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Biomedical subjects

P Lenz

Publications and source records attributed to P Lenz.

At least 37 records · Page 2Linked to original sources
PubMed1995

In vivo excitation of photosensitizers by infrared light.

Use of near infrared instead of visible light would markedly improve tissue penetration, making larger tumors candidates for photochemotherapy. Because common photesensitizers exhibit virtually no absorption in this wavelength region, conditions are required where the simultaneous action of two photons is possible. Healthy tissue (rat ears), sensitized by hematoporphyrin derivative, sulfonated chloroaluminum phthalocyanine or pheophorbide alpha, was irradiated (1064 nm, 10 ns) with power densities up to 200 MW cm-2 and total energy densities up to 200 kJ cm-2. No reproducible photodynamic lesions were observed, but there was sensitizer fluorescence that depended quadratically on the excitation intensity.

Animals↗
PubMed1994

[Spontaneous, massive liver hemorrhage as a complication of thrombolysis with ultra-high dose streptokinase in deep thrombophlebitis].

We report on a rare case of spontaneous, life-threatening liver bleeding as a major complication of thrombolysis using short-term, ultrahigh streptokinase in deep venous thrombosis. The event occurred in a female patient (age 40 years) who presented no contraindication to thrombolytic therapy. Intraabdominal bleeding was suspected during intravenous streptokinase infusion. Emergency laparotomy revealed four liter of unclotted blood resulting from two ruptured subcapsular liver haematomas. Local haemostasis was achieved and the integrity of the liver restored. Multiple transfusions of red blood cells, fresh frozen plasma and fibrinogen were given. The postoperative period was uneventful and the patient recovered gradually. The patient could be discharged from the hospital in good health. Diagnostic and therapeutic approaches to this rare complication of thrombolysis are discussed. Additionally, a brief review of previously reported cases is provided.

Adult↗
PubMed1993

gamma-Tocotrienol as a hypocholesterolemic and antioxidant agent in rats fed atherogenic diets.

This study was designed to determine whether incorporation of gamma-tocotrienol or alpha-tocopherol in an atherogenic diet would reduce the concentration of plasma cholesterol, triglycerides and fatty acid peroxides, and attenuate platelet aggregability in rats. For six weeks, male Wistar rats (n = 90) were fed AIN76A semisynthetic test diets containing cholesterol (2% by weight), providing fat as partially hydrogenated soybean oil (20% by weight), menhaden oil (20%) or corn oil (2%). Feeding the ration with menhaden oil resulted in the highest concentrations of plasma cholesterol, low and very low density lipoprotein cholesterol, triglycerides, thiobarbituric acid reactive substances and fatty acid hydroperoxides. Consumption of the ration containing gamma-tocotrienol (50 mg/kg) and alpha-tocopherol (500 mg/kg) for six weeks led to decreased plasma lipid concentrations. Plasma cholesterol, low and very low density lipoprotein cholesterol, and triglycerides each decreased significantly (P < 0.001). Plasma thiobarbituric acid reactive substances decreased significantly (P < 0.01), as did the fatty acid hydroperoxides (P < 0.05), when the diet contained both chromanols. Supplementation with gamma-tocotrienol resulted in similar, though quantitatively smaller, decrements in these plasma values. Plasma alpha-tocopherol concentrations were lowest in rats fed menhaden oil without either chromanol. Though plasma alpha-tocopherol did not rise with gamma-tocotrienol supplementation at 50 mg/kg, gamma-tocotrienol at 100 mg/kg of ration spared plasma alpha-tocopherol, which rose from 0.60 +/- 0.2 to 1.34 +/- 0.4 mg/dL (P < 0.05). The highest concentration of alpha-tocopherol was measured in plasma of animals fed a ration supplemented with alpha-tocopherol at 500 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Determination of the optical penetration depth in tumours from biopsy samples.

Tumours are examined in a simple sandwich structure which gives the samples a well defined shape and volume. Collimated light is scattered by the sample and analysed using a goniometer. It is found that tumours can be optically characterized by only two parameters. In phantoms, composed in order to approach closely the optical properties of tumours, a relationship is established experimentally between these parameters and the penetration depth. Using this relationship the penetration depth in tumours can be determined for 630 nm and 680 nm wavelength light.

Biopsy↗
PubMed1991

Influence of water conductivity on the efficiency and the reproducibility of electrohydraulic shock wave generation.

