Lung Volumes and Lung Capacity: Definition and Difference

What are Lung Volumes and 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 quantity of air that can be inspired or expired at different phases, namely tidal volume which is air in and out during 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 (With Definitions & Normal Values)

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.

Lung Capacities (Formulas + Normal Values)

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

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

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

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

Differences Between Lung Volumes and Capacities (Table)

The differences between lung volumes and capacities are:

Clinical Significance

The clinical significance of lung volumes and lung capacities is:

• These measurements are essential pulmonary function tests.

• Abnormal values help to diagnose various respiratory diseases like COPD, asthma, and fibrosis.

• By evaluating lung volumes, clinicians can determine breathing efficiency.

• Understanding these respiratory values helps tailor ventilation strategies during anesthesia and ICU.

Lung Volumes and Capacities NEET MCQs (With Answers & Explanations)

Important topics for NEET are:

• Lung Volumes

• Lung Capacities

Practice Questions for NEET

Q1. Which of the subsequent lung volumes or capacities cannot be accurately determined using spirometry, a technique commonly employed in pulmonary function testing?

1. Functional residual capacity (FRC)

2. Residual volume (RV)

3. Total lung capacity (TLC)

4. Vital capacity (VC)

Correct answer: 2) Residual volume (RV)

Explanation:

Spirometry is a technique used to measure lung volumes and capacities, but it is not capable of directly measuring the residual volume (RV). The residual volume is the amount of air that remains in the lungs after maximal exhalation, and it cannot be measured accurately using spirometry alone.

Hence, the correct answer is option 2) Residual volume (RV).

Q2. A person breathes in some volume of air by forced inspiration after having a forced expiration. This quantity of air taken in is

1. Total lung capacity

2. Tidal volume

3. Vital capacity

4. Inspiratory capacity

Correct answer: 3) Vital capacity

Explanation:

The quantity of air taken in after a forced expiration followed by a forced inspiration is known as vital capacity (VC). Speaking mathematically, VC = TV + IRV + ERV.

Where, TV = Tidal volume, IRV = Inspiratory Reserve Volume, and ERV = Expiratory Reserve Volume. Hence, the correct answer is option 3) Vital Capacity.

Q3. In breathing movements, air volume can be estimated by

1. Stethoscope

2. Hygrometer

3. Sphygmomanometer

4. Spirometer

Correct answer: 4) Spirometer

Explanation:

A spirometer is used to estimate the breathing volumes. A spirometer is a medical device that measures the volume of air exchanged during breathing. It helps estimate various lung capacities and is essential for assessing respiratory health and function.

Hence, the correct answer is option 4) Spirometer.

Also Read:

• MCQ Practice on Lung Volumes and Capacities

• Breathing and Exchange of Gases

• Vocal cords

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