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Biomedical subjects

M W Webster

Publications and source records attributed to M W Webster.

At least 145 records · Page 8Linked to original sources
PubMed1976

The use of expanded microporous polytetrafluoroethylene for limb salvage: a preliminary report.

Initial laboratory and clinical evaluations of a new prosthetic material, expanded microporous polytetrafluoroethylene (PTFE), for small vessel replacement is promising and encourages further clinical trial. Frequently the autogenous saphenous vein is not available for bypass procedures, and alternative arterial substitutes have not proved reliable for replacement of small vessels. In this study, 15 patients with impending loss of limb and no available saphenous vein underwent revascularization of the lower extremity with expanded microporous PTFE grafts. Thirteen of 15 patients now demonstrate viable extremities with a resulting over-all early patency and limb salvage rate of 87 percent for this series. Follow-up ranges from one to 8 months. Seven patients had diabetes mellitus and eight had atherosclerotic heart disease. Nine grafts crossed the knee joint. In all patients arterial runoff was poor. Six patients had previous femoropopliteal bypasses, five with autogenous veins and one with Dacron velour. Two patients had multiple previous operations that failed, first with autogenous vein and later with fabric grafts. The current limb salvage and patency rate of 87 percent in high-risk patients suggests that expanded PTFE may be the prosthesis of choice when an autogenous vein is not available and possibly an equally good substitute when the venous autograft is available.

Aged↗
PubMed1975

The permanent gastrostomy. Use of the gastrointestinal anastomotic stapler.

A permanent feeding gastrostomy was quickly and simply constructed in 29 patients with low operative risk using the gastrointestinal anastomotic stapler. The technique consisted of a simple application of this stapler on a carefully selected section of the stomach to form a Janeway type of gastrostomy. Activation of the device placed two double rows of staples and cut between them. This left the mucosa in approximation both in the tube and in the body of the stomach. A few additional Lembert sutures was all that was necessary. There were no suture line leaks nor other complications peculiar to the method.

Adolescent↗
PubMed1975

Mechanisms of hypocalcemia in acute hemorrhagic pancreatitis.

Thyrocalcitonin release mediated by glucagon secreted from the acutely inflamed pancreas has been postulated as a possible mechanism for hypocalcemia in acute pancreatitis. To test this hypothesis, hemorrhagic pancreatitis was induced in a group of thyroidectomized pigs. No source of thyrocalcitonin other than the thyroid has been described in the pig. Their subsequent serum calcium concentrations were compared with those in a group of thyroid intact pigs also given hemorrhagic pancreatitis. The results indicate that the hypocalcemia observed during the first 24 hours following induction of pancreatitis is not related to the presence of an intact thyroid. Differences observed in the degree of hypocalcemia between the two groups 30 to 48 hours after pancreatitis developed may be of significance but could be explained by dilutional differences alone. Thyrocalcitonin apparently has little if any role in the hypocalcemia observed during the course of acute pancreatitis.

Acute Disease↗
PubMedDate not supplied

Modeling the transmural stress distribution during healing of bioresorbable vascular prostheses.

Little attention has been given to the stresses within the wall of bioresorbable vascular prostheses and how they might affect the resorption process. We modeled the graft "complex" (inner tissue capsule, residual graft, and outer tissue capsule) as a three-layered compound tube under internal pressure. Using this biomechanical model, we studied the effects of alterations in the geometry (i.e., radius and thickness) and mechanical properties of each stratum on the overall transmural stress distribution. Hypothetical simulations were performed to investigate the possible sequence of and alterations in the radial and circumferential stresses during the resorption process. Our results suggest that early in the resorption phase, the inner tissue capsule is subjected to compressive hoop stresses and concentrated, large-magnitude compressive radial stresses. This distribution gives way to the more typical distribution for a thick-walled tube when equilibration (i.e., complete resorption) is approached. The prediction of the compressive stresses in the pseudo-intima during early resorption parallels findings of an elevated mitotic index in that region at that time. This leads to a new hypothesis, namely, that compressive stresses, both in-plane and out-of-plane with respect to the regenerated vascular cells, participate in the resorption process of bioresorbable vascular grafts by modulating elevated cellular proliferative activity and may play an important role in other aspects of vascular cell biology. Results of recent experimentation support this hypothesis.

Animals↗
PubMedDate not supplied

Ex vivo biomechanical behavior of abdominal aortic aneurysm: assessment using a new mathematical model.

