Cardiovascular System Practice Questions

Q: How does moderate hyperkalemia primarily affect the resting membrane potential and excitability of cardiac muscle cells?

Decreased excitability due to decreased membrane potential. ***Decreased excitability due to decreased membrane potential*** - Moderate hyperkalemia causes a **decrease (depolarization)** of the **resting membrane potential**, making it less negative. - While initially this might seem to increase excitability, the sustained depolarization inactivates **voltage-gated sodium channels**, thereby *decreasing overall excitability* and slowing conduction velocity. *Increased excitability due to decreased membrane potential* - Although moderate hyperkalemia does cause a **decreased resting membrane potential (depolarization)**, this initial effect does not lead to *increased excitability* in the long term for cardiac muscle. - The sustained depolarization leads to the *inactivation of fast sodium channels*, preventing further action potentials from firing efficiently. *Increased excitability due to increased membrane potential* - This option is incorrect because hyperkalemia causes a *decrease* (depolarization), not an increase, in the **resting membrane potential**. - Additionally, sustained depolarization reduces, rather than increases, excitability in cardiac cells by inactivating sodium channels. *Decreased excitability due to increased membrane potential* - This is incorrect because hyperkalemia results in a *decrease* in the **resting membrane potential** (makes it less negative), not an increase. - While it correctly states decreased excitability, the reasoning for the membrane potential change is flawed.

Q: Cerebral blood flow is regulated by all of the following except:

Calcium ions. ***Calcium ions*** - While **calcium ions (Ca²⁺)** are mechanistically essential for vascular smooth muscle contraction and relaxation, they are **not considered a primary regulatory signal** for cerebral blood flow (CBF) in the same way as the other factors listed. - Ca²⁺ acts as an **intracellular second messenger** that mediates the effects of other regulatory factors (like PCO2, K⁺, and vasoactive substances), rather than being a direct extracellular regulatory signal itself. - The question refers to primary regulatory factors that directly modulate CBF, not the intracellular mechanisms by which vascular smooth muscle responds. *Blood pressure* - **Cerebral autoregulation** maintains relatively constant CBF despite changes in **mean arterial pressure (MAP)** between approximately 60-150 mmHg. - Blood pressure is a **key regulatory factor** - when MAP falls below or exceeds this range, CBF becomes pressure-dependent. - This protective mechanism prevents cerebral ischemia or hyperemia with systemic blood pressure fluctuations. *Arterial PCO2* - **Arterial partial pressure of carbon dioxide (PaCO2)** is one of the **most potent direct regulators** of CBF. - **Hypercapnia** (increased PaCO2) causes cerebral vasodilation and increased CBF (approximately 1-2 mL/100g/min increase per 1 mmHg rise in PaCO2). - **Hypocapnia** (decreased PaCO2) causes vasoconstriction and reduced CBF, utilized therapeutically in managing elevated intracranial pressure. *Potassium ions* - **Increased extracellular K⁺** in the perivascular space causes **direct vasodilation** of cerebral arterioles. - This mechanism is crucial for **neurovascular coupling** (functional hyperemia) - when neurons are active, they release K⁺, which dilates nearby vessels to increase local blood flow. - K⁺-mediated vasodilation helps match cerebral perfusion to metabolic demand during neuronal activity.

Q: Closure of patent ductus arteriosus is stimulated by?

Increase in O2 tension at birth. ***Increase in O2 tension at birth*** - The **patent ductus arteriosus (PDA)** remains open during fetal life due to low oxygen tension and elevated **prostaglandin E2** levels. - At birth, the first breath significantly increases **pulmonary blood flow** and **arterial oxygen tension**, leading to constriction and functional closure of the PDA. *Prostaglandin F2a* - While prostaglandins play a crucial role in vascular tone, **prostaglandin F2a** is not the primary mediator for PDA closure. - **Prostaglandin E2** is primarily responsible for keeping the ductus arteriosus open in utero. *Cyclooxygenase* - **Cyclooxygenase (COX)** is an enzyme involved in the synthesis of prostaglandins. - While inhibitors of COX (e.g., indomethacin) can induce PDA closure by reducing prostaglandin synthesis, COX itself does not directly stimulate closure. *Hypercarbia* - **Hypercarbia** (elevated CO2 levels) is typically associated with **vasodilation**, particularly in the cerebral circulation, and would not promote PDA closure. - It does not directly impact the mechanisms responsible for the constriction of the ductus arteriosus.

