REAL EXAM QUESTIONS AND 100% CORRECT DETAILED ANSWERS (USMLE STEP 1) MEDICAL
EXAMINATION
EXAM OVERVIEW & ESSENTIAL CONTEXT
The NBME Comprehensive Basic Science Examination (CBSE) is a 5½-hour exam covering
material learned in the basic science curriculum and reflecting USMLE Step 1 content . It
contains approximately 200 scored items and is designed to assess readiness for Step 1 .
Scores are reported as an Equated Percent Correct (EPC) score representing the percentage of
content mastered .
Key Scoring Benchmarks:
• Score of ≥55: Strongly encouraged to meet readiness benchmarks
• Score of 51-54: At risk; required to submit practice exam benchmarks
• Score of 40-50: Higher risk; required to meet with dean and create study plan
• Score below 40: Highest risk; administrative leave of absence may be required
SECTION 1: CARDIOVASCULAR SYSTEM (Questions 1-25)
Question 1
A 52-year-old man presents to the emergency department with chest pain radiating to his jaw
while shoveling snow. Pulse is 80/min and blood pressure is 130/70. What is the most
immediate treatment mechanism of action?
, • A) Beta-adrenergic blockade
• B) Increased nitric oxide concentration
• C) Platelet aggregation inhibition
• D) Calcium channel blockade
Correct Answer: B) Increased nitric oxide concentration
Rationale: The patient is experiencing an acute coronary syndrome (angina/myocardial
infarction) precipitated by exertion. The most immediate treatment is sublingual nitroglycerin,
which works by increasing nitric oxide concentration, leading to vasodilation and improved
coronary blood flow .
Question 2
A 64-year-old male presents to the emergency department with shortness of breath and
extreme fatigue. The ECG shows atrial fibrillation, and he has ischemic heart disease. What
medication is likely administered intravenously?
• A) Amiodarone
• B) Digoxin
• C) Ibutilide
• D) Adenosine
Correct Answer: C) Ibutilide
Rationale: Ibutilide is a class III antiarrhythmic used for acute conversion of atrial fibrillation
and atrial flutter. It prolongs action potential duration and refractory period by activating slow
inward sodium current and blocking outward potassium currents .
, Question 3
Which of the following describes pulmonic vascular resistance at its lowest point during
respiration?
• A) End-inspiration
• B) End-expiration
• C) Exhale of tidal volume
• D) Mid-inspiration
Correct Answer: C) Exhale of tidal volume
Rationale: Pulmonary vascular resistance is lowest during exhalation of tidal volume when lung
volumes are near functional residual capacity. At this point, alveolar vessels are not
compressed by overinflation, and extra-alveolar vessels are not excessively stretched .
Question 4
A 66-year-old male with stage IV colon cancer presents with a 3-day history of severe diarrhea
after receiving chemotherapy. What opioid antidiarrheal agent can be prescribed that has no
CNS effects?
• A) Codeine
• B) Loperamide
• C) Diphenoxylate
• D) Morphine
Correct Answer: B) Loperamide