Restricted Pulmonary Function in Cystic Fibrosis

Pulmonary function in patients with cystic fibrosis is characterized primarily by airflow obstruction and hyperinflation of static pulmonary volumes. Elevation in the ratio of residual volume to total lung capacity (RV/TLC) correlates with severity of disease. The TLC calculated from body plethysmographic measurements of thoracic gas volume is usually normal or elevated.’ The TLC by gas dilution techniques (helium dilution of nitrogen washout) may be lower than by plethysmography because of noncommunicating gas volume. Nevertheless, some patients with cystic fibrosis have restricted pulmonary function with reduction in TLC even when measured by body plethysmography. This has been reported occasionally and is thought to represent a severe stage of disease. Here
We conducted this study (1) to better characterize the clinical, radiographic, and pulmonary functional features of restricted patients compared to a matched control group of nonrestricted patients with cystic fibrosis; and (2) to elevate possible mechanisms of restriction.

Materials and Methods
Patients
Twenty patients were selected retrospectively for this study by matched-pair design from 158 patients with cystic fibrosis who received an annual examination during 1984 and 1985 at the University of California San Diego Medical Center. Results of pulmonary function tests of all patients were reviewed to identify restriction by the following criteria: (1) vital capacity (VC) less than or equal to 75 percent of predicted; and (2) TLC by body plethysmography (a) less than or equal to 80 percent of predicted or (b) less than or equal to 85 percent of predicted with airflow obstruction (ratio of the forced expiratory volume in one second [FEVJ/FVC less than 80 percent of predicted; mean forced expiratory flow over the middle half of the FVC [FEF25-75%] less than 65 percent of predicted). The latter criterion was used to define restriction because patients with cystic fibrosis and airflow obstruction typically have measurements of TLC by plethysmography above predicted values (mean values, 109 to 125 percent of predicted in three published series). Thus, even though 85 percent of predicted would be within 95 percent confidence limits for a normal population, it would be considered abnormally low for a patient with cystic fibrosis who has flow obstruction. Patients with evidence of other causes of restrictive pulmonary disease (eg, previous pulmonary resection, pleural effusion, or concurrent pneumonia) were excluded.
Ten patients met the previously specified criteria for restriction (“restricted patients”): six with TLC less than or equal to 80 percent of predicted and four with TLC less than or equal to 85 percent of predicted and airflow obstruction. For each of the ten restricted patients, a control “nonrestricted patient” was selected from the remaining 148 patients matched as closely as possible with respect to sex, age, height, and weight, respectively.
For each of the 20 patients, anteroposterior and lateral chest roentgenograms were selected as close as possible to the date of the pulmonary function tests. In addition, for those patients who returned for the subsequent annual examination in 1985 and 1986, standardized clinical evaluations were performed, and results of repeat pulmonary function tests were obtained.

Category: Pulmonary Function

Tags: airway, cystic fibrosis, Pulmonary Function