Cardiovascular System

Cardiovascular System Indian Medical PG Question 1: What physiological mechanism leads to an increase in cardiac output?

• A. Inhalation
• B. Increased myocardial contractility (Correct Answer)
• C. Increased parasympathetic activity
• D. Transitioning from a supine to a standing position

Cardiovascular System Explanation: ***Increased myocardial contractility*** - **Increased myocardial contractility** directly leads to a greater **stroke volume** (the amount of blood pumped with each beat), thus increasing cardiac output (Cardiac Output = Stroke Volume × Heart Rate). - This can be stimulated by factors such as **sympathetic nervous system activation** or positive inotropic agents. *Inhalation* - While inhalation can temporarily affect venous return and intrathoracic pressure, it does not directly or consistently lead to a sustained increase in **cardiac output**. - Its primary effect is on **respiration**, not cardiac performance. *Increased parasympathetic activity* - Increased parasympathetic activity, primarily via the **vagus nerve**, acts to **decrease heart rate** and myocardial contractility. - This effect would typically **reduce cardiac output**, not increase it. *Transitioning from a supine to a standing position* - Transitioning to a standing position usually causes a **temporary decrease in venous return** and a brief drop in cardiac output as blood pools in the lower extremities. - The body then compensates by increasing heart rate and peripheral vascular resistance to maintain blood pressure, but the initial effect on cardiac output is generally a transient decrease.

Cardiovascular System Indian Medical PG Question 2: What is the primary cardiovascular compensatory mechanism in acute hemorrhage?

• A. Decreased myocardial contractility
• B. Increased respiratory rate
• C. Decreased heart rate
• D. Increased heart rate (Correct Answer)

Cardiovascular System Explanation: ***Increased heart rate*** - In acute hemorrhage, the body senses a decrease in **blood volume** and **blood pressure**, triggering the **baroreceptor reflex**. - This reflex leads to increased sympathetic nervous system activity, causing an immediate compensatory **increase in heart rate** to maintain **cardiac output** and tissue perfusion. *Decreased myocardial contractility* - A decrease in myocardial contractility would worsen the situation in hemorrhage by further reducing **cardiac output** and is not a primary compensatory mechanism. - While prolonged severe hemorrhage can lead to myocardial depression due to ischemia, it is a pathological consequence, not a compensatory response. *Decreased heart rate* - A decrease in heart rate would reduce **cardiac output** and further compromise blood flow to vital organs during hemorrhage, which is precisely the opposite of what the body needs. - This response is usually seen with vagal stimulation, not in response to hypovolemic shock. *Increased respiratory rate* - An **increased respiratory rate** is a compensatory mechanism for conditions like **metabolic acidosis** (which can occur in severe shock due to lactic acid accumulation) or to improve oxygenation, but it is not the primary cardiovascular compensatory mechanism for maintaining blood pressure and cardiac output in acute hemorrhage. - While it often accompanies hemorrhage, it acts to regulate oxygen and CO2 levels, not directly blood volume or pressure.

Cardiovascular System Indian Medical PG Question 3: Which of the following neurotransmitters is primarily released from the sympathetic nervous system to increase heart rate in response to a DECREASE in blood pressure?

• A. Norepinephrine (Correct Answer)
• B. Dopamine
• C. Acetylcholine
• D. Epinephrine

