Effects of Compensatory Lung Growth in Irradiation-Induced Regional Pulmonary Fibrosis in the Baboon1–4

Regional pulmonary fibrosis was induced in juvenile baboons by bilateral exposure of the upper lung zones to 3,000 to 4,000 rads of irradiation with cobalt-60. The resulting lesion was studied by physiologic, histologic, and biochemical analyses. Total lung capacity and vital capacity were decreased in irradiated animals compared to nonirradiated control animals. Decreased lung compliance and diffusing capacity among irradiated animals were due to loss of volume alone. Histologically, lobes obtained surgically 6 months after irradiation and at necropsy 12 months after irradiation showed similar changes. Affected areas showed dense collagenous connective tissue around blood vessels and in thickened alveolar septa. Irradiated lobes had significantly decreased dry weight and lobar content of protein and deoxyribonucleic acid. Although lobar collagen content also was decreased at necropsy, the concentration of collagen was increased in fibrotic areas due to greater loss of other tissue components. Lobar elast...