Biomedical subjects

W Peters

Publications and source records attributed to W Peters.

At least 145 records · Page 8Linked to original sources

PubMed1992

Immunodetection and Identification of N-(o-Hydroxybenzylamino)Purine as a Naturally Occurring Cytokinin in Populus x canadensis Moench cv Robusta Leaves.

A highly specific and sensitive enzyme-linked immunosorbent assay (ELISA) was developed for 9-beta-d-ribofuranosyl-N(6)-(o-hydroxybenzylamino)purine [(oOH)[9R]BAP] and structurally related cytokinins. As little as 3 femtomoles of the compound could be detected by this method. Cross-reactivity studies demonstrated the specificity of four polyclonal antibodies for (oOH)[9R] BAP and its free base in preference to a range of natural cytokinins and other purines. After evaluating the method by internal standardization employing [2-(3)H](oOH)[9R]BAP of high specific radioactivity as recovery marker by dilution analyses and by immunohistograms, it was possible to apply ELISA to quantify (oOH)[9R]BAP in plant extracts. In addition to (oOH)[9R]BAP, an unknown cytokinin reacting with the same antibody was detected in high performance liquid chromatography-fractionated extracts of mature Populus x canadensis Moench cv Robusta. The structure of the new compound was determined by gas chromatography-mass spectrometry and finally confirmed by synthesis as N(6)-(o-hydroxybenzylamino)purine.

Journal Article↗

PubMed1992

Stereotactic localization and guidance using a machine vision technique.

Machine vision techniques (video cameras) can be used to determine the three-dimensional position of objects. This transformation can be accomplished with standard mathematical algorithms. Initial accuracy tests of stereotactic localization with video cameras were performed using a standard Brown-Roberts-Wells (BRW) phantom simulator coupled with the BRW angiographic localizer. Localization accuracy was within 1.5 mm. Potential applications of machine vision techniques include freehand stereotactic localization of the position and orientation of surgical instruments. With sufficient computer speed these techniques can be used for continuous monitoring of the position of instruments within the cranial vault.

Brain↗

PubMed1992

Cellular mechanisms of differential action potential duration restitution in canine ventricular muscle cells during single versus double premature stimuli.

BACKGROUND: We tested the hypothesis that action potential duration (APD) restitution of normal ventricular muscle cells is different during double premature stimuli (S3) compared with a single premature stimulus (S2). We propose a possible ionic mechanism for such a difference. METHODS AND RESULTS: Action potentials and isometric tension were recorded simultaneously from isolated canine right ventricular trabeculae (2 x 2 x 10 mm) (n = 35). APD and tension restitution curves (APD) and peak tension versus diastolic interval [DI] of S2 and S3 were constructed by the extrastimulus method during pacing at 1,500 msec. The following results were obtained. 1) The APD restitution curve of S2 was different from that of S3. During the restitution of S2, an early biphasic upward hump was present at short DIs. In contrast, a smooth exponential rise was consistently seen during S3 restitution. 2) Peak tension remained significantly (p less than 0.001) lower during the restitution of S2 than during S3 restitution at all DIs tested. 3) The variation of APD during the initial 100 msec of DI was significantly longer during S3 than S2 (22 +/- 5 msec versus 41 +/- 5 msec, p less than 0.001). 4) Caffeine (2 mM, n = 5) and ryanodine (10 microM, n = 5) blocked cyclic variations of tension, presumably by blocking cyclic variations of intracellular calcium ion concentrations ([Ca2+]i), and eliminated the differences in APD restitution between S2 and S3. 5) Nisoldipine at high (5 microM) but not at lower (2 microM, n = 5) concentration eliminated the differences in restitution of both APD and tension between S2 and S3. 6) BAY K 8644 (100 nM, n = 5) had no effect on this difference. CONCLUSIONS: Greater variations of APD occur during the restitution of S3 than during S2 at short DIs. These differences appear to be caused by cyclic variations in tension and thus in [Ca2+]i. Calcium-sensitive outward currents could explain these differences in APD restitution.

