MORPHOLOGIC FEATURES AND FUNCTION OF THE AIRWAYS IN EARLY ASBESTOSIS IN THE SHEEP MODEL

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Abstract
Previous studies of asbestos exposure in humans and small animals have suggested that air flow limitation associated with small airway disease may be an early manifestation of asbestosis, but the subject is still controversial. The airway morphologic aspects and function of the sheep model of the disease were presented. Three groups of 6 sheep were exposed to repeated intratracheal injections of 8 saline (control group), 2 mg UICC [International Union Against Cancer] Canadian chrysotile asbestos in saline (low exposure group) or 128 mg of the same fibers (high exposure group). At the end of the 12th mo. of exposure, an alveolitis had developed in the high exposure group only. Detailed pulmonary function tests were followed within 48 h by lung biopsies to which were added air-He flow-volume curves. Lung biopsies in control and low exposure groups did not demonstrate significant morphologic changes; all biopsies in the high exposure group showed alveolitis characterized by an alveolar and interstitial accumulation of macrophages and mononuclear cells without interstitial fibrosis. On all biopsies, over half of the airways were altered by a similar peribronchiolar process, which at times compressed the peripheral airways. Functionally there was no significant difference between low exposure and control groups. Compared with the control group, the high exposure group had significantly lower vital capacity (2.0 + 0.1 vs. 2.9 + 0.1 l, P < 0.01), lower static lung compliance (91 + 13 vs. 132 + 9 ml/cmH2O, P < 0.05), higher isoflow volume (2.15 + 0.08 vs. 1.4 + 0.1 l, P < 0.01) and higher upstream resistance below the isoflow volume (3.3 + 0.2 vs. 1.3 + 0.3 cmH2O l/s, p < 0.02). In the early asbestos-induced peribronchiolar alveolitis of the sheep, which restricted lung volumes, there was a concomitant small airway disease that significantly limited air flow.