How Are Lung Volumes Measured? Methods, Tools, and Practice
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.
For a more detailed account of respiratory mechanisms, go through our additional study materials today! Don’t forget to take a look at the rest of our notes for a detailed insight on various chapters of Biology.
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 Explained: Definitions, Types, and Formulas
1. What are the four primary lung volumes as per the CBSE Class 11 syllabus?
The four primary lung volumes are distinct measurements of air in the lungs that do not overlap. They are:
- Tidal Volume (TV): The amount of air inhaled or exhaled during a normal, quiet breath. It is approximately 500 mL.
- Inspiratory Reserve Volume (IRV): The additional volume of air that can be forcibly inhaled after a normal inspiration. It is about 2500-3000 mL.
- Expiratory Reserve Volume (ERV): The extra volume of air that can be forcibly exhaled after a normal expiration. It is about 1000-1100 mL.
- Residual Volume (RV): The volume of air that remains in the lungs even after a maximal, forceful exhalation. It is about 1100-1200 mL.
2. What is the key difference between a lung volume and a lung capacity?
The key difference lies in how they are measured. A lung volume is a direct, singular measurement of air (like Tidal Volume or Residual Volume). In contrast, a lung capacity is a calculated value, representing the sum of two or more lung volumes. For example, Vital Capacity is not a single volume but the sum of IRV, TV, and ERV.
3. What are the important lung capacities and how are they calculated?
Lung capacities are combinations of different lung volumes. The main capacities are:
- Inspiratory Capacity (IC): The total volume of air a person can inhale after a normal exhalation. Formula: IC = TV + IRV.
- Functional Residual Capacity (FRC): The volume of air remaining in the lungs after a normal exhalation. Formula: FRC = ERV + RV.
- Vital Capacity (VC): The maximum amount of air a person can exhale after a maximal inhalation. Formula: VC = IRV + TV + ERV.
- Total Lung Capacity (TLC): The maximum volume of air the lungs can hold after a maximal inspiration. Formula: TLC = RV + ERV + TV + IRV or TLC = VC + RV.
4. Why can't the Residual Volume (RV) be measured directly using a spirometer?
A spirometer measures the volume of air that is moved in and out of the lungs. The Residual Volume (RV) is, by definition, the air that remains in the lungs after the most forceful exhalation possible. Since this air does not move, it cannot be measured by a spirometer. It is calculated indirectly by subtracting the Expiratory Reserve Volume from the Functional Residual Capacity, which is measured using other techniques like helium dilution.
5. What is the significance of Vital Capacity (VC) in assessing respiratory health?
Vital Capacity (VC) is a crucial indicator of respiratory health because it reflects the strength of the respiratory muscles and the elasticity of the lungs. A lower-than-normal VC may suggest restrictive lung diseases (like fibrosis) or obstructive lung diseases (like asthma or emphysema). Athletes often have a higher VC, indicating efficient and strong respiratory function.
6. How do the lung volumes of a regular athlete typically compare to those of a non-athlete?
An athlete who engages in regular aerobic training typically develops a more efficient respiratory system. While their Total Lung Capacity (TLC) may not be significantly larger, their Vital Capacity (VC) is often greater. This is because they can take deeper breaths (higher IRV) and exhale more forcefully (higher ERV). This adaptation allows for more effective oxygen uptake to meet the high demands of their muscles during exercise.
7. How do external factors like age and altitude affect a person's lung capacities?
Lung capacities are not static and change due to various factors. With age, lung tissue loses elasticity and respiratory muscles may weaken, typically causing a gradual decrease in Vital Capacity after the age of 25-30. Living at high altitude, where oxygen levels are lower, can cause the body to adapt by increasing lung capacity over time to maximise oxygen intake with each breath.
8. If Total Lung Capacity is about 6 litres, why do we only breathe about 500 mL in a normal breath?
This is a matter of energy efficiency. Using the full Total Lung Capacity (TLC) for every breath would require maximal effort from the respiratory muscles and be extremely tiring. Normal, quiet breathing only uses a small fraction called the Tidal Volume (TV). The remaining volumes, the Inspiratory and Expiratory Reserve Volumes, are kept in reserve for when the body's oxygen demand increases, such as during exercise or stress.