Action Potentials↗

PubMed1991

Relation between acute ventricular arrhythmias, ventricular late potentials and mortality in acute myocardial infarction.

The relation between ventricular late potentials and the occurrence of acute (in-hospital) and hyperacute (before hospital admission) ventricular tachycardia or fibrillation was studied in 281 consecutive patients with uninterrupted acute myocardial infarction. The prevalence of late potentials was significantly higher in patients with than without ventricular tachycardia/fibrillation (65 vs 22%; p less than 0.01). These relations persisted among patients with left bundle branch block, although a different definition was used for identifying late potentials in these patients. Multivariate analysis showed that presence of late potentials and peak creatine kinase enzyme level were the only 2 independent variables associated with early ventricular tachycardia/fibrillation. Total in-hospital mortality, as well as in-hospital cardiac mortality, was significantly higher among patients with than without acute ventricular tachycardia/fibrillation. However, at 1 year, mortality rates did not differ between the 2 groups. The following conclusions were drawn from this study: (1) Late potentials are closely related to ventricular tachycardia/fibrillation in hyperacute and acute phases of infarction. (2) Presence of left bundle branch block does not mitigate against the finding of late potentials in these patients. (3) Early ventricular tachycardia/fibrillation in acute infarction is related to large infarctions and to a high in-hospital mortality rate.

Aged↗

PubMed1991

Toxic epidermal necrolysis: a burn-centre challenge.

OBJECTIVE: To describe the clinical features and outcome of patients with toxic epidermal necrolysis. DESIGN: Case series. SETTING: Ross Tilley Burn Centre, Wellesley Hospital, Toronto. PATIENTS: Ten patients (seven women) with toxic epidermal necrolysis referred to the centre from 1984 to 1990. INTERVENTION: Biobrane (Winthrop Pharmaceuticals, New York) was applied to all raw surfaces after the epidermis had been completely separated. It was not removed until the epidermis had regenerated. MAIN RESULTS: The age of the patients varied from 27 to 90 (mean 45) years. The proportion of body surface area involved was 20% to 95% (mean 58.5%). Nine of the patients had received steroids and antibiotics prophylactically before being referred to the burn centre; the steroids were immediately tapered and the antibiotics withdrawn unless there was a specific infection. Urinary tract infection developed in seven patients, respiratory failure in six and systemic sepsis in six. All of the patients ultimately required antibiotics for treatment of systemic infections. Two patients died; both had severe illness before the onset of the toxic epidermal necrolysis. Biobrane provided a marked reduction in pain, eliminated the need for further dressings and allowed early, aggressive physiotherapy. The wounds healed completely within 14 to 21 days, with no significant scarring or need for skin grafting. CONCLUSIONS: The use of a temporary skin substitute is recommended for the treatment of toxic epidermal necrolysis. There is no indication for prophylactic steroid or antibiotic therapy; indeed, such therapy is probably contraindicated.

Adult↗

PubMed1991

The electrical response of maize to auxins.

The electrical response of Zea mays coleoptiles and suspension cultured cells to several growth-promoting auxins (IAA, IBA, 2,4-D, 2,4,5-T, 1-NAA) and some of their structural analogues (2,3-D, 2-NAA) has been tested. In coleoptile two typical electrical responses to IAA are observed: an immediated rapid depolarization, and a hyperpolarization following 7-10 minutes after the first external addition of IAA. Of the other tested compounds only 1-NAA significantly depolarized the cells, whereas all auxins as well as the analogues evoked delayed hyperpolarizations. In contrast, the suspension cells were not hyperpolarized by any of the tested compounds, but were strongly depolarized by IAA, 1-NAA, and to a lesser extent by 2-NAA. In these cells IAA and 1-NAA induced inwardly directed currents of positive charge which both saturated around 12 mA/m2. The strong pH-dependence together with the half-maximal currents 0.49 microM IAA and 0.76 microM 1-NAA point to a symport of the anions with at least 2H+. The delayed plasma membrane hyperpolarization is a different response, and seems to be initiated by the protonated auxin species. In accordance with the current literature, it is interpreted as consequence of a stimulated proton extrusion. The finding that all tested compounds evoked a hyperpolarization, makes this response unspecific. It is concluded that a stimulation of proton extrusion is a necessary, but not sufficient step to induce elongation growth.

