Arterial System Physiology — MCQs
ABPI increases artificially in
What is the physiological response of the kidney during shock?
Pressure difference of 5 mm Hg between the two upper limbs occurs in which congenital heart disease?
All are cardiovascular system changes in pregnancy except.
Risk Scoring System which can be used postoperatively is:
The pH of body fluids is stabilized by buffer systems. Which of the following compounds is the most effective buffer at physiologic pH?
Which of the following can cause delirium?
Which part of the cardiac conduction system has the fastest conduction velocity?
Which of the following decreases during hypovolemic shock?
The relation of the left renal vein with the aorta is -
Arterial System Physiology Indian Medical PG Practice Questions and MCQs
Question 1: ABPI increases artificially in
- A. Ischemic limb ulcers
- B. Intermittent claudication syndrome
- C. Deep vein thrombosis (DVT)
- D. Conditions causing arterial calcification (Correct Answer)
Explanation: ***Conditions causing arterial calcification*** - In cases of **arterial calcification**, particularly in conditions like **diabetes** and **chronic kidney disease**, the blood vessels become stiff and non-compressible. - This stiffness leads to falsely elevated ankle systolic pressures because the cuff cannot effectively compress the calcified arteries, resulting in an artificially high **Ankle-Brachial Pressure Index (ABPI)** reading [2]. *Ischemic limb ulcers* - **Ischemic limb ulcers** are a direct consequence of **peripheral artery disease (PAD)**, which is characterized by reduced blood flow to the extremities [2]. - In these conditions, the ABPI would be **decreased** (typically < 0.9), indicating impaired blood supply, not an increase [2]. *Intermittent claudication syndrome* - **Intermittent claudication** is a classic symptom of **peripheral artery disease (PAD)**, where pain occurs in the legs during exercise due to insufficient blood flow [1]. - This syndrome is associated with a **reduced ABPI**, as arterial narrowing limits oxygen delivery to the muscles during exertion [1]. *Deep vein thrombosis (DVT)* - **Deep vein thrombosis (DVT)** is a condition involving a blood clot in a deep vein, typically in the legs. - DVT does not directly cause an artificial increase in ABPI; it primarily affects venous return and can cause swelling and pain, but not elevated arterial pressure readings [2].
Question 2: What is the physiological response of the kidney during shock?
- A. GFR decreases
- B. Perfusion of kidney decreases
- C. Afferent arteriole resistance increases
- D. Renal blood flow decreases (Correct Answer)
Explanation: ***Renal blood flow decreases*** - During shock, the **primary and most fundamental** physiological change affecting the kidney is a marked **reduction in renal blood flow (RBF)**. - Shock triggers intense **sympathetic activation** and **renin-angiotensin system (RAS) activation**, causing preferential **vasoconstriction** of renal vessels to redirect blood to vital organs (brain, heart). - RBF can drop to as low as **20-30% of normal** in severe shock, making this the hallmark renal response. - This reduction in RBF is the **upstream event** that triggers all other renal changes during shock. *Perfusion of kidney decreases* - While technically correct, "decreased perfusion" is **essentially synonymous** with decreased blood flow in this context. - The term "renal blood flow" is the **standard physiological terminology** used in medical literature to describe this phenomenon, making it the more precise answer. *Afferent arteriole resistance increases* - This is a **mechanism** by which RBF decreases, not the overall response itself. - Increased afferent arteriolar resistance is **secondary** to sympathetic activation and angiotensin II effects during shock. - It describes the "how" rather than the "what" of the kidney's response. *GFR decreases* - GFR reduction is a **consequence** of decreased RBF and increased afferent arteriolar resistance. - While clinically important (oliguria/acute kidney injury), it's a **downstream effect** rather than the primary physiological response. - The relationship: ↓RBF → ↓Glomerular hydrostatic pressure → ↓GFR
Question 3: Pressure difference of 5 mm Hg between the two upper limbs occurs in which congenital heart disease?
- A. HOCM
- B. Coarctation of Aorta
- C. Supra-valvular aortic stenosis (Correct Answer)
- D. TOF
Explanation: ***Supra-valvular aortic stenosis*** - **Supravalvular aortic stenosis** causes a **pressure gradient** across the aortic valve, leading to a significant **pressure difference** between the upper limbs, typically with a **higher pressure** in the right arm. - This is due to the **Coanda effect**, where the high-velocity jet of blood preferentially flows up the **right subclavian artery** as it exits the aorta. *HOCM (Hypertrophic Obstructive Cardiomyopathy)* - HOCM is characterized by hypertrophy of the **left ventricular septum** causing **outflow tract obstruction**, but it does not typically cause a significant **pressure difference** between the upper limbs. - The obstruction primarily affects **ventricular ejection** rather than differential flow to major arteries. *Coarctation of Aorta* - **Coarctation of the aorta** causes a significant **blood pressure difference** between the upper and lower extremities, with higher pressures in the arms [1]. - However, it does not typically cause a marked **pressure difference between the two upper limbs**, unless the coarctation is pre-ductal and affects the subclavian artery circulation asymmetrically, which is less common for a difference of just 5 mmHg. *TOF (Tetralogy of Fallot)* - **Tetralogy of Fallot** is a cyanotic heart disease involving **pulmonary stenosis**, ventricular septal defect, overriding aorta, and right ventricular hypertrophy [2]. - While it causes significant circulatory abnormalities and potential for **hypoxia**, it does not inherently lead to a measurable **pressure difference** between the upper limbs.
