Residual Volume
Also written as: RV — Residual Volume
The volume of air remaining in the lungs after a maximal forced exhalation, which cannot be expelled voluntarily.
Full Definition
Residual volume (RV) is a key lung subdivision that can only be measured indirectly, typically via body plethysmography or helium dilution. In children with obstructive lung disease (e.g., asthma or cystic fibrosis), RV is elevated due to gas trapping behind closed or collapsed airways. The RV/TLC ratio is used as an index of air trapping severity and is particularly informative in paediatric lung function interpretation. Editors should not confuse residual volume with functional residual capacity (FRC), which is the resting end-expiratory lung volume and equals RV plus expiratory reserve volume.
Usage
Usage note: Expand RV on first reference. When reporting RV/TLC ratio, clarify units and reference equations used, as paediatric norms differ from adult values.
In Context
- "An elevated residual volume with an RV/TLC ratio of 0.42 indicated significant air trapping in the adolescent with poorly controlled asthma." — Pulmonary function test report
- "The author conflated residual volume with functional residual capacity; the editor added a footnote clarifying the distinction." — Textbook copyediting note