Isolated abnormal FEF75% detects unsuspected bronchiolar obstruction in CF children

Background: Physiologic detection of bronchiolar obstruction in children with cystic fibrosis (CF) may be clinically unsuspected because of normal routine spirometry despite bronchiectasis on lung CT. Methods: Children from two accredited CF facilities had spirometry obtained every 3 months when clinically stable. Pre-bronchodilator maximum expiratory flow volume curves were retrospectively analyzed over 16 years to detect an isolated abnormal FEF75%, despite normal routine spirometry. Results: At Miller Children’s and Women’s Hospital (MCWH), an abnormal FEF75% was initially detected in 26 CF children at age 7.5 ± 4 (SD) years despite normal routine spirometry initially. FEF75% remained an isolated abnormality for 2.5 ± 1.5 years after it was initially detected in these 26 CF children. At Cohen Children’s Medical Center (CCMC), despite normal routine spirometry initially, abnormal FEF75% occurred in 13 children at age 11.7 ± 4.5 years, and abnormal FEF25–75% in 10 children at age 11.8 ± 5.3 years. Conclusions: FEF75% was most sensitive spirometric test for diagnosing both early and isolated progressive bronchiolar obstruction. Data from CCMC in older children demonstrated the simultaneous detection of abnormal FEF75% and FEF25–75% values consistent with greater bronchiolar obstruction when serial spirometry was initiated at an older age. Impact: There is very little published spirometric data regarding diagnosis of isolated small airways obstruction in CF children.FEF75% can easily detect unsuspected small airways obstruction in CF children with normal routine spirometry and bronchiectasis on lung CT and optimize targeted modulatory therapies.