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S Hessel

Publications and source records attributed to S Hessel.

18 recordsLinked to original sources
PubMed2001

Identification and characterization of a mammalian enzyme catalyzing the asymmetric oxidative cleavage of provitamin A.

In vertebrates, symmetric versus asymmetric cleavage of beta-carotene in the biosynthesis of vitamin A and its derivatives has been controversially discussed. Recently we have been able to identify a cDNA encoding a metazoan beta,beta-carotene-15,15'-dioxygenase from the fruit fly Drosophila melanogaster. This enzyme catalyzes the key step in vitamin A biosynthesis, symmetrically cleaving beta-carotene to give two molecules of retinal. Mutations in the corresponding gene are known to lead to a blind, vitamin A-deficient phenotype. Orthologs of this enzyme have very recently been found also in vertebrates and molecularly characterized. Here we report the identification of a cDNA from mouse encoding a second type of carotene dioxygenase catalyzing exclusively the asymmetric oxidative cleavage of beta-carotene at the 9',10' double bond of beta-carotene and resulting in the formation of beta-apo-10'-carotenal and beta-ionone, a substance known as a floral scent from roses, for example. Besides beta-carotene, lycopene is also oxidatively cleaved by the enzyme. The deduced amino acid sequence shares significant sequence identity with the beta,beta-carotene-15,15'-dioxygenases, and the two enzyme types have several conserved motifs. To establish its occurrence in different vertebrates, we then attempted and succeeded in cloning cDNAs encoding this new type of carotene dioxygenase from human and zebrafish as well. As regards their possible role, the apocarotenals formed by this enzyme may be the precursors for the biosynthesis of retinoic acid or exert unknown physiological effects. Thus, in contrast to Drosophila, in vertebrates both symmetric and asymmetric cleavage pathways exist for carotenes, revealing a greater complexity of carotene metabolism.

Amino Acid Sequence↗
PubMed1995

[Interstitial laser-induced coagulation of the prostate for therapy of benign hyperplasia].

Interstitial laser-induced coagulation (ILC) is a new, minimally invasive, procedure for the treatment of benign prostatic hyperplasia (BPH). It is based on the placement of special light guides in the prostatic tissue, either transurethrally or perineally. The radiation source is a Nd-YAG laser, which is active for 3 or 5 min per fiber placement, respectively, with the power reduced stepwise. The coagulation necroses caused shrink during follow-up, leading to a decrease in the obstruction. In 239 patients treated in this way the mean I-PSS-Score fell from 25.4 to 8.1 points and the quality of life index from 4.1 to 1.6, the urinary peak flow rate increased from 7.7 to 16.3 ml/s, the residual urine volume fell from 151 to 32 ml, and the mean prostate volume declined from 47.4 to 32.2 ml in the first 3 months of follow up; 9.2% of the patients required further treatment within 1 year because of persistent obstruction. The complication rate was low. Statistical analysis showed no factors allowing prediction of the outcome. ILC is an effective method with few side effects and complications, and it has a wide range of indications for all BPH patients.

Aged↗
PubMed1993

Fine structure of zonal changes in experimental Nd:YAG laser-induced interstitial hyperthermia.

Interstitial thermotherapy using Nd:YAG-laser induced hyperthermia is a new stereotactic method for the treatment of brain tumors in poorly accessible regions. To provide a basis for the underlying tissue alterations, we have analyzed the spatial and temporal pattern of interstitial laser hyperthermia lesions in the normal rat brain by histological, immunohistochemical, and electron microscopical methods. The acute changes corresponded to the temperature gradient surrounding the laser probe and showed a distinct zonal architecture. Membrane destruction on a cellular and subcellular level appears to be of major significance in the pathogenesis of the laser lesion. The tissue reaction followed the course known for coagulation necrosis and resulted in a well-defined defect. These results, although limited by the choice of the experimental model, may be helpful in the interpretation of images obtained in future applications of interstitial thermotherapy.

Aluminum Silicates↗
PubMed1993

[Interstitial laser coagulation of benign prostatic hyperplasia].

