Pulmonology USMLE Practice Questions
Respiratory physiology, pathology, and critical care concepts.
5 free pulmonology practice questions
Pick an answer and check it. After each question you get the same explanation StepGenie students see: the stem decoded clue by clue, the reasoning chain with its infographic, why every wrong option is wrong, and the trap the question was built around. Step 1 questions test mechanism; Step 2 CK questions ask for the next step.
A 4-year-old boy is brought to the emergency department by his mother due to worsening cough. He had a mild cough 1 week ago that has progressively worsened and is now described by his mother as sounding like a “bark.” Over the same period, he has had low-grade fevers and rhinorrhea. Today, his temperature is 100.8°F (38.2°C), and physical examination reveals inspiratory stridor. Which of the following is the most likely causative organism?
Correct answer · A
Parainfluenza virus
Decoding the stem
Step-by-step reasoning
Step 1 of 5
Preschool-aged child with a weeklong viral prodrome (rhinorrhea, low-grade fever) suggests a common pediatric respiratory virus.
Step 2 of 5
Development of a barking cough is highly characteristic of croup (laryngotracheobronchitis).
Step 3 of 5
Inspiratory stridor indicates upper airway (subglottic) narrowing rather than lower airway bronchiolitis or pneumonia.
Step 4 of 5
The most common cause of croup is parainfluenza virus, a paramyxovirus.
Step 5 of 5
Therefore, parainfluenza virus is the most likely causative organism in this presentation.
Why not the others?
B. Respiratory syncytial virus
This option implies bronchiolitis, which causes wheezing, crackles, and lower respiratory distress in infants, BUT this child has barking cough and inspiratory stridor (upper airway).
C. Adenovirus
This option implies pharyngitis, conjunctivitis, or hemorrhagic cystitis, BUT the vignette highlights barking cough and stridor, not sore throat or eye findings.
D. Ebstein barr virus
This option implies infectious mononucleosis (fever, fatigue, pharyngitis, lymphadenopathy, splenomegaly), BUT the child has acute upper airway obstruction signs, not systemic mono symptoms.
E. Influenza A virus
This option implies influenza, which causes abrupt high fever, myalgias, and non-productive cough, BUT the hallmark barking cough and stridor of croup are more specific for parainfluenza.
Exam trap
Students may focus only on “cough + fever” and think RSV or influenza; recognizing the barking quality and inspiratory stridor is key for croup (parainfluenza).
The bottom line
Croup (laryngotracheobronchitis) from parainfluenza virus causes barking cough, inspiratory stridor, and low-grade fever in young children.
A previously healthy 2-year-old girl is brought to the clinic due to a 2-day history of a dry, harsh cough that is worse at night. She has had low-grade fever and mild rhinorrhea. Her older brother, who has asthma, recently had a cold. Immunizations are up to date. The child appears in mild respiratory distress. Temperature is 38.1°C (100.5°F), pulse is 140/min, respirations are 35/min, and blood pressure is 99/56 mm Hg. Oxygen saturation on room air is 96%. Physical examination shows clear rhinorrhea and a dry, hoarse cough. Mild inspiratory stridor is heard when the child is agitated but resolves at rest. The remainder of the examination is unremarkable. Which of the following is the most appropriate initial step in management?
Correct answer · G
Cool mist and dexamethasone
Decoding the stem
Step-by-step reasoning
- 1
A 2-year-old with viral prodrome (rhinorrhea, low-grade fever) and a dry, harsh, nocturnal cough suggests viral croup (laryngotracheobronchitis).
- 2
Croup causes subglottic edema leading to barky cough and inspiratory stridor due to upper airway narrowing.
- 3
Severity is graded by stridor and work of breathing: mild = stridor only with agitation, normal oxygenation, minimal distress.
- 4
This child has stridor only when agitated, normal O2 sat (96%), and mild distress → fits mild croup.
- 5
Management of mild croup: single-dose dexamethasone (systemic steroid) to decrease airway inflammation; cool mist/humidified air can provide symptomatic relief.
- 6
Racemic epinephrine and airway interventions (intubation, NIPPV) are reserved for moderate to severe croup with stridor at rest or impending respiratory failure.
Why not the others?
A. Racemic epinephrine
This option implies moderate-severe croup (stridor at rest, significant retractions, or hypoxia), which requires rapid airway caliber improvement. BUT this child has stridor only when agitated, normal oxygen saturation, and mild distress, consistent with mild disease where steroids alone are sufficient initially.