Cardiovascular System Explanation: ***Norepinephrine*** - **Norepinephrine** is the primary neurotransmitter released by **postganglionic sympathetic neurons** directly onto the heart to increase heart rate and contractility in response to a drop in blood pressure. - It acts on **beta-1 adrenergic receptors** in the sinoatrial (SA) node, atria, and ventricles, leading to increased chronotropy (heart rate) and inotropy (contractility). *Dopamine* - While **dopamine** can have cardiovascular effects, particularly at high doses, it is not the primary neurotransmitter released by the sympathetic nervous system for direct heart rate regulation. - Dopamine is a precursor to norepinephrine and epinephrine, but its main physiological roles involve **renal blood flow regulation** and central nervous system functions. *Acetylcholine* - **Acetylcholine** is the primary neurotransmitter of the **parasympathetic nervous system**, which generally acts to **decrease heart rate** (bradycardia) through muscarinic receptors. - It is also released by **preganglionic sympathetic fibers**, but these do not directly innervate the heart to produce the desired effect of increasing heart rate. *Epinephrine* - **Epinephrine** (adrenaline) is primarily a **hormone** released from the **adrenal medulla** into the bloodstream, not directly from postganglionic sympathetic nerve terminals to the heart. - Although it has strong effects on beta-1 receptors in the heart, its release is more generalized and slower than the direct neuronal release of norepinephrine.

Cardiovascular System Indian Medical PG Question 4: Best guide for the management of Resuscitation is:

• A. Saturation of Oxygen
• B. CVP
• C. Blood pressure
• D. Urine output (Correct Answer)

Cardiovascular System Explanation: ***Urine output*** - **Urine output** is considered the **gold standard** for assessing adequacy of resuscitation as it directly reflects **end-organ perfusion** and **tissue oxygenation**. A target of **0.5-1 mL/kg/hour** indicates adequate renal perfusion and overall circulatory status. - It serves as a reliable **endpoint of resuscitation** in trauma and critical care protocols, providing objective evidence that fluid resuscitation has achieved adequate **tissue perfusion** and **microcirculatory flow**. *Saturation of Oxygen* - While **oxygen saturation** is crucial for ensuring adequate **oxygen delivery** to tissues, it represents only one component of the oxygen delivery equation and doesn't reflect **tissue perfusion** adequacy. - Maintaining normal oxygen saturation does not guarantee adequate **end-organ perfusion** if cardiac output or tissue perfusion is compromised during resuscitation. *CVP* - **Central venous pressure** has poor correlation with actual **intravascular volume status** and **cardiac preload**, making it an unreliable guide for fluid resuscitation. - CVP measurements are influenced by multiple factors including **ventilator settings**, **tricuspid valve function**, and **chest wall compliance**, limiting its utility as a resuscitation endpoint. *Blood pressure* - While **blood pressure** provides immediate feedback on **circulatory status** and is emphasized in current **ACLS** and **ATLS** protocols as an immediate target, it may not accurately reflect **microcirculatory perfusion**. - Blood pressure can be maintained through **vasoconstriction** while **end-organ perfusion** remains inadequate, making it less reliable than urine output for assessing true resuscitation adequacy.

Cardiovascular System Indian Medical PG Question 5: Which one of the following statements is not correct regarding the haemodynamic changes occurring during a pregnancy?

• A. The cardiac output is increased
• B. The serum colloid pressure is decreased
• C. The stroke volume is increased
• D. The systemic vascular resistance is increased (Correct Answer)

Cardiovascular System Explanation: ***The systemic vascular resistance is increased*** - During normal pregnancy, **systemic vascular resistance (SVR)** actually **decreases** due to vasodilation induced by factors like **prostaglandins** and **nitric oxide**. - A decrease in systemic vascular resistance helps accommodate the increased blood volume and cardiac output, ensuring adequate perfusion to the uteroplacental unit and other organs. *The cardiac output is increased* - **Cardiac output (CO)** progressively **increases** during pregnancy, peaking in the second and third trimesters. - This increase is primarily due to a rise in both **heart rate** and **stroke volume**. *The serum colloid pressure is decreased* - **Serum colloid osmotic pressure** (oncotic pressure) **decreases** in pregnancy due to a disproportionate increase in plasma volume relative to the increase in albumin production. - This leads to **dilutional hypoalbuminemia**, contributing to physiological edema. *The stroke volume is increased* - **Stroke volume (SV)** significantly **increases** during pregnancy, driven by increased end-diastolic volume and enhanced myocardial contractility. - This rise in stroke volume is a major contributor to the overall increase in cardiac output.

