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Biomedical subjects

D F Williams

Publications and source records attributed to D F Williams.

At least 55 records · Page 3Linked to original sources
PubMed1996

Marsupialization of percutaneous implants in presence of deep connective tissue.

The primary substratum for epithelial migration during marsupialization of percutaneous implants is adjacent connective tissue. The purpose of this investigation was to test the hypothesis that if the latter is composed of deep connective tissue or other deep tissue, it will inhibit this process. One-hundred-forty-two smooth-surfaced polyethylene implants of a simple geometric design were implanted in dorsal skin of 6-8-week-old male C57/BL/6 mice such that the stems passed through and deep to the panniculus carnosus (PC), which is a deep tissue. Animals were sacrificed in groups between 1 and 11 weeks, and the implants and surrounding tissue were harvested, embedded in historesin, and 3-microns thick step serial sections prepared. No implants were lost by extrusion and 133 were suitable for examination. Epithelial investment of the devices proceeded deep to PC around only five of the implants over the time course. In the remainder, the mean distance of the advancing epithelial edge from the upper border of the PC was 0.25 mm by 1 week and this did not change significantly thereafter (p = 0.647). Significant extrusion of all devices occurred (p = 0.0001). It was concluded that these results are consistent with the hypothesis that deep connective tissue, such as the fascia surrounding the PC or muscle tissue such as the PC itself, can act as a functional barrier to marsupialization, and that exfoliation of such devices is not an epithelial function.

Animals↗
PubMed1996

Influence of wall shear rate on parameters of blood compatibility of intravascular catheters.

Three polymeric materials (silicone, PVC and nylon) were compared in an in vitro perfusion model, whereby 5 ml whole blood were perfused along 1 m lengths of polymeric tubing of 1 mm internal diameter at wall shear rates of up to 1000 s-1. Perfusion took place at 37 degrees C for 30 min. The polymers were investigated for platelet activation, granulocyte secretion, complement activation and contact phase activation. These parameters were also analysed in static contact for comparison. All the parameters measured displayed a dependence on wall shear rate. In all the materials studied, platelet adhesion and platelet activation increased with increasing flow rate. Granulocyte elastase release increased slightly with increasing flow rate up to 300 s-1. Complement activation was greatest for PVC at 1000 s-1, greatest for nylon at 100 s-1, but there was no measurable difference at either rate for silicone. All samples caused an increase in clotting time with increasing wall shear rate. PVC was the most platelet compatible material, nylon the worst. Silicone caused least contact phase activation, PVC and nylon the most.

Biocompatible Materials↗
PubMed1996

In-vitro corrosion and wear of titanium alloys in the biological environment.

Cyclic anodic polarization studies were undertaken for several titanium alloys of varying composition and phase structures. All materials were exposed to an accelerated corrosion test using a potentiostat and their electrochemical behaviour was analysed within a potential range of 0 to 5000 mV. The electrolyte used was a phosphate buffered saline (PBS) solution at pH = 5, 7.4 and 9. The polarization curves obtained represented both the passive and active regions of the materials and these curves were used to compare the resistance to pitting corrosion of each material. The sliding-wear of these materials was studied in both non-corrosive and corrosive environments. A simple pin-on-disc type wear apparatus was designed and built to simulate the co-joint action of corrosion and sliding-wear. Using this apparatus, it was also possible to evaluate the effect of wear-accelerated corrosion, which was also evaluated by wearing the surface of the specimens prior to corrosion. It was evident that the mixed phase alpha-beta alloys (Ti-6AI-4V and Ti-6AI-7Nb) possessed the best combination of both corrosion and wear resistance, although commercially pure titanium and the near-beta (Ti-13Nb-13Zr) and beta (Ti-15Mo) alloys displayed the best corrosion resistant properties.

Alloys↗
PubMed1996

Quantitative assessment of the tissue response to films of hyaluronan derivatives.

