Alveolar and bronchial NO not associated with asthma control or severity

MedWire News: A study investigating the clinical potential of alveolar and bronchial nitric oxide (NO) measurements shows that these are not relevant markers in the management of patients with asthma.

Alveolar NO concentrations and exhaled NO fraction (FE_NO) were not associated with asthma control or severity in a sample of asthma patients receiving inhaled corticosteroids and long-acting β2-agonists, report Christophe Delclaux (Paris Descartes University, France) and colleagues in the journal Allergy.

Past studies have shown a relationship between exhaled NO and asthma control, specifically in acute asthma and in the presence of recent asthmatic symptoms. According to the authors, this "emphasizes the ability of exhaled NO to indicate major loss of asthma control."

In this multicentre prospective study, the group wanted to determine whether alveolar NO fraction is associated with the level of asthma control and severity when measured at baseline and during subsequent 3-month follow-up.

In total, 200 patients underwent exhaled NO measurements at multiple constant flows based on a two-compartment model, alveolar and bronchial, of NO exchange. Patients were followed up for 12 weeks.

Alveolar NO and FE_NO did not correlate with asthma control at baseline or during subsequent follow-up, as assessed by scores on the Asthma Control Questionnaire (ACQ) or Asthma Control Diary (ACD).

Similarly, there was no significant relationship between modifications of ACQ and ACD scores over time, either an improvement or deterioration, and initial exhaled NO parameters.

Regarding asthma severity, there was no difference in severity assessed by the Global Initiative for Asthma scores across different exhaled NO values at baseline.

In a post hoc analysis, alveolar NO was negatively correlated to maximal expiratory flow 25–75%, suggesting that alveolar NO is a marker of peripheral airway dysfunction, according to the researchers.

“Alveolar and exhaled NO fractions are not indexes of control or severity in asthmatic children and adults under treatment,” Delclaux et al conclude.

They point out that assessing asthma severity is complex, with some studies suggesting the most clinically useful concept of asthma severity is based on the intensity of treatment required to achieve good asthma control.

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