Lung volumes, compliance, and oxygen-carbon dioxide exchange mechanisms tested on USMLE Step 1.
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- What is tidal volume?
- The volume of air inhaled or exhaled in a single normal, quiet breath
- What is inspiratory reserve volume?
- The additional volume that can be inhaled above a normal tidal inspiration with maximal effort
- What is expiratory reserve volume?
- The additional volume that can be exhaled below a normal tidal expiration with maximal effort
- What is residual volume?
- The volume of air remaining in the lungs after a maximal forced expiration
- Why can residual volume not be measured directly by spirometry?
- Spirometry only measures volumes that are actually exhaled, and residual volume by definition remains in the lung
- What is functional residual capacity, and how is it calculated?
- The volume remaining in the lungs after a normal tidal expiration, calculated as expiratory reserve volume plus residual volume
- What is vital capacity, and how is it calculated?
- The maximum volume that can be exhaled after a maximal inspiration, calculated as tidal volume plus inspiratory reserve volume plus expiratory reserve volume
- What is total lung capacity, and how is it calculated?
- The total volume of air in the lungs after a maximal inspiration, calculated as vital capacity plus residual volume
- What determines functional residual capacity physiologically?
- The point at which the inward elastic recoil of the lung is exactly balanced by the outward recoil of the chest wall
- What is lung compliance?
- The change in lung volume produced per unit change in transpulmonary (distending) pressure
- What happens to lung compliance in emphysema?
- Compliance increases due to loss of elastic recoil from destroyed alveolar walls
- What happens to lung compliance in pulmonary fibrosis?
- Compliance decreases because the stiffened, scarred lung tissue resists expansion
- What substance produced by type II pneumocytes reduces alveolar surface tension and increases lung compliance?
- Pulmonary surfactant
- What is the main phospholipid component of pulmonary surfactant?
- Dipalmitoylphosphatidylcholine (DPPC)
- What law relates alveolar surface tension, radius, and collapsing pressure, explaining why surfactant helps stabilize alveoli of different sizes?
- The law of Laplace, where collapsing pressure equals two times surface tension divided by radius
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