Lung function abnormalities in cystic fibrosis and changes during growth.

Static lung volumes (VC, TLC, FRC, RV), elastic recoil pressure of the lungs (Pst(1) at 100, 90, and 60% of TLC), static lung compliance [Cst(1)], specific airway conductance at FRC level (Gaw/TGVex), forced expiratory volume in the first second (FEV1), maximal expiratory flows (Vmax.) at 25 and 50% of VC and at 60% of TLC, and "upstream" airway conductance (Gus) at 60% of TLC were studied in 28 patients with cystic fibrosis, 5 to 25 years old, over a period of 1 to 5 years. The data were compared individually with normal values, related to body height in the form of regression equations and expressed in percentage of predicted values. From the indices assessing airway function, Vmax. at low lung volumes, Gus at 60% TLC, RV and RV/TLC were the functional parameters most consistently abnormal. Among the indices characterizing lung elasticity, Pst(1) at 60% TLC was the most abnormal. Generally, the values of the majority of lung function indices [VC, TLC, FRC, Pst(1)] declined during growth. Vmax. at all lung volumes and Gus at 60% TLC did not deteriorate with growth probably due to the great abnormality of these parameters already in young patients. It was also observed that lung function did not change significantly over a period of 1 to 5 years corresponding to a 10 cm increase in body height. However, over that period, lung function improved in some of the subjects, did not change in over 50% of the cases and deteriorated in the others.