Pulmonary Pathophysiology (USMLE Step 1)
USMLE Step 1 Practice Question
Today’s question will test your knowledge of an often-tested, high-yield USMLE Step 1 concept. The question is followed by a breakdown of the answer choices and a detailed explanation of the correct answer. Click the ♥️ when you’re done!
A 25-year-old female presents to her primary care physician with a complaint of wheezing and shortness of breath during exercise. She has a history of childhood asthma that was well-controlled with inhaled corticosteroids and albuterol as needed. Her vital signs are within normal limits, and her physical examination is unremarkable except for mild expiratory wheezing. Spirometry reveals a decrease in forced expiratory volume in 1 second (FEV1) from baseline of 20% after exercise challenge. Which of the following best describes the mechanism of action of the most appropriate treatment for her condition?
A. Inhibition of phosphodiesterase activity
B. Inhibition of leukotriene synthesis
C. Stabilization of mast cells
D. Stimulation of beta-adrenergic receptors in bronchial smooth muscle
E. Blockade of histamine receptors
F. Inhibition of muscarinic receptors in bronchial smooth muscle
G. Modulation of calcium influx in bronchial smooth muscle
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ANSWER + QUESTION BREAKDOWN
The Mental Model for this week’s question:
Step 1. Identify the MOA of the most appropriate treatment.
Step 2. Make a diagnosis so I know what I’m treating.
Step 3. Determine the best treatment option and name its MOA.
Step 4. Look for your answer in the answer choices.
GENERAL ANALYSIS
This question involves a 25-year-old female with a history of childhood asthma who presents with wheezing and shortness of breath during exercise. The spirometry results indicate a significant decrease in FEV1 after exercise, consistent with exercise-induced bronchoconstriction (EIB), also known as exercise-induced asthma (EIA). The task is to identify the mechanism of action of the most appropriate treatment for her condition.
ANSWER CHOICES:
ANSWER CHOICE A: Inhibition of phosphodiesterase activity
Phosphodiesterase inhibitors, such as theophylline, increase cyclic AMP levels by preventing its breakdown. This can lead to bronchodilation. While phosphodiesterase inhibitors can be used in asthma management, they are not the first-line treatment for exercise-induced asthma.
ANSWER CHOICE B: Inhibition of leukotriene synthesis
Leukotriene synthesis inhibitors, such as zileuton, reduce inflammation and bronchoconstriction by inhibiting the production of leukotrienes. Leukotriene inhibitors are used in asthma management but are not the primary treatment for acute symptoms of exercise-induced asthma.
ANSWER CHOICE C: Stabilization of mast cells
Mast cell stabilizers, such as cromolyn sodium, prevent the release of inflammatory mediators from mast cells. Mast cell stabilizers can be used for long-term control but are not the most effective for immediate relief of exercise-induced bronchoconstriction.
ANSWER CHOICE D: Stimulation of beta-adrenergic receptors in bronchial smooth muscle
Beta-adrenergic agonists, such as albuterol, stimulate beta-2 receptors in bronchial smooth muscle, leading to muscle relaxation and bronchodilation. Short-acting beta-2 agonists (SABAs) like albuterol are the first-line treatment for preventing and relieving symptoms of exercise-induced asthma. They are typically taken 10-15 minutes before exercise to prevent bronchoconstriction.
ANSWER CHOICE E: Blockade of histamine receptors
Histamine receptor blockers, such as antihistamines, reduce allergic reactions by blocking histamine receptors. While antihistamines can help with allergic symptoms, they are not the primary treatment for exercise-induced bronchoconstriction.
ANSWER CHOICE F: Inhibition of muscarinic receptors in bronchial smooth muscle
Muscarinic receptor antagonists, such as ipratropium, block the action of acetylcholine on muscarinic receptors, leading to bronchodilation. Muscarinic antagonists can be used in asthma management but are not the first-line treatment for exercise-induced asthma.
ANSWER CHOICE G: Modulation of calcium influx in bronchial smooth muscle
Calcium channel blockers reduce calcium influx into smooth muscle cells, leading to muscle relaxation. Calcium channel blockers are not typically used in the treatment of asthma or exercise-induced bronchoconstriction.
FINAL VERDICT…
The patient's symptoms of wheezing and shortness of breath during exercise, along with the spirometry findings, are best managed with a short-acting beta-2 agonist like albuterol. These medications work by stimulating beta-2 receptors in the bronchial smooth muscle, which leads to muscle relaxation and bronchodilation. This mechanism helps to prevent and relieve the bronchoconstriction that occurs during exercise. Albuterol is typically taken 10-15 minutes before exercise to prevent symptoms and can also be used to relieve symptoms if they occur during or after exercise.
FINAL ANSWER: D: Stimulation of beta-adrenergic receptors in bronchial smooth muscle
That’s it for today’s question!
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