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A simple overview of lung function is the intention of this chapter. It is meant to outline basic aspects of respiratory physiology and function, but as with any organ system it is but the tip of the iceberg. The following information is meant as a basic introduction as well as a stimulus for the curious to dig deeper.


Lung volumes can be divided into primary volumes and capacities.

  1. Primary volumes

    1. Tidal volume (TV): The volume of gas that is either inspired or expired during each normal respiratory cycle

    2. Residual volume: The amount of gas that remains in the lungs at the end of a maximal expiratory effort

  2. Capacities

    1. Total lung capacity: The amount of gas contained in the lungs at the end of a maximal inspiratory effort

    2. Vital capacity: The maximum volume of gas exhaled when a patient makes a forceful exhalation after inspiring to the total lung capacity

    3. Functional residual capacity: The volume of gas that remains in the lungs at the end of quiet exhalation

Dynamic lung volumes are as follows:

  1. Forced expiratory volume in 1 second (FEV1): The volume of gas exhaled from the lung after initiation of a forceful exhalation following a maximal inspiration

  2. Forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC) ratio: The ratio of the volume of gas exhaled from the lungs during the first second after forceful exhalation divided by the total volume of gas exhaled after forceful exhalation

Basic Tests of Pulmonary Function

Lung Volumes and Capacities

Despite being simple, Figure 7-1 is an excellent way to understand the various lung volumes and capacities.

Figure 7-1

Lung compartments in normal health and in restrictive and obstructive diseases. Total lung capacity and residual volumes are generally largest in emphysema.

There are three points of reference: (1) total lung capacity which is at the point of maximal inspiratory effort; (2) the total volume at maximal voluntary expiration, or residual volume; and (3) the volume at the end of passive expiration, or functional residual capacity.

This appears to be best reinforced and understood if one performs the maneuvers that are involved in achieving the volumes and capacities.

The lung volumes should be viewed in the context of two opposing forces that are seeking to expand or retract the lung.


The spirometer is widely used in pulmonary function laboratories because it has a nitrogen or helium analyzer, which allows the physician to obtain data concerning lung volumes, capacities, and dynamic lung volumes. By analyzing data obtained with a spirometer, the physician is able to determine ...

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