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17 multiple-choice questions and 4 flashcards on Respiratory System, about 10% of the USMLE Step 1 bank. Every one carries a written rationale.
Respiratory System is one of 10 chapters in CoStudy's USMLE Step 1 — Medical Licensing bank, and it holds 17 of the bank's 172 multiple-choice questions — roughly 10% of the total. That proportion is not arbitrary: chapters follow the certifying body's published exam outline, and the number of questions in each is set by that domain's published weight, so the share of your practice time this chapter takes matches the share of the real exam it accounts for.
Studying by chapter is worth doing once you have a diagnostic score. A single overall percentage tells you whether you are close; it does not tell you which domain is dragging. Working a weak chapter in isolation, and re-testing it in isolation, is the fastest way to move a score that has stalled — and it is why the mock exams in CoStudy report by domain rather than as one number.
10 questions drawn from this chapter, with the full rationale shown — the controlling principle behind the right answer, and why each wrong option tempts and fails.
A 65-year-old smoker presents with a productive cough and 10-kg weight loss over 3 months. CXR shows a lung mass. The MOST important next step is:
Answer: A — Tissue biopsy via bronchoscopy or CT-guided biopsy for histologic diagnosis
A) Histologic confirmation guides treatment (NSCLC vs SCLC vs benign). B/C/D) Each delays appropriate workup.
A 55-year-old woman with long-standing systemic sclerosis presents with progressive exertional dyspnea. Echocardiogram estimates a right ventricular systolic pressure of 65 mmHg (elevated) with a normal left ventricular ejection fraction and normal left atrial size. Right heart catheterization confirms elevated mean pulmonary artery pressure with normal pulmonary capillary wedge pressure. Which class of pulmonary hypertension does this represent?
Answer: D — Group 1 — pulmonary arterial hypertension associated with connective tissue disease
D) Correct: connective tissue diseases (especially systemic sclerosis) are a recognized cause of Group 1 pulmonary arterial hypertension — intrinsic pulmonary vascular remodeling with normal wedge pressure (precapillary PH) and preserved LV function. A) Group 2 (left heart disease) would show an ELEVATED wedge pressure reflecting backward transmission of left-sided pressures — direction reversal trap, ruled out here by the normal wedge and normal LA size/EF. B) Group 3 requires underlying chronic lung disease/hypoxemia, not described here. C) Group 4 requires evidence of chronic thromboembolic disease on imaging (V/Q or CTPA), not given. E) Group 5 is reserved for unclear or multifactorial causes (e.g., sarcoidosis, hematologic disorders) — a less specific, true-but-not-best answer given the clear CTD association.
A 60-year-old man with a 40-pack-year smoking history presents with progressive dyspnea. Spirometry shows FEV1/FVC of 0.55, increased TLC, and decreased DLCO. Which finding on lung biopsy would BEST explain the decreased DLCO?
Answer: C — Destruction of alveolar walls with loss of capillary surface area
C) Correct: emphysema (panacinar or centriacinar) destroys alveolar septa, reducing the surface area for gas exchange and lowering DLCO. A) Mucus gland hyperplasia (Reid index >0.5) defines chronic bronchitis — DLCO is typically normal in pure bronchitis; off-by-one COPD trap. B) Smooth muscle hypertrophy describes asthma (normal or increased DLCO). D) Subepithelial fibrosis with eosinophils is asthma. E) Granulomas suggest sarcoidosis (restrictive pattern, not obstructive).
A 22-year-old tall thin man presents with sudden onset of right-sided pleuritic chest pain and dyspnea. Exam: decreased breath sounds and hyperresonance on the right. He is hemodynamically stable. What is the MOST appropriate next step?
Answer: E — Chest X-ray to confirm pneumothorax
E) Correct: primary spontaneous pneumothorax in a stable patient requires confirmation with chest X-ray before treatment. A) Needle decompression is reserved for TENSION pneumothorax (hypotension, tracheal deviation) — overtreatment trap. C) CTPA is for suspected PE, but his presentation (young, thin, tall, sudden pleuritic pain with hyperresonance) is classic for pneumothorax. D) Bronchoscopy has no role here. B) Heparin would be harmful if the cause is pneumothorax.
What is the primary stimulus driving ventilation in a healthy person?
Answer: D — Elevated PaCO₂ (and pH)
Central chemoreceptors in the medulla respond to CSF [H⁺], which tracks PaCO₂. Even small rises in PaCO₂ powerfully stimulate ventilation. PaO₂ (peripheral chemoreceptors via the carotid/aortic bodies) becomes the dominant drive only at very low PaO₂ (~60 mmHg) — important in chronic CO₂ retainers.
