Question

The volume of air remaining in lungs after a forceful expiration is called:

• A. Tidal volume
• B. Residual volume
• C. Inspiratory reserve volume
• D. Vital capacity

Hint:

The Residual Volume (RV) cannot be measured using a simple spirometer because the air never leaves the respiratory system. It must be calculated using gas dilution methods.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Respiratory volumes represent different quantities of air inhaled, exhaled, or remaining in the lungs during various phases of the breathing cycle.
Even after a person performs the most forceful expiration possible, the lungs are never completely empty of air.

Step 2: Detailed Explanation:
1. Tidal Volume (TV): This is the volume of air inspired or expired during a normal, relaxed breath, which is approximately \(500\) mL in a healthy adult.
2. Residual Volume (RV): This is the specific volume of air that remains trapped in the lungs even after a maximum forced expiration. This volume ensures that the lungs do not collapse and that gas exchange continues even between breaths. Its typical value ranges from \(1100\) mL to \(1200\) mL.
3. Inspiratory Reserve Volume (IRV): The additional volume of air that can be inhaled forcibly after a normal inspiration.
4. Vital Capacity (VC): The maximum volume of air a person can breathe out after a maximum inhalation, encompassing TV, IRV, and ERV.

Step 3: Final Answer:
The volume of air that remains in the lungs after forceful expiration is the Residual Volume.

Answer 2

This question is really asking which lung volume represents air that cannot be pushed out no matter how hard a person exhales. The four terms can be told apart by asking when each one is measured and whether it is under voluntary control, so each option is checked against that test.

1. Tidal volume: This is simply the air moved during one ordinary, relaxed breath, roughly 500 mL. It is measured during quiet breathing, not after a maximal forced exhalation, so it cannot describe air trapped after forceful expiration.
2. Residual volume: This is the air that stays behind in the alveoli and airways even after the most forceful possible exhalation a person can produce. It cannot be expelled voluntarily because complete emptying would collapse the alveoli, and it is exactly the quantity the question describes.
3. Inspiratory reserve volume: This is the extra air that can still be pulled in after a normal inspiration, a volume linked to breathing in further, not to what remains after breathing out fully, so it does not match.
4. Vital capacity: This is the total air that can be actively moved, calculated as tidal volume plus inspiratory reserve volume plus expiratory reserve volume. It describes exchangeable air, whereas the question asks about air left behind that cannot be exchanged out, so this option is the opposite of what is being asked.

Only one of the four terms refers to air that remains trapped in the lungs after a maximal forced exhalation, and that is residual volume.

So the correct answer is Residual volume.