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Chapter 6. Integrated Respiratory System Compliance and the Work of Breathing

A nonsmoking 24-year-old man with no significant past medical history presents with a chief complaint of productive cough in the past 48 hours. Physical examination reveals an expiratory wheeze and his chest x-ray is consistent with a right middle lobe infection; lab results on a yellow-green sputum sample obtained for culture are pending. Compared with this patient’s normal lung function, which of the following is most likely occurring during this phase of his illness?

a. Hyperinflation and peripheral gas trapping

b. Decreased functional residual capacity

c. Reduced respiratory frequency (breaths/min)

d. Elevated FEV1 during a forced vital capacity maneuver

e. Increased expiratory reserve volume

The most correct answer is a.

When otherwise healthy individuals develop an acute respiratory infection as this man apparently has done, most symptoms of respiratory distress including tachypnea (answer c) are attributable to secretions that obstruct intermediate airways. Until cleared, these secretions will promote peripheral gas trapping that reduces the man’s ERV (answer e), expands his FRC (answer b), and limits his peak air flow rates (answer d).

A 27-year-old female patient performs spirometry and a forced vital capacity (FVC) procedure in her physician’s office with the following results: RV = 600 mL; VT = 700 mL; vital capacity = 5.00 L; f = 12 breaths/min; FEV1 = 75%; FEV2 = 90%; FEV3 = 99%. What volume did she expire during the first two seconds of the FVC maneuver?

a. 3.5 L

b. 3.8 L

c. 4.0 L

d. 4.5 L

e. 5.0 L

The correct answer is d.

The woman’s FEV2 = 90%, which when multiplied by her vital capacity of 5.0 L yields 4.5 L of gas exhaled in the first two seconds of her FVC test.

A previously healthy 12-year-old boy becomes trapped horizontally in a ventilation shaft while exploring a building under construction. First-responders determine that he has no obvious bodily injuries, can say his name and age, and laughs in response to a joke, but is short of breath with both arms pressed tightly to his sides. Until he can be extricated, what is the most likely explanation for his respiratory distress?

a. Increased ...

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