Lower probability of FEV1 improvement in asthmatic children exposed to passive smoke

Background: Guidelines advocate the use of spirometry to assess lung function in asthmatic. Inhaled corticosteroid(ICS) therapy is a mainstay of treatment for asthma, but the clinical response is variable. Aim: To assess the time variation of FEV1% in treated children with Persistent Asthma (PA). Methods: 110 children with PA, with two visits between September 2011 and December 2014 at the IBIM pediatric clinic were studied. Spirometry was performed using Pony FX, Cosmed, Italy; values were expressed as %pred using GLI-2012equation. The time trend of FEV1% for each subject was estimated through separate regressions. A linear regression model for the individual slopes (FEV1% average month variations) with respect to the intercepts (initial FEV1% values) was estimated. For the 71 children which had a FEV1%<100 at the first visit, we considered a logit model to evaluate the probability of recovering for different groups, controlling for ICS. Statistical analysis were performed by means of R. Results: For a patient with an initial FEV1%=70, the expected FEV1% month variation is 3.14 (p<0.0001), it decreases by 1.09 (p<0.0001) as the initial FEV1% increases by 10. Regarding to the probability of having an improvement in the lung function (positive variation), a significant difference is observed with respect to passive smoke exposure (PSE). Indeed, the probability of recovering is lower for PSE children (OR=0.30, IC95%=[0.11-0.85]). No significant differences have been found with respect to other subgroups (e.g. for gender, BMI). Conclusions: Children with a worst initial lung condition have a higher rate of increase of the FEV1%. Children with no PSE are more likely to recover from bad lung conditions.