Airway resistance determinants US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Airway resistance determinants. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Airway resistance determinants US Medical PG Question 1: A 13-year-old boy with a history of asthma and seasonal allergies is currently using albuterol to manage his asthma symptoms. Recently, his use of albuterol increased from 1–2 days/week to 4 times/week over the past several weeks, though he does not experience his symptoms daily. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 74/min, and respiratory rate 14/min. His physical examination shows clear, bilateral breath sounds and normal heart sounds. What change should be made to his current treatment regimen?
- A. Add tiotropium
- B. Add formoterol + budesonide twice daily
- C. Add montelukast 5 mg daily
- D. Add fluticasone daily (Correct Answer)
- E. Add salmeterol twice daily
Airway resistance determinants Explanation: ***Add fluticasone daily***
- This patient currently has **mild persistent asthma** based on his increased albuterol use (4 times/week, but not daily). The guideline-recommended step-up for mild persistent asthma is the daily addition of a **low-dose inhaled corticosteroid (ICS)** like fluticasone.
- Adding fluticasone daily addresses the underlying inflammation of asthma, reducing symptoms and the need for frequent albuterol rescue inhaler use.
*Add tiotropium*
- Tiotropium, a **long-acting muscarinic antagonist (LAMA)**, is primarily used for asthma as an add-on therapy for patients whose symptoms are not well-controlled with ICS and long-acting beta-2 agonists (LABAs).
- It is not a first-line agent for initiating controller therapy in mild persistent asthma.
*Add formoterol + budesonide twice daily*
- This combination, a **LABA/ICS**, is indicated for moderate to severe persistent asthma, not mild persistent asthma, or can be used as a reliever in older children/adults with mild asthma (SMART therapy).
- Prescribing it twice daily would be an over-treatment for this patient's current asthma severity.
*Add montelukast 5 mg daily*
- Montelukast, a **leukotriene receptor antagonist**, is an alternative for mild persistent asthma, but **ICS are generally preferred** due to superior efficacy in controlling inflammation.
- While it could be considered, fluticasone (an ICS) is a more effective first-line option for controller therapy in mild persistent asthma.
*Add salmeterol twice daily*
- Salmeterol is a **long-acting beta-2 agonist (LABA)** that should never be used as monotherapy in asthma due to the risk of severe exacerbations and asthma-related death.
- LABAs should always be used in combination with an **inhaled corticosteroid (ICS)**.
Airway resistance determinants US Medical PG Question 2: A 24-year-old male with cystic fibrosis is brought to the emergency room by his mother after he had difficulty breathing. He previously received a lung transplant 6 months ago and was able to recover quickly from the operation. He is compliant with all of his medications and had been doing well with no major complaints until 2 weeks ago when he began to experience shortness of breath. Exam reveals a decreased FEV1/FVC ratio and biopsy reveals lymphocytic infiltration. Which of the following components is present in the airway zone characteristically affected by the most likely cause of this patient's symptoms?
- A. Pseudostratified columnar cells
- B. Goblet cells
- C. Simple cuboidal cells (Correct Answer)
- D. Stratified cuboidal cells
- E. Cartilage
Airway resistance determinants Explanation: ***Simple cuboidal cells***
- The patient's symptoms, history of a lung transplant, and biopsy findings of **lymphocytic infiltration** suggest **bronchiolitis obliterans**, a form of chronic lung allograft dysfunction.
- Bronchiolitis obliterans primarily affects the **small airways** (bronchioles), which are characterized by an epithelial lining of **simple cuboidal cells** and lack cartilage.
*Pseudostratified columnar cells*
- These cells line the **trachea** and **main bronchi** (larger airways), which are typically not the primary site of damage in bronchiolitis obliterans.
- They are part of the **mucociliary escalator** and are also associated with cartilage.
*Goblet cells*
- While present in the **larger airways** along with pseudostratified columnar cells, goblet cells are less prominent or absent in the small bronchioles primarily affected by bronchiolitis obliterans.