Knowledge of the biomechanical behavior of abdominal aortic aneurysm (AAA) as compared to nonaneurysmal aorta may provide information on the natural history of this disease. We have performed uniaxial tensile testing of excised human aneurysmal and nonaneurysmal abdominal aortic specimens. A new mathematical model that conforms to the fibrous structure of the vascular tissue was used to quantify the measured elastic response. We determined for each specimen the yield (sigma y) and ultimate (sigma u) strengths, the separate contribution to total tissue stiffness by elastin (EE) and collagen (EC) fibers, and a collagen recruitment parameter (A), which is a measure of the tortuosity of the collagen fibers. There was no significant difference in any of these mechanical properties between longitudinal and circumferential AAA specimens, nor in EE and EC between longitudinally oriented aneurysmal and normal specimens. A, sigma y, and sigma u were all significantly higher for the normal than for the aneurysmal group: A = 0.223 +/- 0.046 versus A = 0.091 +/- 0.009 (mean +/- SEM; p < 0.0005), sigma y = 121.0 +/- 32.8 N/cm2 versus sigma y = 65.2 +/- 9.5 N/cm2 (p < 0.05), and sigma u = 201.4 +/- 39.4 N/cm2 versus sigma u = 86.4 +/- 10.2 N/cm2 (p < 0.0005), respectively. Our findings suggest that the AAA tissue is isotropic with respect to these mechanical properties. The observed difference in A between aneurysmal and normal aorta may be due to the complete recruitment and loading of collagen fibers at lower extensions in the former. Our data indicate that AAA rupture may be related to a reduction in tensile strength and that the biomechanical properties of AAA should be considered in assessing the severity of an individual aneurysm.

Aged↗
PubMedDate not supplied

Adverse effects associated with the newer inotropic agents.

The ideal inotropic agent should be available for both parenteral and oral administration and be potent and effective long term without significant adverse effects. In recent years, numerous new agents have been developed in an attempt to find a more potent, less toxic alternative to digoxin. beta-Agonists, while useful when given parenterally short term, appear to have their long term oral application limited by adverse effects and the development of tolerance. A number of other non-catecholamine agents, most of which have both inotropic and vasodilator actions, have also been studied. Adverse effects have been relatively frequent and occasionally severe. Of these newer agents none has yet been proven in clinical trials to be safe and effective in the long term.

Adrenergic beta-Agonists↗
PubMedDate not supplied

Recurrence rate of diabetic neurotrophic foot ulcers healed using topical application of growth factors released from platelets.

The purpose of this study was to determine the recurrence rate of diabetic neurotrophic foot ulcers that had healed in a treatment protocol using topically applied growth factors released from platelets. Thirty-six patients with diabetic neurotrophic foot ulcers were entered into a randomized prospective double-blind 20-week trial of topically applied platelet growth factors or buffered saline dressings. Ulcers had been present for 15.5 months (mean, range 2 to 60 months). Sixteen patients (44%) healed and were followed up for as many as 30 months to determine the rate of ulcer recurrence. Eleven patients (68.8%) had ulcers that recurred, including 10 treated with platelet growth factors and one treated with buffered saline solution. These ulcers had been present for 20 months (range 5 to 60 months) before healing. Average time to ulcer recurrence was 2.2 months (range 0.25 to 7 months). Five ulcers (31.2%) remained healed, including four treated with platelet growth factors and one treated with buffered saline solution. These healed, nonrecurring ulcers had been present for 5 months (range 2 to 6 months) before healing. Average follow up was 25 months (range 24 to 30 months). Ulcers were more likely to recur if they had been present longer before healing. If patients were not compliant in wearing footwear to protect the healed ulcer, the ulcers were prone to early recurrence. These data indicate that ulcers healed by using growth factors in the form of a platelet growth factors did not have more durable skin over the ulcer and were prone to early ulcer recurrence.

Journal Article↗
PubMedDate not supplied

Gene expression is altered in perfused arterial segments exposed to cyclic flexure ex vivo.

