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Biomedical subjects

K C Wright

Publications and source records attributed to K C Wright.

At least 19 recordsLinked to original sources
PubMed2001

Surface transformation and photoinduced recovery in CdSe nanocrystals.

CdSe nanocrystals in solution and films can enter a metastable state in which the highly luminescent nanocrystals become dark. This change, which we attribute to a surface transformation, can be caused by heating or by changing the environment of the nanocrystals at room temperature. The metastable transformation is reversed upon illumination of above-band-gap light, at which point the nanocrystals are again highly luminescent.

Journal Article↗
PubMed2001

New embolization coil containing a nitinol wire core: preliminary in vitro and in vivo experiences.

PURPOSE: To improve the stability of the standard stainless steel embolization coil by adding a nitinol wire core. MATERIALS AND METHODS: With use of one coil with a nitinol wire core and one without one, stability and resistance to elongation were measured in vitro. Thirty-one factory-made stainless-steel macrocoils equipped with preshaped nitinol wire cores were acutely deployed into branches of the superior mesenteric artery (SMA) in five pigs (part I of the study). Fifteen homemade retrievable coils with thermal shape memory (TSM) nitinol wire cores were acutely deployed in the abdominal aortae or inferior venae cavae of four pigs (part II). Coils with a superelastic (SE) nitinol wire core (n = 9), a TSM nitinel wire core (n = 5), and without a core (n = 5) were compared in carotid embolization (part III). RESULTS: In vitro, the expansile strength of the reinforced coils was significantly greater and elongation was significantly less than the standard coils (P <.01). In part I, coils were easily deployed via diagnostic catheters. In part II, ability to reposition the coils facilitated optimal coil configuration, which resulted in effective self-anchoring and occlusion. In part III, no coils with a SE core migrated, whereas one of five with a TSM core and three of five without reinforcement migrated immediately. The core significantly increased coil stability and postplacement configuration (P <.01). CONCLUSIONS: Addition of a nitinol wire core increases the intravascular stability of the standard embolization coil by significantly enhancing expansile force and postplacement configuration. The wire core does not adversely affect the handling of the coil. The ability to reposition/retrieve the coil is a desirable feature.

Alloys↗
PubMed2001

Creation of a transrenal arteriovenous dialysis shunt: feasibility study in a swine model.

PURPOSE: To investigate the feasibility of percutaneous renal artery and vein access for the creation of a transrenal arteriovenous hemodialysis graft. MATERIALS AND METHODS: Renal-artery-to-ipsilateral-renal-vein conduits were constructed with use of entirely percutaneous techniques in seven swine. Renal artery and vein access was performed in six animals with use of a retrograde (inside-out) technique and in one animal with use of an antegrade (outside-in) technique. Modified 8-F sheaths were used in the first three animals and Wallgrafts were used in the final four animals to form the arterial and venous limbs of each shunt. The arterial and venous limbs were joined together by a subcutaneous segment of 6-mm reinforced polytetrafluoroethylene (PTFE) in five animals and by external conduits in two animals. Wallgrafts were deployed from the renal artery and vein into the segments of PTFE. The free ends of each conduit were tunneled and joined together to close the arteriovenous circuit. Post-shunt angiography was used in all animals to document successful shunt creation and demonstrate rapid arteriovenous shunting as a determinant of technical feasibility. Two of the seven animals received additional anticoagulation therapy and/or antiplatelet therapy to prevent shunt thrombosis during the follow-up period. The three initial animals were killed within 2 hours of shunt creation, and two of the remaining four animals returned for angiographic follow-up, one on day 2 and one on day 9. All animals underwent a complete necropsy to assess for potential complications including hemorrhage and vascular or bowel injury. RESULTS: Retrograde renal arterial and venous access was successful in all six animals in which it was attempted. Five of six arterial accesses and four of six venous accesses traversed the peritoneum with two arterial accesses and one venous access penetrating a loop of large bowel. Antegrade access was performed and successfully accomplished in the final animal. Brisk arteriovenous shunting was demonstrated on completion angiography in all animals. Graft occlusion was present in the two animals that returned for follow-up and two animals died before follow-up as a result of graft leakage and subsequent hemorrhage. Minimal perinephric and intrarenal hemorrhage was demonstrated at necropsy after shunt insertion in the remaining five animals. Renal infarction was present in all kidneys used for transrenal access. CONCLUSION: The transrenal approach for the creation of a percutaneous arteriovenous shunt is feasible after renal artery and vein access by either the retrograde or antegrade technique. Additional technical refinements of the procedure and the devices used will be necessary before follow-up studies are conducted.

