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Practice sessionHEALTHCARE & MEDICAL EXAMSMEDICAL LICENSING

USMLE (United States Medical Licensing Examination) Practice Exam 06

Practice exam for USMLE (United States Medical Licensing Examination).

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Question 1 of 1000%
Time remaining120:00
Attempts allowedUnlimited
Difficulty mixE • M • H
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Question 1

MEDIUM

A 24-year-old woman comes to the clinic because of episodic wheezing and chest tightness for 6 months, worse with exercise and exposure to cold air. She has no smoking history. Medications include an albuterol inhaler used 2–3 times per week. Vital signs are normal. Spirometry shows FEV1/FVC of 0.68 with an increase in FEV1 by 16% after inhaled bronchodilator. Which of the following is the most likely physiologic mechanism responsible for the improvement in airflow after bronchodilator administration?

Beta-2 agonists relax bronchial smooth muscle, increasing bronchiolar radius; because airway resistance is inversely proportional to radius to the fourth power, small increases in radius markedly decrease resistance and improve FEV1. Surfactant and diffusion capacity changes do not explain rapid bronchodilator response.

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