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Biomedical subjects

S K Williams

Publications and source records attributed to S K Williams.

At least 37 records · Page 2Linked to original sources
PubMed1998

Vein patching reduces neointimal thickening associated with prosthetic graft implantation.

PURPOSE: Modified anastomotic techniques utilizing autogenous vein-cuffs or patches have been devised with the hope of improving prosthetic graft patency. The mechanisms of the presumed improvement in patched anastomoses have never been elucidated and remain speculative. We characterized the healing response of the Taylor vein patch in prosthetic arteriovenous fistulae in a canine model of intimal hyperplasia. METHODS: Six adult dogs underwent placement of bilateral (6 patched, 6 control) 4-mm diameter expanded polytetrafluoroethylene loop femoral artery-vein fistulae. Serial duplex ultrasound examinations confirmed graft patency until explant at 6 weeks. Differential light microscopy with computerized image analysis was performed on serial 5-microm sections. Intimal thickness through the venous anastomosis and outflow veins of Taylor patch and control (nonpatched) grafts were compared. Cell type-specific immunocytochemical antibody stains for smooth muscle cells (alpha SMC actin) and endothelial cells (von Willebrand factor) were performed. RESULTS: Eleven of 12 grafts remained patent for 6 weeks, 1 control graft thrombosed. Mean duplex-derived peak systolic velocities of patched (96 cm/sec) and control (108 cm/sec) grafts were similar. Microscopy revealed more intimal pannus anastomotic suture line ingrowth in controls (mean thickness = 178 microm) than Taylor patched grafts (mean 147 microm, p = 0.0002). Significantly less intimal thickening was present in the outflow vein of patched (mean thickness = 90 microm) versus control grafts (mean 195 microm, P <0.0001). The intima maintained a single cell layer of vWF + endothelial cells, while the majority of the cells comprising the lesion expressed alpha SMC actin. CONCLUSION: Perianastomotic pannus is primarily composed of intimal smooth muscle cells. Neointimal thickening is significantly reduced in prosthetic arteriovenous fistulae created with the Taylor vein patch in a canine model. Reduction in perianastomotic intimal thickening may explain the reported clinical improvement in prosthetic bypass graft patency when modified with vein patch techniques.

Anastomosis, Surgical↗
PubMed1998

Sensory and objective characteristics of broiler meat from commercial broilers fed rendered whole-hen meal.

The objective of the study was to determine sensory and objective characteristics of chicken breast and thigh meat from commercial broilers fed rendered whole-hen meal (RHM), produced from commercial laying hen mortality losses. Breast and thigh muscles from 90 6-wk-old straight-run broilers fed starter and grower diets consisting of either 0, 8, or 12% RHM, were evaluated for sensory characteristics, instrumental texture and compositional profiles. The RHM treatments had no adverse effects (P > 0.05) on juiciness, chicken flavor intensity, tenderness, or compositional profiles for the breast or thigh meat. Off-flavor scores for all treatments were above the threshold value, indicating that the RHM imparted no off-flavors to the breast and thigh meat. Warner-Bratzler shear measurements were similar (P > 0.05) for breast meat from broilers in all treatments. No shear measurements were conducted for the thigh meat. It was concluded that RHM can be incorporated into the diets of chicks at levels of up to 12% without causing objectionable sensory characteristics in the cooked broiler meat.

Animal Feed↗
PubMed1998

Sodium lactate affects sensory and objective characteristics of tray-packed broiler chicken breast meat.

The objective of this study was to determine the antimicrobial properties of sodium lactate solutions adjusted to various pH values. The effectiveness of sodium lactate increases with increased concentrations; however, there are off-flavor development problems associated with increasing concentrations of sodium lactate above 2.0%. This study evaluated the effects of 2% sodium lactate treatments, adjusted to various pH values, on sensory characteristics, instrumental texture, and microbial populations of tray-packed broiler breast meat. Breast meat was treated with either tap water (pH 7.85) or 2% sodium lactate solutions (pH 7.30, 5.50, 5.00, 4.50, and 4.00) and stored at 2 +/- 1 C for 12 d. Approximately 15% of the panelists reported acidic aftertastes in samples treated with pH 5.00 sodium lactate solutions, and 10% of the panelists reported slight sodium or metallic off-flavor in all samples treated with sodium lactate. Instrumental texture measurements were similar (P > 0.05) for all treatments. Sodium lactate (pH 7.30 and 5.50) enhanced (P < 0.05) cooking yields and retarded the growth of spoilage bacteria (pH 5.50 and 5.00). Due to the development of severe discoloration and intense acidic off-odors and -flavors, testing was not conducted on samples treated with pH 4.50 and 4.00 sodium lactate solutions.

