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Biomedical subjects

W Peters

Publications and source records attributed to W Peters.

At least 109 records · Page 6Linked to original sources
PubMed1995

Analysis of silicon levels in capsules of gel and saline breast implants and of penile prostheses.

Although a potential link between silicone-gel breast implants and autoimmune connective tissue disease has been suggested, none has been proven. The potential role of silicone as an immune adjuvant remains very controversial. Currently available techniques do not allow precise measurements of silicone in tissues. However, all compounds containing silicon (including silicone) can be measured accurately. The present study was designed to measure silicon levels in the fibrous capsules of patients with silicone-gel breast implants, saline breast implants, and silicone inflatable penile prostheses. Baseline control silicon levels were obtained from the breast tissue of patients undergoing breast reduction, who had no exposure to breast implants. All silicon measurements were carried out using atomic absorption spectrometry with a graphite furnace. Silicon was measured in a normal heptane extract of silicone from dried tissue. The mean silicon levels in 16 breast tissue control samples from 8 patients undergoing breast reduction varied from 0.025 to 0.742 micrograms/gm with the median mean being 0.0927. The median silicon level in capsules from six patients with saline implants was 7.7 micrograms/gm (range, 1.9-36.6 micrograms/gm). The median silicon level in capsules from five patients with silicone inflatable penile prostheses was 19.5 micrograms/gm (range, 1.9-34.8 micrograms/gm). Although the levels of silicon in capsules of patients with saline breast prostheses and penile implants were higher than in control samples, they were much lower than those from the capsules of the 58 gel implants (median, 9,979 micrograms/gm; range, 371-152,000 micrograms/gm).(ABSTRACT TRUNCATED AT 250 WORDS)

Breast↗
PubMed1995

Analog-digital recording of current and voltage during high voltage DC shocks.

UNLABELLED: Efficient on-line digitization is the prerequisite for computerized analysis of the electrical phenomena occurring during defibrillation. Conventional hardware presently provides only limited time resolution. The performance of various digitization rates for recording of voltage, current, and calculation of derived quantities like impedance, energy, and defibrillator capacitance was investigated. It was assessed both experimentally and by computer simulation of a trapezoidal discharge (of 9 msec duration into a constant resistive load of 50 omega with a defibrillator capacitance of 132 microF). The accuracy achieved with different digitization rates is given. For example, an accuracy of 1% for analog-digital conversion for impedance calculation during this kind of DC shock requires a sampling rate of 8 kHz without, and a rate of 1 kHz with linear interpolation to correct for the hardware dependent error due to sequential sampling. CONCLUSION: Highly efficient analog-digital conversion of delivered voltage and current during DC shocks is available within the limits of conventional inexpensive hardware.

Algorithms↗
PubMed1995

[An unusual series of complications in therapy with implantable cardioverter-defibrillator].

A 48-year-old man with dilative cardiomyopathy and a history of resuscitation due to ventricular fibrillation received an implantable cardioverter-defibrillator (ICD) with epicardial sensing and defibrillation electrodes in March 1990. An early battery depletion due to increased electrical leakage of a filter capacitor necessitated a generator exchange in July 1990. Subsequent inappropriate discharges occurred, but no underlying cause could be documented by history, clinical examination, Holter monitoring, and beepograms. Only 3 months later was it possible to demonstrate oversensing by repeated beepograms, and a new generator and transvenous sensing electrode were implanted in October 1991. Four months later, inappropriate shocks were suspected again. Once more, history, clinical examination, Holter monitoring, and beepograms were without pathological result. At follow-up, repeated beepograms during exercise demonstrated an oversensing, and an insulation defect of the newly implanted sensing electrode close to the edge of the generator could be documented on x-ray. Since replacement of generator and sensing electrode in July 1992 the patient is doing well. He received two appropriate shocks which were associated with presyncope. ICD therapy is very complex and therefore should only be performed in centers providing the necessary personal, apparative and logistic conditions.

