Alveolar nitric oxide and asthma control in mild untreated asthma

Abstract

BACKGROUND: The role of the peripheral airways in asthma is increasingly being recognized as a potential target for the achievement of optimal control of the disease. We postulated that the inflammatory changes of the small airways are implicated in the lack of asthma control in mild asthma. OBJECTIVE: To test this hypothesis, we measured the alveolar fraction of exhaled NO (CalvNO) in patients with mild asthma with different levels of control of symptoms. METHODS: Seventy-eight patients with asthma (35 men, age, 37 +/- 15 years; FEV1 percentage of predicted, 100% +/- 9%) were studied. Asthma control was assessed by using the Asthma Control Test (ACT). Measurements of exhaled NO at multiple constant flows were performed. RESULTS: Bronchial NO concentrations were 27.1 +/- 20 ppb, and CalvNO levels were 5.7 +/- 3.4 ppb. The ACT score was 20 +/- 4.2. The level of asthma control was not associated with bronchial NO concentrations (rs = 0.16, P = .15). However, a significant correlation was found between the ACT score and CalvNO (rs = 0.25, P = .03). Moreover, CalvNO was significantly higher in patients with uncontrolled asthma than in patients with controlled/partially controlled asthma (6.7 +/- 2.6 ppb vs 4.9 +/- 2.6 ppb, respectively, P = .02). In the subgroup of patients with asthma who underwent extrafine inhaled corticosteroid treatment, the magnitude of the inhaled corticosteroid-induced improvement in asthma control positively correlated with baseline CalvNO at 1 month (rs = 0.39, P = .003) and at 3 months (rs = 0.49, P < .0001). CONCLUSIONS: The alveolar component of exhaled NO is associated with the lack of asthma control in patients with mild, untreated asthma. This observation supports the notion that abnormalities of the peripheral airways are implicated in the mildest forms of asthma.