The aim of this study was to evaluate the in vivo response following implantation into a rat model of three innovative hyaluronan derivatives for clinical use: HYAFF 7, HYAFF 11 and HYAFF 11p75 (respectively, the 100% ethyl ester, 100% and 75% benzyl esters). The tissue reaction evoked by films of these new biomaterials implanted into the dorsolumbar musculature of rats was assessed quantitatively using a well established technique based upon an image analysis system. The number of inflammatory cells present and the patterns of cell distribution around the implant up to a distance of 642 microns were examined at different time periods after implantation. Since a well-delineated tissue-material interface was needed for this type of investigation, it was not possible to apply image analysis to sections once dissolution of the implanted materials had begun. Films of both the total esters, HYAFF 7 and HYAFF 11, were found to undergo a slow dissolution process and, after a month, films of these materials were still present at the site of implantation. Differences in response to the two materials were observed only during the first two weeks, particularly with respect to neutrophil distribution and total cellularity. HYAFF 7 was found to be more reactive, with higher numbers of neutrophils near the surface of the implant than HYAFF 11. Thereafter, the differences between the two materials were minimal and owing mainly to a faster dissolution of HYAFF 7 films. After 3 and 5 months, considerable degradation of films of both total esters had occurred. Significant quantities of material appeared inside numerous macrophages with an ED1-positive phenotype. Only a very thin layer of fibrous connective tissue, indicative of low reactivity, was found to surround the site of implantation, separating the dissolved material and the phagocytic cells from healthy muscular tissue. ED2-positive macrophages were primarily confined within the lining connective tissue. The partial benzyl ester, HYAFF 11p75, showed a different behaviour. In fact, evidence of film dissolution was already present a week after the implantation. After two weeks, the implanted films were completely dissolved and numerous ED1-positive macrophages phagocytosing the material were observed at the site of implantation. Therefore, in agreement with previous in vitro studies, which showed a greater susceptibility to degradation of hyaluronan derivatives with lower percentage of esterification, HYAFF 11p75 underwent resorption faster than the corresponding total ester.

Animals↗
PubMed1996

Large-scale selection of CD34+ peripheral blood progenitors and expansion of neutrophil precursors for clinical applications.

Hematopoietic recovery after high-dose chemotherapy is characterized by an obligate period of neutropenia of approximately 8-10 days. It is postulated that if a pool of neutrophil precursors and progenitors were expanded in vitro and reinfused, the duration of neutropenia may be substantially shortened by these cells capable of providing mature neutrophils within days of reinfusion. In this study, peripheral blood progenitor cell products were obtained from six normal donors mobilized with rhG-CSF and two patients mobilized with cyclophosphamide and rhG-CSF. CD34+ cells were isolated using the Isolex immunomagnetic bead method. A mean of 8.26 x 10(7) CD34+ cells with a mean purity of 74.5% were seeded at a concentration of 1 x 10(5)/ml into a 12 day stroma-free liquid culture using gas-permeable bags. A serum-free growth medium supplemented with PIXY321 was used. On day 7, there was a mean cellular expansion of fourfold, at which time the cells were resuspended at the initial concentration, yielding a mean culture volume of 3L (1-6 L). On day 12, there was an additional mean fold cellular expansion of 10 x, achieving an overall mean fold expansion of 41 +/- 16. Cellular characterization of the expanded cells revealed predominantly neutrophil precursors by morphology (mean 70.1%) and flow cytometric analysis. A mean of 52.3% of the expanded cells expressed CD15. Immunohistochemical staining revealed a mean of 7.1% CD41a+ megakaryocytic progenitors in the final cultured cell product. Detectable CD34+ cells were maintained only in those cultures initiated with greater than 90% CD34+ cells. Colony-forming units-granulocyte-macrophage (CFU-GM) were maintained in the 12 day culture at a level similar to the preculture number, whereas CFU mixed were depleted in all samples. On day 0, there were few CFU clusters (colonies containing fewer than 50 cells) identified, but by day 12, a mean total of 8.3 x 10(6) CFU clusters were identified. On day 12, the expanded cells were harvested and pooled using the Fenwal CS3000 Plus blood cell separator and resuspended in Plasma-Lyte-A with 1% human serum albumin. The mean harvest recovery of expanded progenitors was 91%, with a mean viability of 86%.

Adult↗
PubMed1996

Ambient noise interferes with auscultatory blood pressure measurement during exercise.