Q: Which of the following hemodynamic changes is not evident in cardiac tamponade during diastole?

Biphasic venous return. ***Biphasic venous return*** - In **normal conditions**, the jugular venous pulse (JVP) shows a **biphasic pattern** with two descents: the **'x' descent** (atrial relaxation) and the **'y' descent** (rapid ventricular filling). - In **cardiac tamponade**, the elevated intrapericardial pressure prevents effective right ventricular filling during diastole, causing the **'y' descent to be absent or markedly blunted**. - This results in a **monophasic pattern** (only 'x' descent visible), meaning **true biphasic venous return is NOT evident** in cardiac tamponade. - This is the hemodynamic change that is **not present** during diastole in tamponade. *Right atrial and ventricular collapse* - This **IS a hallmark feature** observed in cardiac tamponade via echocardiography, particularly during diastole. - The increased intrapericardial pressure compresses the thin-walled right-sided chambers, causing them to collapse during diastole. *Absent y wave on JVP* - The **'y' descent** on the JVP represents the rapid ventricular filling phase after the tricuspid valve opens. - In cardiac tamponade, the elevated intrapericardial pressure prevents effective right ventricular filling, thus **blunting or completely abolishing the 'y' descent**. - This finding **IS evident** in cardiac tamponade. *Elevated pericardial pressure* - This **IS the fundamental physiological change** in cardiac tamponade, as the accumulation of fluid in the pericardial sac raises the pressure. - This elevated pressure compresses the cardiac chambers and impedes diastolic filling, particularly affecting the right atrium and ventricle due to their lower filling pressures.

Q: What is the purpose of the square wave seen in an ECG recording?

Used for standardization of ECG. ***Used for standardization of ECG*** - The **square wave** at the beginning of an ECG tracing is a **calibration signal**, typically 1 mV in amplitude and 0.2 seconds in duration. - It ensures that the ECG machine is accurately recording the electrical activity, allowing for proper measurement of subsequent waveforms. *Indicates atrial depolarization* - **Atrial depolarization** is represented by the **P wave** on the ECG, which is a small, rounded wave preceding the QRS complex. - The square wave serves a technical purpose for calibration, not a physiological one related to cardiac electrical activity. *Indicates ventricular depolarization* - **Ventricular depolarization** is represented by the **QRS complex**, which is a sharp, prominent deflection following the P wave. - This complex reflects the rapid electrical activation of the ventricles, very different from the calibration square wave. *Indicates ventricular repolarization* - **Ventricular repolarization** is represented by the **T wave**, which is typically a rounded wave following the QRS complex. - This physiological event is distinct from the initial square wave, which is an artifact generated by the ECG device for calibration.

Q: Immediate physiological response to sudden decrease in blood volume is

Release of epinephrine. ***Release of epinephrine*** - A sudden decrease in blood volume triggers the **sympathetic nervous system** to release **epinephrine** (and norepinephrine) from the adrenal medulla. - Epinephrine causes **vasoconstriction** and increases **heart rate** and **contractility** to maintain blood pressure and cardiac output. *Release of angiotensin* - **Angiotensin** is part of the **renin-angiotensin-aldosterone system (RAAS)**, which is activated in response to decreased blood volume and renal perfusion. - While important for long-term blood pressure regulation and fluid balance, its release is not the **immediate physiological response** compared to catecholamines. *Release of thyroxine* - **Thyroxine** (thyroid hormone) primarily regulates **metabolism** and is not involved in the immediate compensatory mechanisms for sudden blood volume changes. - Its effects are **slow** and long-lasting, unlike the rapid response needed. *Shift of fluid from intracellular to interstitial compartment* - Fluid shifts due to changes in **osmolarity** or **hydrostatic pressure** do occur, but the immediate response to a sudden volume decrease involves **neurohormonal activation**. - A shift from the **intracellular** to the **extracellular** (interstitial and intravascular) compartment would actually help restore blood volume, but this is a *consequence* of compensatory mechanisms, not the primary and immediate physiological *response*.

