Lung elastic recoil in cystic fibrosis.

The pressure-volume behavior of the lung was studied in 24 patients with 
cystic fibrosis. Isovolume flow-pressure relationships were measured in 7 of these 
patients, and a modification of the flow-volume test was evaluated for 
detection of flow reduction in a separate group of 63 patients. 
Relative to results in a control group of 31 normal subjects, 
13 of the 24 patients had grossly abnormal pressure-volume curves with 
excessive stiffness of the lung near maximum volume and loss of 
recoil at lower volume. Closing volumes in these patients were often 
high enough to cause significant disturbances in gas exchange and the 
elevated closing volumes were quantitatively explained by the low values for 
elastic recoil. The modified flow-volume test detected mild flow reduction in 
many patients who otherwise had normal pulmonary function tests. Loss of 
recoil per se did not account for the low maximum expiratory 
flows, since "upstream" resistances were high. However, pressure-flow curves were effort-dependent 
at high lung volumes even in patients with severe airway obstruction, 
showing that time constants of emptying varied widely in these patients. 
It was concluded that deterioration of lung function in cystic fibrosis 
involves more than airway obstruction and that the worsening gas trapping 
is explained by a progressive loss of lung elastic recoil. 