- Their characteristic function is mucus production, not the specific epithelial type of the affected bronchioles.
*Stratified cuboidal cells*
- This cell type is **rare** in the respiratory tract and is not characteristic of the small airways affected by bronchiolitis obliterans.
- Stratified epithelia are typically seen in ducts of glands or specialized transitional zones, not the functional bronchioles.
*Cartilage*
- Cartilage provides structural support to the **trachea and main bronchi**, but it is **absent** in the small airways (bronchioles) that are the primary target of bronchiolitis obliterans.
- The presence of cartilage would indicate a larger airway, contradicting the pathophysiology of this condition.
Airway resistance determinants US Medical PG Question 3: A 26-year-old woman comes to the emergency room because she had difficulty breathing during an exercise session. She also has a cough and end-expiratory wheezing. Besides these symptoms, she has a normal physical appearance. She has experienced similar breathing problems during exercise in the past, but never during rest. She is afebrile. What is the best treatment in this case?
- A. Systemic corticosteroids
- B. No therapy, only avoidance of exercise
- C. Short acting β2-agonists (Correct Answer)
- D. Aminophylline
- E. Long acting β2-agonists
Airway resistance determinants Explanation: ***Short acting β2-agonists***
- The patient presents with classic symptoms of **exercise-induced bronchoconstriction (EIB)**, including dyspnea, cough, and wheezing during exercise.
- **Short-acting β2-agonists (SABAs)** like albuterol are the first-line treatment for EIB, providing rapid bronchodilation and symptom relief when used before exercise.
*Systemic corticosteroids*
- **Systemic corticosteroids** are potent anti-inflammatory agents used for severe or persistent asthma exacerbations, but they are not indicated for acute management of mild to moderate EIB.
- Long-term use of systemic corticosteroids carries significant side effects, making them unsuitable for routine pre-exercise use.
*No therapy, only avoidance of exercise*
- While avoiding exercise would prevent symptoms, it is not a practical or desirable solution for a generally healthy 26-year-old woman.
- Effective pharmacologic options exist to allow patients with EIB to continue exercising safely.
*Aminophylline*
- **Aminophylline** is a methylxanthine that acts as a bronchodilator but has a narrow therapeutic index and significant side effects, making it a less preferred option than SABAs for EIB.
- Its use is typically reserved for severe, refractory asthma and not for acute, exercise-induced symptoms.
*Long acting β2-agonists*
- **Long-acting β2-agonists (LABAs)** are used for daily control of persistent asthma, often in combination with inhaled corticosteroids.
- While they can provide sustained bronchodilation, they are not ideal for acute, on-demand relief for EIB due to their slower onset of action compared to SABAs.
Airway resistance determinants US Medical PG Question 4: A researcher is studying receptors that respond to epinephrine in the body and discovers a particular subset that is expressed in presynaptic adrenergic nerve terminals. She discovers that upon activation, these receptors will lead to decreased sympathetic nervous system activity. She then studies the intracellular second messenger changes that occur when this receptor is activated. She records these changes and begins searching for analogous receptor pathways. Which of the following receptors would cause the most similar set of intracellular second messenger changes?
- A. Muscarinic cholinoreceptors in the gastrointestinal tract
- B. Growth hormone receptors in the musculoskeletal system
- C. Vasopressin receptors in the kidney
- D. Dopamine receptors in the brain (Correct Answer)
- E. Aldosterone receptors in the kidney
Airway resistance determinants Explanation: ***Dopamine receptors in the brain***
- The described presynaptic receptors for epinephrine that decrease sympathetic activity are **alpha-2 adrenergic receptors**, which are **G inhibitory protein (Gi)-coupled receptors**.
- Gi-coupled receptors **inhibit adenylyl cyclase**, leading to a **decrease in intracellular cAMP**, a signaling pathway shared by **D2 dopamine receptors**.
