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 Flashcard 1 of 5

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 5

Question: _____ have both unitary and multiunit smooth muscle systems

Answer: Blood vessels

Cardiovascular System Flashcard 3 of 5

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

Answer: 450

Cardiovascular System Flashcard 4 of 5

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

Answer: decrease

Cardiovascular System Flashcard 5 of 5

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

Answer: 1