Death, Sudden, Cardiac↗
PubMed1994

Is there a relationship between autoantibodies and silicone-gel implants?

The present study was conducted to determine if 200 patients with silicone-gel implants demonstrated elevated levels of autoantibodies, compared with a similar group of 100 age-matched control subjects without breast implants. These results were then compared with 29 patients who had demonstrated implant rupture. Differences in the frequency of autoantibody levels were determined by the chi-squared test. Differences in autoantibody titers were determined by Wilcoxon's signed rank test. Differences were considered significant with p > 0.05. The prevalence of a positive antinuclear antibody (ANA) test (dilution 1:100) in the 200 patients with breast implants was 26.5% compared with 28% in the 100 control subjects. In 29 patients with implant rupture, only 17.2% tested ANA positive. These values were not significantly different. In addition, there were no significant differences between the ANA titers of positive patients in each group. In each of the three groups, all patients who tested ANA positive were analyzed to assess the frequency and titer of other autoantibodies, including anti-DNA, anti-cardiolipin, anti-SSA, anti-SSB, anti-SM, anti-RNP, and anti-Scl-70. There were no significant differences between the frequency or titer of any of these autoantibody levels in each of the three groups of patients. These studies strengthen the concept that there is no conclusive evidence that silicone-gel implants are related to the development of connective tissue disease.

Adult↗
PubMed1994

Factors affecting the rupture of silicone-gel breast implants.

Between January 1990 and April 1993, over 500 patients with silicone-gel breast implants were clinically assessed regarding their implant status. Of these, 57 patients requested implant removal. Reasons for removal were capsular contracture (39 patients), possible implant rupture, suggested by ultrasound testing or mammography (7 patients), "silicone phobia" (7 patients), and asymmetry (4 patients). Of the 102 implants that were removed, 60% were intact, 33% were ruptured, and 7% were leaking. There was a positive correlation between duration of implantation time and the number of ruptured and leaking implants. Of the 45 implants that had been in place for 5 years or less, 93% were intact. Of the 29 implants that had been in place for 6 to 10 years, only 31% were intact (59% were ruptured and 10% were leaking). Similar results were obtained in 20 implants after 11 to 15 years (30% were intact, 55% were ruptured, and 15% were leaking). Of 8 implants that were in place for 16 to 26 years, 50% were intact and 50% were ruptured. In this study, the integrity of breast implants was not related to the degree of capsular contracture.

Adult↗
PubMed1994

Radiation necrosis overlying the ankle joint after injection with yttrium-90.

A 35-year-old woman with rheumatoid arthritis presented with radiation necrosis and an open wound overlying her ankle joint, 8 months after injection with yttrium-90 to facilitate radiosynovectomy. This problem was successfully treated by surgical excision of the area of radiation damage and closure with a fasciocutaneous flap.

Adult↗
PubMed1994

Evaluation of 0.75% metronidazole gel in acne--a double-blind study.

Metronidazole, an imidazole, is an antibiotic with established efficacy against anaerobic bacteria. To date, however, there are no published data concerning the efficacy of topical metronidazole in the treatment of acne. This randomized, double-blind prospective clinical study of 96 patients was performed to investigate the efficacy and tolerability of 0.75% metronidazole gel vs. placebo in the treatment of mild to moderate acne. The results of this study showed no significant benefit in using 0.75% metronidazole gel over placebo in reducing counts of inflamed and non-inflamed lesions of acne. There was also no statistically significant difference between the two groups at any stage in the trial when skin tolerability was assessed.

Acne Vulgaris↗
PubMed1994

Transmyocardial impedance during single and multiple internal ventricular defibrillation shocks.

