The exhaled gas is tested to determine how much of the tracer gas was absorbed during the breath.

By calculating the dilution of the tracer gas, the test can also be used to estimate the total lung capacity.

For this test, you breathe air that contains a tracer gas through a tube.

In more recent applications, hydrogen is used pure or mixed with nitrogen (sometimes called forming gas) as a tracer gas for minute leak detection.

A common method for measuring ventilation effectiveness is to use a tracer gas.

Then, a tracer gas is added to the air.

The airflow can be deduced by looking at the change in concentration of the tracer gas over time.

Sulfur hexafluoride is also routinely used as a tracer gas in laboratory fume hood containment testing.

During a ventilation scan, a radioactive tracer gas or mist is inhaled into the lungs.

Then you breathe regular air while the amount of tracer gas you exhale is monitored.