Propofol* - Propofol is a potent **vasodilator** and can cause significant **myocardial depression**, leading to hypotension. - Its cardiovascular effects are often more pronounced than those of other induction agents, necessitating careful titration. *Ketamine* - Ketamine causes indirect cardiovascular stimulation (due to **sympathetic nervous system activation**), but direct myocardial depression. - While it often increases heart rate and blood pressure, this is a compensatory mechanism and its direct effect on the myocardium is depressant.
Want unlimited practice?
Get full access to all questions, explanations, and performance tracking.
Start For Free