Search PubMed⌕ Search

Biomedical subjects

K Stokes

Publications and source records attributed to K Stokes.

At least 19 recordsLinked to original sources
PubMed1995

Glass wool-H2O2/CoCl2 test system for in vitro evaluation of biodegradative stress cracking in polyurethane elastomers.

Environmental stress cracking (ESC) in polyetherurethanes has been demonstrated in animal models. However, duplication of this phenomenon in vitro has been a challenge. The glass wool-H2O2/CoCl2 test system was designed to provide oxidation components found in vivo, i.e., hydroxyl radical (HO.), molecular oxygen (O2), and superoxide (O2-.) required for auto-oxidation of polyetherurethanes. The in vitro test is not only reliable in duplicating the characteristics of in vivo stress cracking in polyetherurethanes at 37 degrees C, but also accelerates ESC as much as seven times. The test results on several types of polyurethanes showed that Tecothane 80A was as vulnerable to biodegradative stress cracking in vitro as Pellethane 2363-80A, while the new generation of polyurethanes, Corethane, demonstrated great resistance against stress cracking.

Biodegradation, Environmental↗
PubMed1995

Portal vein: US-guided localization prior to transjugular intrahepatic portosystemic shunt placement.

To mark the portal vein prior to transjugular intrahepatic portosystemic shunt (TIPS) placement, metallic coils adjacent to (n = 18) and a wire within (n = 18) the portal vein were placed with ultrasonographic (US) guidance. The mean number of punctures for successful portal vein entry was 3.0 with coils and 2.9 with a wire, and the mean total procedure time was 127.5 and 110.0 minutes, respectively (differences, not significant), and mean time at US was 20 and 10 minutes, respectively.

Adult↗
PubMed1994

Transesophageal echocardiography assisted retrieval of embolized inferior vena cava stent.

A 32-year-old male with Budd-Chiari syndrome and stenosis of the inferior vena cava presented to the hospital with severe abdominal pain. Two contiguous, 14 mm, overlapping (joined) Palmaz stents were placed across the area of stenosis in the inferior vena cava. The stents later embolized to the left pulmonary artery and were retrieved non-surgically over a Grollman balloon catheter with transesophageal echocardiographic assistance. This case report highlights the advantages and limitations of transesophageal echocardiographic assistance in such a procedure.

Adult↗
PubMed1994

Percutaneous localization of small pulmonary metastases, enabling limited resection.

An adolescent patient with Ewing's sarcoma, who had undergone three previous thoracotomies for pulmonary metastases, presented with two further left-sided pulmonary metastases, measuring 5 mm and 10 mm in diameter. Chemotherapeutic options were limited, and pulmonary irradiation was inadvisable because of compromised respiratory function. Surgical resection was the favored therapeutic option. A method of accurately localizing the small lesions was devised, using a percutaneous needling technique under computed tomography guidance and the injection of barium and methylene blue. This localization enabled resection of the lesions, with minimal excision and manipulation of the surrounding normal parenchyma. This technique is useful for removal of small impalpable metastases when other modalities of therapy are not appropriate.

Adolescent↗
PubMed1994

Magnetic resonance angiography in transjugular intrahepatic portosystemic stenting: comparison with contrast hepatic and portal venography.

In order to highlight the role of magnetic resonance angiography [MRA] in the assessment of patients pre-transjugular intrahepatic portosystemic shunt (TIPS) stenting, the MRA images of portal and hepatic veins of 21 patients were compared with the images from contrast portal and hepatic venograms performed on the same patients at the time of TIPS stenting (20 patients). MRA enabled accurate, non-invasive, multiplanar imaging of portal and systemic venous anatomy in each of the patients studied. MRA facilitated accurate determination of vessel patency and flow direction, images correlating exactly with contrast venograms of hepatic and portal veins in each case. In one patient, identification of occult hepatocellular carcinoma extending to the portal vein lead to the postponement of the TIPS procedure.

Adult↗
PubMed1994

A comparison of operation, endoscopic retrograde cholangiopancreatography, and percutaneous transhepatic cholangiography in biliary complications after hepatic transplantation.