This study was designed to investigate whether the acoustical characteristics of the Korotkoff sounds (K-sounds) were altered during exercise and/or masked by the ambient noise. After signing informed consent, 11 subjects (8 females, 3 males; 27 +/- 2 yr; 166.2 +/- 3.2 cm; 62 +/- 5 kg; means +/- SD) underwent a cycle ergometer exercise test that increased in workload by 30 W every 3 min until volitional fatigue. Heart rate, auscultatory systolic (SBP) and diastolic blood pressure (DBP), and oxygen consumption were monitored 1 and 2 min into each work stage. The auscultatory K-sounds were recorded with a microphone mounted in a stethoscope tube for later frequency (Hz) and sound pressure level (dB SPL) analysis. Frequency and SPL of ambient noise (99 +/- 13 Hz and 64 +/- 1 db at maximum, respectively) increased during the exercise test to magnitudes similar to the SBP and DBP K-sounds (166 Hz, 66 db; and 128 Hz, 69 db, respectively). Additionally, the ambient noise was responsible for a significant damping of the frequency and SPL of the measured blood pressure K-sounds and a rise in the measured frequency of the SBP K-sounds. Furthermore, we observed "inaudible" K-sounds at lower frequencies than adjoining audible K-sounds (100 Hz vs 126 Hz), supporting the known underestimation of SBP by auscultation. The increase in ambient noise during exercise testing dampens and may mask the auscultatory K-sounds, thus making detection of the proper K-sounds during exercise difficult at best. Furthermore, the presence of inaudible K-sounds may further explain the published discrepancies between auscultatory and intraarterial blood pressure measurements during exercise.

Acoustics↗
PubMed1995

Surgical management of submacular hemorrhage. A series of 47 consecutive cases.

BACKGROUND: The development of a thick submacular hemorrhage usually carries a poor visual prognosis. The surgical removal of submacular blood may improve the otherwise poor outlook in these cases. SUBJECTS AND METHODS: Forty-seven consecutive patients underwent vitrectomy with surgical removal of submacular hemorrhage. The patient population consisted of two consecutive groups. Group 1 (1989 to 1991) included 23 patients (20 with age-related macular degeneration [ARMD], one with idiopathic submacular hemorrhage, one with presumed ocular histoplasmosis syndrome [POHS], and one with angioid streaks) who underwent mechanical clot extraction. Group 2 (1991 to 1993) included 24 patients (19 with ARMD, two with POHS, two with arterial macroaneurysm, and one with angioid streaks) who underwent tissue plasminogen activator-assisted drainage of thick submacular hemorrhage. The dose of tissue plasminogen activator ranged from 10 to 40 micrograms. All patients had surgery within 72 hours of diagnosis. RESULTS: In group 1, the mean size of the submacular hemorrhage was 11 disc areas (range, 1 to 16 disc areas). Mean follow-up was 40 weeks. Mean postoperative visual acuity for eyes with ARMD was 20/200. (Visual acuity improved in six eyes, was stable in seven eyes, and deteriorated in seven eyes.) All three of the eyes without ARMD had visual improvement with a mean postoperative visual acuity of 20/70. Overall, visual acuity stabilized or improved in 13 (57%) of 23 patients and decreased in 10 (43%) patients. In group 2, the mean size of the submacular hemorrhage was 11 disc areas (range, 3 to 16 disc areas). Mean follow-up was 24 weeks. Mean postoperative visual acuity for eyes with ARMD was 20/480 (visual acuity was stable in 15 eyes, improved in two eyes, and deteriorated in two eyes). Four of five eyes without ARMD had visual improvement and one was stable, with a mean postoperative visual acuity of 20/60. Visual acuity stabilized or improved in 22 (92%) of 24 patients and decreased in two (8%). The degree of clot lysis was variable. CONCLUSIONS: Submacular hemorrhage secondary to ARMD has a poor visual prognosis, with or without surgical drainage. The addition of tissue plasminogen activator-assisted clot lysis does not appear to significantly improve the visual outcome following surgery. The determination of whether surgical intervention is appropriate in these cases requires a prospective, randomized clinical trial.

Aged↗
PubMed1995

Echographic pseudoextension of uveal melanomas.

BACKGROUND: Standardized echography is routinely utilized to assess uveal melanomas. Echographic pseudoextension is defined as normal structures mimicking intrascleral or extrascleral extension of tumor on echography. METHODS: The records of 151 consecutive uveal melanoma patients evaluated with standardized echography over a 6-year period (1986-1991) were reviewed to identify those in which pseudoextension or true extension was diagnosed. RESULTS: Fourteen (9%) cases of pseudoextension were noted, with causes including juxtapapillary tumor location (seven cases), extraocular muscle insertion (five cases), vortex ampullae (one case), and post-brachytherapy changes (one case). Clinical, echographic, and/or histopathologic follow-up confirmed absence of true extension. Six (4%) cases of true extrascleral extension were identified and confirmed histopathologically. CONCLUSION: Differentiating extraocular tumor extension from pseudoextension is critical, and use of standardized A-scan and contact B-scan echography is integral in this assessment.

