Stephen L. Hilbert
Center for Devices and Radiological Health
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The Journal of Thoracic and Cardiovascular Surgery | 1999
Stephen L. Hilbert; Rafael E. Luna; Jun Zhang; Yining Wang; Richard A. Hopkins; Zu-Xi Yu; Victor J. Ferrans
OBJECTIVE The purpose of this study was to determine whether apoptosis of endothelial and connective tissue cells is responsible for the loss of cellularity observed in implanted aortic allograft valves. METHODS Fresh (n = 6) and cryopreserved (n = 4) aortic allograft valves were retrieved at 2 days to 20 weeks after implantation in an ovine model. Sections of these valves were studied with the use of histologic and electron microscopic methods, nick end-labeling and dual immunostaining for factor VIII-related antigen and proliferating cell nuclear antigen, followed by counterstaining for DNA and laser scanning confocal fluorescence microscopic observation. RESULTS The endothelial cells and cusp connective tissue cells of implanted valvular allografts showed loss of proliferating cell nuclear antigen (indicative of cessation of mitotic activity) and evidence of apoptosis (nick end labeling). The latter was manifested by nuclear condensation and pyknosis, positive nick end labeling, and formation of intra- and extracellular apoptotic bodies derived from the fragmentation of apoptotic cells. These changes began to develop at 2 days after implantation, peaking at 10 to 14 days, and became complete by 20 weeks, at which time the valves had the typical acellular morphologic features of allografts implanted for long periods of time. CONCLUSIONS Apoptosis occurs in endothelial cells and cuspal connective tissue cells of implanted allografts and appears to be a cause of their loss of cellularity. This apoptosis may be related to various factors, including immunologic and chemical injury, and hypoxia during valve processing and reperfusion injury at the time of implantation.
Journal of Vascular and Interventional Radiology | 2004
William F. Pritchard; Diane Wray-Cahen; John W. Karanian; Stephen L. Hilbert; Bradford J. Wood
PURPOSE The principal risks of needle biopsy are hemorrhage and implantation of tumor cells in the needle tract. This study compared hemorrhage after liver and kidney biopsy with and without radiofrequency (RF) ablation of the needle tract. MATERIALS AND METHODS Biopsies of liver and kidney were performed in swine through introducer needles modified to allow RF ablation with the distal 2 cm of the needle. After each biopsy, randomization determined whether the site was to undergo RF ablation during withdrawal of the introducer needle. Temperature was measured with a thermistor stylet near the needle tip, with a target temperature of 70 degrees C-100 degrees C with RF ablation. Blood loss was measured as grams of blood absorbed in gauze at the puncture site for 2 minutes after needle withdrawal. Selected specimens were cut for gross examination. RESULTS RF ablation reduced bleeding compared with absence of RF ablation in liver and kidney (P <.01), with mean blood loss reduced 63% and 97%, respectively. Mean amounts of blood loss (+/-SD) in the liver in the RF and no-RF groups were 2.03 g +/- 4.03 (CI, 0.53-3.54 g) and 5.50 g +/- 5.58 (CI, 3.33-7.66 g), respectively. Mean amounts of blood loss in the kidney in the RF and no-RF groups were 0.26 g +/- 0.32 (CI, -0.01 to 0.53 g) and 8.79 g +/- 7.72 (CI, 2.34-15.24 g), respectively. With RF ablation, thermal coagulation of the tissue surrounding the needle tract was observed. CONCLUSION RF ablation of needle biopsy tracts reduced hemorrhage after biopsy in the liver and kidney and may reduce complications of hemorrhage as well as implantation of tumor cells in the tract.
