Laminar vs. turbulent flow US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Laminar vs. turbulent flow. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Laminar vs. turbulent flow US Medical PG Question 1: Which of the following physiologic changes decreases pulmonary vascular resistance (PVR)?
- A. Inhaling the inspiratory reserve volume (IRV)
- B. Exhaling the entire vital capacity (VC)
- C. Exhaling the expiratory reserve volume (ERV)
- D. Breath holding maneuver at functional residual capacity (FRC)
- E. Inhaling the entire vital capacity (VC) (Correct Answer)
Laminar vs. turbulent flow Explanation: ***Inhaling the entire vital capacity (VC)***
- As lung volume increases from FRC to TLC (which includes inhaling the entire VC), alveolar vessels are **stretched open**, and extra-alveolar vessels are **pulled open** by the increased radial traction, leading to a decrease in PVR.
- This **maximizes the cross-sectional area** of the pulmonary vascular bed, lowering resistance.
*Inhaling the inspiratory reserve volume (IRV)*
- While inhaling IRV increases lung volume, it's not the maximal inspiration of the entire VC where **PVR is typically at its lowest**.
- PVR continues to decrease as lung volume approaches total lung capacity (TLC).
*Exhaling the entire vital capacity (VC)*
- Exhaling the entire vital capacity leads to very low lung volumes, where PVR significantly **increases**.
- At low lung volumes, **alveolar vessels become compressed** and extra-alveolar vessels **narrow**, increasing resistance.
*Exhaling the expiratory reserve volume (ERV)*
- Exhaling the ERV results in a lung volume below FRC, which causes a **marked increase in PVR**.
- This is due to the **compression of alveolar vessels** and decreased radial traction on extra-alveolar vessels.
*Breath holding maneuver at functional residual capacity (FRC)*
- At FRC, the PVR is at an **intermediate level**, not its lowest.
- This is the point where the opposing forces affecting alveolar and extra-alveolar vessels are somewhat balanced, but not optimized for minimal resistance.
Laminar vs. turbulent flow US Medical PG Question 2: A 57-year-old man with a history of coronary artery disease has been brought to the emergency department due to the sudden onset of chest pain. He was diagnosed with hypertension 12 years ago and takes enalapril regularly. The patient is hypotensive to 70/42 mm Hg, and on further examination his skin is cold and clammy. He is diagnosed with a life-threatening condition that resulted from inadequate circulation of blood, with decreased cardiac output and high pulmonary capillary wedge pressure. Which of the conditions below can cause the same disorder?
I. Acute myocardial infarction
II. Atrial fibrillation
III. Hemorrhage
IV. Valvular stenosis
V. Pulmonary embolism
VI. Sepsis
- A. I, II, IV (Correct Answer)
- B. I, II, IV, V
- C. I, IV, VI
- D. I, II, III
- E. I, IV, V
Laminar vs. turbulent flow Explanation: ***I, II, IV (Acute myocardial infarction, Atrial fibrillation, Valvular stenosis)***
- The patient's presentation with **hypotension**, **cold and clammy skin**, **decreased cardiac output**, and **high pulmonary capillary wedge pressure** is characteristic of **cardiogenic shock**.
- **Acute myocardial infarction** causes cardiogenic shock through direct myocardial damage and pump failure, leading to elevated left ventricular filling pressures and high PCWP.
- **Atrial fibrillation** can cause cardiogenic shock through loss of atrial kick (reducing CO by 20-30%), rapid ventricular rates impairing diastolic filling, and tachycardia-induced cardiomyopathy—all resulting in pump failure with elevated PCWP.
- Severe **valvular stenosis** (aortic or mitral) causes cardiogenic shock by obstructing cardiac output and causing backward transmission of pressure, resulting in elevated PCWP.
*I, II, IV, V*
- This option incorrectly includes **pulmonary embolism** as a cause of cardiogenic shock with **high pulmonary capillary wedge pressure**.
- While pulmonary embolism causes profound hypotension and shock, it produces **obstructive shock** with **low or normal PCWP** due to right ventricular outflow obstruction and right heart failure, not left heart pump failure.