Adult↗
PubMed1995

Quantifying the soft tissue response to implanted materials.

As the diversity of biomaterials increases, new developments are aimed at these materials becoming interactive rather than passive with respect to the environment they are placed in. The need accurately and reproducibly to assess the response of the body to these materials increases. Historically, quantification of tissue responses has taken many forms but with the continuing development of powerful computers, our ability to quantify the tissue response to implanted materials has become a reality. Computer systems can now analyse sections automatically and then go on to sort the huge quantities of data created, into in depth patterns and cross comparisons so that subtle changes in tissue responses can be detected and understood.

Biocompatible Materials↗
PubMed1995

Reversible loss of light perception after vitreoretinal surgery.

PURPOSE: We studied reversible loss of light perception after vitreoretinal surgery to show that functional vision can return in some patients. METHODS: We reviewed the medical records of seven patients who had postoperative reversible loss of light perception in the eye that underwent vitreoretinal surgery. Differences in the postoperative courses and interventions were studied. RESULTS: Five of the seven patients had diabetes mellitus but none had hypertension. The indications for vitreoretinal surgery were severe proliferative diabetic retinopathy in five patients and retinal detachment with advanced proliferative vitreoretinopathy in two patients. Seven patients had reversible loss of light perception within the first three postoperative days. Six of the seven patients had an intraocular pressure greater than 26 mm Hg at the time the eye had no light perception. Decreasing the intraocular pressure was associated with return of light perception in five of seven patients. Return of useful vision was gradual. Four of seven patients had a visual acuity of 20/400 or better one month after surgery, and all seven had a visual acuity of 20/400 or better three months after surgery. Visual acuity in four eyes improved further to 20/70 or better at six months or more after surgery. CONCLUSION: Reversible loss of light perception after vitreoretinal surgery does occur in some patients. Monitoring vision and intraocular pressure is important because prompt treatment may assist in the recovery of functional vision.

Adult↗
PubMed1995

Pharaoh ant (Hymenoptera: Formicidae) colony development after consumption of pyriproxyfen baits.

Pharaoh ant, Monomorium pharaonis (L.), colonies were effectively controlled following ingestion of pyriproxyfen formulated in peanut butter oil. Pyriproxyfen, a juvenile hormone analog, reduced egg production in the queens, decreased the amount of brood due to delayed death in the eggs and larvae, caused death of pupae about 3 wk after treatment, and decreased the number of workers due to attrition and toxic effects. Queens, which continued to produce a small amount of eggs, eventually died. Queen death may have been caused by lack of workers required to tend them, old age or toxic effects. At concentrations of 0.25, 0.5 and 1%, pyriproxyfen was more effective than the once commercially available bait, Pharorid (methoprene) for the control of the Pharaoh ant.

Animals↗
PubMed1995

Vitrectomy for vitreomacular traction syndrome with macular detachment.

PURPOSE: To describe the clinical characteristics of the vitreomacular traction syndrome with macular detachment and to report our surgical experience with this condition. METHODS: A retrospective chart and photographic review was performed on nine patients (nine eyes) who had a symptomatic decrease in visual acuity from a macular traction retinal detachment caused by vitreomacular traction syndrome. Vitrectomy was performed in each eye to reattach the retina. RESULTS: Intraoperative observation confirmed partial posterior vitreous separation with adherence of the posterior hyaloid to the detached retina and separation of the posterior hyaloid from the attached retina. After surgery the macula was reattached in seven eyes (78%). Visual acuity was improved in four eyes, stable in four eyes, and worse in one eye. CONCLUSION: Macular detachment may occur secondary to vitreomacular traction syndrome. Although the retina may be reattached surgically in these cases, visual improvement may be limited by chronic detachment, premacular fibrosis, cystoid macular edema, or macular schisis.

Aged↗
PubMed1995

Multiple fire ant stings indoors.