Question 4: All are cardiovascular system changes in pregnancy except.
- A. Increase in blood volume
- B. Increase in heart rate
- C. Increase in peripheral resistance (Correct Answer)
- D. Increase in cardiac output
Explanation: ***Increase in peripheral resistance*** - During normal pregnancy, **peripheral vascular resistance actually decreases** due to the effects of hormones like progesterone and the presence of the low-resistance uteroplacental circulation. - This decrease in resistance helps accommodate the increased blood volume and cardiac output. *Increase in cardiac output* - **Cardiac output increases significantly** during pregnancy (by 30-50%) to meet the metabolic demands of the growing fetus and maternal tissues. - This is primarily achieved through an increase in both stroke volume and heart rate. *Increase in blood volume* - **Blood volume increases substantially** (by 30-50%) during pregnancy, with plasma volume increasing more than red blood cell mass. - This expansion supports the increased cardiac output and placental perfusion. *Increase in heart rate* - **Heart rate increases** during pregnancy, typically by 10-20 beats per minute, contributing to the overall increase in cardiac output. - This physiological adaptation helps maintain adequate circulation.
Question 5: Risk Scoring System which can be used postoperatively is:
- A. ASA American Society of Anaesthesiologist
- B. MET Metabolic Equivalent Task
- C. POSSUM Physiologic and Operative Severity Score for Enumeration of Mortality and Morbidity (Correct Answer)
- D. RCRI Revised Cardiac Risk Index
Explanation: ***POSSUM (Physiologic and Operative Severity Score for enUmeration of Mortality and Morbidity)*** - **POSSUM** is a risk scoring system specifically designed to predict **postoperative mortality and morbidity** based on physiological and operative factors. - It includes both **preoperative physiological variables** and **intraoperative findings** to provide a comprehensive risk assessment after surgery. *ASA (American Society of Anesthesiologists)* - The **ASA physical status classification system** is used to assess a patient's **preoperative health status** and predict anesthetic risk, not directly postoperative outcomes. - It is determined **before surgery** to categorize patients into different classes based on their overall health and presence of co-morbidities. *MET (Metabolic Equivalent Task)* - **METs** are a measure of **exercise capacity** and reflect a person's functional status, often used in preoperative cardiac risk assessment. - They are used to gauge a patient's ability to perform physical tasks, not as a direct predictor of postoperative complications. *RCRI (Revised Cardiac Risk Index)* - The **RCRI** is used to predict the risk of **major cardiac events** in patients undergoing non-cardiac surgery. - It is primarily a **preoperative tool** focused on cardiac risks, not a general predictor of all postoperative morbidity and mortality.
Question 6: The pH of body fluids is stabilized by buffer systems. Which of the following compounds is the most effective buffer at physiologic pH?
- A. NH4OH, pKa = 9.24
- B. Na2HPO4, pKa = 12.32
- C. NaH2PO4, pKa = 7.21 (Correct Answer)
- D. CH3CO2H, pKa = 4.75
Explanation: ***NaH2PO4, pKa = 7.21*** - A buffer's maximum effectiveness is typically within 1 pH unit of its **pKa value**. - With a **pKa of 7.21**, the H2PO4⁻/HPO4²⁻ buffer system (phosphate buffer) is optimally positioned to buffer fluctuations around the physiologic pH of **7.35-7.45**. - This makes the phosphate buffer system highly effective in intracellular and urinary pH regulation. *NH4OH, pKa = 9.24* - This compound is a **weak base** with a pKa of 9.24, meaning it would be effective at a pH much higher than the physiologic range. - Its buffering capacity would be minimal at **pH 7.4**, as the system would be predominantly in one form, reducing its ability to resist pH changes. *Na2HPO4, pKa = 12.32* - This represents the **second dissociation** of phosphoric acid (HPO4²⁻ ⇌ PO4³⁻ + H⁺) with a very high **pKa of 12.32**. - This dissociation occurs at extremely alkaline pH levels, far above the physiological range. - At physiologic pH, this equilibrium would be almost entirely shifted to HPO4²⁻, providing no buffering capacity. *CH3CO2H, pKa = 4.75* - **Acetic acid** has a pKa of 4.75, making it an effective buffer in the acidic range (around pH 3.75-5.75). - It would be almost entirely dissociated at **physiologic pH**, offering very little buffering capacity against pH changes in body fluids.
