ORGANIZATION OF COLLAGEN AND ELASTIC FIBERS STUDIED IN STRETCH PREPARATIONS OF WHOLE MOUNTS OF HUMAN VISCERAL PLEURA

Fibers of the collagenous and elastic systems are most relevant in the double mechanical action of visceral pleura (VP), i.e. volume limitat ion and the generation of elastic recoil pressure. In this work we stu died the organization of these fibrous components of VP in two situati ons: normal lungs and bullous disease. We employed histochemical metho ds on conventional histological slides and on thin spreads of whole mo unts of visceral pleura. In addition, the scanning electron microscope was also used. According to our results, pleural function is made pos sible by the combination of both the elastic and collagenous fiber sys tems, each one having its intrinsic organizational pattern. Marked alt erations of pleural bullous structure are observed with changes in lun g volume. Fibers of the elastic and collagenous systems are clearly in terdependent elements. Collagenous fibers are interwoven in a plaited structure that closely resembles the osiers of a wicker basket, indica ting that collagen fibers allow for lung volume increase up to a point of maximal stretching of the system. The pleural contribution to lung elastic recoil pressure originates from the elastic network which tur ns back to its resting position when inspiratory pressures are negligi ble. The pleural immobility in bullous disease is associated with an a lmost complete absence of elastic fibers and the presence of very thic k collagen fibers, suggestive of a cicatricial process, devoid of any characteristic pattern of distribution.