The progressive spread and increasing colony density of imported fire ants throughout the southeastern United States will result in increasing numbers of individuals with untoward reactions to the stings of these insects. In order to alert physicians that imported fire ant colonies may exist within homes and other inhabited dwellings and result in multiple stings to the occupants and to provide information about the management of this problem, we report two cases where individuals were stung indoors by imported fire ants. One of these cases involved the attack of a bed-bound patient by a colony of ants. The other report documents the establishment of an intact fire ant colony within an inhabited dwelling. Physicians should become familiar with the biology of these insects to assist patients in dealing with this problem.

Adult↗
PubMed1994

Pars plana vitrectomy for treatment of stage 2 macular holes.

OBJECTIVE: To assess the anatomic outcome and visual acuities at follow-up after pars plana vitrectomy in the management of stage 2 macular holes. DESIGN: Retrospective. SETTING: Retina Consultants, Ltd, St Louis, Mo. PATIENTS: Thirty-three patients, aged 43 to 75 years, with stage 2 macular holes. INTERVENTION: Total pars plana vitrectomy with separation of the posterior hyaloid membrane and injection of intraocular gas followed by postoperative face-down positioning. MAIN OUTCOME MEASURES: Visual acuity and anatomic appearance of the macular hole. RESULTS: Postoperatively, 20 (61%) of 33 eyes attained a visual acuity of 20/50 or greater. Twenty (61%) of 33 eyes showed an improvement in visual acuity, while nine (27%) of 33 were stable. Four (12%) of 33 eyes showed a decline in postoperative visual acuity with progression to a stage 3 macular hole. Twenty-five (76%) of 33 eyes showed stabilization or improvement in the appearance of the macular hole. CONCLUSIONS: Pars plana vitrectomy in conjunction with postoperative intraocular gas tamponade may result in visual and anatomic stabilization or improvement in eyes with stage 2 macular holes. However, because of limited natural history data, it is unknown whether these results are any better than those that might occur without surgery.

Adult↗
PubMed1994

Granule secretion markers on fluid-phase platelets in whole blood perfused through capillary tubing.

The effect of material composition and shear rate on fluid-phase platelet activation was investigated using a capillary perfusion model. Citrated whole blood was perfused along the lumens of tubes constructed from silicone, PVC, Pellethane, W124 (an experimental polyetherurethane), and glass. Platelet activation was determined by measuring the increase in alpha-granule membrane protein P-selectin (GMP-140, CD62) and the lysosomal granule membrane protein GP-53 (CD63) on fluid-phase platelets by flow cytometry. All tubes caused an increase over the negative control in the number of P-selectin and GP-53 molecules detectable on the surface of these platelets. The activation response of platelets to changes in shear rate was also investigated. It was found that lysosomal release paralleled alpha-granule release in glass, but not in Pellethane, over a range of wall shear rates (100-1,000 s-1).

Biomarkers↗
PubMed1994

Molecular biointeractions of biomedical polymers with extracellular exudate and inflammatory cells and their effects on the biocompatibility, in vivo.

The stability of biomedical polymers in physiological environments is crucial for the normal operation of devices, as well as determining their effect on the tissue response. Degradation is an important factor in polymer biocompatibility, since the environment of the human body can be aggressive to polymers. Most implanted polymers suffer degradation to some extent, and the kinetics and mechanisms of the processes can be affected significantly by various biologically active species, especially enzymes, lipids, peroxides, free radicals and phagocytic cells. The degradation of poly(caprolactone) and poly(DL-lactic acid) under controlled in vivo conditions was studied using a poly(methyl methacrylate) chamber designed to control the exposure of polymers to physiological environments. In particular they may be designed to allow access of extracellular exudate only or access to cells as well as the fluid. The chambers, sealed with filters of pore size either 0.45 micron (impervious to cells) or 3.0 microns (allowing cells to enter the chamber), were implanted subcutaneously into experimental animals for 10, 20 and 30 wk periods. Degradation and molecular interactions of the polymers were characterized by gel permeation chromatography and scanning electron microscopy. The extracellular exudate formed within the implanted chamber is active in promoting the degradation of some biomedical polymers. Inflammatory cells are involved in the biodegradation of implanted polymers by releasing biologically active species such as free radicals into the area surrounding the implant. The data have demonstrated that the hydroxyl radical is likely to be one of the main causes of polymer degradation.

Animals↗