Archives of Pathology & Laboratory Medicine | 2000
Kazuhiro Matsui; William Riemenschneider; Stephen L. Hilbert; Zu-Xi Yu; Kazuyo Takeda; William D. Travis; Joel Moss; Victor J. Ferrans
BACKGROUND Little is known of the morphology of the pneumocytes lining the parenchymal cysts in lymphangioleiomyomatosis (LAM). OBJECTIVE To evaluate the structural characteristics of the alveolar epithelial cells in LAM. METHODS Immunohistochemical and electron microscopic studies were performed on lung tissue from 22 women with pulmonary LAM. RESULTS Epithelial cells that reacted with PE-10 (a mouse monoclonal antibody that recognizes the surfactant apoprotein A in type II pneumocytes) and TTF-1 (an antibody that identifies nuclear transcription factor found in type II pneumocytes) were the predominant cell type lining the surfaces of lesions of LAM and normal areas of lung. Scanning and transmission electron microscopic studies confirmed that these cells were type II pneumocytes as demonstrated by (1) apical microvilli, (2) electron-dense lamellar bodies, and (3) cytoplasmic projections that extended from the basal surfaces into the underlying connective tissue, where they made extensive contact with interstitial connective tissue cells. A few cells had morphologic characteristics of type I pneumocytes, including large flat surfaces lacking microvilli. Cells that appeared intermediate between type I and type II pneumocytes were observed occasionally. CONCLUSIONS These observations and the reactivity of these cells with antibody to proliferating cell nuclear antigen demonstrate that extensive hyperplasia of type II pneumocytes is a major characteristic of LAM.
Archive | 1989
Stephen L. Hilbert; Victor J. Ferrans; Michael R. Jones
The evolution of cardiac valve substitutes for the management of valvular heart disease has been taking place for approximately a quarter-century. A heterogeneous group of components, including pyrolytic carbon, polymeric, and tissue-derived materials, have been configured into mechanical, polymeric, bioprosthetic, and biologic valve designs.1–11 For the purpose of this review, however, only tissue-derived xenograft and allograft cardiac Valves are discussed.
Archive | 2005
Stephen L. Hilbert; Frederick J. Schöen; Victor J. Ferrans
and clinical experience has served to identify clearly the pathologic changes that occur following the implantation of fresh and allograft heart valves in the systemic circulation in juvenile sheep and in human patients. The morphologic findings in this series of investigations demonstrate that a marked reduction in mitotic activity occurs in both the endothelial cells and connective tissue cells of the allografts within a few days of implantation. The allograft valve cusps become acellular within one to two weeks of implantation. We have provided evidence, based on animal studies, that apoptosis is a major cause of the loss of cell viability in allografts during the first 30 days after implantation. We have shown that these changes occur in optimally harvested and processed fresh and cryopreserved allograft valves. The documentation of apoptosis by histochemical staining and by the ultrastructural demonstration of apoptotic bodies within allograft leaflets will have to be confirmed in clinically explanted allograft valves. These findings are in conflict with the expectation that viable cells are retained and are capable of replicating and participating in the remodeling of the allograft cusp. The temporal evolution of the microscopic appearance of explanted cryopreserved allografts following implantation suggests that changes related to harvesting, handling, ischemic time, freezing and thawing are the factors which are most responsible for the loss of donor cell viability. Moreover, excessive neutrophilic and/or mononuclear inflammatory cell infiltrates are absent in most explanted cryopreserved valves at all time points, including those concurrent with histologic deterioration and loss of cellular staining. This leads to the conclusion that immunologic phenomena cannot be causally implicated in the processes involved in allograft degeneration. Moreover, evidence of immunologic injury to the valves is not seen (i.e., no valvular scarring or loss of cellularity) even in heart transplant patients in whom immunologic phenomena caused cardiac allograft failure, or in patients who sustained multiple episodes of parenchymal rejection. Collectively, these results suggest that despite the demonstrable ability of allograft valves to