What Are the Types of Lung Volumes and How Are They Measured
Lungs are a pair of organs located within the chest, which help in breathing. In simple words, lungs remove carbon dioxide and bring oxygen to the blood. Lungs are the primary respiratory organs of animals. In spite of the functionality, the structure and capacities are different amongst various species.
Different animals have different lung capacities based on the size of the body and the activities they perform. For example, the lung capacity of an elephant is greater than that of a human due to its large body size. Also, the lung capacity of animals like cheetahs and gazelles is very high because they require a large amount of oxygen for their muscles in order to run at very high speed.
A human lung has a capacity to hold a maximum of six litres of air. The device that is used to measure the volume of air involved is called a spirometer. It is a medical apparatus that is used to determine the amount of air you are able to breathe in and out and the time you take to completely exhale the air after you take a deep breath.
Lung volume and lung capacity are used to measure air present in the lungs. Lung volume measures the amount of air present for a living being to inhale or exhale. On the other hand, lung capacity is the volume of air in the lungs upon the maximum effort of inspiration.
Lung Volumes and Capacities
The lung is the primary respiratory organ of animals. However, the structure and capacities are different amongst various species. For example, the structure of a dog’s lungs is smaller than humans. Also, the lungs of a sparrow are different as they can fly.
Lung volumes and capacities are two significant terms in the respiratory system. It is determined based on human breath, which is a full respiratory circle of one inspiration and expiration.
Lung Volume vs Lung Capacity
There is a stark difference between these two terms. The first one shows the quantity of air for a single function. For example, breathing in or out. The last one tells the maximum amount of air lungs can hold. For instance, it is the sum of two or more lung volumes.
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Lung Volumes and Lung Capacities
Tidal Volume
The tidal volume is the total amount of air inhaled or exhaled during normal breathing. On an average 500 ml of air is utilised during normal respiration in a healthy man.
Inspiratory Reserve Volume
An inspiratory reserve volume is a supplementary volume, ranging between 2500 to 3100 ml of air which could be inhaled effectively after the inspiration of a standard Tidal Volume.
Expiratory Reserve Volume
The extra volume of air that can be exhaled from the lungs with effort following a normal tidal volume expiration. An expiratory reserve volume is about 1200 ml that could be forcibly exhaled out after the expiration of a standard tidal volume.
Residual Volume/Reserve Volume
The residual volume is the total volume of air that is around 1100 ml to 1200 ml, residing in the lungs after the reserve volume is exhaled or breathed out.
Lung Capacity
Total Lung Capacity
The total lung capacity is the total volume of air in the lungs after a forced inspiration. The lung capacity of a healthy man is around 6000 ml.
TLC = TV + ERV + IRV + RV
Vital Capacity
The vital capacity is the total volume of air that can be breathed out after inhalation limit or maximum air that a person can breathe in after forced expiration. It is an essential measure of a person’s respiratory health. A decreased vital capacity indicates restrictive lung disease where the lungs cannot expand completely. In the general case of normal vital capacity, the improper functioning of lungs indicates obstructive lung disease, where the lungs are blocked in the airways.
VC = TV + ERV + IRV
Inspiratory Capacity
The amount of extra air inhaled above tidal volume during a forceful inspiration. The average inspiratory reserve volume is about 3000 mL in males and 2100 mL in females.
IC = TV + IRV
Functional Residual Capacity
Functional Residual Capacity is the volume remaining in the lungs after a normal exhalation. In a healthy individual, this is about 3L.
FRC = ERV + RV
Respiratory Volumes and Capacity Measurement
Primarily, the following methods are most popular in calculating these two factors:
Nitrogen washout - It helps in calculating anatomical/serial dead space.
Helium dilution - These measures total lung capacity.
Relevant MCQs
The amount of air a person cannot breathes out is about 1200 ml. It is-
Residual volume
Vital capacity
Expiratory reserve volume
Ans. a)
What is the function of alveoli?
Removing air
Gaseous exchanges and diffusion
Allowing air to enter alveoli
Ans. b)
3. A person normally passively inhales and exhales 500 mL of air. This is the _______.
Tidal volume
Expiratory capacity
Residual Volume
Ans. a)
FAQs on Lung Volumes and Their Physiological Significance
1. What are lung volumes?
Lung volumes are the measurable amounts of air present in the lungs during different phases of the breathing cycle. In respiratory physiology, lung volumes describe how much air is inhaled, exhaled, or remains in the lungs.
- They are measured using spirometry.
- They include tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume.
- They help assess lung function in health and disease.
2. What is tidal volume?
Tidal volume is the amount of air inhaled or exhaled during a normal, quiet breath. The tidal volume (TV) in a healthy adult is about 500 mL per breath.
- It occurs during relaxed breathing.
- It does not include forced inhalation or exhalation.
- It is important for maintaining normal gas exchange in the alveoli.
3. What is inspiratory reserve volume (IRV)?
Inspiratory reserve volume is the maximum amount of additional air that can be inhaled after a normal tidal inspiration. The inspiratory reserve volume (IRV) is usually about 2500–3000 mL in adults.
- It is measured after a normal breath in.
- It represents the extra capacity of the lungs during forced inhalation.
- It contributes to overall vital capacity.
4. What is expiratory reserve volume (ERV)?
Expiratory reserve volume is the maximum amount of air that can be forcibly exhaled after a normal tidal exhalation. The expiratory reserve volume (ERV) is about 1000–1200 mL in healthy adults.
- It is measured after a normal breath out.
- It reflects the ability to expel additional air from the lungs.
- It also contributes to vital capacity.
5. What is residual volume and why is it important?
Residual volume is the amount of air that remains in the lungs after maximum forced exhalation. The residual volume (RV) is about 1100–1200 mL in adults.
- It prevents lung collapse by keeping the alveoli partially inflated.
- It allows continuous gas exchange between breaths.
- It cannot be measured directly by simple spirometry.
6. What is the difference between lung volumes and lung capacities?
Lung volumes are individual air measurements, while lung capacities are combinations of two or more lung volumes. In respiratory physiology:
- Lung volumes include TV, IRV, ERV, and RV.
- Lung capacities include vital capacity (VC), total lung capacity (TLC), inspiratory capacity (IC), and functional residual capacity (FRC).
- Capacities are calculated by adding specific volumes together.
7. What is vital capacity?
Vital capacity is the maximum amount of air that can be exhaled after a maximum inhalation. The vital capacity (VC) equals tidal volume + inspiratory reserve volume + expiratory reserve volume.
- VC = TV + IRV + ERV
- It measures the functional strength of the lungs.
- It decreases in restrictive lung diseases such as fibrosis.
8. What is total lung capacity?
Total lung capacity is the total amount of air the lungs can hold after maximum inhalation. The total lung capacity (TLC) equals vital capacity plus residual volume.
- TLC = VC + RV
- It includes all four lung volumes.
- It is typically about 6000 mL in a healthy adult male.
9. How are lung volumes measured?
Lung volumes are measured using spirometry and specialized pulmonary function tests. The main methods include:
- Spirometry – measures TV, IRV, ERV, and vital capacity.
- Helium dilution or body plethysmography – used to measure residual volume and total lung capacity.
- Breathing into a calibrated device that records air movement.
10. Why are lung volumes important in respiratory physiology?
Lung volumes are important because they help assess breathing efficiency and diagnose respiratory diseases. In human physiology:
- They indicate how well the lungs expand and contract.
- They help detect obstructive diseases like asthma and restrictive diseases like pulmonary fibrosis.
- They guide treatment decisions and monitor disease progression.