B. Ceftriaxone
This option implies bacterial infection (eg, epiglottitis, bacterial tracheitis) with high fever, toxic appearance, drooling, or severe distress. BUT this child has a viral prodrome, low-grade fever, is nontoxic, and has classic barky cough without signs of invasive bacterial disease.
C. Emergent intubation
This option implies impending respiratory failure (severe work of breathing, cyanosis, altered mental status, silent chest). BUT the child is alert, has only mild distress, stridor only with agitation, and normal oxygen saturation, so emergent airway control is not indicated.
D. Bronchoscopy
This option implies concern for foreign body aspiration or structural airway lesion (sudden onset cough, focal wheeze, unilateral decreased breath sounds). BUT symptoms evolved over 2 days with viral prodrome and classic croup findings, not acute aspiration.
E. Albuterol nebulizer
This option implies lower airway disease like asthma or bronchiolitis (wheezing, prolonged expiratory phase). BUT exam shows inspiratory stridor (upper airway) and no wheezing, so a beta-2 agonist will not address the pathology.
F. Chest x-ray
This option implies uncertainty about diagnosis or concern for pneumonia/foreign body. BUT the clinical picture is classic for mild croup, and imaging is not needed before starting appropriate therapy; management is clinical.
H. Noninvasive positive pressure ventilation
This option implies significant respiratory distress or failure (tachypnea with retractions, hypercapnia, hypoxia). BUT this child has only mild distress, normal oxygen saturation, and is maintaining her airway well, so NIPPV is unnecessary and excessive.
Exam trap
Students see stridor and jump to racemic epinephrine or intubation. The key is when stridor occurs: only with agitation = mild croup, treat with steroids (± cool mist) first.
The bottom line
Mild croup (parainfluenza): barky cough, inspiratory stridor only with agitation → treat with steroids ± cool mist; racemic epinephrine for moderate–severe.
A previously healthy 21-year-old man is brought to the emergency department 4 hours after the sudden onset of shortness of breath and sharp, left-sided pleuritic chest pain. He has a 3-year history of smoking 1 pack of cigarettes daily. He is 188 cm (6 ft 2 in) tall and weighs 70 kg (154 lb), with a BMI of 19.8 kg/m². On physical examination, tactile fremitus is decreased and breath sounds are diminished over the left lung field. Which of the following is the most likely cause of this patient’s symptoms?
Correct answer · B
Rupture of a subpleural bleb
Decoding the stem
Step-by-step reasoning
Step 1 of 5
Tall, thin, young male smoker with sudden unilateral pleuritic chest pain and dyspnea suggests primary spontaneous pneumothorax rather than chronic lung disease.
Step 2 of 5
Decreased tactile fremitus and decreased breath sounds over one lung field indicate air in the pleural space, not fluid or consolidation.
Step 3 of 5
In a previously healthy young person, the usual cause of air in the pleural space is rupture of apical subpleural blebs into the pleural cavity.
Step 4 of 5
Blebs are small subpleural air collections in the lung apex; smoking and tall body habitus predispose to their formation and rupture.
Step 5 of 5
Rupture allows air to escape from the lung into the pleural space → lung collapses partially → acute dyspnea + pleuritic chest pain + decreased breath sounds/fremitus.
Why not the others?
G. Inflammation of the costal cartilage
This option implies costochondritis, which causes localized reproducible chest wall pain, BUT it does not cause decreased breath sounds or fremitus over a lung field.
A. Embolic occlusion of the pulmonary artery
This option implies pulmonary embolism, which causes acute dyspnea and pleuritic pain, BUT lung exam is often normal or may have crackles—not focal decreased fremitus and breath sounds from pneumothorax.
C. Fibrosis of the pulmonary parenchyma
This option implies interstitial lung disease, causing chronic progressive dyspnea and dry cough, BUT the patient has sudden symptoms and focal exam findings, not chronic diffuse disease.
D. Infection with gram-positive diplococci
This option suggests Streptococcus pneumoniae pneumonia, which causes fever, productive cough, and increased tactile fremitus over consolidation, BUT this patient has decreased fremitus and no infectious signs.
E. Destruction of the central portion of the acinus
This option refers to centrilobular emphysema from chronic smoking, which causes chronic dyspnea and hyperresonance, BUT not sudden unilateral pleuritic pain with focal decreased breath sounds in a young adult.
F. Hyperresponsiveness of the bronchial system
This option implies asthma, which presents with episodic wheezing, cough, and diffuse bronchospasm, BUT exam would show bilateral wheezes, not unilateral decreased breath sounds/fremitus from pneumothorax.