*I, IV, VI*
- This option incorrectly includes **sepsis** and excludes **atrial fibrillation**.
- **Sepsis** causes **distributive shock** characterized by **low systemic vascular resistance** and typically **low or normal PCWP** initially, though late septic cardiomyopathy can occur, it does not present with the classic high PCWP pattern described.
*I, II, III*
- This option incorrectly includes **hemorrhage** as a cause of cardiogenic shock.
- **Hemorrhage** causes **hypovolemic shock** with **low cardiac output** due to reduced preload and **low PCWP**, not the high PCWP characteristic of cardiogenic shock.
*I, IV, V*
- This option incorrectly includes **pulmonary embolism** and excludes **atrial fibrillation**.
- **Pulmonary embolism** causes **obstructive shock** with right ventricular dysfunction and **low or normal PCWP**, not the elevated PCWP seen in cardiogenic shock from left heart pump failure.
Laminar vs. turbulent flow US Medical PG Question 3: An 83-year-old male presents with dyspnea, orthopnea, and a chest radiograph demonstrating pulmonary edema. A diagnosis of congestive heart failure is considered. The following clinical measurements are obtained: 100 bpm heart rate, 0.2 mL O2/mL systemic blood arterial oxygen content, 0.1 mL O2/mL pulmonary arterial oxygen content, and 400 mL O2/min oxygen consumption. Using the above information, which of the following values represents this patient's cardiac stroke volume?
- A. 30 mL/beat
- B. 70 mL/beat
- C. 40 mL/beat (Correct Answer)
- D. 60 mL/beat
- E. 50 mL/beat
Laminar vs. turbulent flow Explanation: ***40 mL/beat***
- First, calculate cardiac output (CO) using the **Fick principle**: CO = Oxygen Consumption / (Arterial O2 content - Venous O2 content). Here, CO = 400 mL O2/min / (0.2 mL O2/mL - 0.1 mL O2/mL) = 400 mL O2/min / 0.1 mL O2/mL = **4000 mL/min**.
- Next, calculate stroke volume (SV) using the formula: SV = CO / Heart Rate. Given a heart rate of 100 bpm, SV = 4000 mL/min / 100 beats/min = **40 mL/beat**.
*30 mL/beat*
- This answer would result if there was an error in calculating either the **cardiac output** or if the **arteriovenous oxygen difference** was overestimated.
- A stroke volume of 30 mL/beat with a heart rate of 100 bpm would yield a cardiac output of 3 L/min, which is sub-physiologic for an oxygen consumption of 400 mL/min given the provided oxygen content values.
*70 mL/beat*
- This stroke volume is higher than calculated and would imply either a significantly **lower heart rate** or a much **higher cardiac output** than derived from the Fick principle with the given values.
- A stroke volume of 70 mL/beat at a heart rate of 100 bpm would mean a cardiac output of 7 L/min, which is inconsistent with the provided oxygen consumption and arteriovenous oxygen difference.
*60 mL/beat*
- This value is higher than the correct calculation, suggesting an error in the initial calculation of **cardiac output** or the **avO2 difference**.
- To get 60 mL/beat, the cardiac output would need to be 6000 mL/min, which would mean an avO2 difference of 0.067 mL O2/mL, not 0.1 mL O2/mL.
*50 mL/beat*
- This stroke volume would result from an incorrect calculation of the **cardiac output**, potentially from a slight miscalculation of the **arteriovenous oxygen difference**.
- A stroke volume of 50 mL/beat at 100 bpm would mean a cardiac output of 5 L/min, requiring an avO2 difference of 0.08 mL O2/mL, which is not consistent with the given values.
Laminar vs. turbulent flow US Medical PG Question 4: A 60-year-old male engineer who complains of shortness of breath when walking a few blocks undergoes a cardiac stress test because of concern for coronary artery disease. During the test he asks his cardiologist about what variables are usually used to quantify the functioning of the heart. He learns that one of these variables is stroke volume. Which of the following scenarios would be most likely to lead to a decrease in stroke volume?
