Five- to seven-year course of pulmonary function in cystic fibrosis.

The pulmonary function records of 132 patients with cystic fibrosis followed for 
5 to 7 years were reviewed. Changes in forced vital capacity, 
1-sec forced expiratory volume, mean forced expiratory flow during the middle 
half of the forced vital capacity, and 1-sec forced expiratory volume 
as a percentage of forced vital capacity were examined. There was 
considerable variation in the rates of change, but the general pattern 
was consistent with a theory of exponential decline, mean forced expiratory 
flow during the middle half of the forced vital capacity showing 
the earliest and most dramatic changes. The pulmonary function of 33 
patients (25 per cent) remained stable or improved throughout follow-up, possibly 
reflecting mild forms of lung disease or the efficacy of therapy. 
Twenty of these patients (15 per cent) maintained completely normal pulmonary 
function. The rate of decline in pulmonary function values, with progress 
of the disease, was steeper in the female patients. 