Consequences of Expiratory Flow Limitation at Rest in Subjects with Cystic Fibrosis.

RATIONALE: Expiratory flow limitation at resting tidal volume (EFLTV) presents a severe mechanical constraint in chronic lung diseases and has not yet been studied longitudinally in cystic fibrosis.

OBJECTIVES

To study the effect of EFLTV as it emerged from simple spirometry on lung function and clinical status in cystic fibrosis.

METHODS

Best year spirometry that included tidal flow/volume curves and the related clinical data were retrospectively collected over 12 ± 3.0 yr/person from 108 subjects with cystic fibrosis. The year in which forced expiratory flow, midexpiratory phase (FEF25-75%, L/s) was equal to tidal peak expiratory flow (L/s) was defined as EFLTV-onset year.

MEASUREMENTS AND MAIN

RESULTS

EFLTV occurred in 55 (51%) subjects, at age 23 ± 6 years. At EFLTV onset, tidal peak expiratory flow and FEF25-75% values were 1.44 ± 0.23 L/s and FEV1 was 62 ± 10% predicted. Within the following 2 years, FEV1 dropped to 48 ± 11% predicted, and 35 (63%) of the subjects reported shortness of breath at rest. Hospital days increased from 5.3 ± 24.6 to 24.12 ± 9.0 d/yr (P = 0.0001). Of the 55 subjects, 29 (53%) received transplant or died, with survival time being 6.9 ± 3.9 years.

CONCLUSIONS

EFLTV onset may be an important pathophysiological event that could influence the natural history of lung function decline in subjects with cystic fibrosis. This may lead to a significant deterioration in lung function in the following 2 years alongside an increase in the number of hospitalization days. The monitoring of FEV1 alone does not offer as good a threshold signal, because values are only moderately reduced. Therefore, identifying EFLTV appearance is potentially a signal for therapeutic intervention. Further studies are warranted to confirm our findings.