Certain regions of coronary and other arteries undergo cyclic flexure due to attachment to the heart or crossing of joints. Such motion gives rise to fluctuations in transmural stress and luminal shear stress. It is well known that cyclic variation of these biomechanical forces influences many aspects of vascular cell biology including gene expression. The purpose of this work was to investigate the hypothesis that cyclic flexure of arterial segments influences their gene expression. Bilateral porcine femoral arteries were obtained fresh from the abattoir. One vessel was mounted in an ex vivo perfusion system and subjected to an intraluminal pressure of 60 mmHg and flow of 50 ml/min to serve as a control. The other vessel was mounted in a second perfusion system with similar hemodynamic conditions, but also subjected to controlled cyclic bending consistent with that found in coronary arteries in vivo. Reverse transcriptase-polymerase chain reaction analysis demonstrated that E-selectin and matrix metalloproteinase-1 (MMP-1) were consistently and significantly downregulated in the specimens subjected to 4 h of cyclic bending as compared to the control (n = 8, p < 0.05). Our results show that cyclic flexure of arterial segments in vitro may influence their gene expression. Further investigation should follow this novel observation and focus on other known mediators to more carefully elucidate the consequence of cyclic flexure on arterial pathobiology.

Actins↗
PubMedDate not supplied

In vivo three-dimensional surface geometry of abdominal aortic aneurysms.

Abdominal aortic aneurysm (AAA) is a local, progressive dilation of the distal aorta that risks rupture until treated. Using the law of Laplace, in vivo assessment of AAA surface geometry could identify regions of high wall tensions as well as provide critical dimensional and shape data for customized endoluminal stent grafts. In this study, six patients with AAA underwent spiral computed tomography imaging and the inner wall of each AAA was identified, digitized, and reconstructed. A biquadric surface patch technique was used to compute the local principal curvatures, which required no assumptions regarding axisymmetry or other shape characteristics of the AAA surface. The spatial distribution of AAA principal curvatures demonstrated substantial axial asymmetry, and included adjacent elliptical and hyperbolic regions. To determine how much the curvature spatial distributions were dependent on tortuosity versus bulging, the effects of AAA tortuosity were removed from the three-dimensional (3D) reconstructions by aligning the centroids of each digitized contour to the z axis. The spatial distribution of principal curvatures of the modified 3D reconstructions were found to be largely axisymmetric, suggesting that much of the surface geometric asymmetry is due to AAA bending. On average, AAA surface area increased by 56% and abdominal aortic length increased by 27% over those for the normal aorta. Our results indicate that AAA surface geometry is highly complex and cannot be simulated by simple axisymmetric models, and suggests an equally complex wall stress distribution.

Aorta, Abdominal↗
PubMedDate not supplied

The management of aortoenteric and paraprosthetic fistulae.

Aortoenteric and aortic paraprosthetic fistulae are devastating complications. Most authors recommend total excision of the graft and revascularization of the lower extremities by extra-anatomic bypass. We reviewed the University of Pittsburgh experience with these fistulae in 15 patients between 1977 and 1987. There were 9 aortoenteric fistulae (AEF) and 6 paraprosthetic fistulae (PPF). Seven of the 9 AEF had no abscess surrounding the graft, but communication of the intestine with the aortic anastomosis. One patient died during operation. Six patients underwent a local repair or in situ replacement of the graft. All 6 of those patients survived operation without limb loss. Two of the 9 patients with AEF had evidence of graft infection and underwent total excision of the graft and extra-anatomic reconstruction. Both patients died, one of sepsis and one of aortic stump rupture. All 6 patients with PPF had clinical and operative evidence of overt graft infection and underwent total graft excision and extra-anatomic bypass. Two of these patients died secondary to sepsis. We conclude that AEF, without evidence of graft infection, were safely treated by local repair. Patients with PPF had infected grafts requiring graft removal with significant morbidity and mortality.

Aged↗
PubMedDate not supplied

Oxygen diffusion in chronic venous ulceration.

A diffusion barrier to oxygen caused by fibrin deposition around dilated, proliferating capillaries in patients with venous hypertension may contribute to the development of venous ulceration. This diffusion barrier was studied in 18 patients with venous ulcers using the transcutaneous oxygen (TcPO2) monitor (TCM204 Radiometer, America). TcPO2 sensors were placed adjacent to venous ulcers on lower limbs and on the chest and foot of each patient. Readings were taken after a sensor temperature of 44 degrees C was reached (10-15 minutes). TcPO2 values were markedly decreased in skin adjacent to the ulcers (10 +/- 2 mmHg) compared with those of the chest (64 +/- 2 mmHg) and foot (43 +/- 2 mmHg). Inhalation of 100% oxygen for 10 minutes increased chest TcPO2 in all patients (145 +/- 8 mmHg) and increased TcPO2 in skin around the ulcers in 17 of 18 patients (61 +/- 13 mmHg). This study supports the existence of a local pathologic barrier to oxygen diffusion in patients with venous ulcers.

Aged↗