*Muscarinic cholinoreceptors in the gastrointestinal tract*
- Most muscarinic receptors (M1 and M3) in the GI tract are **Gq-coupled**, leading to an **increase in phospholipase C (PLC) activity**, ultimately increasing intracellular **IP3 and DAG** and promoting smooth muscle contraction.
- This mechanism is distinct from the **Gi-mediated inhibition of cAMP** described for the presynaptic adrenergic receptor.
*Growth hormone receptors in the musculoskeletal system*
- Growth hormone receptors are **tyrosine kinase-associated receptors** (specifically, they are linked to **JAK/STAT pathways**), not G protein-coupled receptors.
- Their intracellular signaling involves **protein phosphorylation cascades**, which are fundamentally different from second messenger changes involving cAMP.
*Vasopressin receptors in the kidney*
- Vasopressin (ADH) acts on **V2 receptors** in the kidney, which are **G stimulatory protein (Gs)-coupled receptors**.
- Activation of V2 receptors leads to an **increase in adenylyl cyclase activity** and thus an **increase in intracellular cAMP**, the opposite effect of the described Gi-coupled receptor.
*Aldosterone receptors in the kidney*
- Aldosterone receptors are **intracellular steroid hormone receptors** that directly bind to DNA and regulate gene transcription.
- They do not engage in rapid intracellular second messenger changes like G protein-coupled receptors, but rather alter **protein synthesis** over hours to days.
Airway resistance determinants US Medical PG Question 5: Which neurotransmitter is primarily responsible for parasympathetic effects on heart rate?
- A. Norepinephrine
- B. Dopamine
- C. Acetylcholine (Correct Answer)
- D. Epinephrine
Airway resistance determinants Explanation: ***Acetylcholine***
- **Acetylcholine** is the primary neurotransmitter released by postganglionic parasympathetic neurons.
- It acts on **muscarinic receptors** (M2 receptors) in the heart to decrease heart rate.
*Norepinephrine*
- **Norepinephrine** is primarily associated with the **sympathetic nervous system**, increasing heart rate and contractility.
- It acts on **beta-1 adrenergic receptors** in the heart.
*Dopamine*
- **Dopamine** is a precursor to norepinephrine and epinephrine, and primarily functions as a neurotransmitter in the **central nervous system** and in regulating renal blood flow.
- While it can have cardiac effects, it is not the primary neurotransmitter for parasympathetic actions on heart rate.
*Epinephrine*
- **Epinephrine** (adrenaline) is a hormone released by the adrenal medulla and a neurotransmitter in the sympathetic nervous system, causing an **increase in heart rate** and contractility.
- It works through **beta-1 adrenergic receptors**, antagonistic to parasympathetic effects.
Airway resistance determinants US Medical PG Question 6: A 7-year-old boy with asthma is brought to the physician because of a 1-month history of worsening shortness of breath and cough. The mother reports that the shortness of breath usually occurs when he is exercising with his older brother. His only medication is an albuterol inhaler that is taken as needed. The physician considers adding zafirlukast to his drug regimen. Which of the following is the most likely mechanism of action of this drug?
- A. Antagonism at muscarinic receptors
- B. Blockade of 5-lipoxygenase pathway
- C. Inhibition of mast cell degranulation
- D. Inhibition of phosphodiesterase
- E. Antagonism at leukotriene receptors (Correct Answer)
Airway resistance determinants Explanation: ***Antagonism at leukotriene receptors***
- **Zafirlukast** is a **leukotriene receptor antagonist** (LTRA) that blocks the action of leukotrienes at their CysLT1 receptors.
- This action helps to reduce **bronchoconstriction**, airway edema, and inflammation, which are key features of asthma pathophysiology.
*Antagonism at muscarinic receptors*
- This is the mechanism of action for **anticholinergic bronchodilators** like **ipratropium** or **tiotropium**, which are not **zafirlukast**.
- These drugs primarily prevent **acetylcholine-induced bronchoconstriction** but do not target the leukotriene pathway.
