Lung Volumes and Capacities
Start with the big picture
Tidal volume is the air moved during a quiet breath, while inspiratory and expiratory reserve volumes represent additional air that can be inhaled or exhaled. Residual volume remains after maximal expiration and is not measured by simple spirometry. Capacities are formed by combining volumes: functional residual capacity is ERV plus RV, vital capacity is IRV plus TV plus ERV, and total lung capacity is VC plus RV. Spirometry measures several volumes and capacities, but RV, FRC, and TLC require methods such as helium dilution, nitrogen washout, or body plethysmography. The lesson also introduces contrasting disease patterns: obstruction tends to increase RV and TLC while reducing VC and the FEV₁/FVC ratio; restriction reduces lung volumes and capacities, with a normal or increased ratio.
What you'll learn
- Define the principal lung volumes, including tidal volume, reserve volumes, and residual volume.
- Relate FRC, VC, and TLC to their component volumes.
- Identify which lung measurements cannot be obtained by spirometry alone.
- Compare obstructive and restrictive patterns in lung volumes and FEV₁/FVC.
- Describe how spirometry contributes to assessment of pulmonary disease.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