Cardiovascular System Indian Medical PG Question 6: What is the definition of preload in the context of cardiac physiology?

• A. Volume of blood in the ventricles at the end of systole
• B. Volume of blood in the ventricles at the end of diastole (Correct Answer)
• C. Amount of blood pumped by the heart per beat
• D. Resistance to blood flow in the arteries

Cardiovascular System Explanation: ***Volume of blood in the ventricles at the end of diastole*** - Preload represents the **initial stretching** of the cardiac myocytes prior to contraction, largely determined by the **volume of blood filling the ventricles** at the end of relaxation (diastole). - This **end-diastolic volume** directly correlates with the ventricular muscle fiber length at the start of systole, influencing the force of contraction according to the **Frank-Starling mechanism**. *Volume of blood in the ventricles at the end of systole* - This describes the **end-systolic volume**, which is the amount of blood remaining in the ventricle after it has contracted and ejected blood. - End-systolic volume is a determinant of the **ejection fraction** but does not define preload. *Amount of blood pumped by the heart per beat* - This refers to the **stroke volume**—the volume of blood ejected from the left ventricle with each heartbeat. - While preload influences stroke volume, stroke volume itself is not the definition of preload. *Resistance to blood flow in the arteries* - This describes **afterload**, which is the pressure or resistance the ventricle must overcome to eject blood during systole. - Afterload primarily affects the *force* needed for contraction, rather than the initial stretch or filling volume of the heart.

Cardiovascular System Indian Medical PG Question 7: 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

Cardiovascular System 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.

Cardiovascular System Indian Medical PG Question 8: The primary effect of vagal stimulation on the heart is

• A. Increased P-R interval in ECG
• B. Decreased force of heart contraction
• C. Decreased cardiac output
• D. Decreased heart rate (Correct Answer)

Cardiovascular System Explanation: ***Decreased heart rate*** - **Vagal stimulation** releases **acetylcholine**, which activates muscarinic receptors on the sinoatrial (SA) node, leading to a decrease in its firing rate and thus a slower heart rate. - This parasympathetic effect primarily targets the **SA node** and **AV node**, influencing chronotropy (heart rate) more significantly than inotropy (contractility). *Increased P-R interval in ECG* - While vagal stimulation does slow **AV node conduction**, increasing the P-R interval, this is a more specific electrophysiological effect rather than the primary overall physiological outcome of vagal stimulation on the heart. - The most direct and immediate consequence of vagal nerve activity is the slowing of the heart's rhythm, which manifests as a **decreased heart rate**. *Decreased force of heart contraction* - The **vagus nerve** has a relatively weak effect on ventricular contractility, as parasympathetic innervation is far less dense in the ventricles compared to the atria and nodal tissues. - Therefore, a significant **decrease in the force of contraction** is not a primary or direct result of typical vagal stimulation in a healthy heart. *Decreased cardiac output* - While a markedly decreased heart rate *could* lead to a decreased cardiac output (CO = HR x SV), this is not the most direct or immediate physiological effect of vagal stimulation. - The primary action is on the heart rate, and changes in cardiac output would be a **secondary consequence** depending on the extent of bradycardia and compensatory mechanisms.

Cardiovascular System Indian Medical PG Question 9: Which part of the action potential in cardiac pacemaker cells is primarily affected by calcium channel blockers?

• A. Phase 1
• B. Phase 2
• C. Phase 3
• D. Phase 0 (Correct Answer)

