The Single Breath Nitrogen Test

Abstract

In the search for sensitive tests for the early detection of airways obstruction, the single breath N₂-test is one of the most promising. It is furthermore relatively inexpensive and easy to perform. The subject expires maximally to residual volume (RV) and then inspires a vital capacity (VC) of oxygen. From total lung capacity (TLC) he expires slowly (expired flow rate about 0.3 1/s) back to RV. The N₂-concentration versus inspired and expired volume are recorded on an X-Y-recorder (1, 2). Four phases are usually identified on these curves: phase I represents pure dead space, phase II represents a combination of dead space and alveolar gas, phase III represents alveolar gas and finally phase IV indicates the existence of airway closure and this phase is also called closing volume (CV). It is particularly the slope of phase III which appears to be promising in terms of sensitivity to presumed early changes in the airways or in the lung parenchyma.