We report on the new method of interstitial laser coagulation for the treatment of benign prostatic hyperplasia (BPH). The procedure is based on the interstitial application of Nd:YAG laser irradiation, delivered through a new light guide system. Such light applicators coagulate constant tissue volumes in a homogeneous manner, as proven by in vitro studies in different tissues, including surgically removed prostate adenoma. The extent of the coagulation is determined by laser power and irradiation time. At 5 W, for example, and during a 10-min period, this zone reached a diameter of up to 20 mm. Temperatures generated in the process were over 100 degrees C, as measured by time/space resolution. These results were confirmed by in vivo studies in canine prostates. In the course of 7 weeks, the coagulated areas formed scars with degeneration and fibrosis, accompanied by marked shrinking. Neighbouring organs were not affected. The method was successfully transferred to clinical practice. The application of the light guides to the lateral lobes was performed percutaneously from the perineum under transrectal ultrasound guidance. The median lobe was punctured transurethrally under direct vision. Twenty-seven patients with an average age of 67.7 years were treated between July 1991 and March 1992. At the time of evaluation 15 patients had a follow-up of more than 2 months. They experienced a mean increase of peak flow rate from 6.6 to 15.2 ml/s and a mean decrease of residual volume from 206 to 38 ml. This was accompanied by a marked lessening of symptoms. The average prostate weight decreased from 63 to 44 g. Sexually active patients did not experience retrograde ejaculation.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1991

In vitro ablation of normal and diseased vascular tissue by a fiber-transmitted holmium laser.

An in vitro study was performed to test the ablative potential of a fiber-transmitted pulsed holmium laser (2.1 microns) applied to normal vascular wall, lipomatous plaques, and calcified plaques. Different fluences per pulse of 42, 80, 205, and 315 J/cm2 were used. Ablation of normal tissue and lipomatous plaques was achieved with all power settings. Effective ablation of calcified plaques, however, occurred only after a minimum fluence of 205 J/cm2, and the effect was significantly less pronounced compared to ablation of soft lesions.

Angioplasty, Laser↗
PubMed1991

Thermal effects and histologic changes from Nd:YAG laser irradiation on normal and diseased aortic tissue using a novel angioplasty catheter with a mobile optical fiber: an in vitro assessment.

Although various laser angioplasty devices are currently being examined, thermal damage and perforation of the vessel wall remains the major acute complication of vascular laser recanalization. Consequently, the aim of this study was to investigate the thermal effects and histologic changes from laser irradiation (Nd:YAG, 1064 nm) on normal and diseased aortic tissue using a novel angioplasty device. During laser emission the coaxially guided optical fiber tip was positioned in reference to the end hole of the metallic capped probe as follows: (1) at the end hole (metal-cap position), (2) protruding 10 mm from that end hole (bare-fiber position), (3) withdrawn 5 mm into the metal cap's lumen (hot-tip position). In total, 96 laser impacts (25 joule: 5 W, 5 s, each) were produced on normal and atherosclerotic aorta in air through a 0.2-mm-core-diameter silica quartz fiber, with direct contact on the intimal surface of the target tissue by both the fiber and the metal cap and by either the fiber or the metal cap (n = 32 each). Tissue temperature was measured by means of special sensors positioned opposite the irradiated intimal spot in direct contact with the adventitial surface. Morphohistologic evaluation of lesions was performed and injury indexes were determined.

Angioplasty, Laser↗
PubMed1990

Laser balloon angioplasty: technical realization and vascular tissue effects of a modified concept.