Animals↗
PubMed1998

Sensory and objective characteristics of broiler meat from commercial broilers fed rendered spent hen meal.

The objective of the study was to determine sensory and objective characteristics of broiler breast and thigh meat from commercial broilers fed rendered spent hen meal (RSHM) from hatch to 42 d of age. Breast and thigh muscles from 90, 6-wk-old straight-run broilers (i.e., mixed male and female broilers) fed starter and grower diets consisting of either 0, 8, or 12% RSHM were evaluated for sensory characteristics, instrumental texture, and compositional profiles. The RSHM treatments had no adverse effects (P > 0.05) on juiciness, chicken flavor intensity, tenderness, or compositional profiles for the breast or thigh meats. Off-flavor scores for all treatments were above the threshold value, indicating that the RSHM imparted no off-flavors to the breast and thigh meats. Warner-Bratzler shear measurements were similar (P > 0.05) for breast meat from broilers in all treatments. No shear measurements were conducted for the thigh meat. It was concluded that RSHM can be incorporated into the diets of broilers at levels of up to 12% without causing objectionable sensory characteristics in the cooked broiler meat.

Animal Feed↗
PubMed1997

Effects of balloon dilatation on ePTFE structural characteristics.

The search for less invasive treatments for cardiovascular disease has lead to the development of endovascular stent grafts, metallic and alloy stents surrounded by prosthetic vascular graft material. Introduced intravascularly, the deployment of stent grafts requires balloon dilatation of the device which results in expansion of the stent along with the vascular graft material. We hypothesized that balloon dilatation of stent grafts would alter the physical structure of the prosthetic graft material. In this study, noncompliant angioplasty balloons were used to dilate expanded polytetrafluoroethylene (ePTFE), a material commonly used for endovascular stent-graft technology. The maximal outer diameter (inflated balloon within the lumen) and the recoiled outer diameter (balloon removed) of two types of ePTFE, 3-mm inside diameter (i.d.) thin wall (30-micron internodal distance) and 4-mm i.d. standard wall (30-micron internodal distance), were measured to compare material recoil. Following balloon dilatation, ePTFE samples were prepared for scanning electron microscopic examination and the following parameters were measured: wall thickness, internodal distance, nodal width, interfiber distance, and fiber width. Following primary dilatation, both types of ePTFE recoiled approximately 20% regardless of inflated balloon diameter. However, following eight repetitive balloon dilatations, recoil decreased to approximately 10%. Scanning electron microscopic analysis revealed variations in internodal distance and significant decreases in wall thickness, nodal thickness, and interfiber distance. Fiber width was significantly decreased following dilatation of 3 mm, but not 4 mm ePTFE. Our data support our initial hypothesis that balloon dilatation alters the structure of ePTFE.

Blood Vessel Prosthesis↗
PubMed1997

Differential healing and neovascularization of ePTFE implants in subcutaneous versus adipose tissue.

The preclinical evaluation of polymer biocompatibility is often performed using animal subcutaneous implant models. The choice of subcutaneous tissue as the implant site is due to a number of factors including simplicity of the surgery involved. Results from subcutaneous implants cannot necessarily be extrapolated to other tissues due to the differences in cellular composition of tissues. We have evaluated and compared the healing characteristics of expanded polytetrafluoroethylene (ePTFE) discs implanted in either subcutaneous tissue or epididymal fat pad tissue in rats. Following 3 and 5 weeks of implantation, the healing characteristics of discs were evaluated histologically with particular emphasis on tissue and polymer neovascularization. Implants placed in subcutaneous tissue exhibited limited formation of new microvascular elements within and directly in contact with the polymer, and the formation of an extensive fibrous capsule. In contrast, ePTFE implanted in the epididymal fat pads of rats exhibited extensive neovascularization of tissue surrounding the polymer, penetration of these microvascular cells into the graft interstices for distances < or = 100 microns and no morphological evidence of a fibrous capsule. The rat epididymal fat pad provides an alternative tissue for polymer healing evaluations. Due to the extensive presence of fat in subcutaneous tissue in humans, we suggest the fat pad model provides a more relevant preclinical evaluation of the healing characteristics of polymers used clinically in anatomic positions which contain significant amounts of fat.

Adipose Tissue↗
PubMed1997

The effects of porosity on endothelialization of ePTFE implanted in subcutaneous and adipose tissue.