*Blockade of 5-lipoxygenase pathway*
- This is the mechanism of **zileuton**, a **leukotriene synthesis inhibitor**, which prevents the formation of all leukotrienes.
- While it targets leukotrienes, it is distinct from **receptor antagonism**, which is how **zafirlukast** works.
*Inhibition of mast cell degranulation*
- This is the mechanism of **mast cell stabilizers** such as **cromolyn sodium** or **nedocromil**, which prevent the release of inflammatory mediators.
- This action differs from the direct receptor blockade provided by **zafirlukast**.
*Inhibition of phosphodiesterase*
- This is the mechanism of **methylxanthines** like **theophylline**, which increase intracellular cAMP and lead to **bronchodilation**.
- This is a distinct pharmacological class and mechanism from **zafirlukast**.
Airway resistance determinants US Medical PG Question 7: A 21-year-old lacrosse player comes to the doctor for an annual health assessment. She does not smoke or drink alcohol. She is 160 cm (5 ft 3 in) tall and weighs 57 kg (125 lb); BMI is 22 kg/m2. Pulmonary function tests show an FEV1 of 90% and an FVC of 3600 mL. Whole body plethysmography is performed to measure airway resistance. Which of the following structures of the respiratory tree is likely to have the highest contribution to total airway resistance?
- A. Conducting bronchioles
- B. Terminal bronchioles
- C. Segmental bronchi (Correct Answer)
- D. Respiratory bronchioles
- E. Mainstem bronchi
Airway resistance determinants Explanation: ***Segmental bronchi***
- In healthy individuals, **medium-sized bronchi** (including segmental and subsegmental bronchi, approximately generations 4-8) contribute approximately **80% of total airway resistance**.
- While **Poiseuille's Law** states resistance is inversely proportional to radius to the fourth power (R ∝ 1/r⁴), the key factor is the **total cross-sectional area** and **degree of branching**.
- Medium-sized bronchi have moderate individual resistance and **limited parallel branching**, making them the dominant site of resistance.
- This is why diseases affecting medium-sized airways (e.g., asthma, bronchitis) cause significant increases in airway resistance.
*Terminal bronchioles*
- Although individual terminal bronchioles have small radii and high individual resistance, there are **millions of them arranged in parallel**.
- With parallel resistances, total resistance decreases: 1/R_total = 1/R₁ + 1/R₂ + 1/R₃...
- The **massive number** of small airways means their collective resistance is actually quite **low** (~10-20% of total).
- This is why small airways disease is called the "**silent zone**" - significant pathology can occur before detection.
*Conducting bronchioles*
- These airways also benefit from extensive **parallel branching**, reducing their contribution to total resistance.
- They contribute less than medium-sized bronchi due to their large cumulative cross-sectional area.
*Respiratory bronchioles*
- Part of the **respiratory zone** with the largest total cross-sectional area in the lungs.
- Minimal contribution to airway resistance due to enormous parallel arrangement.
- Primary function is **gas exchange**, not air conduction.
*Mainstem bronchi*
- These large airways have **low individual resistance** due to large diameter.
- Together with the trachea, they contribute approximately **20% of total airway resistance**.
- Not the primary site despite being early in the airway tree.
Airway resistance determinants US Medical PG Question 8: A 60-year-old woman with a history of emphysema has been referred by her pulmonologist for follow-up pulmonary function testing. During the test, the patient reaches a point where her airway pressure is equal to the atmospheric pressure. Which of the following is most likely to be found during this respiratory state?
- A. Pulmonary vascular resistance is at a maximum
- B. Transmural pressure of the lung-chest wall system is at a maximum
- C. Transmural pressure of the chest wall is at a minimum
- D. Pulmonary vascular resistance is at a minimum (Correct Answer)
- E. Transmural pressure of the lung-chest wall system is at a minimum
Airway resistance determinants Explanation: ***Pulmonary vascular resistance is at a minimum***
- When airway pressure equals atmospheric pressure during a pulmonary function test, the lungs are at **functional residual capacity (FRC)** or resting state.
