Single-breath nitrogen test

Buist, A. S., and B. B. Ross. Predicted values for closing volumes using a modified single breath nitrogen test. Amer. Rev. Respir. Dis. 107 744-752, 1973. 

Fig. 14. Typical tracing obtained during the single-breath nitrogen test.

The single-breath nitrogen (Ng) test is a simple, sensitive test whose major usefulness is in its diagnostic value in the early stages of airway obstruction. This test is also valuable in the assessment of anatomical dead space, uneven ventilation, and abnormal intrapulmonary gas mixing (Buist, 1975). 

It is calculated by measuring the nitrogen concentration in expired gas after a single breath of 100% oxygen. The nitrogen wash-out test is the same method used to measure anatomical dead space. Closing volume increases with age and reaches the standing FRC at 70 years and the supine FRC at 40 years. 

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