The role of circulating cells in the healing of vascular prostheses.

PURPOSE: Cells covering the flow surface of vascular prostheses are derived in part from endothelium of adjacent native artery and from capillaries that extend through the pores of the graft. This study is designed to determine whether these endothelial-like cells can also originate from circulating blood cells and if so to identify them with protein markers. METHODS: Pledgets of vascular graft material were suspended within the aortas of dogs with metal stents that isolated the pledgets from the aortic wall. Explanted pledgets were examined for cells containing factor VIII-related antigen and other markers identified with monoclonal antibodies. RESULTS: A monolayer of cells that stained positive for factor VIII formed on pledgets after 7 days. Pledgets removed after 55 days had endothelial cells, smooth muscle cells, macrophages, monocytes, and capillary-like structures which were identified by staining for the monoclonal antibodies 43 beta E3 (vimentin), HHF35 (alpha and gamma muscle actin), CGA7 (smooth muscle actin), and HAM56 (macrophage). Woven and knitted polyester and extruded polytetrafluoroethylene pledgets healed in a similar manner. CONCLUSION: The origin of the cells identified is speculative but they appear to have been derived from circulating cells, possibly stem cells, which are capable of differentiation because the pledgets on which the cells were identified were isolated from aortic wall endothelium and perivascular capillaries.

A collagen coated vascular prosthesis.

A woven, double velour Dacron vascular graft was made nonporous by coating it with a layer of collagen prepared from fresh, young calf skin. Grafts were implanted in the thoracic aorta of 24 mongrel dogs and were examined at intervals up to 180 days. The grafts did not require preclotting or special preparation before being implanted. They sutured easily and did not bleed. When explanted all grafts were patent and covered with neointima. The bovine collagen was almost completely resorbed by 90 days and was replaced with native tissue. The collagen was neither thrombogenic, antigenic, cytotoxic, or pyrogenic.

A new woven double velour vascular prosthesis.

A new woven double velour vascular prosthesis designed to minimize intraoperative blood loss was implanted in 24 animals. Grafts were examined at 3 to 12 month intervals for healing and were compared to woven non-velour grafts implanted in 13 control animals. At 12 months, the velour grafts were 93 to 98% covered with neointima while the control grafts were only 86% covered with neointima. The neointima on the velour grafts was thinner (60 mu) and more vascular than that on the control grafts. Woven double velour grafts were implanted in 20 patients. Minimal bleeding occurred through the grafts which did not require preclotting, were easy to sew, and did not fray.

Thin alveolar epithelial partitions across connective tissue gaps in the alveolar wall of the human lung: ultrastructural observations.

We describe sharply localized attenuated areas in the alveolar walls of 17 of 25 human specimens. In these areas the connective tissue scaffolding of the alveolar septum was interrupted, and the thickness of the alveolar wall was reduced to that of a single or double layer of alveolar epithelium, devoid of basal laminae. Serial sections proved that most such gaps were bridged by a thin partition of intact epithelium continuous with Type I cells at the borders of the gap. These areas were observed infrequently during a systematic ultrastructural survey of specimens from grossly normal areas of lung tissue obtained at surgery or at autopsy. The mean diameter of 25 gaps bridged by a double layer of epithelium was 4.1 +/- 2.0 micrometers, whereas that of 49 gaps bridged by a single layer of epithelium was 5.0 +/- 1.9 micrometers. This contrasted with the mean diameter of 329 interalveolar pores, which was 6.5 +/- 2.4 micrometers (p less than 0.01). The number of profiles of epithelial partitions per centimeter of section profiles of interalveolar septums examined correlated directly with the number of pore profiles (p less than 0.003). This correlation, and the stepwise increase in size of gaps beginning with those bridged by 2 layers of epithelium and moving to those with only a single layer and finally to interalveolar pores, suggests that the epithelium-covered gaps are a transitional stage in the development of pores. This hypothesis is strengthened by the rare occurrence of epithelium-covered gaps in which the epithelial partition is itself interrupted.

Early ultrastructural changes in papain-induced experimental emphysema.

These studies show that very soon after exposure of canine lungs to crude papain mixed with a marker (India ink), the alveolar surface-active lining was both morphologically and functionally altered, and alveolar macrophages were destroyed in significant numbers. These changes occurred before other identifiable major alterations. The morphologic changes were characterized by replacement of the normal alveolar surface lining by an amorphous material adhering to the alveolar surfaces and penetrating the pores of Kohn, which were significantly enlarged. Type II epithelial cells and alveolar macrophages were increased in number, with a significant proportion of the latter observed to be disintegrating. Polymorphonuclear leukocytes were also noted in increased numbers, but this was also observed in control lungs (instilled only with saline plus India ink). Functionally the alveolar surface lining as studied in lung extracts showed an abnormal stability index after either in vivo or in vitro exposure to crude papain. These findings suggest that the early effects of this exogenous protease on the lung are interrelated, alveolar surface lining injury appearing to set the stage for accelerated macrophage lysis, with the probable release of phagocytosed exogenous protease as well as intracellular endogenous proteases. These events may represent early steps in the pathogenesis of experimental papain-induced pulmonary emphysema.

Ultrastructural studies of canine interalveolar pores (of Kohn).

Normal canine lungs were prepared for ultrastructural studies using two different routes for fixation: the airways route and the vascular route. Using the airways route, under conditions of controlled pressure, scanning and transmission electron microscopic studies of alveolar surfaces allowed identification of an average of 19 alveolar pores per exposed alveolar surface, each pore averaging approximately 3 micron. in diameter. The alveolar surface was honeycombed in appearance, with the walls of multiple capillaries bulging into the alveolar space. Using the other route, vascular perfusion of the lungs with the fixative and controlling pressures in both the vascular and airway compartments, scanning electron microscopic studies showed that most exposed alveoli exhibited a smooth or slightly wrinkled surface, essentially devoid of pores and averaging only three pores per alveolus. By transmission electron microscopy, alveolar surfaces were found to be covered with an extracellular material suggestive of lung surfactant; alveolar pores, averaging approximately 1 micron. in diameter, were filled with the same material. It is concluded that most alveolar pores of normal dogs are bridged by and filled with lung surfactant. These findings can be demonstrated most reliably by using vascular perfusion of the lungs for introducing the fixative.