Small Airway Involvement in Pediatric Severe Asthma: Association with Clinical and Functional Characteristics

<bold>Background:</bold> in spirometry Small Airways Involvement (SAI) has been defined in different ways: 1) caliber reduction (FEF25-75 < 65%), 2) relative caliber reduction (dysanapsis = FEF25-75/FVC < 80% with FEF25-75 > 65%, and 3) bronchodilator response in FVC > 10% (air trapping by SAI). These variables and their associations have not been studied in pediatric Severe Asthma (SA). <bold>Aims:</bold> to investigate SAI in children with Severe Asthma and describe its clinical and functional associations. <bold>Methods:</bold> basal data were obteined from children with SA followed in a prospective observational study. Pre and post β2 spirometries were obtained from first visit. The population was divided in groups: A) SAI without major airway involvement (SAI criteria and FEV1 ≥ 80%); B) Major and Small Airway Involvement (M-SAI) (FEV1 < 80% and SAI); C) No airway involvement-NAI (FEV1 ≥ 80% and not SAI). The association of each group with BMI, spirometric values, FeNO, asthma control (ACT), Sleep Disordered Breathing (SDB=Pediatric Sleep Questionnaire ≥ 0.33), rhinitis, and severe exacerbations in the previous year was estimated (Fischer exact test). <bold>Results:</bold> 113 patients: 42% SAI; 15% M-SAI; and 43% No airway involvement. 45% females, 34% overweight-obesity, 28% FENO > 30 ppb, 65% controlled asthma, 51% SDB, 38% no treatment adherence and 36% improper inhaler technique. SAI was associated with improper inhaler technique (p 0.002), no treatment adherence (p 0.01) and SDB (p 0.01). <bold>Conclusions:</bold> In our children with Severe Asthma SAI was significantly associated with SDB, improper inhaler technique and no treatment adherence.