Nitrogen washout

Nitrogen washout is a pulmonary function test used to measure the volume of gas in the lungs, known as the Functional Residual Capacity (FRC). The test is performed by having the patient breathe 100% oxygen, which washes out the nitrogen in the lungs. The nitrogen concentration is then measured in the exhaled gas, and the FRC is calculated based on the rate of nitrogen washout.

Procedure

The nitrogen washout test begins with the patient breathing room air, which contains approximately 78% nitrogen. The patient is then switched to breathing 100% oxygen. As the patient exhales, the nitrogen concentration in the exhaled gas is measured. The FRC is calculated based on the rate at which the nitrogen concentration decreases.

The test is typically performed in two stages: the single breath nitrogen washout and the multiple breath nitrogen washout. The single breath test measures the FRC at the end of a normal exhalation, while the multiple breath test measures the FRC at the end of a deep exhalation.

Clinical significance

The nitrogen washout test is used to diagnose and monitor a variety of lung diseases, including chronic obstructive pulmonary disease (COPD), asthma, and pulmonary fibrosis. It can also be used to assess the effectiveness of treatment for these conditions.

In patients with lung disease, the FRC is often increased due to air trapping in the lungs. This can result in a slower rate of nitrogen washout, which can be detected by the test.

Limitations

While the nitrogen washout test is a valuable tool in the diagnosis and monitoring of lung disease, it has some limitations. The test requires patient cooperation and may not be suitable for patients who are unable to follow instructions or who have severe lung disease. In addition, the test may not be accurate in patients with significant airway obstruction or uneven distribution of gas in the lungs.

See also

• Pulmonary function test
• Lung volumes
• Spirometry

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