Pulmonary function and response to exercise in cystic fibrosis.

Results of physiological studies at rest and during exercise in 41 patients with cystic fibrosis of the lungs are presented. The patients were evenly distributed by age between 5 and 21 years, and were grouped into 3 clinical grades corresponding to mild, moderate, and fairly severe disease. There was a linear relation between tests of lung mechanics such as the FEV and the MVV and the clinical grading. These tests also correlated well with one another. Certain tests, notably those reflecting parenchymal damage such as the TL showed a non-linear relation to clinical severity, deteriorating more rapidly from grade 2 to 3 than from grade 1 to 2. A very specific pattern emerged of enlargement of physiological deadspace even in the mildest cases. As the disease progressed, venous admixture occurred at rest, which was initially returned to normal by exercise. In the severest cases, there was never a complete return to normal. These changes may be explicable in terms of pathology. Exercise was limited by pulmonary mechanics. Total ventilation was increased to accommodate the increased deadspace so that arterial Pco remained normal. Cardiac output was normal. Adequate evaluation of the pulmonary physiological abnormality could be obtained by measuring the FEV (or MVV), TL, and maximum work load possible, but very useful extra information is obtained by measuring arterial saturation (or venous admixture) and dead space.