Small airways functioning in obesity asthma patients – a cross-sectional study

<b>Background:</b> In the last years, there has been interest in the role of small airways abnormalities in asthma. However, the role of small airways functioning in obese asthma patients is not well described. <b>Aim:</b> To explore differences in small-airways functioning between obese and non-obese asthma patients; To explore differences in small-airways functioning between obese asthma patients with and without increased factional exhaled nitric oxide (Fe_NO). <b>Methods:</b> The Netherlands Epidemiology of Obesity (NEO) study is a population based cohort study in 6671 participants of whom 513 had asthma. 57 patients were excluded due to missing values. Differences in small airways functioning (forced expiratory flow at 25-75% of FVC (FEF_25-75)) between obese (BMI≥30 kg/m²) and non-obese asthma patients were explored using linear regression analysis. In the non-obese and obese subgroups FEF_25-75 was compared between patients with high (≥25 ppb) and low (&lt;25 ppb) Fe&lt;_NO levels. Analyses were adjusted for confounders. <b>Results:</b> Among 465 asthma patients, 51% was obese and 25% had high FeNO levels. The predicted FEF_25-75 did not differ between non-obese and obese asthma patients (adjusted mean difference (MD) -0.66 % predicted, 95% CI: -4.6 to 5.9). In non-obese asthma patients, the FEF_25-75 did not differ significantly between patients with low and high Fe_NO (adjusted MD -8.7 %, 95% CI: -17.5 to 0.1). In obese asthma patients, the FEF_25-75 was lower in patients with high Fe_NO compared to patients with low Fe_NO (adjusted MD -10.7 %, 95% CI -18.9 to -2.5). <b>Conclusions:</b> Obese and non-obese asthma patients do not differ regarding small airways functioning. Small airways functioning was decreased in patients with high Fe_NO levels, suggesting that FEF_25-75 might contribute to the diagnosis of asthma.