Measurement of anatomic dead space is by

The anatomic dead space can be measured by analysis of the single-breath N2 curves. From mid-inspiration, the subject takes as deep a breath as possible of pure O2, then exhales steadily while the N2 content of the expired gas is continuously measured. The initial gas exhaled (phase I) is the gas that filled the dead space and that consequently contains no N2. This is followed by a mixture of dead space and alveolar gas (phase II) and then by alveolar gas (phase III). The volume of the dead space is the volume of the gas expired from peak inspiration to the midpoion of phase II.Ref: Ganong review of medical physiology 23rd edition Page no: 600