Biological Transport↗

PubMed1991

Excimer laser ablation of fibrocartilage: an in vitro and in vivo study.

To date, lasers have found only limited applications in orthopedics. We employed a 308 nm XeCl excimer laser for ablation of fibrocartilage, in order to investigate the feasibility of excimer laser assisted meniscectomy. Experiments were conducted both in vitro and in vivo. For the in vitro study, human menisci, obtained during surgery and autopsy, were irradiated via a 600 microns core fiber at radiant exposures ranging between 20 mj/mm2 and 80 mj/mm2, at 20 Hz. Ablation rate measurements and histological analysis of the samples were performed. The ablation rates were found to range from 3 microns/pulse to 100 microns/pulse depending on the radiant exposure and/or the applied pressure on the fiber delivery system. Thermographic analysis was also performed during pulsed excimer as well as CW Nd:Yag and CW CO2 laser irradiation. Temperatures were lower for excimer laser (Tmax less than 65 degrees) than CW ND: Yag (Tmax less than 210 degrees) or CW CO2 (Tmax less than 202 degrees) laser. For the in vitro study, medial meniscectomy was performed in 15 rabbits with the excimer laser and a CW Nd:Yag laser in the right and left knee respectively. Excimer laser irradiation was performed at 70 mj/mm2. Nd:Yag irradiation was performed via a 600 microns core fiber at power outputs between 20 to 40 W for 10 and 20 seconds duration. The healing response to injury was investigated by histological analysis of the menisci after 1 day, 1, 2, 4, and 8 weeks following the laser procedure. Excimer laser treated menisci showed less inflammatory reaction and noticeable repair with minimal inflammatory response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Public pensions in transition: an optimal policy path.

"The main purpose of this paper is to analyze problems of financing an old-age insurance when birth rates are low and population declines or fertility fluctuates with time....[The author] investigates a theoretical model which analyzes the welfare optimal combination of private savings via the capital market and the state forced savings via a PAYG [pay-as-you-go] financed public pension system. Long-run effects as well as short-run implications are considered. The economic properties of an optimal steady state are determined and additionally an optimal transition path--the best feasible conversion policy--which leads to the new steady state is specified."

Demography↗

PubMed1991

Comparative investigations of the morphology and chemical composition of the eggshells of Acanthocephala. I. Macracanthorhynchus hirudinaceus (Archiacanthocephala).

Eggshells of Macracanthorhynchus hirudinaceus (Archiacanthocephala) were investigated for their fine structure as well as their chemical composition. The acanthor larvae are surrounded by four eggshells (E1-4) separated by interstices of low electron density (G1-4). As these envelopes are secreted in different sequences and are reinforced to different degrees, their appearance varies throughout development. The outermost eggshell (E1) of this species has a tripartite appearance; it contains neither chitin nor keratin. Keratin appears in E2 and E3. It was localized electron microscopically using anti-keratin and, for the first time by fluorescence microscopy with the bromobimane reaction. Keratin occurs in two forms: in the second envelope (E2) it consists of twisted struts of filaments, whereas in the innermost sublayer of the third envelope (E3) it shows a conspicuous cross-striation; in the first and second sublayers of E3, neither keratin nor a discernible structure is present. Chitin occurs in the innermost layer (E4). The interstices G1, G3 and G4 seem to contain glycoproteins, whereas interstice G3 seems to contain some type of carbohydrate. After the extraction of proteins including keratin with sodium dodecyl sulfate (SDS) and dithiothreitol (DTE) only layers E1 and E4 remained.