A modified concept using a movable fiber with radial light dispersion was developed for combining mechanical balloon dilatation and intraluminal circumferential Nd-Yag laser irradiation of the arterial wall. The aims of the study were the technical feasibility and the acute and chronic vascular tissue effects of laser-assisted balloon dilatation. The carotid arteries (n = 9 dogs) and femoral arteries (n = 5 dogs) of dogs were mechanically dilated and simultaneously circumferentially irradiated through the balloon by 1,064 nm Nd-Yag laser (20-25 W). Temperature at the adventitial surface was kept constant at 50 degrees C, 60 degrees C, 70 degrees C, or 80 degrees C for either 8 or 15 seconds by a computerized feedback system for temperature control. Angiographic and histological results were available acutely, subacutely (2 days), and at 3 months. Angiographically, stable and smooth enlargement of the lumen was demonstrated acutely. At 3 months, occlusions, probably thrombotic in origin, had occurred in 5 of the carotid arteries and none of the femoral arteries. Histologically, laser-induced coagulation of the arterial wall with loss of cellular elements was demonstrated. Collagen and elastic fibers remained relatively intact. In two carotid arteries intimal proliferation was observed at the treated site. Thus, this technique appears to be technically feasible, yet further study is needed to assess its potential to reduce or repair acute vascular complications (dissections) and to reduce restenoses after percutaneous transluminal coronary angioplasty (PTCA). However, the clinical value of this technique appears to be limited in view of the thromboses and reactive proliferations observed in this preliminary study.

Angioplasty, Balloon↗
PubMed1990

[Laser angioplasty and the removal of calcified plaques. An in vitro study].

The ablative potentials of five different lasers on normal and diseased vascular tissue were tested in vitro. Post-mortem aortic specimens of normal wall, lipomatous and calcified plaques were exposed to both continuous wave lasers (argon, neodymium-YAG 1064 nm) coupled to hot-tipped or sapphire tipped fibres and pulsed lasers (Excimer 193 nm, CO2, erbium-YAG). Histomorphological changes and penetration were evaluated microscopically. Pulsed lasers of all wavelengths used were able to ablate vascular tissue of all stages including heavily calcified plaques. Thermal lasers were able to penetrate the normal wall and lipomatous plaques, but did not reach any evident reaction on calcified plaques. Thermal lasers may have only limited potentials in angioplasty, since ablation of calcified plaques is not possible.

Angioplasty, Balloon↗
PubMed1990

Application systems for intracorporeal laser-induced shockwave lithotripsy using the Nd:YAG Q-switched laser.

For laser-induced shockwave lithotripsy, the electromagnetic energy of a laser light pulse is converted intracorporeally into the acoustic energy of a shockwave. The lithotriptor is based on a specially developed, Q-switched Nd:YAG laser whose high power light pulses (70 mJ, 25 nsec) are coupled into a flexible quartz fiber with a core diameter of 600 mum. Using focusing elements, energy densities higher than 6 x 10 5 J m -2 can be achieved, resulting in an optical breakdown in water followed by a shockwave. As a result of different absorption mechanisms, the breakdown threshold can be decreased by placing a metallic target into the laser beam. The different shockwave formations of such optomechanical transducers have been measured. First clinical applications have been performed.

Equipment Design↗
PubMed1990

Vascular tissue ablation by an erbium-YAG laser: a fiber-transmittable pulsed laser in the infrared range.

Vascular tissue ablation by an erbium:YAG laser of 2,940 nm was tested in-vitro with the application of increasing energies from 20 to 80 mJ per pulse. Effective ablation of normal vascular tissue, lipomatous atheromas and calcified plaques was achieved. Penetration depth was considerably diminished in the presence of calcifications. The lasered craters showed smooth surfaces and were regularly shaped. The solid state erbium:YAG, which is transmittable by fluoride fibers, offers theoretical advantages for laser angioplasty.

Aortic Diseases↗
PubMed1989

Effects of Nd-YAG laser and cryosurgery on the oral mucosa in rabbits.

In 32 rabbits, lesions of comparable depths were created in the oral mucosa using a Nd-YAG laser (Medilas II, 1.06 microns, MBB Co., Munich) and a cryosurgery unit (Kryo-S, Erbe Co., Hannover). Histologic specimens were examined between 1 h and up to 8 weeks following operation. The laser lesion was restricted horizontally to the laser-exposed area; the full extent of the lesion could already be seen after 1 day. Cryosurgical lesions showed their maximum extent 3 days following treatment. Wound healing processes following laser application, were accelerated compared to cryosurgical procedure.

Animals↗
PubMed1989

[Use of the thermal laser effect of laser irradiation for cardiovascular applications exemplified by the Nd:YAG laser].