Little is known about the transmyocardial impedance during internal ventricular defibrillation. In a canine model, using high rate on-line digitization, random shock delivery, and titanium electrodes, we determined the relationship among voltage, current, and impedance, delivered energy, and defibrillation success within the individual and within successive defibrillation shocks. Impedance decreased with repeated defibrillation in 10 of 11 dogs. Impedance always increased during trapezoidal discharges, whereas voltage decreased. Impedance was lower with high energy-voltage shocks in all dogs. Visually, voltage and current waveform did not show a phase shift. There was no difference in the total energy delivered and the energy converted into heat by the resistive part of the impedance. With a formula valid only for resistive loads, the capacitance of the defibrillator was calculated to be within the measurement accuracy and tolerance of the factory-provided value of 132 microF. Polarization voltage was consistently observed. Thus the transmyocardial impedance during defibrillation is primarily resistive, nonlinear voltage dependent, and declines with successive shocks. Defibrillation success was not influenced by these phenomena.

Animals↗
PubMed1994

Three-point transformation for integration of multiple coordinate systems: applications to tumor, functional, and fractionated radiosurgery stereotactic planning.

The accuracy of an optimized three-point transformation method and its usefulness for integrating multiple independent coordinate systems has been described. Such integration can be implemented to accomplish complex stereotactic procedures which may require the use of multiple image data sets and combinations of frame-based and frameless stereotactic systems. This report details the application of an optimized transformation for intracranial lesion biopsy and/or resection, radiofrequency pallidotomy for treatment of Parkinson's disease, and fractionated stereotactic radiosurgery in a total of 68 patients. For approach to intracranial lesions, a noninvasive definition of image coordinate systems with multiple radiodense scalp markers was cross-registered with a standard stereotactic guidance system. This method allowed for elective acquisition of stereotactic image sets without requiring head frame fixation until the time of the operative procedure. In planning pallidotomy procedures, spatial cross-registration of CT and MR image coordinates were performed to target the posteroventral pallidum. CT coordinates were defined by the standard picket fence algorithm while MR images were referenced with multiple scalp markers. The addition of MR data sets improved anatomic resolution in the regions of the basal ganglia and commissures. Fractionated radiosurgery was accomplished by cross-registration of CT, MR, and plain radiographs using BRW localizers coupled with multiple scalp markers. A daily check of target positioning was performed with the BRW angiograph localizer. The average calculated error was 2.83 mm with a standard deviation of 1.66 mm which remained within the average scan slice thickness of 3.63 mm. In all cases surgical targets were reached without complication.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Present development concerning antimalarial activity of phospholipid metabolism inhibitors with special reference to in vivo activity.

The systematic screening of more than 250 molecules against Plasmodium falciparum in vitro has previously shown that interfering with phospholipid metabolism is lethal to the malaria parasite. These compounds act by impairing choline transport in infected erythrocytes, resulting in phosphatidylcholine de novo biosynthesis inhibition. A thorough study was carried out with the leader compound G25, whose in vitro IC50 is 0.6 nM. It was very specific to mature parasites (trophozoïtes) as determined in vitro with P. falciparum and in vivo with P. chabaudi -infected mice. This specificity corresponds to the most intense phase of phospholipid biosynthesis activity during the parasite cycle, thus corroborating the mechanism of action. The in vivo antimalarial activity (ED50) against P. chabaudi was 0.03 mg/kg, and a similar sensitivity was obtained with P. vinckei petteri, when the drug was intraperitoneally administered in a 4 day suppressive test. In contrast, P. berghei was revealed as less sensitive (3- to 20-fold, depending on the P. berghei-strain). This difference in activity could result either from the degree of synchronism of every strain, their invasion preference for mature or immature red blood cells or from an intrinsically lower sensitivity of the P. berghei strain to G25. Irrespective of the mode of administration, G25 had the same therapeutic index (lethal dose 50 (LD50)/ED50) but the dose to obtain antimalarial activity after oral treatment was 100-fold higher than after intraperitoneal (or subcutaneous) administration. This must be related to the low intestinal absorption of these kind of compounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Preliminary experience using an optimized three-point transformation algorithm for spatial registration of coordinate systems: a method of noninvasive localization using frame-based stereotactic guidance systems.