In an electrohydraulic generator, two underwater metal electrodes are connected with a capacitor charged to a high voltage. When the circuit is switched on, a plasma is generated reaching temperatures of thousands of K, resulting in a compressive pressure pulse. The formation of the plasma is a nonreproducible phenomenon inducing great variations of the pressure pulse. When the electrodes are immersed in an electrolyte instead of degassed water, the conditions of electrical discharge are dramatically modified. The latency time and the amplitude of the oscillations of the discharge current decrease as the conductivity of the electrolyte increases. For a conductivity of 7 omega.cm, there is no latency, and the critically damped discharge is achieved. The expanding pressure wave is increased by 10%, and the mean peak pressure value over 120 shocks at the second focus after focalization is increased by 50%. The relative standard deviation of the pressure value at the second focus is only 5%, while it is about 30% in ordinary water. The fragmentation efficiency is considerably increased because total fragmentation is obtained in 220 shocks instead of 450 shocks in ordinary water when standard stones are used, and in 131 shocks instead of 304 shocks when gallstones are used. Last, we show that the wear of the electrodes is reduced by a factor 8 when electrolyte is used. The improvement is supposed to have two causes: First, the energy is delivered into the medium in a shorter time, and, second, the center of the shock wave is always located at the same place. The decreased wear should make it possible to treat a much greater number of patients without changing electrodes, and the enhancement of the pressure should increase the efficiency of the fragmentation of the gallstones without aggravating the patient's pain.

Efficiency↗
PubMed1991

[Study of pressure resistance of galvano-crowns].

Ceramic veneered galvano crowns demonstrated an axial loading limit of 220 N on incisors and of 297 N on canines. Compressive strength values are only slightly lower at 45 degrees loading. These use of a bonding agent did not significantly affect strength.

Chromium Alloys↗
PubMed1990

Effect of dietary canola and reference oils upon serum lipids and platelet aggregation.

To compare Canola a terrestrial (n-3) oil with fish oil (n-3) and common vegetable oil (n-6) in decreasing serum lipids and platelet aggregation, various oils were included in Chow-based diets and fed to rats in an eight-weeks feeding trial. The Chow diet contained 2% cholesterol along with either Canola, menhaden, safflower, or partially hydrogenated soy oil, or no oil addendum. The menhaden oil group was the only one to show a significant reduction in serum cholesterol and triglycerides and at the same time yielded the most uniform decrease in platelet aggregability. However, this same group was also the only one to show a decrease in serum tocopherol levels, suggesting that improving an atherogenic risk profile may require antioxidant supplementation. In these rat trials, Canola oil supplementation did not yield the same results measured during menhaden supplementation.

Animals↗
PubMed1990

Therapy of diseased stroke-prone spontaneously hypertensive rats with nimodipine.

We investigated the therapeutic effect of nimodipine or parathyroidectomy in old, diseased stroke-prone spontaneously hypertensive rats by observing 98 male 1-year-old rats over 5 months. After stroke had occurred, the rats were divided into three groups: 1) parathyroidectomy, 2) nimodipine, and 3) controls. In the nimodipine group, the rats survived longer than those in the other groups. Blood pressure of the controls did not differ from the nimodipine-treated and parathyroidectomy animals. The increase in calcium content of brain and kidney tissues and of plasma renin activity, urea, and creatinine was attenuated by nimodipine or parathyroidectomy. The histology of the kidneys revealed widespread fibrinoid necrosis of arteries in all rats. In the nimodipine-treated or parathyroidectomy groups, healing of the lesions was detectable. Cerebral lesions were mainly characterized by fibrinoid necrosis. Nimodipine-treated as well as parathyroidectomied animals showed significantly fewer hypertensive cerebral lesions. In old, diseased stroke-prone spontaneously hypertensive rats, therapy with nimodipine or parathyroidectomy increased their survival rate. The cerebrovascular and renovascular lesions of treated animals were attenuated, and morphologic signs of healing were observed. Reduction of calcium overload by nimodipine or parathyroidectomy, even in an advanced stage of disease, had a therapeutic effect.

Aging↗
PubMed1989

[Comparison of two powder-stream systems for tooth polishing].

The effect of two airpolishing systems on the surface roughness of polished ceramic test pieces was compared and evaluated using standardized procedures. Test pieces resembling enamel in hardness were treated with these air-polishing systems. Using a Perthometer surface roughness was found to increase significantly. Thus the possible effects of airpolishing systems on the enamel surface should be considered. Efficiency of extrinsic stain removal was studied by SEM and documented. Photographic techniques provided information on the homogeneity of the sodium bicarbonate spray.

Bicarbonates↗
PubMed1989

[Experiments on abrasion and wear of dental diamond instruments].

