Question

Volume of air remained in lungs after normal expiration is known as

• A. Vital capacity
• B. Residual volume
• C. Functional residual capacity
• D. Expiratory reserve volume

Hint:

Remember the formula: $FRC = ERV + RV$. This is the "resting volume" of the lungs.

Answer 1

The Correct Option is C

Step 1: Understanding Respiratory Volumes and Capacities:
Respiratory capacities are combinations of two or more respiratory volumes. We need to identify the term for the volume of air present in the lungs at the end of a normal (tidal) expiration.
Step 2: Analyzing the Definitions:

Tidal Volume (TV): Volume of air inspired or expired during normal respiration ($\approx 500$ ml).
Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration ($\approx 1100-1200$ ml).
Expiratory Reserve Volume (ERV): Additional volume of air that can be forcibly expired after a normal expiration ($\approx 1000-1100$ ml).
Vital Capacity (VC): Maximum volume of air a person can breathe in after a forced expiration ($ERV + TV + IRV$).

Step 3: Calculating the Volume after Normal Expiration:
When a person exhales normally, they expel the Tidal Volume. The air left inside consists of the air that \textit{could} be exhaled forcibly (ERV) plus the air that \textit{cannot} be exhaled (RV). \[ \text{Volume remaining} = ERV + RV \] This sum is defined as the Functional Residual Capacity (FRC).
Step 4: Final Answer:
The correct term is Functional Residual Capacity.