- A. Anxiety
- B. Heart failure (Correct Answer)
- C. Exercise
- D. Pregnancy
- E. Digitalis
Laminar vs. turbulent flow Explanation: ***Heart failure***
- In **heart failure**, the heart's pumping ability is impaired, leading to a reduced **ejection fraction** and thus a decreased **stroke volume**.
- The weakened myocardium cannot effectively contract to expel the normal volume of blood, resulting in lower blood output per beat.
*Anxiety*
- **Anxiety** typically causes an increase in **sympathetic nervous system** activity, leading to increased heart rate and myocardial contractility.
- This often results in a temporary **increase in stroke volume** due to enhanced cardiac performance, not a decrease.
*Exercise*
- During **exercise**, there is a significant **increase in venous return** and sympathetic stimulation, leading to increased **end-diastolic volume** and contractility.
- This physiological response causes a substantial **increase in stroke volume** to meet the body's higher oxygen demands.
*Pregnancy*
- **Pregnancy** leads to significant **physiological adaptations** to accommodate the growing fetus, including a substantial increase in **blood volume**.
- This increased blood volume and cardiac output result in an **increase in stroke volume** to maintain adequate perfusion for both mother and fetus.
*Digitalis*
- **Digitalis** is a cardiac glycoside that **increases intracellular calcium** in myocardial cells, enhancing the **force of contraction**.
- This positive inotropic effect leads to an **increased stroke volume** by improving the heart's pumping efficiency.
Laminar vs. turbulent flow US Medical PG Question 5: A 69-year-old woman is admitted to the hospital with substernal, crushing chest pain. She is emergently moved to the cardiac catheterization lab where she undergoes cardiac angiography. Angiography reveals that the diameter of her left anterior descending artery (LAD) is 50% of normal. If her blood pressure, LAD length, and blood viscosity have not changed, which of the following represents the most likely change in LAD flow from baseline?
- A. Decreased by 93.75% (Correct Answer)
- B. Increased by 6.25%
- C. Decreased by 25%
- D. Decreased by 87.5%
- E. Increased by 25%
Laminar vs. turbulent flow Explanation: ***Decreased by 93.75%***
- This option is correct based on Poiseuille's Law, which states that flow is proportional to the **fourth power of the radius (r^4)**. A 50% decrease in diameter means a 50% decrease in radius (0.5r).
- The new flow would be (0.5)^4 = 0.0625 times the original flow. Therefore, the decrease in flow is 1 - 0.0625 = 0.9375, or **93.75%**.
*Increased by 6.25%*
- This answer incorrectly suggests an **increase** in flow, which is contrary to the effect of a narrowed artery.
- While 6.25% represents the new flow as a percentage of baseline (since 0.0625 = 6.25%), the vessel stenosis causes a **decrease**, not an increase in flow.
*Decreased by 25%*
- This calculation might arise from considering a linear relationship (e.g., radius decreases by 50%, so flow decreases by 50% of 50%, which is incorrect).
- It does not account for the **fourth power relationship** between radius and flow according to Poiseuille's Law.
*Decreased by 87.5%*
- This percentage represents a calculation error, likely from misapplying the fourth power relationship or confusing the calculation steps.
- It does not accurately reflect the dramatic reduction in flow caused by a 50% reduction in vessel diameter.
*Increased by 25%*
- This option implies a significant increase in blood flow, which would not happen with a **stenosed artery**.
- It completely contradicts the physiological response to a **narrowed vessel**.
Laminar vs. turbulent flow US Medical PG Question 6: A 72-year-old man arrives at the emergency department 30 minutes after developing rapid onset right-sided weakness and decreased sensation on the right side of his body. The patient’s wife also reports that he has had difficulty forming sentences. His wife adds that these symptoms were at their maximum within a few minutes of the incident and began to resolve almost instantaneously. The patient says he had a related episode of painless visual loss in his left eye that resolved after about 10–20 minutes about 3 months ago. His past medical history includes diabetes mellitus type 2 and essential hypertension. The patient reports a 50 pack-year smoking history. His blood pressure is 140/60 mm Hg, and his temperature is 36.5°C (97.7°F). Neurological examination is significant for a subtle weakness of the right hand. A noncontrast CT scan of the head is unremarkable, and a carotid Doppler ultrasound shows 10% stenosis of the right internal carotid artery and 50% stenosis of the left internal carotid artery. Which of the following is the expected change in resistance to blood flow through the stenotic artery most likely responsible for this patient’s current symptoms?