BACKGROUND: Biliary complications (BC) remain a significant cause of morbidity and mortality after orthotopic liver transplantation (OLT). STUDY DESIGN: In an effort to determine the incidence of BC after OLT and the success of management options, 157 hepatic transplants performed from January 1987 to July 1991 were reviewed. RESULTS: The incidence of BC was 25 percent, with a one year mortality rate of 43.5 percent compared with 23.4 percent for patients in a control group (p < 0.05). Most BC occurring before postoperative day 30 presented as leaks, with a one year mortality rate of 50 percent (p < 0.03 versus control group). Biliary complications presenting after postoperative day 30 presented as strictures, with a one year mortality rate of 36.8 percent (p = NS versus control group). Endoscopic retrograde cholangiopancreatography (ERCP), percutaneous transhepatic cholangiography (PTHC), and operative treatment were analyzed to determine relative patency rates after intervention for BC. The analysis showed that ERCP and PTHC were equivalent, with a one year patency rate of 45 percent. Operative treatment had a patency rate of 89 percent (p < 0.05 compared to ERCP and PTHC). CONCLUSIONS: The results from ERCP and PTHC may be useful for delineation of rejection versus BC after OLT. However, operative treatment is significantly more effective for definitive treatment of BC after OLT.

Adult↗
PubMed1993

Treatment of hepatocellular carcinoma using doxorubicin/ethiodized oil/gelatin powder chemoembolization.

BACKGROUND: Hepatocellular carcinoma (HCC) is a common malignancy worldwide with limited effective therapeutic options available or appropriate for cirrhotic patients. METHODS: Chemoembolization, using sequential intra-arterial doxorubicin/ethiodized oil and gelatin sponge particle/ethanol embolization, was used to treat patients with unresectable HCC localized to the liver. Fifty-two patients were treated in this manner from 1988 to 1992. The objective response was determined by sequential computed tomography (CT) scans. RESULTS: Of the 47 patients evaluable for response, 20 (43%) achieved a partial response, and 12 (26%) achieved a minor response. Sixteen patients underwent repeated chemoembolization for locally recurrent disease as many as three times after the initial procedure. All 52 patients were evaluable for survival and toxicity, with a median follow-up of 14 months. Twelve-month survival was 60%, and median survival was 16 months. This compares favorably with values reported in the literature of approximately 20% and 6-14 weeks, respectively. There was a 17% 30-day mortality, with a slightly higher risk for patients with portal vein obstruction. Other toxicities generally were mild and transient, including fever, pain, encephalopathy, and malaise. CONCLUSIONS: Chemoembolization may enhance survival for patients with unresectable, localized HCC. It appears to be an effective alternative to standard treatment, even in cirrhotic patients.

Adult↗
PubMed1993

Human plasma alpha 2-macroglobulin promotes in vitro oxidative stress cracking of Pellethane 2363-80A: in vivo and in vitro correlations.

It is hypothesized in this study that the phenomenon of environmental stress cracking (ESC) in polyetherurethane is caused by a synergistic action of biological components in the body fluids, oxidative agents, and stress. An in vitro system is designed to mimic the in vivo system; human plasma contains certain biological components that can act as a stress cracking promoter, while H2O2 (Co) solution provides an oxidative reaction comparable to that observed in the respiratory burst of adherent macrophages and foreign-body giant cells. It is demonstrated that the phenomenon of in vivo stress cracking in Pellethane 2363-80A is duplicated by an in vitro system that involves a pretreatment of prestressed specimens with human plasma at 37 degrees C for 7 days followed by oxidation in 10% hydrogen peroxide with 0.10M cobalt chloride at 50 degrees C for 10 days. The pretreatment with plasma has a synergistic effect with the oxidation by H2O2 (Co) treatment to produce ESC. A plasma component responsible for promoting stress cracking in Pellethane polyurethane is identified to be alpha 2-macroglobulin (alpha 2M).

Animals↗
PubMed1992

Phase I clinical and pharmacokinetics study of high-dose toremifene in postmenopausal patients with advanced breast cancer.

