Study objective: We hypothesized that the radiographic distribution of disease is important in determining pulmonary function, with the lower lung zones of more importance than the upper lung zones. To test this hypothesis, we retrospectively studied patients with cystic fibrosis, a disease with a known proclivity for the upper lung zones.
Subjects and methods: Two hundred seventy-six chest radiographs obtained at 2- to 3-year intervals from 51 patients were scored by two radiologists using a 100-point visual severity scale. The distribution of disease was assessed by dividing the lungs into four equal horizontal zones and scoring each zone for the severity of disease. There were 146 concurrent chest radiographs and pulmonary function tests from which multiple linear regression was used to correlate these zonal scores with FEV1/FVC percent predicted.
Results: There was excellent interobserver agreement, intraclass correlation coefficients >0.7. The distribution of disease became predominant in the upper lung zones as the patients aged. Although the median score in the upper lung zones was nearly twice that of the lower lung zones, the lower lung zones were nearly three times (partial F ratio; 6.9 lower zone score vs 2.4 upper lung zone score) as important in determining pulmonary function.
Conclusion: The regional distribution of disease is important in determining pulmonary function. Sparing of the lower lung zones is important in preserving pulmonary function.