- A. It will double
- B. No change
- C. It will be 8 times greater
- D. It will be 4 times greater
- E. It will be 16 times greater (Correct Answer)
Laminar vs. turbulent flow Explanation: ***It will be 16 times greater***
- According to **Poiseuille's law**, resistance to blood flow is inversely proportional to the fourth power of the radius (R ∝ 1/r⁴).
- In vascular medicine, **50% stenosis** refers to a 50% reduction in the vessel **diameter**, which also means the radius is reduced by 50% (halved).
- When the radius is halved, resistance increases by a factor of (1/0.5)⁴ = 2⁴ = **16 times**.
- The **left internal carotid artery** with 50% stenosis is responsible for the patient's symptoms (right-sided weakness and aphasia indicate left hemisphere pathology).
*It will be 8 times greater*
- This would occur if the radius were reduced to approximately 63% of its original size (1/0.63⁴ ≈ 8).
- This does not correspond to a 50% stenosis.
*It will double*
- A doubling of resistance would occur if the radius were reduced by approximately 16% (to 84% of original).
- This represents much less severe stenosis than described in this case.
*It will be 4 times greater*
- A four-fold increase would result from reducing the radius by approximately 29% (to 71% of original).
- This would correspond to approximately 30% stenosis by diameter, not 50%.
*No change*
- Any degree of **stenosis** reduces the vessel radius and significantly increases resistance according to Poiseuille's law.
- A 50% stenosis causing a 16-fold increase in resistance can critically reduce blood flow, especially during periods of increased demand or reduced perfusion pressure, leading to **TIA** symptoms as seen in this patient.
Laminar vs. turbulent flow US Medical PG Question 7: A 72-year-old woman presents to the emergency department for vision loss. She was reading a magazine this afternoon when she started having trouble seeing out of her left eye. Her vision in that eye got progressively darker, eventually becoming completely black over the course of a few minutes. It then returned to normal after about 10 minutes; she reports she can see normally now. She had no pain and no other symptoms then or now. Past medical history is notable for hypertension and hyperlipidemia. A high-pitched sound is heard when the diaphragm of the stethoscope is placed on her left neck, but her physical exam is otherwise unremarkable; vision is currently 20/30 bilaterally. The etiology of her symptoms most likely localizes to which of the following anatomic locations?
- A. Left atrium
- B. Subclavian artery
- C. Temporal artery
- D. Carotid artery (Correct Answer)
- E. Vertebral artery
Laminar vs. turbulent flow Explanation: ***Carotid artery***
- The sudden, temporary vision loss (amaurosis fugax) in one eye, described as a "curtain coming down," is a classic symptom of an **embolus originating from the ipsilateral carotid artery**.
- The **bruit** heard in the left neck further points to significant **carotid artery stenosis**, which can be a source of these emboli to the **ophthalmic artery**.
*Left atrium*
- An embolus from the left atrium (e.g., in atrial fibrillation) would typically cause symptoms of a **cerebral stroke** or vision loss in **both eyes** if it affects a major supplying vessel before the intracranial branches, or could affect the carotid artery system, but the neck bruit directly implicates the carotid.
- While a source of emboli, the direct finding of a neck bruit makes the carotid the more immediate and specific localization.
*Subclavian artery*
- **Subclavian artery** stenosis can cause **subclavian steal syndrome**, leading to vertebrobasilar insufficiency and symptoms like **dizziness** or **syncope**, but generally does not cause unilateral amaurosis fugax.
- Its territory primarily supplies the arm and posterior circulation, not the anterior cerebral circulation or ophthalmic artery directly as suggested by amaurosis fugax.
