Residual volume

Residual volume (RV) is the volume of air remaining in the lungs after a maximal exhalation. It is a component of lung volumes and capacities, which are measured in pulmonary function tests.

Definition

Residual volume is defined as the volume of air still remaining in the lungs after the most forcible expiration possible. This volume cannot be measured, only calculated. It is a standard part of lung volumes, along with tidal volume, inspiratory reserve volume, and expiratory reserve volume.

Measurement

Residual volume can be measured using a number of techniques, including body plethysmography, helium dilution, and nitrogen washout. These techniques are often used in pulmonary function tests to assess lung health and diagnose respiratory conditions.

Body Plethysmography

Body plethysmography is a method of measuring lung volumes that involves the use of a body box or plethysmograph. The subject breathes against a closed system, and changes in pressure allow for the calculation of lung volumes, including residual volume.

Helium Dilution

The helium dilution technique involves the subject breathing in a known volume of helium. The concentration of helium in the lungs is then measured, and this information is used to calculate lung volumes.

Nitrogen Washout

In the nitrogen washout technique, the subject breathes 100% oxygen, and the exhaled gas is analyzed for nitrogen content. The volume of nitrogen washed out of the lungs is used to calculate lung volumes.

Clinical Significance

Residual volume can be increased in conditions such as chronic obstructive pulmonary disease (COPD) and asthma, where airway obstruction leads to air trapping in the lungs. Conversely, it can be decreased in conditions such as restrictive lung disease, where lung expansion is limited.

See Also

• Lung volumes
• Pulmonary function tests
• Chronic obstructive pulmonary disease
• Asthma
• Restrictive lung disease