Exam trap
Tall, thin young smoker with pleuritic pain can tempt choices like PE or pneumonia. Focal decreased fremitus/breath sounds must steer you to spontaneous pneumothorax from subpleural bleb rupture.
The bottom line
Primary spontaneous pneumothorax from apical subpleural bleb rupture in tall, thin young smoker → acute pleuritic chest pain, dyspnea, ↓ breath sounds, ↓ fremitus.
A 28-year-old woman, gravida 3 para 2, at 34 weeks’ gestation presents with a 1-day history of dyspnea, dry cough, and chest pain. Vital signs show tachycardia with a pulse of 112/min, respiratory rate of 24/min, and blood pressure of 108/78 mm Hg. Oxygen saturation on room air is 90%. Physical examination is notable for jugular venous distention and bilateral pitting edema below the knees, which is more pronounced on the right. There is dullness to percussion over the right lung base. Which of the following is the most likely diagnosis?
Correct answer · C
Pulmonary embolism
Decoding the stem
Step-by-step reasoning
- 1
Pregnancy, especially in the third trimester, is a hypercoagulable state (↑ clotting factors, venous stasis, endothelial injury risk).
- 2
Unilateral-predominant leg edema in this setting strongly suggests deep vein thrombosis (DVT) in the lower extremity.
- 3
DVT can embolize to the pulmonary arteries, causing pulmonary embolism with sudden dyspnea and pleuritic chest pain.
- 4
The PE acutely increases pulmonary vascular resistance → acute right ventricular strain, presenting with jugular venous distention.
- 5
Impaired pulmonary perfusion leads to hypoxemia (O2 sat 90%) and can cause pulmonary infarction with a pleural effusion, giving dullness to percussion at the lung base.
- 6
This constellation—late pregnancy, DVT signs, acute dyspnea/chest pain, hypoxemia, JVD, pleural effusion—is classic for pulmonary embolism, not other listed diagnoses.
Why not the others?
A. Aortic dissection
This option implies tearing chest/back pain, pulse/BP asymmetry, possible mediastinal widening, BUT the patient has JVD, unilateral leg edema, and pleural effusion suggesting PE/DVT, not aortic pathology.
B. Spontaneous pneumothorax
This option implies sudden dyspnea and pleuritic pain with hyperresonance and decreased breath sounds, BUT this patient has dullness to percussion (effusion) and DVT signs, arguing against pneumothorax.
D. Panic attack
This option implies anxiety, hyperventilation, paresthesias, normal O2 saturation, and no objective cardiopulmonary signs, BUT this patient has hypoxemia, JVD, unilateral edema, and percussion changes—true organic disease.
E. Bacterial pneumonia
This option implies fever, productive cough, focal crackles, and consolidation (dullness possible), BUT there is no fever or sputum, and pregnancy with unilateral leg swelling/JVD favors PE over infection.
F. Myocardial infarction
This option implies crushing substernal chest pain, often radiating to arm/jaw, with ischemic ECG changes and risk factors, BUT this young pregnant woman has pleuritic features, leg edema, and JVD suggesting PE, not MI.
G. Acute pericarditis
This option implies sharp chest pain improved by sitting up, pericardial friction rub, and diffuse ST elevation, BUT leg DVT signs, hypoxemia, and pleural effusion point toward PE instead.
Exam trap
Pregnancy can make dyspnea seem physiologic or anxiety-related, tempting choices like panic attack; instead, recognize pregnancy as a major VTE risk and prioritize PE.
The bottom line
Pulmonary embolism in late pregnancy: acute dyspnea, pleuritic chest pain, hypoxemia, JVD, unilateral leg edema, pleural effusion (dullness to percussion).
A 24-year-old man with a history of polysubstance use disorder, depression with multiple prior suicide attempts, neuropathic pain, and schizophrenia is brought to the emergency department by police after being found unconscious and covered in bruises outside a bar. Noncontrast head CT is unremarkable. An arterial blood gas is obtained and shows the following: Labs: - pH: 7.29 - PaCO2: 95 mm Hg - PaO2: 70 mm Hg - Bicarbonate: 24 mEq/L Which of the following is the most likely etiology of this patient’s current presentation?
Correct answer · E
Heroin
Decoding the stem
Step-by-step reasoning
- 1
ABG shows low pH (7.29) with very high PaCO₂ (95) and normal HCO₃⁻ (24) → primary acute respiratory acidosis without renal compensation.
- 2
Acute respiratory acidosis implies alveolar hypoventilation (reduced minute ventilation), classically from CNS respiratory center depression, neuromuscular failure, or severe airway disease.
