Understanding how our lungs function is crucial not only for medical studies but also for appreciating the miracle of every breath we take. Pulmonary volumes and capacities help measure how much air our lungs can hold, inhale, and exhale under different physiological conditions.
In this article, we’ll break down each volume and capacity, explain it in simple terms, show the formulas, and offer memory aids—ideal for NEET prep and biology boards.
What Are Pulmonary Volumes?
Pulmonary volumes are basic measurements of air movement during breathing. These include:
- Tidal Volume (TV)
- Inspiratory Reserve Volume (IRV)
- Expiratory Reserve Volume (ERV)
- Residual Volume (RV)
Each of these has a defined amount of air (in mL) and contributes to overall lung function.
1. Tidal Volume (TV)
Volume: ~500 mL
Definition: The amount of air inhaled or exhaled during normal breathing at rest.
💡 Think of it as: "Breathe in, breathe out — without effort."
2. Inspiratory Reserve Volume (IRV)
Volume: 2,500–3,000 mL
Definition: Extra air you can inhale after a normal inhalation.
💡 Tip: Imagine taking a deep breath after a normal breath — that deep breath is IRV.
3. Expiratory Reserve Volume (ERV)
Volume: 1,000–1,100 mL
Definition: Extra air you can force out after a normal exhalation.
💡 Analogy: Blowing out candles with force after a calm exhale — that extra blow is ERV.
4. Residual Volume (RV)
Volume: 1,100–1,200 mL
Definition: Air that remains in your lungs even after forcefully exhaling everything you can.
💡 Note: This air keeps your alveoli from collapsing.
Pulmonary Capacities
Pulmonary capacities are combinations of two or more volumes. These give a complete picture of lung function.
5. Vital Capacity (VC)
Volume: 4,000–4,600 mL
Formula:
VC = TV + IRV + ERV
Definition: Maximum air exhaled after a maximum inhalation. It reflects the functional capacity of the lungs.
✅ Clinical Use: Measured during spirometry tests.
6. Inspiratory Capacity (IC)
Volume: 3,000–3,500 mL
Formula:
IC = TV + IRV
Definition: Total air a person can breathe in after a normal exhalation.
🧠 Memory Tip: "IC is everything you can inhale."
7. Expiratory Capacity (EC)
Volume: 1,500–1,600 mL
Formula:
EC = TV + ERV
Definition: Maximum air exhaled after a normal inhalation.
📌 Clinical Insight: Low EC may indicate lung or chest wall disorders.
8. Functional Residual Capacity (FRC)
Volume: 2,100–2,300 mL
Formula:
FRC = ERV + RV
Definition: Air remaining in lungs after normal expiration. Prevents alveolar collapse.
9. Total Lung Capacity (TLC)
Volume: 5,100–5,800 mL
Formula:
TLC = VC + RV
Definition: Total air your lungs can hold after the deepest inhalation possible.
🏥 Diagnostic Use: Reduced TLC in restrictive lung diseases; increased in obstructive ones.
Table: Pulmonary Volumes vs Capacities
| Type | Volume (Approx.) | Formula | Description |
|---|---|---|---|
| Tidal Volume (TV) | 500 mL | – | Air in normal breathing |
| Inspiratory Reserve (IRV) | 2,500–3,000 mL | – | Extra inhaled after normal breath |
| Expiratory Reserve (ERV) | 1,000–1,100 mL | – | Extra exhaled after normal breath |
| Residual Volume (RV) | 1,100–1,200 mL | – | Air left in lungs after forced exhalation |
| Vital Capacity (VC) | 4,000–4,600 mL | TV + IRV + ERV | Max air exhaled after max inhalation |
| Inspiratory Capacity (IC) | 3,000–3,500 mL | TV + IRV | Max air inhaled after normal exhalation |
| Expiratory Capacity (EC) | 1,500–1,600 mL | TV + ERV | Max air exhaled after normal inhalation |
| Functional Residual (FRC) | 2,100–2,300 mL | ERV + RV | Air left in lungs after normal exhalation |
| Total Lung Capacity (TLC) | 5,100–5,800 mL | VC + RV | Entire volume lungs can hold |
How Are These Measured?
Pulmonary function tests like spirometry are used to measure most volumes (except RV and capacities involving RV, which require body plethysmography).
Relevance in NEET and Medical Exams
- NEET Biology: Often asks formula-based MCQs (e.g., TLC = ?)
- Physiology Viva/Practicals: Used in interpreting spirometry
- Nursing & Allied Exams: Questions on lung function parameters
Common MCQ:
Q: If TV = 500 mL, IRV = 3,000 mL, and ERV = 1,100 mL, what is VC?
A: VC = TV + IRV + ERV = 500 + 3,000 + 1,100 = 4,600 mL
Importance in Health and Disease
- COPD (Chronic Obstructive Pulmonary Disease) – ↑RV, ↓VC
- Asthma – Variable volumes, increased resistance
- Pulmonary Fibrosis – ↓TLC and VC
- COVID-19 Recovery – Spirometry used to monitor recovery
FAQs on Pulmonary Volumes and Capacities
Q1. Why is Residual Volume important?
A1. It prevents the lungs from collapsing by keeping alveoli open.Q2. Which lung volume can’t be measured by spirometry?
A2. Residual Volume (RV) and capacities involving it (FRC, TLC).Q3. What is the largest lung capacity?
A3. Total Lung Capacity (TLC), up to ~5,800 mL.Q4. What affects lung capacity?
A4. Age, gender, physical fitness, altitude, and health conditions.