Healing of biomaterial implants varies depending on the type and structure of material and the tissue surrounding the implant. In this study we examined structural differences of 30 microm, 60 microm, and 100 microm expanded polytetrafluoroethylene (ePTFE) using scanning electron microscopy, and we also investigated differences in healing for these three different porosity ePTFE grafts implanted within subcutaneous tissue and adipose tissue. Scanning electron microscopic examination of 30 microm, 60 microm, and 100 microm ePTFE revealed structural differences and differences in fiber density within the internodal space. Circular patches (6 mm in diameter) of 30 microm ePTFE were implanted within subcutaneous tissue and epididymal fat pads of male Sprague-Dawley rats. After 5 weeks, the implants were removed and analyzed for fibrous capsule formation, endothelialization, and for activated monocytes and macrophages in association with the material. Histological evaluation revealed dense fibrous capsule formation surrounding only the 30 microm ePTFE subcutaneous implants. From immunohistochemistry data obtained, we generated an Endothelialization Index (measure of neovascularization) and a Monocyte/Macrophage Index (measure of inflammatory response) for each sample. Consistently, 60 microm ePTFE had the greatest Endothelialization Index at both implant sites while 100 microm ePTFE generally had the largest values for the Monocyte/Macrophage Index. These data indicate that both the structure of the material and the site of implant influence the healing characteristics of ePTFE and suggest that activated monocytes and/or macrophages associated with the implant may inhibit endothelialization of ePTFE.

Adipose Tissue↗
PubMed1997

Immunocytochemical determination of cell type and proliferation rate in human vein graft stenoses.

PURPOSE: Vascular reconstructions are prone to fail as a result of the development of stenotic lesions, which have historically been attributed to myointimal hyperplasia. In animal models, these lesions are associated with marked proliferative smooth muscle cell (SMC) response to vascular injury. However, recent studies using sensitive immunocytochemical techniques in human lesions have generally failed to detect significant cellular proliferation. To clarify the role of cellular proliferation in humans, we characterized the cellular composition and proliferative index of 14 early infrainguinal vein graft stenoses. METHODS: All infrainguinal vein grafts at our institution are prospectively enrolled in a duplex surveillance protocol, the details of which have been previously reported. Among 98 grafts placed within the last year, 11 patients were identified with 14 progressive, focal, high-grade lesions that met previously established threshold criteria for prophylactic revision to prevent graft thrombosis. Lesions were first detected from 1 week to 7 months after surgery and were removed and replaced with segmental interposition grafts (1.5 to 10 months). Freshly excised lesions were placed in Methyl Carnoy's fixative, paraffin embedded, and serially sectioned. The cellular composition of each lesion was determined with cell-specific immunochemical reagents: alpha SMC actin, von Willebrand factor (endothelial cell), CD 68 (macrophage), and CD 45RB (monocyte). Actively proliferating cells were identified using antibody to proliferating cell nuclear antigen (PCNA). The identity of PCNA-positive cells was determined by double-label immunocytochemical staining, and the proliferative index (PCNA-positive cells/total cells x 100) was calculated by computer-assisted counts of representative gridded cross-sections of each lesion. RESULTS: All excised lesions demonstrated marked thickening with severe luminal encroachment and were highly cellular, with a predominance of alpha SMC actin+. Endothelial cells on the blood flow surface were present to a variable degree, and seven lesions exhibited striking numbers of macrophages and monocytes. The latter cell types were most abundant near microvessels in the deep neointima and adventitia. Active cellular proliferation was identified primarily in SMCs, with a mean PCNA index of 1.34%. However, significant PCNA reactivity was not limited to SMCs, but was also identified in macrophages and monocytes, particularly in lesions greater than 3 months old. CONCLUSIONS: Previous immunocytochemical studies of human coronary restenosis atherectomy specimens have generally detected low rates of cellular proliferation (0.5%), but these lesions may not truly represent myointimal hyperplasia, rather a mixture of atherosclerosis, thrombosis, and "restenosis." In contrast, the present study of early human vein graft lesions detected by duplex surveillance indicates that significant cellular proliferation occurs, although rates are lower than those obtained in animals such as the rat carotid injury model. In addition, although SMCs are the predominant proliferating cell type in human vein grafts, our identification of proliferating monocytes and macrophages raises the question of the contribution of an inflammatory component to the development of human lesions. The present study represents the first report of PCNA determination in a series of human infrainguinal vein grafting procedures.

Cell Division↗
PubMed1997

Development and evaluation of a chicken breakfast sausage manufactured with mechanically deboned chicken meat.