Toremifene is an antiestrogen that binds strongly to estrogen receptors (ER). A total of 19 previously treated postmenopausal women with metastatic breast cancer whose performance status was good and whose ER status was positive or unknown were studied to determine the maximum tolerated dose of toremifene. Cohorts of patients received 200, 300, or 400 mg/m2 p.o. daily until relapse or unacceptable toxicity had occurred. Nausea, vomiting, and dizziness were dose-related. Three of five patients receiving 400 mg/m2 experienced moderate or severe vomiting and another developed reversible disorientation and hallucinations. Mild sweating, peripheral edema, vaginal discharge, and hot flushes were encountered at all doses. Reversible corneal pigmentation was identified in seven cases but was not of clinical importance. The pharmacokinetics of toremifene was studied weekly and in detail on day 42 using a high-performance liquid chromatographic (HPLC) assay that identified the parent compound and three active metabolites, N-desmethyltoremifene, (deaminohydroxy)toremifene, and didemethyltoremifene. Steady state was achieved at 1-3 weeks. The toremifene area under the curve and the maximal concentration were dose-dependent at high doses. The recommended phase II dose is 300 mg/m2 p.o. daily.

Adult↗
PubMed1991

[Early and late results of percutaneous transluminal angioplasty (PTA) in diabetic patients].

Results of 127 iliac and femoropopliteal transluminal angioplasties in 97 diabetic patients are presented. Patients who had undergone iliac (n = 70), femoral (n = 41), and popliteal (n = 16) angioplasties for stenoses up to 15 cm long were followed up for 6-60 months. In diabetic patients presenting with only claudication or adequate runoff, the 5-year iliac patency rate was 76% and the femoral patency rate was 60%; these results were comparable with those found in non-diabetic patients. For limb salvage, 3-year patency rates were 66% for iliac, 37% for femoral, and 37% for popliteal angioplasties, and 5-year patency rates were 29% for iliac, 7% for femoral, and 0% for popliteal angioplasties. Our findings suggest that the overall decreased PTA success rates typically associated with diabetes are due to the larger percentage of these patients who present with symptoms of severe peripheral vascular disease and not to the presence of diabetes per se.

Adult↗
PubMed1990

Cellular interactions with biomaterials: in vivo cracking of pre-stressed Pellethane 2363-80A.

The phenomenon of stress cracking of Pellethane 2363-80A (PEU) was investigated using the cage implant system. A cytotoxic polyvinylchloride (PVC) and a silicone rubber containing an anti-inflammatory steroid were used to create inflammatory environments in which the biostability of the pre-stressed PEU was tested. These coimplants provided alternative in vivo environments to study in vivo polymer interactions. The inflammatory responses to the implanted cages were monitored by analyzing the exudates aspirated from the cages at different implantation times over 21 days. The pre-stressed PEU specimens were retrieved after 5, 10, and 15 weeks postimplantation and examined by optical microscopy (OM) and scanning electron microscopy (SEM). The results support the conclusion that in vivo cracking of stressed (strained) Pellethane 80A is related to cell-polymer interactions. Severe cracking or rupture of the implanted PEU specimens was observed as early as 5 weeks postimplantation. Molecular chain degradation of the implanted specimens was evident from molecular weight measurements. Neither surface cracking nor degradation of macromolecules was found on the pre-stressed PEU specimens with the added cytotoxic PVC implanted over 15 weeks. No cracking was observed on the pre-stressed specimens in the presence of steroid silicone rubber, even after 10 weeks implantation.

Animals↗
PubMed1990

A new efficient NanoTip lead.

The ideal lead has low, stable acute and chronic thresholds, high pacing impedance, and good sensing. Leads with low, stable thresholds have been developed, but pacing impedance has been in the 600 omega region. One way to increase pacing impedance is to decrease the electrode's surface area. The threshold performance and sensing ability of less than 5 mm2 electrodes have been considered questionable, up to now. We have developed a 1.5 mm2 porous, platinized, steroid-eluting electrode and have demonstrated in canine studies that it has excellent performance. Chronic thresholds are low at about 0.65 +/- 0.28 V (ventricular) and 0.42 +/- 0.12 V (atrial) at 0.5 msec. Chronic pacing impedance is in the 1200-1300 omega region, but mean chronic R and P wave source impedance is less than or equal to 1500 omega. Sensing is excellent, with almost double the P wave amplitudes usually measured in the canine.

