Progressive Flow-to-Volume Dysanapsis in Cystic Fibrosis

Abstract

Airways obstruction and lung volume restriction, major features of lung disease in cystic fibrosis (CF), may regress independently, causing dysanapsis between these parameters. To explore the significance of dysanapsis (FEF(25-75)/FVC) ratio in CF. Yearly best spirometry data, collected during 8.6 ± 1 year per patient, was determined from 93 patients with CF. Three groups were formed according to initial FEV(1). Group-N (n = 35; control, FEV(1) above 80%predicted); Group-B (n = 38; FEV(1) below 80% predicted); and Group-LT (n = 20; data collected before lung transplantation). The yearly decline in spirometry indices was defined in relation to the preceding year. Decline exceeding -2 z scores from Group-N in each index was considered "rapid decline." Group-N's yearly decline of FEV(1), FEF(25-75), and FEF(25-75)/FVC were similar and reached -1.88 ± 2.93%, -1.41 ± 3.37%, and -1.81 ± 4.48%, respectively. Rapid decline was equal to -6.5%, -10.8%, and -8.1%, respectively. Group-B's indices declined faster than that of Group-N, but did not exceed 1 z score. Group-LT showed a rapid decline solely in FEF(25-75)/FVC (mean z score = -6.4 ± 2.5; P < 0.0001), which sprouted abruptly from the regular course of regression 4 ± 1.3 years before transplantation. The rapid decline in FEF(25-75)/FVC was found in 19 of 20 patients from Group-LT and five patients from other groups (now waiting for transplantation). The phenomenon did not correlate with initial FEV(1) (%predicted) or age. Having airway hyperreactivity increased the risk of rapid decline in FEF(25-75)/FVC. Roughly 4 years before lung transplantation and independent of FEV(1) (%predicted), FEV(1) decline rate, or age, an abrupt rapid dysanapsis occurs. Findings imply insufficient ventilation/lung volume unit and insinuate a powerful marker for estimating lung translation time in CF.