Transit time analysis of the forced expiratory vital capacity in cystic fibrosis.

Transit time analysis of the forced expiratory vital capacity maneuver was applied 
to 37 patients with cystic fibrosis 8 to 22 years of 
age. This analysis divides the vital capacity into segments of air 
and assigns a transit time to each segment. The characteristics of 
the distribution of these transit times are used as measurements of 
pulmonary function. The quantities were compared with the forced vital capacity, 
1-sec forced expiratory volume, ratio of 1-sec forced expiratory volume to 
vital capacity, peak flow, forced expiratory flow during the middle half 
of the forced vital capacity, maximal expiratory flow at 25 per 
cent of the vital capacity, specific airway conductance, and arterial PO2 
of these patients. The standard deviation of the transit times was 
the most frequently abnormal. The mean transit time had the largest 
range of values in terms of its own standard deviation, and 
it was the best single estimate of over-all lung function because 
it correlated almost equally with large and small airway function. The 
coefficient of cariance of transit times was specific in detecting abnormality 
of small airways and was as sensitive in the detection of 
minimal lung disease as the standard deviation of transit times. 