Lung Volumes and Lung Capacity: Definition and Difference

Lung volumes and capacities are essential concepts in understanding the functioning of the respiratory system. They measure the amount of air the lungs can hold during various breathing phases, such as normal breathing, deep inhalation, and exhalation. In this article, Lung Volumes and Lung Capacities are discussed. Lung volumes and capacity is a topic of the chapter Breathing and Exchange of Gases in Biology.

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1. What are Lung Volumes and Lung Capacities?
2. Lung Volumes
3. Lung Capacities

What are Lung Volumes and Lung Capacities?

Lung volumes and lung capacities are significant parameters of respiratory physiology that allow for determining the functionality of the lungs. Lung volumes are also defined as the precise quantity of air that can be inspired or expired at different phases, namely tidal volume which is air in and out during ordinary breathing, inspiratory reserve volume expiratory reserve volume and residual volume.

Lung capacities are sums of these volumes and refer to the amount of air the lungs can contain or deliver, like vital capacity, which is the amount of air that expires after a maximal inspiratory effort –the maximum amount of air that expires after completion of forced inspiration and total lung capacity which is the sum of all the lung volumes. As opposed to lung volumes, which determine the amount of air inside the lungs or the ability of the lungs to contain air, lung capacities give an overview of the lungs’ efficient capacity as well as their capacity to intake and utilise air.

Lung Volumes

The lung volume can be defined by the following components:

Tidal Volume (TV)

• Definition: Tidal volume refers to the volume of air that is inhaled or expelled during normal, quiet respiration.

• Normal Values: Generally, it tends to be 500 mL per breath in adults A trigger in the respiratory tract causes the adult to breathe in approximately 500 mL of air per breath.

Inspiratory Reserve Volume (IRV)

• Definition: Inspiratory reserve volume is the amount of air which can be taken in during a forced inspiration in addition to that which was inspired during normal respiration.

• Normal Values: It is usually estimated to be between 2500 to 3000 millilitres in an adult.

Expiratory Reserve Volume (ERV)

• Definition: ERV is the volume of air that can be forcibly expired after a normal expiration of the vital capacity.

• Normal Values: Generally in adults about 1400 mL a day or about 4800 mL in the body.

Residual Volume (RV)

• Definition: The amount of air left in the lungs when the individual has expelled as much air as he could is known as residual volume.

• Normal Values: It is normally 1,200 mL for adults but it depends on the gender and age of the people.

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Lung Capacities

The lung capacity can be explained using the following:

Inspiratory Capacity (IC)

• Definition: Inspiratory capacity is the patient’s ability to take the maximum possible amount of air into the lungs from a resting state.

• Normal Values: In general, mobile total blood volume varies from 3500 ml in adults of average weight, whether it is male or female.

• IC = TV + IRV

Components:

• Tidal Volume (TV): The extent of the volume of air that is moved in through the mouth or nose and out through the mouth in normal respiration.

• Inspiratory Reserve Volume (IRV): The amount of air which can be drawn into the lungs besides the normal inspiration.

Functional Residual Capacity (FRC)

• Definition: It is the total volume of air that can be left in the lungs after the individual has expelled the air mandatory for respiration.

• Normal Values: Normally ranges from 2400mL in adults, to as much as 3500mL in warm, working conditions, and consuming foods high in protein and carbohydrate.

• FRC = ERV + RV

Components:

• Expiratory Reserve Volume (ERV): The amount of air that can be expelled from the lungs through force after the normal expulsion of air.

• Residual Volume (RV): The quantity of air left in continuance in the lungs after normal expiration.

Vital Capacity (VC)

• Definition: Vital capacity is the maximum volume that can expire after reaching the maximum inspiration.

• Normal Values: Normally, is approximately 4800 mL in adults.

• VC = TV + ERV + IRV

Components:

• Tidal Volume (TV): Tidal volume refers to the volume of air that is inhaled or expelled during normal, quiet respiration.

• IRV (Inspiratory Reserve Volume): The amount of air which can be drawn into the lungs besides the normal inspiration.

• ERV (Expiratory Reserve Volume): The amount of air that can be expelled from the lungs through force after the normal expulsion of air.

Total Lung Capacity (TLC)

• Definition: TLC, Total lung capacity, is the amount of air that fills the lungs to their maximum.

• Normal Values: Normally in adults, it should be around 6000 mL.

• TLC = TV + ERV + IRV + RV

Components:

• Tidal Volume (TV): Tidal volume refers to the volume of air that is inhaled or expelled during normal, quiet respiration.

• Inspiratory Reserve Volume (IRV): The amount of air which can be drawn into the lungs besides the normal inspiration.

• Expiratory Residual Volume (ERV): The amount of air that can be expelled from the lungs through force after the normal expulsion of air.

• Residual Volume (RV): The quantity of air left in continuance in the lungs after normal expiration.

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