Animals↗
PubMed2001

Iatrogenic Horner's syndrome in an experimental pig.

An adult domestic female pig (Sus scrofa) exhibited clinical signs of right-sided Horner's syndrome after experimental placement of a woven aortic stent followed by aortic catheterization. The clinical signs included a miotic pupil, ptosis of the upper eyelid, prolapse of the nictitating membrane, and enophthalmos. Necropsy revealed a large mass in the right midcervical region that encased or was in contact with the carotid artery, internal jugular vein, and vagus nerve. Closer evaluation of the mass revealed that it was a small piece of surgical suture material that was embedded within the lumen of the carotid artery. This extrinsic material served as a nidus for an inflammatory reaction involving the vagus nerve.

Animals↗
PubMed2000

Animal models for atherosclerosis, restenosis, and endovascular graft research.

Animal models have significantly advanced our understanding of the mechanisms of atherosclerosis and restenosis formation and the evaluation of therapeutic options. The current focus of research is on preventive strategies against restenosis and includes pharmacologic and biologic interventions directed primarily against smooth muscle cell proliferation, endovascular devices for recanalization and/or drug delivery, and an integrated approach using both devices and pharmacobiologic agents. Devices aimed at the percutaneous endoluminal exclusion of aortic aneurysms have also generated interest recently. The experience over many decades with animal models in vascular research has established that a single, ideal, naturally available model for atherosclerosis, restenosis, or for that matter aneurysm formation, does not exist. Presently, rabbits and pigs are favored for the former two areas of study, and dogs and sheep appear to provide suitable models for testing devices for endoluminal repair of aneurysms. The development of transgenic variants of currently available models may widen our options in the future. Nevertheless, an appreciation of the individual features of natural or stimulated disease in each species is of the utmost importance for the proper design and execution of relevant experiments.

Animals↗
PubMed2000

A double coaxial delivery system for deployment of a two-stage stent-graft. An experimental feasibility study.

PURPOSE: To design and test a delivery system for successive, rapid two-stage deployment of an aortic stent graft. MATERIAL AND METHODS: An aortic stent graft was made that consisted of two separate parts. A delivery system composed of two independent coaxial mechanisms was fabricated and used to deploy the stages of the graft in dogs' aortas. RESULTS: Delivery was successful in all four dogs, and required less than 2 min in each animal. CONCLUSION: The double coaxial delivery system enabled quick endovascular assembly of a two-stage aortic stent-graft.

Animals↗
PubMed1999

Preliminary results with a new vascular basket occluder in swine.

PURPOSE: To experimentally evaluate a new self-anchoring vascular occlusion device suitable for use in large, high-flow vessels. MATERIALS AND METHODS: A basket-shaped occluding device consisting of a nitinol frame (with or without polyester threads) covered with Dacron was evaluated in the common iliac arteries and abdominal aortae of normal pigs. One occluder was placed in each recipient vessel. Angiography was performed before and after placement of each occluder. RESULTS: Precise placement of the device was achieved in all cases. Mechanically, all but one occluder worked dependably. Angiographically, devices without polyester threads produced only partial occlusion. Devices with threads produced complete occlusion in all but one abdominal aorta, in which partial occlusion occurred because the occluder opened asymmetrically. Complete iliac arterial occlusion occurred within 2-8 minutes of placement and aortic occlusion was achieved within 8-20 minutes. At necropsy, all devices were found to be securely anchored against the vascular wall. CONCLUSION: Preliminary results indicate that this vascular basket occluder containing polyester threads is easy to place precisely, produces rapid embolization, and demonstrates good self-anchoring ability in a high-flow arterial model.

Angiography↗
PubMed1999

Experimental evaluation of cellulose acetate NF and ethylene-vinyl alcohol copolymer for selective arterial embolization.

PURPOSE: Studies were conducted in rabbits to evaluate two new liquid polymeric compounds developed for selective arterial embolization. MATERIALS AND METHODS: The compounds consisted of cellulose acetate NF (Embolyx C) or ethylene-vinyl alcohol copolymer (Embolyx E) dissolved in anhydrous dimethyl sulfoxide (DMSO) containing 30% tantalum powder. Acute renal embolization was performed to determine an optimal method of administration and level of embolization. Kidneys were embolized with and without flow around the catheter. DMSO was also injected in the same manner. Tissue sections were examined radiographically and microscopically. Tumor embolization was performed to evaluate the efficacy of the polymers and compare their embolic effects with polyvinyl alcohol (PVA) particles and gelatin sponge (Gelfoam) powder. An embolic agent, saline, or DMSO was injected into the deep femoral artery feeding an intramuscular VX2 carcinoma. Animals were followed up for 3 weeks. RESULTS: Viscosity and administration technique affected polymer distribution and depth of penetration. Embolization with the test polymers was quicker and more easily achieved than with PVA or Gelfoam, and no recanalization occurred. Both polymers were as effective as PVA particles for tumor ablation, but DMSO caused some vascular damage. CONCLUSION: Although use of DMSO has some drawbacks, the results of this study warrant further investigation of the Embolyx polymers for tumor embolization.

