Skip to main content
Fig. 1 | Respiratory Research

Fig. 1

From: Diagnostic accuracy of capnovolumetry for the identification of airway obstruction – results of a diagnostic study in ambulatory care

Fig. 1

Tracing of a volume-based capnogram during a single expiration. The capnogram is divided into four phases: phase 1, the CO2-devoid volume of the dead space; phase 2, transition between airway and alveolar gas; phase 3, alveolar part; phase 4, final emptying of the lung (in tidal breathing normally absent or inconspicuous). (A) Parameters of capnographic measurement: s2 and s3 represent the slopes (concentration vs. volume) of the expiratory CO2-curve in phase 2 and phase 3, respectively. The volume expired during phase 2 or phase 3 is termed ‘volume phase 2’ or ‘volume phase 3’. In order to compute the parameters ‘area phase 2’ and ‘area phase 3’ a horizontal line at the end-tidal CO2 concentration is drawn. The area above the CO2 concentration curve bounded by the horizontal line in phase 2 and phase 3, respectively, represent the parameters ‘area phase 2’ and ‘area phase 3’. These areas are complements of the areas under the curve. The angle alpha (α) is formed by the slopes of phases 2 and 3

Back to article page