Exhaled carbon monoxide is not flow dependent in children with cystic fibrosis and asthma

Study objectives: Exhaled nitric oxide (eNO) and carbon monoxide (eCO) concentrations are elevated in inflammatory airway diseases like asthma and have been investigated as potential diagnostic markers. For eNO concentrations knowledge about the inverse flow dependency is essential for reproducibility and comparability of measurements. The aim of this investigation was to evaluate a possible expiratory flow dependency of eCO in children with different inflammatory airway diseases. Design: ENO and eCO concentrations were measured electrochemically and via chemiluminescence in the exhaled air of 20 healthy children, 17 stable cystic fibrosis (CF)-patients and 15 steroid-naive asthmatics in a combined analyzer at five different expiratory flows (10, 20, 45, 86, 184 ml/sec). Results: ECO was not flow dependent in any of the three groups. At 45 ml/sec the mean eCO-conceritration of healthy, children was 3.72 +/- 0.23 ppm, of CF-patients 3.67 +/- 0.37 ppm and of asthmatics 4.99 +/- 0.45 ppm. Elevated eCO (p<0.0122) was found in asthmatics but not in CF-children. There was no age dependency and no correlation between eNO and eCO. Conclusions: In contrast to CF-patients in the exhaled air of steroid-naive asthmatics elevated eCO concentrations are found that may serve as non-invasive inflammatory marker. In contrast to eNO, eCO did not show any expiratory flow dependency.