Angiography↗
PubMed1998

The bacteriological screening of donated human milk: laboratory experience of British Paediatric Association's published guidelines.

This study was undertaken to assess the application of the British Paediatric Association's (BPA) published guidelines to the bacteriological screening of breast milk donated to a District General Hospital milk bank. Samples of donated milk were subjected to bacterial counts and provisional identification after both 24 and 48 h incubation on cysteine lactose electrolyte-deficient (CLED) and Columbia blood agar. 21.8% (76 out of 348) donations of milk failed to reach the BPA acceptable criteria. The organisms responsible for the rejection of these samples were all evident within 24 h incubation, and were not significantly confined to one medium. A large percentage of rejected samples originated from a small number of donor mothers; 63.2% came from one donor. In applying BPA guidelines, both CLED and Columbia blood agar were found to be equally effective in screening for unacceptable organisms in prepasteurization donated breast milk. The 24 h period allowed for bacteriological screening, prior to pasteurization of milk samples, was sufficient to allow the growth of all potentially pathogenic bacteria in this study. To prevent the donation of consistently contaminated milk, more active communication between the milk bank staff and the donor is recommended.

Acinetobacter↗
PubMed1997

Technical aspects of catheter-related interventions in the liver of the rabbit.

PURPOSE: On the basis of 89 different vascular interventions performed in the livers of 39 rabbits, we attempted to establish the feasibility and technical limitations of these procedures. MATERIAL AND METHODS: Forty-five selective hepatic artery catheterizations were carried out using 0.66-mm and 1.0-mm catheters, including superselective proper hepatic catheterizations (n = 14) using a specially designed 0.66-mm introducer/catheter system. The portal system was investigated with both direct (n = 5) and indirect (arterial) (n = 4) portography. Hepatic, vein catheterizations were performed in 22 cases. RESULTS: With the 0.66-mm system, spasm occurred in one of 11 cases in the proper hepatic artery, and no spasm was observed in the common hepatic and celiac arteries. Both arterial portography and hepatic venography were easily performed and were a precise and repeatable method. CONCLUSION: The 0.66-mm system has proved to be advantageous over the 1.0-mm catheterization in avoiding arterial spasm. Direct portography as well as catheterization of the hepatic vein from a jugular approach are hazardous, leading to serious complications including the death of the animal.

Animals↗
PubMed1996

Superselective arterial catheterization in the rabbit.

RATIONALE AND OBJECTIVES: To improve the safety and success of selective and superselective arterial catheterization in the rabbit. METHODS: A 2-F catheter introducer system was devised that consisted of the sheath of an 18-gauge, 5.1-cm sheath needle and a hemostatic valve attached to the hub of the sheath. The system was tested in 14 adult male New Zealand white rabbits with regard to ease of insertion and facilitation of superselective arterial catheterization. RESULTS: The introducer system was easily placed in all rabbits, and no bleeding was seen around the sheath at the puncture site. Preshaped 2-F polyethylene catheters were readily inserted through the assembly and sheath. The valve prevented bleeding from around the catheter, and the side-arm flush tube served as a route for heparinization. The system greatly facilitated the manipulation of 2-F angiographic catheters. CONCLUSION: Use of the introducer system with a 2-F polyethylene angiographic catheter improved the success of selective and superselective arterial catheterization in the rabbit.

Angiography↗
PubMed1996

Percutaneous intratumoral injection of cisplatin microspheres in tumor-bearing rats to diminish acute nephrotoxicity.

Poly(D,L-lactide) microspheres loaded with cisplatin (PLA-CDDP MS) were prepared by a solvent evaporation technique for direct intratumoral injection. The microspheres, 50-100 microns, containing 40.04% of cisplatin produce sustained release in vitro. PLA-CDDP MS (6 mg/kg body weight of cisplatin) suspensions were injected intratumorally into mammary tumors in rats. Cisplatin solution (6 mg/kg body weight) was injected either intratumorally or intraperitoneally in two groups. After treatments, the tumor size decreased in each of the groups as a function of time. Sixteen days post-injection, the tumors had either disappeared or significantly shrunk. PLA-CDDP MS had a similar antitumor effect compared with cisplatin aqueous solution. Blood urea nitrogen, serum creatinine and histopathology examinations revealed that the renal toxicity in the PLA-CDDP MS group was significantly less than in the control groups. These results indicate that intratumoral injection of PLA-CDDP MS maintains anticancer potency and reduces acute renal toxicity.