Leghorn spent hen mechanically deboned chicken meat (MDCM) was utilized in the preparation of a value-added chicken sausage. The sausage was manufactured by combining MDCM with hand-deboned skinless chicken thigh meat, fat replacer ingredients (blend of modified food starch and oat flour), and either 1) no ingredient with antioxidant properties, 2) Colorlife powdered rosemary concentrate, 3) Herbalox Type O oleoresin rosemary extract or 4) Tenox 6 antioxidant. The 454-g sausage chubs were stored at 4 +/- 1 C (refrigerated) and -20 +/- 1 C (frozen) for 10 d and 6 mo, respectively. A shelf life evaluation (based on daily examination of product, panelists responses, and psychrotrophic organism counts) of 8 d and 6 mo was attained for the sausage stored at 4 +/- 1 and -20 +/- 1 C, respectively. Flavor intensity, texture, and color were maintained for all treatments, and no significant (P > 0.05) off-flavors were detected through 8 d and 6 mo storage. Colorlife and Herbalox rosemary ingredients, and Tenox 6 antioxidant had no adverse effects on sensory characteristics of the chicken sausage. Psychrotrophic organisms increased with increased storage time for the refrigerated sausage, and remained static for the frozen sausage.

Animals↗
PubMed1996

High-speed particle separation and steric inversion in thin flow field-flow fractionation channels.

The performance of thin (down to 71 microns thick) flow field-flow fractionation (flow FFF) channels was examined at both high channel flow-rates (up to approximately 47 ml/min) and cross flow-rates (up to approximately 11 ml/min). High levels of retention were observed, suggestive of good performance characteristics. Supporting this expectation, four sizes (0.04-0.30 microns) of polystyrene latex microbeads were baseline separated in under 3 min. Nonetheless, a plate height analysis showed that performance was still less than theoretically expected. Fast steric-hyperlayer separations of larger latex beads were observed in the same systems. Furthermore, it was shown that the steric inversion diameter was shifted down to approximately 0.23 micron thus expanding the size range to which this FFF mode is applicable. The steric inversion phenomenon observed using narrow latex standards was shown to be consistent with that found for a polydisperse polyvinylchloride latex.

Chemical Fractionation↗
PubMed1996

Effects of basic fibroblast growth factor on human microvessel endothelial cell migration on collagen I correlates inversely with adhesion and is cell density dependent.

Angiogenesis, new vessel growth from existing vessels, is critical to tissue development and healing. Much is known about the molecular and cellular elements of angiogenesis, such as the effects of growth factors and matrix molecules on proliferation and migration. However, it is not clear how these elements are coordinated to produce specific microvascular beds. To address this, the effects of basic fibroblast growth factor (bFGF) on beta 1 integrin-mediated adhesion relative to migration in human microvessel endothelial cells (HMVEC) was examined. Using two assays of migration that differ in the density of cells being examined, bFGF stimulated single cell migration and reduced cell migration from a confluent monolayer on collagen I. Adhesion to collagen I of HMVEC treated at low density (2-4 x 10(4) cells/cm2) with bFGF for 22 h was reduced, while bFGF increased cell adhesion of HMVEC treated at high density (6-8 x 10(4) cells/cm2). Adhesion of both bFGF-treated and untreated HMVEC was mediated by the beta 1 integrin matrix receptor. Basic FGF treatment did not significantly alter surface expression of the beta 1 integrin subunit. Reduction in bFGF-mediated adhesion correlated with delayed cell spreading and altered organization of beta 1 integrin into substrate contacts. Thus, integrin-mediated cell adhesion in microvessel endothelial cells is sensitive to regulation by a growth factor. Furthermore, the nature of the response to this signal depends on another cell regulator, cell density. In addition, modulation of cell adhesion by a growth factor may be a central regulatory feature in controlling endothelial cell migration.

Antibodies↗
PubMed1996

CD18 antibody treatment limits early myocardial reperfusion injury after initial leukocyte deposition.

