Figure 2.

Off-line FeNO measurement during tidal breathing. Mixed (oral and nasal) expired air is sampled via a face mask, connected to an NO-inert balloon via a nonrebreathing valve. To reduce contamination by ambient NO, the inspiratory port can be connected to a NO-free air reservoir (not shown). The measurement should be considered successful if the infants maintains a quite tidal breathing during the whole procedure, if the facemask is tightly fitted to nose and mouth and if at least five tidal breaths are collected.