Progressive flow-to-volume dysanapsis in cystic fibrosis: a predictor for lung transplantation?

Rationale: Airways obstruction and lung volume restriction, major features of lung disease in cystic fibrosis (CF), may regress independently, causing dysanapsis between these parameters.

Objectives: To explore the significance of dysanapsis (FEF(25-75)/FVC) ratio in CF.

Methods: 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."

Measurements And Main Results: 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.

Conclusions: 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.