Lung volumes are also known as respiratory volumes. It refers to the volume of gas in the lungs at a given time during the respiratory cycle. Lung capacities are derived from the sum of the different lung volumes. The average total lung capacity of an adult male is about 6 liters. Lung volumes measurement is an integral part of pulmonary function testing. These volumes tend to vary depending on respiratory depth, ethnicity, gender, age, body composition and some respiratory diseases.

Lung volumes are defined as static and dynamic lung volumes. Static lung volumes are based on the completion of maneuvers without being correlated with time, while dynamic lung volumes are obtained from measurements taken during forced inspiration and expiration maneuvers.

Static Lung Volumes

The air volume in the lungs and intrathoracic airways is determined by the elastic properties of the lung parenchyma and surrounding organs and tissues, surface tension, the power of the respiratory muscles, lung reflexes and airway properties. The interaction between the lungs and the chest wall during tidal breathing is the most important factor determining lung volumes. It is based on the completion of maneuvers without being associated with time.

Static Lung Volumes;

• Tidal volume
• Inspiratory reserve volume
• Expiratory reserve volume
• Residual volume

Breath Volume – Tidal Volume (TV)

It is the volume of air inhaled or exhaled during normal breathing. This demonstrates the functions of the respiratory centres, respiratory muscles and mechanics of the lung and chest wall.
Normal adult value is around 10% of vital capacity (VC), about 300-500ml (6-8ml/kg); however, it can increase up to 50% with exercise.

Inspiratory Reserve-Reserve Volume (IRV)

It is the volume of air that enters the lungs with maximal inspiration after a normal inspiration. The IRV is usually kept in reserve, but is used during deep breathing. Normal adult value is 1900-3300ml.

Expiratory Reserve-Reserve Volume (ERV)

It is the volume of air that can be forced out after expiration of the normal tidal volume. Normal adult value is 700-1200ml. ERV decreases with obesity or upper abdominal surgery.

Residual (Residual) Volume (RV)

It is the volume of air remaining in the lungs after the strongest possible expiration. The average adult value is around 1200ml. It is measured indirectly and cannot be measured by spirometry. (RV=FRC-ERV)

Dynamic Lung Volumes

Lung volumes that depend on the velocity of air exiting the lungs are called dynamic lung volumes.

Dynamic Lung Volumes;

• forced expiratory volume
• Maximum voluntary ventilation

Forced Expiratory Volume (FEV1)

It is used to define the amount of air removed from the lungs against time. The amount of air exhaled in the first second of expiration is measured. (FEV1) 80% of normal volumes are expelled in the first second. It is significantly reduced in obstructive diseases.

Maximum Voluntary Ventilation

Maximum voluntary ventilation; It is the maximum amount of air a person can take in one minute. The person breathes quickly and deeply for 15 seconds. The amount of air that can be taken in during this period is multiplied by 4 to determine the maximum amount of air.

Lung Capacities

Lung capacities are derived from the sum of the different lung volumes. The average total lung capacity of an adult male is about 6 liters.

Lung Capacities;

• vital capacity
• inspiratory capacity
• functional residual capacity
• Total lung capacity

Vital Capacity (VC)

It is the sum of the maximum amount of air exhaled after maximum inspiration. The value is approximately 4800mL and varies with age and body size. Tidal volume is calculated by adding the inspiratory reserve volume and the expiratory reserve volume. VC = TV + IRV + ERV.

Inspiratory Capacity (IC)

It is the volume of air taken in with a maximal inspiration after the normal resting expiration level. It is calculated from the sum of the inspiratory reserve volume and the tidal volume. (IC = IRV + TV) It is about 75% of vital capacity.

Functional Residual Capacity (FRC)

It is the amount of air remaining in the lungs at the end of a normal expiration. It is calculated by adding the residual and expiratory reserve volumes. The normal value is about 1800 – 2200 mL. (FRC = RV + ERV.)

Total Lung Capacity (TLC)

It is the total amount of air contained in all parts of the lungs after maximal inspiration. It is the sum of vital capacity and residual volume. (TLC=VC+RV) Approximately 6 liters.

Changes in Lung Volume and Capacity

In Obstructive Diseases;
Total Lung Capacity (TLC): Unchanged or Increased
Vital Capacity (VC): Decreases
Functional Residual Capacity (FRC): Increases
Residual Volume (RV): Increases
Forced Vital Capacity (FVC): Decreases
Forced Expiratory Volume (FEV1): Decreases
FEV1/FVC : Decreases

In restrictive diseases;
Total Lung Capacity (TLC): Decreased
Vital Capacity (VC): Decreases
Functional Residual Capacity (FRC): Decreases
Residual Volume (RV): Decreases
Forced Vital Capacity (FVC): Decreases
Forced Expiratory Volume (FEV1): Decreases
FEV1/FVC : Does not change or increases

References

1. Saryal, Sevgi. “AKCİĞER VOLÜMLERİ.” Bulletin of Thoracic Surgery/Toraks Cerrahisi Bülteni 10.1 (2017).
2. Guyton C, Hall, E. Test book of medical physiology. Elsevier Inc. Philadelphia, Pennsylvania. 2006; p.475-477.
3. Ranu H, Wilde M, Madden B. Pulmonary function tests. Ulster Med J. 2011;80(2):84-90.
4. Lutfi MF. The physiological basis and clinical significance of lung volume measurements. Multidiscip Respir Med. 2017;12:3. Published 2017 Feb 9. doi:10.1186/s40248-017-0084-5