Sorachai Srisuma MD PhD Sorachai Srisuma MD PhD ssrisuma@rics.bwh.harvard.edu

When, as a result of dynamic compression, mid-size
airways in the base of the lungs collapse during the
"single breath nitrogen washout test," the
percentage of nitrogen in mixed exhaled air
markedly increases.
This is because once the basal airways close, only
the apical airways remain open and continue to
empty.
Because of their low compliance, the apical alveoli
receive less of the inhaled oxygen, thus when they
alone are emptying, the percentage of nitrogen in
the mixed exhaled air markedly increases.