Techniques of percutaneous transluminal application of laser energy for vessel recanalization have been used clinically since 1983. The commonly used Nd:YAG and argon lasers achieve ablation of atherosclerotic plaques by thermal action (vaporization). In order to reduce undesirable thermal damage in the neighborhood of the target tissue and to avoid vessel perforation, optimal irradiation parameters, modified (atraumatic) fiber tips (hot tips, sapphires), and steerable catheter systems needed to be implemented. Favorable results from peripheral application have encouraged use in the coronary circulation. More recently, coagulative tissue effects of circumferential irradiation of the vessel wall during balloon dilatation have been used for stabilization of acute and late results after mechanical balloon angioplasty. Enhancement of the differential light absorption of atherosclerotic plaque by use of biological dyes may further improve selective intravascular laser application. Intraoperative ECG-guided laser coagulation of arrhythmogenic areas of myocardium is a method for treatment of malignant arrhythmias. Transluminal non-operative application of myocardial laser photocoagulation has now been tested experimentally and shown to be safe and effective. There was no arrhythmogenicity or thermal damage of coronary arteries associated with this method. Innovative techniques such as nanosecond pulsed excimer lasers (athermal action) and development of "intelligent" lasers--which are equipped with spectroscopy-guided feedback systems for plaque recognition--have opened new perspectives and will further improve safety and efficacy of clinical laser application. However, according to current experience, the thermally acting Nd:YAG laser is an effective and versatile mode of laser therapy for selected cardiovascular indications.

Angioplasty, Balloon↗
PubMed1987

Comparative investigations of the effects of the neodymium:YAG laser at 1.06 microns and 1.32 microns on tissue.

The beneficial deep homogeneous coagulation of neodymium (Nd):YAG laser radiation at 1.06 microns owing to low absorption and high scattering in tissue has been documented widely. For another Nd:YAG laser wavelength at 1.32 microns the absorption coefficient of water and saline is approximately ten times higher than at 1.06 microns. This results in more efficient energy conversion into heat in tissue at 1.32 microns. The extinction coefficient in blood at 1.32 microns is only one-third of that at 1.06 microns. We would expect this to result in less heat dissipation by blood and deeper penetration in tissue at 1.32 microns. Nevertheless, at this wavelength scattering also contributes to an effective, uniform distribution of the laser light in the tissue. Animal experiments have been done to examine the effect of wavelength, irradiation time, and beam geometry on tissue damage and to assess its possible clinical uses. The results imply that the 1.32 microns wavelength will produce further indications for the use of the Nd:YAG laser in surgery.

Animals↗
PubMed1987

Health technology assessment: problems and challenges.

From a national perspective, the central prerequisite of the proper application of medical technology is the timely determination of efficacy, cost, safety, and societal impact. This applies to both the introduction of the new methods and the retirement of older methods that may have outlived their usefulness. Within that framework, the rapid diffusion of innovative methods of great value must be balanced against the cost of premature enthusiasm for techniques with little or no incremental diagnostic or therapeutic gain. A nongovernmental Council on Health Care Technology Assessment of the Institute of Medicine-National Academy of Sciences was established by the Congress in 1986. The Council was charged to serve as an information clearing-house, a center to promote research and education, and a stimulus to establish better methods of assessment and more prompt identification of potentially important technologies. It represents virtually all of the constituencies concerned with adequate evaluation of new and existing methods. The Council confronts the critical problems of timing, bias, the quality of primary data collection, new methods of secondary data analysis, the nature of the "laboratory" in which technology assessment is best accomplished, the "exploitative" character of technology assessment research, appropriate diffusion, and ethnical issues. The appropriate use of technology in modern health care depends on the resolution of these issues.

Organizations↗
PubMed1986

Laser-induced alteration of collagen substructure allows microsurgical tissue welding.

Tissue welding is a potentially important biomedical application of laser technology. The structural alterations basic to this phenomenon were studied in experimental repair of lesions of the rat carotid artery and sciatic nerve. A modified neodymiumdoped yttrium-aluminum-garnet laser operating at a wavelength of 1.319 micrometers was used in conjunction with conventional suture techniques. Histological and fine-structural analysis revealed a homogenizing change in collagen with interdigitation of altered individual fibrils that appeared to be the structural basis of the welding effect.

Animals↗