Animals↗
PubMed1996

Isolation of Mycoplasma hominis using the BACTEC 9000 series blood culture system.

Mycoplasma hominis has been implicated as an important cause of septicaemia. There have been reported variances in the ability of blood culture systems to support the growth of this organism. In this study the ability of the BACTEC 9000 series automated system to grow and detect M hominis was assessed. Three of five wild M hominis strains grew in the BACTEC Anaerobic Plus/F medium but growth was not flagged by the detection mechanism of the system. It is recommended that users of the BACTEC 9000 series should use a seven day protocol and perform terminal subculture for suspected cases of M hominis septicaemia.

Bacteriological Techniques↗
PubMed1996

Cystic fibrosis and the pseudomonads.

The microbiology of pulmonary disease in cystic fibrosis has altered over the past 10 years. The major pathogens in this disease are now Pseudomonas aeruginosa and, increasingly, Pseudomonas cepacia. P. aeruginosa respiratory infection in these patients is rarely eradicated and this is often the only pathogen found at post-mortem. The most important points in the pathogenesis of this infection are probably the protective role of the bacterial mucoid exopolysaccharide and the interaction of various other bacterial factors with the immune system of the body. P. cepacia has recently emerged as the common isolate from the lungs of cystic fibrosis patients. The actual role of this organism in the progression of lung disease is poorly understood. There has been some speculation about the role of cross-infection in the acquisition of both of these organisms. The treatment of these infections is problematical because of the altered antimicrobial pharmaco-kinetics within the cystic fibrotic lung and the resistant properties of the organisms involved. Approaches which have been suggested recently include immunological interventions and genetic therapy.

Anti-Bacterial Agents↗
PubMed1995

Hepatic arterial infusion of recombinant platelet factor-4 suppresses metastases to the lungs from tumors implanted into the livers of rabbits.

BACKGROUND: This study evaluated the toxicity (Part I) and antitumor effects (Part II) associated with hepatic arterial infusion of recombinant platelet factor-4 (rPF4), an antiangiogenic protein. METHODS: Healthy rabbits (Part I) and rabbits with tumors implanted in their livers (Part II) received saline or rPF4 via hepatic arterial infusion. Three saline-receiving and four rPF4-receiving animals died 2-3 days postinfusion from gastroduodenal thromboembolism. The remaining animals were necropsied 3, 7, 10, or 14 days postinfusion. Blood analyses and hepatic angiography were performed before infusion and at the time of sacrifice. RESULTS: In Part I, focal coagulation necrosis of the hepatic parenchyma was observed in 1 of 11 rabbits that received saline and in 6 of 10 that received rPF4. In Part II, hepatic arterial infusion of rPF4 had no effect on growth of the implanted liver tumors. However, the protein significantly reduced the incidence of lung metastasis. CONCLUSIONS: Intraarterial infusion of rPF4 significantly reduced the incidence of lung metastasis. Nonheparin systemic anticoagulation may be needed during catheterization and infusion procedures to prevent thromboemboli.

Animals↗
PubMed1994

In vivo and electron microscopic studies of rat liver after intravenous injection of polyamino acid microspheres.

In vivo and electron microscopy were used to study the hepatocellular responses of rat livers to intravenously injected polymeric microspheres. Two microsphere preparations with different surface characteristics and degradability were used in this study. In vivo microscopy revealed that both poly(benzyl L-glutamate) (PBLG) and poly(hydroxypropyl L-glutamine) (PHPG) microspheres caused disturbance in the microcirculation of rat liver up to 2 months after injection. The observed changes included stagnant flow and adherence of white blood cells to the endothelial lining of venules an sinusoids. Kupffer cell (KC) activation following phagocytosis of microspheres was evidenced by the enlargement of KCs and increased number of KCs taking up fluorescent latex particles. Electron microscopy of rat livers revealed a wide range of hepatocellular injury associated with the administration of PBLG and PHPG microspheres. These results indicate that a small amount of remaining microspheres is sufficient to induce continuous disturbance to hepatic microcirculation and that particulate drug carriers should be designed to be rapidly degraded so that the return to normal liver function is possible.

Animals↗