*Temporal artery*
- **Temporal arteritis** (Giant Cell Arteritis) can cause sudden vision loss, often irreversible, and is usually associated with **headaches**, **jaw claudication**, and a very high **ESR**, none of which are reported here.
- While it affects the ophthalmic artery, the absence of pain and the transient nature of the vision loss (amaurosis fugax) make it less likely than an embolic event.
*Vertebral artery*
- The **vertebral arteries** supply the **posterior circulation** of the brain, leading to symptoms such as **diplopia**, **vertigo**, **ataxia**, or **hemiparesis**, but not isolated unilateral amaurosis fugax.
- Problems in this artery typically manifest as **vertebrobasilar insufficiency**, which affects both eyes or causes other brainstem symptoms, not transient unilateral blindness.
Laminar vs. turbulent flow US Medical PG Question 8: A 29-year-old man presents to his primary care provider complaining of testicular pain. He reports a four-day history of dull chronic pain in his left testicle that is worse with standing. His past medical history is notable for asthma and major depressive disorder. He takes inhaled albuterol as needed and sertraline. He is sexually active with a single female partner and always uses barrier protection. His temperature is 99.2°F (37.3°C), blood pressure is 125/75 mmHg, pulse is 85/min, and respirations are 17/min. Physical examination reveals a non-tender twisted mass along the left spermatic cord that disappears when the patient lies supine. This patient’s condition most likely stems from decreased laminar flow at which of the following vascular junctions?
- A. Descending aorta – Left testicular artery
- B. Left testicular vein – Left suprarenal vein
- C. Left testicular vein – Inferior vena cava
- D. Left testicular vein – Left renal vein (Correct Answer)
- E. Left testicular vein – Left internal iliac vein
Laminar vs. turbulent flow Explanation: ***Left testicular vein – Left renal vein***
- This clinical presentation of a **nontender, twisted mass along the spermatic cord** that disappears when supine is classic for a **varicocele**. Varicoceles are more common on the left side due to the **anatomic drainage of the left testicular vein** into the left renal vein at a **perpendicular angle**.
- This perpendicular angle, along with the **increased length of the left testicular vein** and its drainage into the higher-pressure left renal vein, creates conditions for **increased hydrostatic pressure** and **decreased laminar flow**, leading to venous engorgement and varicocele formation.
*Descending aorta – Left testicular artery*
- This junction involves an **artery**, not a vein. Varicoceles are caused by **venous insufficiency and dilatation**, not arterial issues.
- The left testicular artery branches directly from the aorta and supplies blood to the testicle; problems with this junction would typically manifest as **ischemia or arterial insufficiency**, not venous congestion.
*Left testicular vein – Left suprarenal vein*
- While the left suprarenal vein also drains into the left renal vein, the **left testicular vein does not directly connect to the left suprarenal vein**.
- This junction is not anatomically relevant to the direct drainage pathway causing a varicocele.
*Left testicular vein – Inferior vena cava*
- The **right testicular vein drains directly into the inferior vena cava**, explaining why varicoceles are less common on the right side.
- The left testicular vein typically drains into the left renal vein, not directly into the inferior vena cava.
*Left testicular vein – Left internal iliac vein*
- The **left internal iliac vein primarily drains pelvic structures** and has no direct anatomical connection or primary drainage role for the left testicular vein.
- The testicular veins follow a retroperitoneal course and do not typically involve the internal iliac venous system in their main drainage.
Laminar vs. turbulent flow US Medical PG Question 9: A 31-year-old female with a history of anxiety has a panic attack marked by dizziness, weakness, and blurred vision. Which of the following most likely accounts for the patient’s symptoms?
- A. Oxygen toxicity
- B. Increased arterial CO2
- C. Carotid artery obstruction
- D. Decreased cerebral blood flow (Correct Answer)
- E. Decreased respiratory rate
Laminar vs. turbulent flow Explanation: ***Decreased cerebral blood flow***
- During a panic attack, **hyperventilation** leads to a drop in arterial CO2, causing **cerebral vasoconstriction** and reduced blood flow to the brain.
- This reduction in cerebral blood flow manifests as neurological symptoms like **dizziness, blurred vision, and weakness**.
