Exhaled nitric oxide in schoolchildren with asthma

Abstract

Background: The fraction of nitric oxide in exhaled air (FENO) is believed to reflect the degree of allergic inflammation present in the lower airways. The diffusing capacity of NO in the airways (DawNO) and the concentration of this gas in the airway wall (FawNO) can be evaluated by determining FENO with different exhalation flow-rates. FENO measurements could be used for studies of the link between nasal and bronchial inflammation in children with allergic rhinitis and asthma.

Aims: The aims of studies I and II were to determine the optimal exhalation flow-rate for measurement of FENO, as well as the levels of DawNO and FawNO in healthy and asthmatic schoolchildren of different ages. Studies III and IV were designed to investigate the possible effects (as reflected by FENO values) of either a nasal challenge with an allergen or nasal treatment with a steroid on bronchial inflammation in allergic schoolchildren suffering from mild-to moderate asthma and rhinitis.

Methods: 15 schoolchildren with asthma and 15 healthy controls participated in studies I and 11; 19 asthmatic children allergic to cats and 10 healthy controls were examined in study III; and 40 children with allergies to animal dander, asthma and mild-to moderate rhinitis participated in study IV. In study III the children were challenged by inserting a cat allergen extract into their nose; while in study IV the subjects were randomly allocated to receive nasal treatment with either mometasone furoate or a placebo. FENO was measured using chemiluminescence at different exhalation flow-rates in studies I and 11 and at a standardised flow-rate of 50 ml/s in studies III and IV. In studies III and IV allergic inflammation was also assessed by measuring the percentage of eosinophils among blood leukocytes and the ECP level in nasal lavage.

Results: In order to achieve optimal reproducibility and maximal ability to discriminate between allergic and healthy children, together with patient comfort, the effect of varying the exhalation flowrate on measurement of FENO was tested and a standard flow-rate of 50 ml/s chosen for routine use. Elevated levels of DawNO and FawNO were observed in the asthmatic children, while a positive correlation between DawNO and the volume of the respiratory dead space was seen only in healthy children. The FENO values were correlated with the percentage of blood eosinophils in both studies III and IV. We did not observe any increase in FENO following nasal challenge with an allergen. Nor was FENO decreased by nasal treatment with steroids, even though there was a decrease in the level of ECP in nasal lavage in this treated group.

Conclusions: An exhalation flow-rate of 50 ml/s should be used routinely in connection with measurement of FENO during a single-breath exhalation by schoolchildren. The increased DawNO value in asthmatic children may be related to the total area of the mucosal surface releasing NO, so that allergic inflammation in the peripheral airways might be associated with an increase in this parameter. The exhaled level of NO was not influenced by nasal challenge with an allergen or nasal treatment with steroids. Thus, our present findings do not support a direct relationship between nasal and bronchial inflammation in mild-to-moderate allergic airway disease.