Acanthocephala↗

PubMed1991

Acute effects of intravenous propafenone on the internal ventricular defibrillation threshold in the anesthetized dog.

In 10 treated and 2 control dogs, the short-term effects of intravenous propafenone (2 mg/kg/10 minutes, followed by 1 mg/min [n = 2] or 25 micrograms/kg/min [n = 8]) on the internal ventricular defibrillation energy requirements (DER) were investigated. Multiple stored energy levels were randomly tested and the percent successful defibrillation was plotted against the stored energy, and the raw data were fit by logistic regression. The energy at 50% (E50) and 80% (E80) defibrillation success increased after propafenone by a mean of 75% (8.4 +/- 2.4 to 14.7 +/- 5.9 joules, p less than or equal to 0.05) and 59% (11.1 +/- 3.5 to 17.6 +/- 6.7 joules, p less than or equal to 0.05), respectively. Plasma propafenone levels ranged from 778 to 2554 ng/ml (1495 +/- 592 ng/ml) at the beginning to 833 to 2193 ng/ml (1297 +/- 389 ng/ml) at the end of the defibrillation trials. Two dogs served as controls and received Ringer's solution instead of propafenone and showed the temporal stability of the preparation. In conclusion, intravenous propafenone increases the internal ventricular DER in this canine model. This may have important clinical implications in patients with automatic implantable cardioverter-defibrillators (AICDs) receiving concomitant antiarrhythmic drug therapy and in patients undergoing therapy with intravenous propafenone.

Animals↗

PubMed1991

'Special effects' burn injuries.

Three patients are presented with significant flame burns, resulting from accidents occurring during 'special effects' situations in the entertainment industry. These occurred as a result of the spontaneous combustion of various materials, during events in live theatre (gun powder), a television commercial (artificial 'rocket fuel'), and a video presentation (magnesium oxide). All three patients sustained flash burns to the face and hands. One patient sustained a significant bilateral corneal injury, a gamekeeper's thumb, and a permanent continuous right-sided high frequency tinnitus, in addition to his burn injury. Photographic documentation of all three patients is presented. The total loss of time from work for all patients was 6 months. All these injuries were potentially preventable.

Accidents, Occupational↗

PubMed1991

The chemotherapy of rodent malaria. XLVI. Reversal of mefloquine resistance in rodent Plasmodium.

Multiple drug resistance in Plasmodium falciparum is already showing evidence of extending to mefloquine, which at present is one of the few alternative antimalarials for the prevention or treatment of infection with such parasites. Neither verapamil nor cyproheptadine, which reverse chloroquine (CQ) resistance in P. falciparum and in rodent malaria parasites, reverse resistance to mefloquine (MEF) in the MEF-resistant NS/1100 line of P. yoelii ssp. NS. On the other hand, such resistance is clearly reversed when mefloquine is administered to infected mice together with penfluridol.

Animals↗

PubMed1991

A simple method for excystation of Giardia lamblia cysts.

Fresh Giardia lamblia trophozoites were isolated by in vitro excystation of purified cysts from the faeces of Saudi patients. The method consisted of mixing one part of the cyst suspension with nine parts of 1 N hydrochloric acid, at pH 2, then culturing the excysted trophozoites in modified TYI-S-33 medium in sealed glass vials. During the excystation process most cysts developed a space between the trophozoite and the cyst wall, and after several steps of enlargement the trophozoite emerged at the posterior end of the cyst. Keeping the cysts at 4 degrees C for more than 10 days did not affect the excystation process. Trophozoites obtained by this method can be cryopreserved and recultured without significant loss of activity. This is a simple and rapid method of obtaining G. lamblia trophozoites from cysts in stools or from other sources.