Q: Which of the following is considered the most important cerebral vasodilator in physiological conditions?

Carbon dioxide (CO2). ***Carbon dioxide (CO2)*** - CO2 is the **most important physiological cerebral vasodilator** under normal conditions - CO2 diffuses readily across the blood-brain barrier into brain tissue - It forms carbonic acid (H2CO3), which dissociates to H+ and HCO3-, decreasing **extracellular pH** - This pH change directly relaxes cerebral arterioles, increasing cerebral blood flow - Even small changes in PaCO2 (arterial CO2 tension) cause significant alterations in cerebral blood flow *Hydrogen ions (H+)* - While hydrogen ions directly influence cerebral vasodilation by affecting pH, they are primarily generated from **CO2 metabolism** - H+ ions do not cross the blood-brain barrier as readily as CO2 - The direct effect of H+ is secondary to CO2's role, making H+ an important downstream mediator rather than the primary trigger *Sodium ions (Na+)* - Sodium ions play critical roles in **neuronal excitation** and **membrane potential maintenance** - They are not directly involved in the physiological regulation of cerebral blood vessel tone - Changes in Na+ concentration do not directly cause vasodilation or constriction in cerebral arteries under normal conditions *Calcium ions (Ca2+)* - Calcium ions are crucial for **vascular smooth muscle contraction** - Increased intracellular Ca2+ leads to vasoconstriction, while decreased Ca2+ promotes vasodilation - However, Ca2+ is a mediator of smooth muscle contraction/relaxation rather than the primary physiological stimulus for cerebral vasodilation

Q: Which heart sound occurs during late diastole due to atrial contraction against a stiff ventricle?

S4. ***S4*** - The **S4 heart sound** occurs during **late diastole** when the atria contract to push blood into a **stiff or non-compliant ventricle**. - It results from the **atrial kick** forcing blood into a ventricle with decreased compliance, often associated with conditions like **left ventricular hypertrophy**, **hypertensive heart disease**, or **aortic stenosis**. - S4 occurs **before S1** (before AV valve closure) and is sometimes called an **atrial gallop**. - It is typically **abnormal** in adults and suggests impaired ventricular compliance. *S1* - **S1** represents the sound of **AV valve closure** (mitral and tricuspid valves) at the **onset of systole**. - It marks the beginning of **ventricular contraction** and is typically the loudest heart sound. - S1 occurs when ventricular pressure exceeds atrial pressure, causing the AV valves to close. *S2* - **S2** represents the sound of **semilunar valve closure** (aortic and pulmonic valves) at the **end of systole**. - It marks the beginning of **ventricular relaxation** (diastole) and is commonly split during inspiration. - S2 occurs when ventricular pressure falls below aortic and pulmonary artery pressures. *S3* - The **S3 heart sound** occurs during **early diastole** as blood rapidly fills a volume-overloaded or dysfunctional ventricle. - It is often associated with conditions like **congestive heart failure**, **dilated cardiomyopathy**, or volume overload. - S3 is sometimes referred to as a **ventricular gallop** and can be normal in children and young adults.

Q: What is the effect of positive G-force on cardiac output?

Decreased cardiac output due to G-force. ***Decreased cardiac output due to G-force*** - **Positive G-forces** push blood downwards towards the lower extremities, leading to a significant **reduction in venous return** to the heart. - Reduced venous return directly translates to a **decreased preload** and subsequently a **decreased cardiac output**, as less blood is available for pumping. *Increased cerebral arterial pressure due to G-force* - **Positive G-forces** cause blood to pool in the lower body, leading to a **decrease in arterial pressure** in the upper body and brain, not an increase. - This **reduced cerebral perfusion** is the reason for symptoms like **lightheadedness** and **G-LOC (G-induced loss of consciousness)**. *Increased venous return due to G-force* - **Positive G-forces** exert a force on the blood that acts in the same direction as gravity (head-to-foot), actively **pulling blood away from the heart** and into the lower extremities. - This gravitational pooling of blood in the dependent parts of the body significantly **reduces venous return** to the right atrium, rather than increasing it. *Increased pressure in lower limb due to G-force* - While there is indeed **increased hydrostatic pressure** in the lower limbs due to the pooling of blood under positive G-forces, this is a consequence of blood being pulled away from the central circulation. - This increased pressure in the lower limbs does not lead to an increased cardiac output; instead, it's a symptom of the **reduced central blood volume** and **decreased venous return**.