Question 7: Which of the following can cause delirium?
- A. Barbiturates
- B. Hypoxia
- C. Alcohol withdrawal
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Barbiturates**, **hypoxia**, and **alcohol withdrawal** are all well-established causes of delirium, affecting the brain's cognitive function. - Delirium is a state of **acute brain failure** characterized by fluctuating attention, altered consciousness, and cognitive dysfunction, often *multifactorial*. *Barbiturates* - These drugs are **CNS depressants** and can cause delirium, especially in susceptible individuals or with overdose. - They can lead to **sedation**, confusion, and a paradoxical agitated state, contributing to delirium. *Hypoxia* - **Lack of oxygen to the brain** is a significant cause of delirium as neurons are highly sensitive to oxygen deprivation. - This can result from various conditions such as **respiratory failure**, anemia, or circulatory compromise, directly impairing brain function. *Alcohol withdrawal* - Abrupt cessation of alcohol in dependent individuals causes severe **CNS hyper-excitability**, leading to delirium tremens. - Symptoms include **agitation**, hallucinations, confusion, and autonomic instability characteristic of delirium.
Question 8: Which part of the cardiac conduction system has the fastest conduction velocity?
- A. Sinoatrial (SA) node
- B. Bundle of His fibers
- C. Purkinje fibers (Correct Answer)
- D. Atrioventricular (AV) node
Explanation: ***Purkinje fibers*** - They possess the **fastest conduction velocity** in the heart (2-4 m/s), necessary for rapid and synchronized ventricular contraction. - This rapid conduction ensures that all parts of the ventricles contract almost simultaneously, maximizing pumping efficiency. **Sinoatrial (SA) node** - The SA node is the primary pacemaker of the heart, setting the heart rate due to its intrinsic rhythmicity. - It has a relatively **slow conduction velocity** (0.05 m/s) which allows time for proper impulse generation and transmission. **Bundle of His fibers** - The Bundle of His transmits impulses from the AV node to the bundle branches. - While faster than the AV node (1-1.5 m/s), its conduction velocity is significantly **slower** than that of the Purkinje fibers. **Atrioventricular (AV) node** - The AV node introduces a crucial delay in impulse conduction, allowing sufficient time for atrial contraction and complete ventricular filling before ventricular systole. - It has the **slowest conduction velocity** (0.02-0.05 m/s) in the entire cardiac conduction system.
Question 9: Which of the following decreases during hypovolemic shock?
- A. Stroke volume (Correct Answer)
- B. Systemic resistance
- C. Heart rate
- D. Sympathetic activity
Explanation: ***Stroke volume*** - In **hypovolemic shock**, there is a significant reduction in **preload** (venous return to the heart) due to decreased blood volume. - This reduced preload directly leads to a decrease in the amount of blood ejected by the heart with each beat, hence a drop in **stroke volume**. *Systemic resistance* - **Systemic vascular resistance (SVR)** typically **increases** during hypovolemic shock due to compensatory vasoconstriction. - This **vasoconstriction** is mediated by the sympathetic nervous system to maintain blood pressure and vital organ perfusion. *Heart rate* - **Heart rate** generally **increases** in hypovolemic shock as a compensatory mechanism to maintain cardiac output. - The **tachycardia** attempts to offset the decrease in stroke volume caused by reduced blood volume. *Sympathetic activity* - **Sympathetic nervous system activity** **increases** significantly during hypovolemic shock. - This increase in activity leads to the release of **catecholamines** (**epinephrine** and **norepinephrine**), causing vasoconstriction, increased heart rate, and increased myocardial contractility to counteract the shock state.
Question 10: The relation of the left renal vein with the aorta is -
- A. Anterior, above the Superior mesenteric artery
- B. Anterior, below the Superior mesenteric artery (Correct Answer)
- C. Anterior, below the Inferior mesenteric artery
- D. Posterior, below the Superior mesenteric artery
Explanation: Anterior, below the Superior mesenteric artery - The left renal vein typically passes anterior to the aorta. - It then runs inferior to the superior mesenteric artery. Anterior, above the Superior mesenteric artery - The renal vein does not typically course above the superior mesenteric artery when it crosses the aorta. - Its usual anatomical position is to pass under this artery. Anterior, below the Inferior mesenteric artery - While anterior to the aorta, the renal vein is positioned more superiorly, at the level of the superior mesenteric artery, not the inferior mesenteric artery. - The inferior mesenteric artery originates much lower on the aorta compared to the renal vein's crossing point. Posterior, below the Superior mesenteric artery - The renal vein is consistently located anterior to the aorta, not posterior. [1] - A posterior relationship would be structurally incorrect for the renal venous drainage into the inferior vena cava.
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