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Ventilation and Lung Mechanics Quiz
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Which definition best describes functional residual capacity in spirometry?
- A The volume of air present in the lungs at the end of quiet expiration You picked ✓
- B The volume of air moved into and out of the lungs during a normal breath You picked ✕
- C The volume of air remaining in the lungs after a forced expiration You picked ✕
- D The volume of air that can be inspired after a normal tidal inspiration You picked ✕
- E The maximal volume of air that can be expelled after maximal inspiration You picked ✕
Correct!
Incorrect
The answer is A: The volume of air present in the lungs at the end of quiet expiration
Explanation
Why A is correct
See Spirometry. Option A is correct. Functional residual capacity (FRC) is the volume of air in the lungs at the end of quiet expiration, when the person has breathed out normally and the muscles are relaxed. In spirometry (a breathing test in which the patient breathes in and out through a device that records lung volumes) a capacity is a combination of two or more volumes. FRC is the expiratory reserve volume (the extra air that can be forced out after a quiet breath out) plus the residual volume (the air that stays in the lungs even after a maximal breath out, because the lungs need some air in them to stay expanded). The FRC is also the resting point of the respiratory system: at the end of quiet expiration the inward recoil of the lungs and the outward recoil of the chest wall are balanced, so the muscles do no work. FRC and residual volume are raised in diseases with air trapping, such as COPD. A simple memory aid: FRC is the lungs' resting position after a calm breath out.
- Definition: functional residual capacity (FRC) is the volume of air in the lungs at the end of quiet expiration
- Made up of: expiratory reserve volume plus residual volume
- Resting point: inward recoil of the lungs balances outward recoil of the chest wall, so the muscles do no work
Why the other options are incorrect
- B. The volume of air moved into and out of the lungs during a normal breath: This is the tidal volume. It is the size of one quiet breath, not the volume left in the lungs afterwards. Your answer
- C. The volume of air remaining in the lungs after a forced expiration: This is the residual volume, the air that stays in the lungs even after the biggest possible breath out. Functional residual capacity also includes the expiratory reserve volume. Your answer
- D. The volume of air that can be inspired after a normal tidal inspiration: This is the inspiratory reserve volume, the extra air that can be breathed in beyond a normal breath. It is a reserve above the resting level and not the volume left in the lungs. Your answer
- E. The maximal volume of air that can be expelled after maximal inspiration: This is the vital capacity, the largest breath out possible after a full breath in. It measures how much air can be moved, not the resting volume. Your answer
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1
Which statement best describes the immediate mechanical consequence of air entering the pleural space in a pneumothorax?
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2
During quiet tidal breathing in a healthy adult, which component accounts for most of the energy expenditure of ventilation?
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