This study describes the use of an optimized three-point transformation algorithm to spatially cross-register a volumetric computerized tomographic scan or magnetic resonance image data set with the coordinate system of a stereotactic frame. This algorithm was tested for accuracy using a scanned phantom in which calculated targets, using the Brown-Roberts-Wells (BRW) frame picket-fence algorithm as a standard, could be compared to physical targets measured using a BRW arc and phantom. These target values were then compared to target values calculated with the optimized three-point algorithm. This method was used for target localization in 21 patients. Following this noninvasive localization method, the standard BRW stereotactic system was used for guidance. The application accuracy of this frameless localization technique was within the limits of the scan slice thickness in 16 of 21 cases, with an average error of 2.11 mm in an average scan slice thickness of 3.1 mm. Intracranial targets were successfully reached in all cases without morbidity or mortality. The algorithm can be customized to cross-register image data sets with the coordinate systems of a wide variety of stereotactic guidance systems. The method increases the convenience and flexibility of frame-based stereotactic guidance by providing a means of noninvasive localization that can be accomplished electively at a separate time from the guidance part of a stereotactic operative procedure.

Aged↗
PubMed1994

Patient-controlled analgesia in burn patients: a critical review of the literature and case report.

Although patient-controlled analgesia has been well documented as effective in various types of patients, it has not been adequately studied in burn patients. In this paper, the authors review the literature on PCA in burn patients and present two cases. Flaws in most published studies make it difficult to determine the efficacy of PCA in burn patients. Both the literature and experience indicate that many patients with acute burns are not suitable candidates for PCA. The cases illustrate the different methods patients may use to achieve adequate analgesia with PCA. Both patients and nurses face a steep learning curve in using PCA for management of procedural pain in burn care.

Adult↗
PubMed1994

Clostridium septicum abscess in hepatic metastases: successful medical management.

Clostridium septicum bacteremia is frequently associated with hematologic and colonic malignancies and neutropenia. It frequently produces 'metastatic' gangrene with excessive mortality. Standard therapy usually includes surgical debridement and antibiotics. We present a patient with metastatic breast cancer treated with high-dose chemotherapy and bone marrow transplantation. She was treated successfully with antibiotics alone despite developing Cl. septicum bacteremia and gas in hepatic metastases. The pathophysiology of this infection is reviewed.

Adult↗
PubMed1994

Antimalarial activity of the bicyclic peroxide Ro 42-1611 (arteflene) in experimental models.

The sesquiterpene peroxide Ro 42-1611 (arteflene), a synthetic derivative of yingzhaosu, was evaluated extensively against various drug-sensitive and drug-resistant lines of Plasmodium falciparum in vitro and P. berghei in vivo in mice. The potential therapeutic and prophylactic activities were studied comparatively with the standard antimalarials chloroquine, mefloquine and quinine, as well as qinghaosu and the derivatives artemether and artesunic acid. Experimentally arteflene proved to be a highly effective antimalarial drug. In vivo it is active at low doses against blood stages of P. berghei in mice after oral or parenteral administration. It has a rapid onset of drug action and a long lasting suppressive effect when given after infection, as well as a good potential for prophylactic activity when given before infection. The suppressive and prophylactic properties are comparable to chloroquine and superior to qinghaosu, artemether and artesunic acid. In vitro the compound showed no signs of cross-resistance with existing antimalarials. It was consistently rather more active against drug-resistant than against drug-sensitive strains of P. falciparum. Drug interaction studies in vitro and in vivo with chloroquine, mefloquine and quinine revealed an additive to synergistic effect with arteflene. Antagonism with these drugs was not observed. Compared with standard antimalarials the activity of arteflene in vitro is lower than would be expected from the in vivo results. This may be due to pharmacokinetic properties of the compound and the formation of an active metabolite which sustains the activity of arteflene in vivo.

Animals↗