induce a detectable humoral and/or cellular allogeneic response, some valves, depending on yet defined processing or innate variables, may be relatively resistant to immune injury, perhaps due to some combination of high flow, lack of valvular microvasculature, or low alloantigen expression, and/or lower expression of relevant adhesion or co-stimulator molecules. However, a recent study showed that all the aortic valve allografts explanted from infants had failed due to aortic insufficiency. Intimal hyperplasia, extensive fibrous sheath formation and focal infiltrates of B-lymphocytes (CD20positive) and T-lymphocytes (CD43-positive) were observed in the allografts retrieved from the infants.We are not aware of any investigations which have clearly demonstrated immunologically mediated allograft dysfunction, although many studies do indicate that 26 Implications of Explant Pathology Studies
Archive | 2005
Stephen L. Hilbert; Frederick J. Schöen; Victor J. Ferrans
An increase in the actuarial freedom from primary tissue failure and reoperation has been reported following the use of cryopreserved allograft heart valves. It has been hypothesized that the increased durability of cryopreserved heart valves is related to the retention of viable cuspal cells; however, other investigators have suggested that this observation is the consequence of tissue processing methods which do not necessarily preserve cell viability but minimally damage the valvular extracellular matrix. If the retention of viable donor cuspal fibroblasts is responsible for the noted increase in allograft valve durability, then every effort should be made to optimally harvest and process allograft heart valve tissue in a manner that ensures minimal loss of viable cuspal cells. Currently, in most clinical centers, allograft heart valves are harvested, disinfected and cryopreserved in the following manner: 1) warm ischemic time (see discussion to follow) is generally restricted to 24 hours or less; 2) cold temperatures (4°C) are used for dissection to procure the allograft and for subsequent transportation; 3) disinfection typically involves the immersion of the allograft for 24 hours (4°C) in solutions containing antibiotics (e.g., cefoxitin, lincomycin, polymyxin B, vancomycin); 4) the use of dimethlysulfoxide (10%) as a cryoprotectant, and 5) controlled-rate freezing (1 degree per minute to -70°C) of the allograft valve and subsequent storage in liquid nitrogen vapor (-170°C). Independent of the processing method selected, there is an obligatory interval of time, referred to as the warm ischemic time, which elapses from the cessation of the donor’s heartbeat to the initial cooling of the allograft in transport media. The duration of warm ischemia represents a period of potential cellular injury and cell death, which significantly alters the number of viable cells present in the cusp at the time of implantation. Detailed ultrastructural studies evaluating the extent of cellular injury induced by increasing the duration of the warm ischemic intervals have been conducted on porcine, and human aortic and pulmonary valves. Morphologic indicators of reversible cellular injury (dilatation of endoplasmic reticulum, cytoplasmic edema, mitochondrial swelling) are observed early (e.g., 40 minutes) after the death of the donor and gradually progress to irreversible injury (mitochondrial flocculent densities, karyolysis, cell disruption) through 12 hours of warm ischemia. A significant increase (i.e., 10% to 25%) in the number of irreversibly injured cells occurs between 12 and 24 hours of warm ischemia. Approximately 40% of the cuspal cells in human cryopreserved allograft valves demonstrate ultrastructural evidence of irreversible injury following 16 to 20 hours of warm ischemia. As the warm ischemic time increases, a progressive loss of endothelial cells, fibroblasts and myofibroblasts occurs. Endothelial cell loss was most notable initially, while the 24 Effects of Preimplantation Processing on Allograft Valves
The Journal of Thoracic and Cardiovascular Surgery | 1987
Stephen L. Hilbert; Victor J. Ferrans; Tomita Y; Eidbo Ee; Michael Jones
American Journal of Tropical Medicine and Hygiene | 1997
Zilton A. Andrade; Sonia G. Andrade; Moysés Sadigursky; Robert J. Wenthold; Stephen L. Hilbert; Victor J. Ferrans
Journal of Biomedical Materials Research | 1990
Stephen L. Hilbert; Mary K. Barrick; Victor J. Ferrans
Journal of Biomedical Materials Research | 1986
Stephen L. Hilbert; Victor J. Ferrans; W. Milton Swanson