A flow- and pressure-controlled offline method of exhaled nitric oxide measurement in children.

Background: Exhaled nitric oxide (eNO) is a noninvasive marker of airway inflammation. However, previous studies show that the offline value is lower than the online value.

Objective: To compare a standard offline eNO measurement apparatus with a modified apparatus that can monitor flow volume and respiratory pressure.

Methods: We studied 73 cooperative individuals aged 5 to 28 years (32 children: mean age, 8.3 years; 41 adults: mean age, 21.5 years). We modified the standard device by including a flow meter with a manometer and attaching a plastic tube connected to a 3-way valve to control the resistance. The online and offline (measured using the modified device and the standard device) eNO determinations were compared in a single session and were analyzed using a nitric oxide analyzer.

Results: There was a good relationship between the online and modified offline eNO measurements in children. The modified offline method showed a stronger correlation with the online method (r = .97 vs. r = .92), and the modified offline eNO value was more similar to the online eNO value than to the standard offline value. The mean difference between the online and standard offline eNO values was 52%, whereas the mean difference between the online and modified offline eNO values was only 10%.

Conclusions: Using the offline method, we can easily control the resistance and flow volume to reach the same value measured by the online method in childhood respiratory diseases.