Following myocardial ischemia, initial reperfusion with whole blood impairs the recovery of ventricular function. The exact mechanisms underlying early myocardial reperfusion injury are not clear, but leukocytes play an important role. In this study, we tested if treating the initial blood reperfusate with a monoclonal antibody (CL26) against the leukocyte adhesion protein (CD18 would reduce the leukocyte contribution to early reperfusion injury. We reasoned that blocking CD18 would reduce the initial retention of leukocytes in the heart and thereby limit the inflammatory response. Rat hearts were isolated and perfused at constant flow with a red cell-rich solution (K2RBC). The perfusate was not recirculated. Baseline measures were made of coronary flow, perfusion pressure, and ventricular pump function. No-flow, normothermic ischemia was induced for 30 min, followed immediately by reperfusion, at the preischemic flowrate, with diluted whole blood (DWB, treated with either vehicle or CL26). Reperfusion was continued with K2RBC for 40 min more, during which postischemic measures were made. We found that the cardiac retention of leukocytes was not significantly different for the two groups, nor were the recoveries of ventricular function. Later in reperfusion (R35), the coronary blood flowrate and the coronary vascular resistances were not different; however, the recoveries of ventricular pump function were significantly different (+dP/dt @ R35 (%Pre-I): Vehicle: 27 +/- 9% (n = 8); CL26: 51 +/- 6% (n = 7); P < 0.05). Also, at R35, the voltage required to capture and pace the vehicle-treated hearts was significantly greater than the voltage required to pace the CL26 hearts (P < 0.05). Because the coronary flowrate and leukocyte retention were similar for both groups, the improved recovery observed in the CL26-treated group was not due to either improved flow or to reduced leukocyte retention. Rather, the findings suggest that the beneficial effect of antibody treatment was to attenuate step(s) in the acute inflammatory response that occurred after the initial deposition of leukocytes in the heart.

Animals↗
PubMed1996

Stimulation of angiogenesis by canine parathyroid tissue.

BACKGROUND: Autotransplanted parathyroid tissue is capable of inducing neovascularization in vivo, restoring calcium homeostasis with regulatory control. The mechanisms of parathyroid-induced neovascularization remain to be determined. Using an unique three-dimensional in vitro model, we tested the ability of parathyroid tissue to stimulate angiogenesis. METHODS: Healthy 1 mm3 fragments of normal canine parathyroid tissue were cocultured with freshly isolated microvessels that were embedded in a collagen I gel. After 7 days the gels were stained with Gs-1 lectin, a specific marker for rat endothelium. With image analysis the microvessel density (as the percentage of area) was determined. RESULTS: A significant increase in mean microvessel density (20.90% +/- 1.28 versus 16.51% +/- 1.66%) was seen with parathyroid coculture compared with control (n = 17, p < 0.05). There was no difference in microvessel density between controls and microvessels exposed to increasing concentrations of parathyroid hormone or calcium. The density of seeded microvessels influenced the effect of parathyroid stimulation of angiogenesis. The effect was apparent only at low seeding densities. CONCLUSIONS: We conclude that parathyroid tissue intrinsically stimulates angiogenesis in vitro by a secreted product, independent of calcium or parathyroid hormone.

Animals↗
PubMed1996

Measurement of endothelial cell migration using an improved linear migration assay. Presented at the 1995 Microcirculatory Society Meeting.

OBJECTIVE: The under-agarose migration assay developed for use with endothelial cells provides a measurement of the intrinsic migratory behavior of a cell population. However, the assay is labor intensive and lacks experimental flexibility. This migration assay has been refined and tested on human microvessel endothelial cells in the presence of a migration stimulus or on differing matrix-coated substrates. METHODS: The improved assay retains the linear geometry and mathematical basis of the under-agarose assay. Cells migrating from a cell reservoir formed with a Delrin insert are counted using an automated image-analysis system utilizing a high-contrast, fluorescent nuclear stain. From the cell counts, a stochastic measure of random migration is calculated. RESULTS: Values for random migration between the improved migration assay and the traditional under-agarose assay were very similar. Furthermore, a stochastic measure of endothelial cell migration on fibronectin was determined. CONCLUSIONS: This improved linear migration assay permits readily obtainable measures of endothelial cell migration for a number of experimental conditions. Improvements in the assay include the use of a removable fence for forming cell reservoirs, a nuclear stain to facilitate cell counting, and a more comprehensive analysis of the cell migration.

Animals↗
PubMed1996

Health perceptions and self-care response to illness among users of medical and alternative health services in St Andrew, Jamaica.

Do persons who utilize the services of the alternative therapist demonstrate a greater self-care response to illness? This cross-sectional study was done to compare the health perceptions and self-care response to minor illness among users of conventional medical care and alternative therapy. Data were collected with a pre-tested, self-administered questionnaire to 99 patients of medical practitioners and 74 of alternative therapists. Results indicated statistically significant differences in some health perceptions such as ways to improve general health and responsibility for personal health. For both groups there were similarities in socio-demographic characteristics and self-care responses to minor illness, such as headaches, constipation, diarrhoea, sinus congestion and colds or flu. Also, results reflected a common practice of self-management of minor illness and an overlap in attendance by patients to both groups of practitioners. Recommendations are made for the public to be guided in its practice of self-management of minor illness and that a regulatory body be set up to govern the practice of alternative therapy in Jamaica.

Adult↗