Lung Volumes and Capacities

The total volume contained in the lung at the end of a maximal inspiration is subdivided into volumes and subdivided into capacities.

There are 4 volume subdivisions They do not overlap They can not be further divided When added together equal total

lung capacity

Lung Capacities

Are subdivisions of the total volume that include two or more of the 4 basic lung volumes

Basic Lung Volumes

Tidal Volume: TVThe amount of gas inspired or

expired with each normal breath.About 500 ml

Basic Lung Volumes

Inspiratory Reserve Volume: IRVMaximum amount of additional

air that can be inspired from the end of a normal inspiration.

Basic Lung Volumes

Expiratory Reserve Volume: ERVThe maximum volume of

additional air that can be expired from the end of a normal expiration.

Basic Lung Volumes Residual Volume: RV

The volume of air remaining in the lung after a maximal expiration. This is the only lung volume which cannot be measured with a spirometer. Gas dilution tech

nitrogenhelium

Body Plethysmograph

Lung Capacities Total Lung Capacity: TLC

The volume of air contained in the lungs at the end of a maximal inspiration.

Called a capacity because it is the sum of the 4 basic lung volumes

TLC= RV+IRV+TV+ERV

Lung Capacities

Vital Capacity: VC The maximum volume of air that can be

forcefully expelled from the lungs following a maximal inspiration.

Called a capacity because it is the sum of inspiratory reserve volume, tidal volume and expiratory reserve volume.

VC= IRV+TV+ERV = TLC - RV

Lung Capacities

Functional Residual Capacity: FRC The volume of air remaining in the

lung at the end of a normal expiration.

Called a capacity because it equal residual volume plus expiratory reserve volume.

FRC= RV+ERV

Lung Capacities Inspiratory Capacity: IC

Maximum volume of air that can be inspired from end expiratory position.

Called a capacity because it is the sum of tidal volume and inspiratory reserve volume.

This capacity is of less clinical significance than the other three.

IC= TV+IRV

Respiratory Diseases Restrictive Disease:

Makes it more difficult to get air in to the lungs. They “restrict” inspiration. Decreased VC; Decreased TLC, RV, FRC Includes:

Fibrosis Sarcoidosis Muscular diseases Chest wall deformities

Respiratory Diseases

Obstructive Disease Make it more difficult to get air out of the

lungs. Decrease VC; Increased TLC, RV, and FRC Includes:

Emphysema Chronic bronchitis Asthma