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.