Animals↗
PubMed1990

The in vivo auto-oxidation of polyether polyurethane by metal ions.

The first large scale use of polyether polyurethane elastomers in long term human implants was as insulation for cardiac and neurologic pacing leads. While the performance of these polymers has generally been very good over a 14-year period, several failure mechanisms have been discovered that involve interactions between the devices, materials and the body. One of these is auto-oxidation of soft segment ether through the intermediate action of certain transition metal ions, derived from conductor wires by corrosion processes. Biologically produced oxidants appear to be an accelerating factor. In this study, Pellethane 2363-80A tubing containing conductor coils or mandrels of various metals or controls were implanted in rabbits. Explants were analyzed as a function of implant time by optical and scanning electron microscopy, electron dispersive analysis by X-ray, stress-strain, FTIR, GPC and AA spectrophotometry. Only cobalt produced bulk oxidative degradation while surface damage was found in the presence of cobalt bearing alloys. No evidence of significant auto-oxidation was found in the presence of silver, nickel, chromium, molybdenum, iron, titanium, platinum, 304 stainless steel, glass or empty tubing. The combination of polyether polyurethane and metals (especially those containing cobalt) in an implantable device must be carefully evaluated for biostability prior to human use.

Biocompatible Materials↗
PubMed1989

Sequence specificity of pausing by DNA polymerases.

We have constructed recombinant M13 DNA templates containing stretches of oligo (purines) and oligo (pyrimidines). Each of these inserts hinders the advancement of the large fragment of E. coli Pol I during DNA synthesis. The pattern of blockage is independent of changes in KCl or Mg2+ concentrations and pausing is moderately alleviated at lower pH. Blockage is not affected by either the concentration of template or by the position of the DNA primer. The pattern of pause sites is similar for calf thymus DNA polymerase-alpha, implying that replicative barriers are determined by the structure of the DNA at its growing point. There is a lack of correlation between the position of pause sites with different inserts and known alternate DNA structures. Thus, the homo-oligomeric inserts may possess a different structure when complexed with DNA polymerase. This concept accounts for the appearance of unique new upstream and downstream pause sites that result from the insertion of each oligonucleotide.

Base Sequence↗
PubMed1988

The porous titanium steroid eluting electrode: a double blind study assessing the stimulation threshold effects of steroid.

A transvenous pacing lead with a porous electrode which slowly elutes the steroid, dexamethasone sodium phosphate, has been developed. Previous investigations show low and constant stimulation thresholds persisting over at least the first two years post-implantation. As it is not known whether this low threshold results from the steroid or electrode configuration, a double blind study was designed to compare the same electrode configuration with and without steroid over a 2-year follow-up period. There were ten patients in each group with similar age, sex, indications for pacing and implantation data. Regular measurements of postoperative pulse duration thresholds were performed using a customized VVIM pulse generator programmed to 1.5 V output. For the first two days post-implantation, there were no statistical differences in the pulse duration thresholds between the two pacing leads. From 2 weeks to 2 years the pulse duration thresholds for the steroid leads remained almost constant, whereas the leads without steroid showed a typical rise. The difference in pulse duration thresholds between the two groups of leads from two weeks onwards confirmed that it was the steroid rather than the electrode configuration which prevented the rise in chronic stimulation threshold.

Aged↗
PubMed1987

Promotion of diabetes onset by stress in the BB rat.

The purpose of the present study was to address the question of whether environmental stress affects the age of onset and incidence of overt insulin-dependent diabetes mellitus in an animal model of human Type 1 (insulin-dependent) diabetes. Thirty-five diabetes prone BB rats of both sexes were divided into two groups: experimental animals were exposed to multiple, concurrent, and unpredictable environmental stressors, while littermate controls were exposed to a standard lab environment. Groups were housed in two separate, sound attenuated, independently ventilated, and restricted rooms. By age 150 days, experimental group animals had developed overt diabetes at a significantly earlier age.

Animals↗