Q.18 The amount of air that moves into the lungs with each normal inspiration is known as
1. inspiratory reserve volume
2. expiratory reserve volume
3. vital capacity
4. tidal volume
Tidal Volume: Air Moved in Normal Breathing Explained
Tidal volume is the amount of air that moves into the lungs during each normal inspiration, making option 4 the correct answer.
Lung Volumes Overview
Tidal volume (TV) is the air inhaled or exhaled in a single normal breath at rest, typically 500 mL in adults.
It contributes to minute ventilation (TV × respiratory rate).
Other volumes measure maximum efforts or reserves.
Correct Answer: Tidal Volume
Option 4 matches “normal inspiration” exactly, as TV handles routine quiet breathing.
This excludes forced or reserve efforts.
Diaphragm contraction drives TV via pressure changes.
Option Explanations
| Option | Volume Type | Typical Value | Why Incorrect/Correct |
|---|---|---|---|
| 1. Inspiratory reserve volume | Extra air inhaled beyond TV | ~3000 mL | Forced deep breath, not normal. |
| 2. Expiratory reserve volume | Extra air exhaled after TV | ~1100 mL | Post-normal exhale reserve, not inspiration. |
| 3. Vital capacity | TV + IRV + ERV | ~4600 mL | Total usable volume, not per normal breath. |
| 4. Tidal volume | Normal breath air | ~500 mL | Exact match for routine inspiration. |
Physiological Importance
TV maintains O₂/CO₂ balance without strain; adjustments occur during exercise.
In clinical settings, low TV protects lungs in ventilation.
