Pulmonary volumes and Capacities

Most lung volumes and capacities can be measured with a spirometer. Total lung capacity, functional residual capacity, and residual volume cannot be measured with a spirometer.

Pulmonary Volumes and Capacities

Figure 37-3 shows a record of consecutive breathing cycles at different depths of inhalation and exhalation. This image was taken using a device called a spirometer.

The total volume of the lung is equal to the maximum volume to which the lungs can expand. Four lung volumes are shown on the left side of Figure 37-1.

• Tidal volume (VT) is the amount of air (approximately 500 ml) that is inhaled and exhaled in each normal breath. • Inspiratory Reserve (IRV) is the additional volume of air (approximately 3000 mL) that can be ingested over and above the normal tidal volume.

• Expiratory reserve (ERV) is the amount of extra air (approximately 1100 ml) that can be exhaled by forced exhalation after the end of normal exhalation.

• The residual air volume (RV) is the amount of air that remains in the lungs after the most intensive exhalation (approx. 1200 ml).

Vital capacity is a combination of two or more lung volumes. Spirometry is listed in Figure 37-1 and can be explained as follows:

Inspiratory capacity (IC) is equal to tidal volume plus inspiratory reserve. This is the amount of air (about 3,500 ml) that a person can inflate to the maximum, starting from normal exhalation levels.

• Functional Remaining Capacity (FRC) is equal to the expiratory reserve capacity plus the remaining capacity. This is the amount of air left in the lungs at the end of normal exhalation (about 2,300 ml).

Vital capacity (VC) is equal to inspiratory reserve + tidal volume + expiratory reserve. This is the maximum amount of air that a person can expel after first filling the lungs to the maximum and then releasing to the maximum (about 4600 ml).

• Total lung capacity (TLC) is the maximum volume to which the lungs can be expanded with the maximum possible expiratory effort (approximately 5800 ml); Equals vital capacity plus residual volume.