Q: Baroreceptors are related to which vessels?

Carotid sinus. ***Carotid sinus*** - Baroreceptors are located in the **carotid sinus**, which is a dilated region at the **bifurcation of the common carotid artery** into the internal and external carotid arteries. - These **arterial baroreceptors** detect changes in blood pressure and send signals via the **glossopharyngeal nerve (CN IX)** to the cardiovascular centers in the medulla. - The carotid sinus is one of the two major baroreceptor sites (the other being the aortic arch). *External carotid artery* - While it originates from the common carotid artery at the bifurcation, the **external carotid artery** itself does not contain baroreceptors. - Its main function is to supply blood to the face, scalp, and superficial structures of the head and neck. *Subclavian artery* - The subclavian artery is a major artery supplying the upper limb and does **not contain baroreceptors**. - Its primary role is to supply blood to the arms, chest wall, and neck. *Brachiocephalic trunk* - The brachiocephalic trunk (innominate artery) gives rise to the right common carotid artery and right subclavian artery, but it **does not house baroreceptors**. - Baroreceptors are located more distally in the carotid sinus and aortic arch.

Question 1

How does moderate hyperkalemia primarily affect the resting membrane potential and excitability of cardiac muscle cells?

Accepted Answer

Decreased excitability due to decreased membrane potential

Answer

Increased excitability due to increased membrane potential

Answer

Increased excitability due to decreased membrane potential

Answer

Decreased excitability due to increased membrane potential

Question 2

Cerebral blood flow is regulated by all of the following except:

Accepted Answer

Calcium ions

Answer

Blood pressure

Answer

Arterial PCO2

Answer

Potassium ions

Question 3

Closure of patent ductus arteriosus is stimulated by?

Accepted Answer

Increase in O2 tension at birth

Answer

Prostaglandin F2a

Answer

Hypercarbia

Answer

Cyclooxygenase

Question 4

Which of the following hemodynamic changes is not evident in cardiac tamponade during diastole?

Accepted Answer

Biphasic venous return

Answer

Right atrial and ventricular collapse

Answer

Absent y wave on JVP

Answer

Elevated pericardial pressure

Question 5

What is the purpose of the square wave seen in an ECG recording?

Accepted Answer

Used for standardization of ECG

Answer

Indicates atrial depolarization

Answer

Indicates ventricular depolarization

Answer

Indicates ventricular repolarization

Question 6

Immediate physiological response to sudden decrease in blood volume is

Accepted Answer

Release of epinephrine

Answer

Release of angiotensin

Answer

Release of thyroxine

Answer

Shift of fluid from intracellular to interstitial compartment

Question 7

Which of the following is considered the most important cerebral vasodilator in physiological conditions?

Accepted Answer

Carbon dioxide (CO2)

Answer

Hydrogen ions (H+)

Answer

Sodium ions (Na+)

Answer

Calcium ions (Ca2+)

Question 8

Which heart sound occurs during late diastole due to atrial contraction against a stiff ventricle?

Accepted Answer

S4

Answer

S1

Answer

S2

Answer

S3

Question 9

What is the effect of positive G-force on cardiac output?

Accepted Answer

Decreased cardiac output due to G-force

Answer

Increased cerebral arterial pressure due to G-force

Answer

Increased venous return due to G-force

Answer

Increased pressure in lower limb due to G-force

Question 10

Baroreceptors are related to which vessels?

Accepted Answer

Carotid sinus

Answer

Subclavian artery

Answer

External carotid artery

Answer

Brachiocephalic trunk

Cardiovascular System — MCQs

Cardiovascular System — MCQs

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