- At FRC, **pulmonary vascular resistance (PVR)** is at its lowest point due to the optimal balance between alveolar and extra-alveolar vessel compression/distension.
- Extra-alveolar vessels are compressed at low lung volumes, while alveolar vessels are compressed at high lung volumes. At FRC, both are optimally distended, resulting in **minimal PVR**.
*Pulmonary vascular resistance is at a maximum*
- PVR increases at very low lung volumes (due to extra-alveolar vessel compression) and very high lung volumes (due to alveolar vessel compression).
- The resting state (airway pressure equals atmospheric pressure) corresponds to FRC, where PVR is **minimal, not maximal**.
*Transmural pressure of the lung-chest wall system is at a maximum*
- Transmural pressure of the lung-chest wall system represents the pressure difference across the entire respiratory system.
- This pressure is higher during inspiration or forced expiration when the system is stretched or compressed.
- At FRC (airway pressure equals atmospheric pressure), the system is at **resting equilibrium**, not at maximal transmural pressure.
*Transmural pressure of the chest wall is at a minimum*
- Transmural pressure across the chest wall is the difference between intrapleural pressure and atmospheric pressure.
- This pressure is not at a minimum when airway pressure equals atmospheric pressure.
- Chest wall transmural pressure is actually minimal near **residual volume (RV)**, where the chest wall recoils inward most strongly.
*Transmural pressure of the lung-chest wall system is at a minimum*
- Transmural pressure of the lung-chest wall system reflects the elastic recoil forces of the combined system.
- At FRC (airway pressure equals atmospheric pressure), elastic recoil forces are balanced at equilibrium, but transmural pressure is **not at a minimum**—it represents the neutral resting state.
Airway resistance determinants US Medical PG Question 9: 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)
Airway resistance determinants 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.
Airway resistance determinants US Medical PG Question 10: A 55-year-old man comes to the physician because of episodic retrosternal chest pain and shortness of breath for the past 6 months. His symptoms occur when he takes long walks or climbs stairs but resolve promptly with rest. He has a history of chronic obstructive pulmonary disease, for which he takes ipratropium bromide. His pulse is 81/min and blood pressure is 153/82 mm Hg. Physical examination shows mild expiratory wheezing over both lungs. Additional treatment with a beta blocker is considered. Which of the following agents should be avoided in this patient?
- A. Betaxolol
- B. Esmolol
- C. Bisoprolol
- D. Atenolol
- E. Labetalol (Correct Answer)
Airway resistance determinants Explanation: ***Labetalol***
- **Labetalol** is a **non-selective beta-blocker** with additional **alpha-1 blocking activity**.
- Its **non-selective beta-blocking** effects can exacerbate **bronchoconstriction** in patients with **COPD**, leading to worsening respiratory symptoms.
*Betaxolol*
- **Betaxolol** is a **beta-1 selective blocker (cardioselective)**, meaning it primarily targets the heart.
- While no beta-blocker is entirely safe in **COPD**, cardioselective agents are generally preferred due to their reduced risk of **bronchospasm**.
*Esmolol*
- **Esmolol** is an **ultra-short-acting**, **beta-1 selective blocker** often used for acute cardiac conditions.
- Its **cardioselective nature** and rapid metabolism make it relatively safer in patients with **COPD** compared to non-selective agents.
*Bisoprolol*
- **Bisoprolol** is a **highly beta-1 selective blocker** commonly used for chronic cardiac conditions.
- Its high **cardioselectivity** minimizes its impact on **bronchial beta-2 receptors**, making it a safer option for patients with **COPD**.
*Atenolol*
- **Atenolol** is a **beta-1 selective blocker** used for conditions like hypertension and angina.
- Like other cardioselective beta-blockers, it has a lower risk of causing **bronchoconstriction** in patients with **COPD** compared to non-selective agents.
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