Upper and lower airway patency are associated in young children.
Although allergic rhinitis and asthma frequently coexist, the nature of this association is poorly understood. Therefore, we examined whether upper and lower airway patency are associated. We investigated 221 6-year-old children from the Copenhagen Prospective Study on Asthma in Childhood birth cohort, assessing upper airway patency by acoustic rhinometry before and after alpha-agonist, and lower airway patency by spirometry before and after beta2-agonist. Furthermore, we measured blood eosinophil count, nasal eosinophilia, total IgE, and fraction of exhaled nitric oxide. Associations were investigated by generalized linear models. Decongested nasal airway patency and post-beta2 FEV(1) were significantly associated (P = .007). The association remained significant after adjustments for sex, body size, FVC, and atopic diseases (beta-coefficient 2.85 cm(3); 95% CI, 0.42 to 5.29; P = .02). Baseline values of upper and lower airway patency were also significantly associated (beta-coefficient 0.89 cm(3); 95% CI, 0.26-1.51; P = .01). In addition, blood eosinophil count and nasal eosinophilia were inversely associated with decongested nasal airway patency, beta-coefficient -0.42 cm(3) (95% CI, -0.77 to -0.07; P = .02) and beta-coefficient -0.47 cm(3) (95% CI, -0.89 to -0.05; P = .03), respectively. We found a strong and consistent association between upper and lower airway patency. This may be due to a common pathology, as suggested by the inverse association between decongested nasal airway patency, blood eosinophil count, and nasal eosinophilia. Alternatively, the association between upper and lower airway patency might reflect a physiologic background for the common comorbidity.