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 α-agonist, and lower airway patency by spirometry before and after β2-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-β2 FEV1 were significantly associated (P = .007). The association remained significant after adjustments for sex, body size, FVC, and atopic diseases (β-coefficient 2.85 cm3; 95% CI, 0.42 to 5.29; P = .02). Baseline values of upper and lower airway patency were also significantly associated (β-coefficient 0.89 cm3; 95% CI, 0.26-1.51; P = .01). In addition, blood eosinophil count and nasal eosinophilia were inversely associated with decongested nasal airway patency, β-coefficient –0.42 cm3 (95% CI, –0.77 to –0.07; P = .02) and β-coefficient –0.47 cm3 (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.