Animals↗

PubMed1991

The chemical peel.

Chemical peeling of facial skin has become a valuable adjunct in the armamentarium of the facial aesthetic surgeon. Among the various techniques available, phenol solutions are the most commonly used. Peeling produces a controlled, partial-thickness chemical burn of the epidermis and the outer dermis. Several techniques are available to "fine tune" the depth of the peel. Regeneration of peeled skin results in a fresh, orderly, organized epidermis. In the dermis, a new 2- to 3-mm band of dense, compact, orderly collagen is formed between the epidermis and the underlying damaged dermis, which results in effective ablation of the fine wrinkles in the skin and a reduction of pigmentation. These clinical and histological changes are long lasting (15-20 years) and may be permanent in some patients. Because of the metabolism and systemic complications of phenol, patient selection should involve systemic evaluation of liver, renal, and cardiac function, as well as an evaluation of the skin quality and medication status of the patient. Because of potential cardiac arrhythmias, peeling must be performed in a medically supervised environment, with continuous cardiac monitoring. The local complications of peeling include pigmentation changes, scarring, milia, ectropion, infection, activation of herpes simplex, and toxic shock syndrome.

Adult↗

PubMed1991

The rectus femoris myocutaneous flap for closure of difficult wounds of the abdomen, groin, and trochanteric areas.

The rectus femoris myocutaneous flap has proved to be an effective means of closing particularly difficult wounds in 2 patients. One patients had a massive defect in the lower abdomen, pubic, and right groin area after the radical resection of a recurrent pleomorphic liposarcoma of the spermatic cord. The second patient presented with a huge, right greater trochanteric wound measuring 15 cm in diameter. Both patients progressed to relatively uneventful primary healing.

Adult↗

PubMed1991

Pathogenicity and antigenic components of excysted Giardia lamblia isolated from patients in Riyadh, Saudi Arabia.

Giardia lamblia cysts were isolated from patients in Riyadh, Saudi Arabia. Cysts and trophozoites (from axenically excysted cysts) were given orally by gavage to mice to establish the pathogenicity of the Riyadh isolate. There was no effect of varying the dose of administered parasite on parasite excretion or morbidity. A typical pathologic pattern of giardiasis was demonstrated by histologic methods and electron microscopy. Antigenic components of the Riyadh isolate were compared with the Portland strain and with Entamoeba histolytica by gel diffusion immunoprecipitation and immunoblotting. There were few antigens in common between Riyadh isolate and the Portland strain, and little cross-reactivity of the Riyadh isolate with Entamoeba histolytica was observed.

Animals↗

PubMed1991

[Innovation in antiparasitic agents].

The emergence of new parasitic diseases has encouraged studies on the elucidation of the mode of action of new and old antiparasitic drugs, and has led to the development of new chemical series. Resistance occurs rapidly when a single drug is used massively in human and animals. A better knowledge of the mode of action allow synergistic combination of compounds, slow-release devices proposed for cattle. Another alternative is to improve bioavailability of antiparasitic drugs by targetting at the parasite molecular level with prodrugs, drug-carriers as liposomes, nanoparticles. The use of new compounds should be expected with relative optimism.

Animals↗

PubMed1991

High-pressure injection injuries.

High-pressure injection injuries are potentially disabling forms of trauma. Three cases are presented of patients who sustained high-pressure injuries from paint, air and water. Injuries from paint require emergency surgical débridement and exploration because of the extreme tissue toxicity of the injected material. The patient in this study had a favourable outcome after delayed closure of his wound and extensive physiotherapy. High-pressure injuries resulting from air and water can be managed conservatively, as in the two patients reported in this paper. Their treatment included tetanus prophylaxis, irrigation, dressings, splinting, admission to hospital, intravenous broad-spectrum antibiotics, radiologic assessment and careful neurovascular evaluation. Surgical débridement and exploration were not necessary.

Accidents, Occupational↗