A 55-year-old man with no smoking history is diagnosed with a peripheral lung adenocarcinoma. Genetic testing reveals an EGFR mutation. Which therapy is MOST likely to be effective?
Answer: E — Erlotinib
E) Correct: erlotinib is an EGFR tyrosine kinase inhibitor specifically effective in EGFR-mutated NSCLC adenocarcinoma (especially in nonsmokers, women, Asian populations). A) Cisplatin/etoposide is the regimen for small cell lung cancer — wrong histology. C) Imatinib targets BCR-ABL in CML and c-KIT in GIST — wrong target; off-by-one TKI trap. D) Trastuzumab targets HER2 (breast/gastric cancers). B) Rituximab targets CD20 on B-cells (lymphomas).
First-line therapy for an acute asthma exacerbation includes:
Answer: D — Inhaled short-acting beta-2 agonist (e.g., albuterol) for bronchodilation, plus systemic corticosteroids for inflammation — escalating to oxygen, ipratropium, magnesium, IV therapies as needed
D) Standard acute asthma management. A/B/C) Each contradicts.
A 45-year-old man with HIV (CD4 count 180) presents with a 3-week history of cough, night sweats, and weight loss. CXR shows a cavitary lesion in the right upper lobe. Sputum is positive for acid-fast bacilli. Which process BEST describes the pathogenesis of this presentation?
Answer: B — Reactivation of latent infection in an immunocompromised host, with caseating granuloma formation and cavitation in the apex
B) Correct: upper-lobe cavitary disease with systemic symptoms in an immunosuppressed host (low CD4) is classic for reactivation TB — high oxygen tension in the apices favors mycobacterial growth, and caseating granulomas with central necrosis produce cavities. A) Primary TB typically produces a Ghon complex (peripheral lung focus + hilar nodes) without cavitation and is often subclinical — off-by-one TB-stage trap; this patient's presentation (cavitary, apical, chronic symptoms) fits reactivation, not primary infection. C) Miliary TB shows diffuse micronodular ('millet seed') pattern, not a single cavitary lesion. D) Hypersensitivity pneumonitis is a distinct process unrelated to AFB-positive sputum. E) Bronchiectasis shows dilated, thickened airways, not cavitary consolidation, and would not explain AFB positivity.
A 30-year-old woman develops acute hypoxemic respiratory failure 48 hours after being treated for septic shock. CXR shows diffuse bilateral infiltrates. PaO2/FiO2 ratio is 150. Pulmonary capillary wedge pressure is normal, and echocardiogram shows normal cardiac function. Which is the MOST likely underlying pathophysiology?
Answer: B — Diffuse alveolar damage with increased capillary permeability from inflammatory injury
B) Correct: ARDS following a systemic inflammatory trigger (sepsis) produces diffuse alveolar damage — neutrophil-mediated injury to the alveolar-capillary membrane causes protein-rich (noncardiogenic) pulmonary edema, refractory hypoxemia (low PaO2/FiO2), and bilateral infiltrates with a NORMAL wedge pressure and normal cardiac function, distinguishing it from cardiogenic edema. A) Cardiogenic edema would show elevated wedge pressure and reduced ejection fraction — direction reversal trap, since both cause bilateral infiltrates and hypoxemia. D) Volume overload alone would also raise wedge pressure; the normal echo and wedge pressure argue against a purely hydrostatic mechanism. C) PE causes a perfusion defect without diffuse bilateral infiltrates. E) Mucus plugging causes focal, not diffuse bilateral, findings.
A 68-year-old woman with a history of breast cancer presents with sudden dyspnea and pleuritic chest pain. D-dimer is elevated. Which finding on V/Q scan would be MOST specific for pulmonary embolism?
Answer: B — Perfusion defect with normal ventilation in the same segment
B) Correct: PE classically produces a mismatch — segmental perfusion defect with preserved ventilation (the embolus blocks blood flow but air still reaches alveoli). A) Matched defects suggest parenchymal disease (pneumonia, COPD) — direction reversal trap. C) Increased perfusion is not the pattern of obstruction. D) Decreased ventilation with normal perfusion describes a mucus plug or atelectasis, not PE. E) Diffuse bilateral uptake is nonspecific or normal.
1 cards from the 4 in this chapter.
Restrictive vs obstructive lung disease (PFT)?
Restrictive: ↓FEV1, ↓FVC, normal/↑ FEV1/FVC. Obstructive: ↓FEV1, ↓FEV1/FVC.
These are a sample. The full Respiratory System chapter runs 21 items with per-chapter progress tracking, on the web and in the iOS app.
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