Body mass index, lung function, and FeNO in children with positive bronchodilator response: a cross-sectional study

Objective To investigate the association between body mass index (BMI) and pulmonary function in pediatric outpatients with positive bronchodilator response. We hypothesized that BMI is associated with impaired pulmonary function in this population. Methods This cross-sectional study was conducted at the Department of Pediatrics of Mianyang Central Hospital from January 2024 to December 2024. A total of 430 children aged 4–14 years who met the inclusion criteria were enrolled. Based on body mass index (BMI), participants were categorized into an higher BMI group ( n = 78), a normal BMI group ( n = 338), and an lower BMI group ( n = 14). Pulmonary function tests were performed to measure forced vital capacity (FVC), forced expiratory volume in 1 s (FEV 1 ), FEV 1 /FVC ratio, maximum mid-expiratory flow (MMEF), and forced expiratory flow at 25%, 50%, and 75% of FVC (FEF 25 , FEF 50 , FEF 75 ). Bronchodilator responsiveness was evaluated after salbutamol inhalation by measuring changes in FEV 1 and FVC, including absolute and percentage increases. Fractional exhaled nitric oxide (FeNO) levels were measured using standardized procedures. Correlations between BMI, FeNO levels, and pulmonary function parameters were analyzed. Statistical analysis was performed using appropriate tests. A two-tailed P value < 0.05 was considered statistically significant. Results No significant differences were observed in baseline pulmonary function parameters, including FVC% predicted, FEV 1 % predicted, FEV 1 /FVC, MMEF, FEF 25 , FEF 50 , and FEF 75 , across BMI groups (all P > 0.05). A significant difference in FEV 1 /FVC was observed between boys and girls ( P < 0.05). After bronchodilator testing, a significant difference was observed only in the absolute increase in FVC among BMI groups ( P = 0.016), whereas no significant difference was found in FEV 1 improvement. Fractional exhaled nitric oxide (FeNO) levels were positively correlated with the absolute increase in FVC ( r = 0.165, P = 0.002). Conclusion No significant differences were observed in baseline pulmonary function parameters across BMI groups in children aged 4–14 years. However, differences in bronchodilator-induced changes in FVC were identified among different BMI categories, and FeNO levels were positively associated with bronchodilator-induced changes in FVC. These findings indicate that body mass index and FeNO are independently associated with bronchodilator-related changes in lung function in this population, which may be relevant when interpreting pediatric pulmonary function test results.