- 3
This young man is unconscious, with a strong history of polysubstance use, and no CT evidence of neurologic catastrophe → intoxication is most likely.
- 4
Among common drugs of abuse, opioids (e.g., heroin) directly depress the medullary respiratory center → decreased respiratory rate and tidal volume → CO₂ retention.
- 5
Metabolic status (normal HCO₃⁻, no anion gap data) and absence of severe hypotension or specific toxidrome signs make pure CNS respiratory depression from heroin overdose the best fit.
Why not the others?
A. Alcohol
This option implies ethanol intoxication, which can cause CNS depression and hypoventilation, BUT significant alcohol intoxication often causes a mixed disorder (e.g., metabolic acidosis from lactic acidosis/ketoacidosis) rather than a clean, isolated acute respiratory acidosis with normal bicarbonate.
B. Amitriptyline
This option implies TCA overdose, which typically causes anticholinergic signs (hyperthermia, dry skin, dilated pupils), QRS prolongation, hypotension, and seizures, and often a metabolic acidosis, BUT the stem and ABG lack these features and instead show pure respiratory acidosis from hypoventilation.
C. Cocaine
This option implies sympathomimetic toxicity, which causes agitation, tachycardia, hypertension, hyperthermia, and often hyperventilation/respiratory alkalosis or metabolic acidosis from increased activity, BUT this patient is unconscious with hypoventilation and CO₂ retention, the opposite of the expected cocaine effect.
D. Ethylene glycol
This option implies toxic alcohol ingestion, which causes severe high anion gap metabolic acidosis, flank pain, calcium oxalate crystals, and renal failure, BUT the patient’s bicarbonate is normal and the primary disturbance is respiratory acidosis, not a metabolic acidosis.
Exam trap
The broad history of polysubstance use (alcohol, cocaine, TCAs, toxic alcohols) tempts buzzword matching. Instead, the ABG pattern (isolated acute respiratory acidosis) must anchor you to opioid-induced hypoventilation (heroin).
The bottom line
Acute opioid (heroin) overdose causes hypoventilation → isolated respiratory acidosis (↓pH, ↑PaCO₂, normal HCO₃⁻) with hypoxia and CNS depression.
Source: StepGenie question bank. Questions are written by StepGenie, not taken from NBME or USMLE materials, and are chosen for this page by how students actually performed on them (first-attempt accuracy on StepGenie). Selection last refreshed September 5, 2026.
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About Pulmonology
Complete review of respiratory mechanics, gas exchange, obstructive and restrictive lung diseases, pulmonary vascular disorders, and ventilator management. StepGenie breaks down complex spirometry and ABG interpretations.
Key Topics Covered
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Pulmonology — Frequently Asked Questions
How do you separate obstructive from restrictive lung disease on spirometry?
Look at the FEV1 to FVC ratio first. A reduced ratio means obstruction, as in asthma and COPD, because airflow out is limited. A normal or increased ratio with reduced total lung capacity means restriction, as in pulmonary fibrosis or chest wall disease. Once the pattern is set, the rest of the vignette tells you which specific disease it is.
What pulmonology topics are highest-yield for the USMLE?
Obstructive versus restrictive patterns, asthma and COPD pathophysiology and treatment, pneumonia organisms by clinical setting, pulmonary embolism workup, ARDS, and acid-base interpretation of arterial blood gases. Gas exchange physiology, especially the alveolar gas equation and the A-a gradient, connects many of these and is worth learning properly.
What does a widened A-a gradient tell you about hypoxemia?
It separates causes inside the lung from causes outside it. A normal A-a gradient with hypoxemia points to hypoventilation or high altitude, where the lung itself is working. A widened gradient points to a problem with gas exchange, such as ventilation-perfusion mismatch, shunt, or a diffusion barrier. Checking the response to supplemental oxygen then separates shunt from V/Q mismatch.
How should you approach a suspected pulmonary embolism question?
Anchor on pretest probability rather than jumping to a test. Low probability with a negative D-dimer effectively rules it out, while high probability moves straight to CT pulmonary angiography. The exam commonly tests when D-dimer is useless, since it rises non-specifically in pregnancy, malignancy, infection and the postoperative period.
Are the pulmonology practice questions on this page free?
Yes. The 5 questions above come from StepGenie's question bank and can be answered here without an account, with the full explanation shown after each one. From the link under the set you can try three more Pulmonology questions in the dashboard preview, also without an account; a free account is what lets you choose the system and keep going.