In spite of identical ISO standards for shape, grain size, and largest head diameter of diamond abrasive instruments there are major differences in the machining performance among the various makes. These differences are largely due to variations in shape and diamond partical size. Diamond burs from different manufacturers of the same visual shape and particle size do not show any significant differences in performance. However, not only the abrasive performance but to a greater extent the design of the preparation margin determine the selection of a bur. It would be desirable that manufacturers be more specific about the particle size used and the shape of the bur, since the ISO standard does not include sufficiently accurate data about diamond particle size and shape design. The life of a diamond instrument is limited by the wear of its tip. Here the diamond layer wears off faster than on the rest of the instrument. This calls for early replacement of the instrument in clinical use even if the shaft still might be functionable.

Carbon↗
PubMed1989

[Studies on the compressive strength of ceramic veneers].

Ceramic veneers were constructed following either a chamfer or a shoulder preparation (with rounded internal line angles). In laboratory tests both veneer forms displayed adequate compressive strengths. A beveled incisal finish line proved to be slightly superior to complete incisal coverage.

Aluminum↗
PubMed1988

Determination of plasminogen activator inhibitor (PAI) capacity of human plasma in presence of oxidants: a novel principle.

A new functional assay of PAI-activity in human plasma is described. Hitherto known assays for fast acting PAI have some disadvantages: predilution and/or acidification steps of the sample to afford the required inactivation of alpha-2-antiplasmin (A2-PI). This approach in contrast implicates test performance in presence of chloramine T (CT), an oxidant that destroys plasma antiplasmin activity without impairing significantly the activity of urokinase (u-PA) or plasmin. The following reaction conditions were found optimal: 50 microliter of undiluted plasma, anticoagulated with citrate or EDTA, were first incubated with 1 IU u-PA in a Tris-buffer, pH 8.4 and then with Glu-plasminogen (0.85 mumol/l final), CT (2.5 mmol/l final), tranexamic acid (0.9 mmol/l final) for 5 min. at 37 degrees C. After addition of 0.3 mmol/l of the chromogenic plasmin substrate H-D-Nva-CHA-Lys-pNA (pNA = para nitroanilide) and of NaCl (250 mmol/l final) a linear kinetic with delta A405/t in the range of 0.2/min for normal plasma was recorded. In an endpoint version of the test the chromogenic substrate can be added together with plasminogen resulting an A/t2-kinetic. Dilution studies showed a linear calibration curve from 0 to 14 arbitrary u-PA inhibiting units (AU)/ml plasma. By means of PAI-standard plasmas PAI-capacity values of 20 healthy volunteers (10 males/10 females) (x = 26 years, sigma = 4.2) were determined. They ranged from 0.4 - 6.9 (x = 1.3, sigma = 0.9) AU/ml plasma. Plasma samples containing more than 14 AU/ml were prediluted with PAI-deficient plasma. Intra- and inter-assay coefficients of variation (CV) were determined to be 1.3 +/- 0.6 and 4.3 +/- 0.5%, respectively. The values of this assay correlate well with those obtained by acidification of the samples. However, the possibility of measuring plasma PAI (and PA) activities by means of a simple and direct approach can be considered as an important progress with regard to routine hospital practice. The presented oxidative inactivation of A2-PI mimics the leukocyte attack phase, suggesting that activated leukocytes create a microenvironment of uncontrolled plasmin activity.

Adult↗
PubMed1987

A highly sensitive bacterial assay for toxins based on swarming inhibition, and comparison with the cup plate assay based on growth inhibition.

The motility inhibition of the swarming bacteria Proteus mirabilis and Azospirillum brasilense was found to be an appropriate parameter to indicate toxic effects caused by some mycotoxins, lactones and anhydrides of dicarboxylic acids. If these substances are in contact with the motile bacteria the following phenomena can be observed: at a certain toxin concentration the swarming of the bacteria is inhibited. If the concentration is increased the swarming ceases, and at still higher concentrations the bacteria are inactivated. In some instances swarming is stimulated at very low toxin doses. The sensitivity of this assay is comparable to the cup plate assay based on growth inhibition with Bacillus thuringiensis [Lenz, P. et al., Toxicology, 40 (1986) 199, Boutibonnes et al., Pharmacology, 11 (1983) 430] and in some cases it is even higher.

Anhydrides↗
PubMed1986

Development of sensitive bacterial tests, exemplified by two mycotoxins.

For a sensitive bacterial test for mycotoxins the cup plate assay, based on growth inhibition, was optimised with Bacillus thuringiensis as test strain. Bacillus thuringiensis allowed the detection of 1.25 microgram kojic acid. A minimal amount of 12.5 micrograms kojic acid or 1.25 micrograms patulin was detectable by means of pigment suppression with isolated mutants of Serratia marcescens, whereas the wild type of this strain was insensitive.

Bacillus thuringiensis↗