nitrogen washout

Indications

• measurement of anatomic dead space in the lung during a respiratory cycle
• estimation of functional residual capacity & absolute lung volume

Procedure

• a single nitrogen breath, or multiple breaths
• breath of 100% oxygen with exhalation through a one-way valve
• nitrogen content & volume are measured
• a plot of the nitrogen concentration vs expired volume is obtained that shows increasing nitrogen concentration from zero to the % of nitrogen in the alveoli*

* the nitrogen concentration is initially zero because the subject is exhales the dead space oxygen they just breathed in

More general terms

• pulmonary function test (PFT)