*Oxygen toxicity*
- This typically occurs with exposure to **high partial pressures of oxygen**, often in diving or hyperbaric oxygen therapy.
- Symptoms include **seizures, visual changes, and nausea**; it is not associated with panic attacks or their physiological responses.
*Increased arterial CO2*
- Panic attacks involve **hyperventilation**, which causes a decrease, not an increase, in arterial CO2 (hypocapnia).
- Increased arterial CO2 (hypercapnia) usually leads to **vasodilation**, which would increase cerebral blood flow rather than decrease it.
*Carotid artery obstruction*
- This condition involves a physical blockage in the carotid arteries, reducing blood flow to the brain, which can cause symptoms similar to those described.
- However, such an obstruction is a **structural problem** and not an acute physiological response to a panic attack in a young patient without other risk factors.
*Decreased respiratory rate*
- Panic attacks are characterized by **hyperventilation**, meaning an increased respiratory rate and depth, not a decreased one.
- A decreased respiratory rate would lead to an **increase in arterial CO2**, which is contrary to the physiological changes seen in a panic attack.
Laminar vs. turbulent flow US Medical PG Question 10: An otherwise healthy 65-year-old man comes to the physician for a follow-up visit for elevated blood pressure. Three weeks ago, his blood pressure was 160/80 mmHg. Subsequent home blood pressure measurements at days 5, 10, and 15 found: 165/75 mm Hg, 162/82 mm Hg, and 170/80 mmHg, respectively. He had a cold that was treated with over-the-counter medication 4 weeks ago. Pulse is 72/min and blood pressure is 165/79 mm Hg. Physical examination shows no abnormalities. Laboratory studies, including thyroid function studies, serum electrolytes, and serum creatinine, are within normal limits. Which of the following is the most likely underlying cause of this patient's elevated blood pressure?
- A. Decrease in arterial compliance (Correct Answer)
- B. Increase in left ventricular end-diastolic volume
- C. Increase in aldosterone production
- D. Decrease in baroreceptor sensitivity
- E. Medication-induced vasoconstriction
Laminar vs. turbulent flow Explanation: ***Decrease in arterial compliance***
- In elderly patients, **systolic hypertension** (isolated or combined) is commonly caused by **stiffening of the large arteries** (aorta and its major branches), which is a decrease in **arterial compliance**. This leads to a higher systolic pressure needed to eject blood into the stiffened vessels.
- The patient's age (65), persistent elevated systolic blood pressure readings with relatively normal diastolic pressure (though slightly elevated), and the absence of other obvious causes point towards **age-related arterial stiffness**.
*Increase in left ventricular end-diastolic volume*
- An increase in **left ventricular end-diastolic volume (LVEDV)** typically increases **preload** and **cardiac output**, which can contribute to hypertension.
- However, primary hypertension in older adults is more directly linked to **arterial stiffness**, which impacts systolic pressure more profoundly than changes in LVEDV alone.
*Increase in aldosterone production*
- Increased **aldosterone production** (primary hyperaldosteronism) causes hypertension primarily by increasing **sodium and water retention**, leading to **volume expansion** and often accompanied by **hypokalemia**.
- This patient has **normal serum electrolytes**, making primary hyperaldosteronism less likely as the primary cause of his hypertension.
*Decrease in baroreceptor sensitivity*
- A decrease in **baroreceptor sensitivity** can contribute to **blood pressure lability** and impaired compensatory responses to postural changes, but it is not the primary underlying mechanism for sustained, consistently elevated systolic blood pressure in essential hypertension in the elderly.
- While age can affect baroreceptor function, **arterial stiffness** is a more direct cause of the observed systolic hypertension.
*Medication-induced vasoconstriction*
- Some over-the-counter medications, particularly **decongestants** (e.g., pseudoephedrine), can cause **vasoconstriction** and elevate blood pressure.
- However, the patient's cold was 4 weeks ago, and his current symptoms and blood pressure elevations are sustained and occurred *after* the cold resolved and with normal examination, suggesting a more chronic rather than acute medication-induced effect.
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