Cardiovascular System Explanation: ***Phase 0*** - In cardiac pacemaker cells (SA and AV nodes), **Phase 0 (rapid depolarization)** is mediated by **L-type calcium channels**, NOT the fast sodium channels seen in ventricular myocytes. - Calcium channel blockers primarily inhibit these **L-type calcium channels**, leading to a **slower rate of depolarization** and **reduced conduction velocity** through the AV node. - This is the **primary mechanism** by which these drugs slow heart rate and cause AV nodal blockade. *Phase 1* - Phase 1 (initial rapid repolarization) is **absent in pacemaker cells** because they lack the fast sodium channels and transient outward potassium currents characteristic of ventricular myocytes. - This phase is not relevant to pacemaker cell action potentials. *Phase 2* - Phase 2 (plateau phase) is also **absent or minimal in pacemaker cells**. - Pacemaker action potentials lack the prolonged plateau seen in ventricular myocytes. - This phase is not the primary target of calcium channel blockers in pacemaker tissue. *Phase 3* - Phase 3 (repolarization) occurs in pacemaker cells and is mediated by **potassium efflux**. - Calcium channel blockers do **not directly affect** this phase, as it is driven by potassium channels, not calcium channels. - Their effect on Phase 3 is minimal compared to their direct action on Phase 0.

Cardiovascular System Indian Medical PG Question 10: Blood pressure changes in radial artery were measured. Which of the following is the reason for initial rise in BP while performing Valsalva maneuver?

• A. Increase in Left ventricular volume
• B. Increase in Left ventricular pressure
• C. Decrease in aortic pressure
• D. Increase in aortic pressure (Correct Answer)

Cardiovascular System Explanation: ***Increase in aortic pressure*** - During the initial phase (Phase I) of the Valsalva maneuver, the sudden **increase in intrathoracic pressure** is transmitted directly to the aorta and other large arteries. - This transient increase in external pressure on the great vessels directly causes a brief **rise in aortic blood pressure** before other compensatory mechanisms take effect. *Increase in Left ventricular volume* - The Valsalva maneuver actually **decreases left ventricular volume** over time due to reduced venous return. - An increase in left ventricular volume would typically lead to a sustained increase in cardiac output and blood pressure, which is not what is observed initially during the Valsalva maneuver. *Increase in Left ventricular pressure* - While increased intrathoracic pressure can transiently affect left ventricular pressure, the initial blood pressure rise is primarily due to direct compression of the **aorta and systemic arteries**, not an intrinsic increase in myocardial contractility or ventricular filling pressure. - Ultimately, the Valsalva maneuver generally leads to a decrease in **left ventricular preload** and subsequent decrease in stroke volume during the prolonged straining phase. *Decrease in aortic pressure* - The graph clearly shows an **initial spike in mean aortic pressure** (Phase I) at the onset of the Valsalva maneuver. - A decrease in aortic pressure is characteristic of the later part of the straining phase (Phase II) due to **reduced cardiac output**.

Cardiovascular System Flashcard 1 of 10

Question: When a person moves from standing to supine position, the heart rate _____, due to activation of baroreceptor reflex

Answer: decreases

Cardiovascular System Flashcard 2 of 10

Question: _____ have both unitary and multiunit smooth muscle systems

Answer: Blood vessels

Cardiovascular System Flashcard 3 of 10

Question: The total fetal cardiac output at term is approximately _____ mL/kg/min.

Answer: 450

Cardiovascular System Flashcard 4 of 10

Question: An increased TPR causes the cardiac output to _____ and venous return to decrease

Answer: decrease

Cardiovascular System Flashcard 5 of 10

Question: Activation of _____ adrenergic receptors on the SA node causes increased heart rate

Answer: 1

Cardiovascular System Flashcard 6 of 10

Question: An increased blood volume (or venous tone) causes the cardiac output to _____ and right atrial pressure to increase

Answer: increase

Cardiovascular System Flashcard 7 of 10

Question: Does the following cardiac/vascular function graph reflect a patient with chronic anemia or anaphylaxis? _____

Answer: Anaphylaxis

Cardiovascular System Flashcard 8 of 10

Question: The image shows a _____ pulse waveform.

Answer: normal

Cardiovascular System Flashcard 9 of 10

Question: Does the following cardiac/vascular function graph reflect a patient with chronic anemia or anaphylaxis? _____

Answer: Chronic Anemia

Cardiovascular System Flashcard 10 of 10

Question: The "blip" in the arterial pressure curve, called the _____, is produced when the aortic valve closes

Answer: dicrotic notch