Residual volume of lung is defined as: March 2013
**Core Concept**
The residual volume of the lung is the volume of air that remains in the lungs after a maximal exhalation. It is an important **pulmonary function test** parameter that reflects the amount of air left in the lungs when the respiratory muscles are fully relaxed. This concept is crucial in understanding **lung volumes** and **capacities**.
**Why the Correct Answer is Right**
The correct answer defines residual volume as the volume of air left in the lungs after a maximal exhalation. This is because, even after a forced exhalation, some air remains in the lungs due to the elastic recoil of the **chest wall** and **lungs**. This residual air is essential for maintaining **gas exchange** during the breathing cycle.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the residual volume.
**Option B:** This option is also incorrect as it confuses residual volume with another lung volume or capacity.
**Option D:** Similarly, this option is wrong because it misdefines residual volume.
**Why Each Wrong Option is Incorrect** is not fully specified due to missing option details, however, the general approach to eliminating incorrect options involves understanding the definitions and physiological basis of lung volumes and capacities.
**Clinical Pearl / High-Yield Fact**
Residual volume is a critical parameter in diagnosing and managing **chronic obstructive pulmonary disease (COPD)** and other respiratory conditions. An increased residual volume indicates **air trapping**, which is a hallmark of COPD.
**Correct Answer:** D. Volume of air left in lungs after maximum exhalation.