HOTTIP Research Articles

Vascular recanalization using an electric thermal cauterizing catheter--in vitro experiences with a new catheter system

Recanalisation of arteriosclerotic occlusions by means of laser angioplasty, Kensey catheter and the "hot tip" catheter is undergoing early, successful clinical trials. The thermo-cautery catheter described in this paper uses the well known technique of cutting with high frequency electric currents in order to achieve vascular recanalisation. Seven attempts were made to recanalise occlusions at post mortem; four were successful, but perforation occurred in three. Histologically we found a narrow rim of carbonisation of tissues surrounded by a zone of homogenisation and a transitional zone.

Percutaneous laser angioplasty in the treatment of peripheral vascular disease.

For a long time the treatment of peripheral vascular diseases mainly was a surgical one. Improvements in drug therapy and success of PTCA have increased the interest in a more conservative therapy. So laser promised to be another tool in the percutaneous treatment of peripheral vascular diseases. First successful experiments were followed by the experience of technical problems and side effects of this new method. First clinical studies in occluded human femoral arteries were started at Stanford University in 1983. The results, published in 1985, showed that occlusive lesions in this vascular region could be successfully reopened by a percutaneous approach. But in cases of severe calcification the danger of perforation or dissection was significantly increased. Moreover the newly created channel proved to be too small for a sufficient revascularization, so that this method had to be combined with balloon angioplasty. By the development of the metalcapped "hot tip", laser energy was totally changed into thermal energy. By this new system greater channels of 2 up to 2.5 mm could be created and by the special design of the metalcap thermal injury to the arterial wall could be decreased. Nevertheless perforation occurred also with this system. Moreover, additional balloon angioplasty was still necessary in proximal segments of the femoral artery. Futural developments of greater metal heads may lead to the exclusive use of the "hot tip" especially in more distal parts. Longterm results will show, if laser angioplasty is comparable to other conventional methods like balloon angioplasty or surgery. There is still a long way to go, until the ideal of reopening atherosclerotic stenoses only by laser energy can be reached.

In Vitro Effects of Nd:YAG Laser Radiation on Blood: A Quantitative and Morphologic Analysis

Use of the Neodymium: yttrium -aluminum -garnet (Nd:YAG) laser to recanalize stenosed arteries may require delivery of the beam through blood. To assess the degree of hemolysis and debris formation, 54 samples of citrated whole blood were exposed to Nd:YAG laser radiation of varying powers (10, 20 and 30 watts) and duration (1, 2.5 and 5 seconds). Compared to control samples which were not subjected to laser light, there was no significant decrease in hematocrit (41 to 40.5 +/- 5%), hemoglobin concentration (13.8 to 13.8 +/- .06 g/1OO ml), or increase in "free" hemoglobin concentration. Debris weight (from .45 +/- .002 to .45 +/- .002 mg), as well as the white blood cell count, was also not significantly changed (from 5,400 to 5,200 +/- 240 WBC/cm). Light microscopy examination of debris from samples of whole blood, washed erythrocytes, and platelet-rich plasma subjected to the laser at 30 watts for five seconds failed to demonstrate the presence of membrane denaturation of blood elements, as compared with the morphologic changes observed in whole blood samples exposed to a "hot tip" rather than Nd:YAG laser radiation. Nd:YAG laser can be used intravascularly without fear of hemolysis or debris "micro-embolization" up to a power of 30 watts for five seconds.

接触法によるレーザー血管形成術の臨床応用

Contact laser thermal angioplasty with metal hot tip heated by argon laser (Trimedyne Inc.) was performed on 34 arteries (7 iliac, 20 femoral and 7 popliteal arteries) of 22 patients from arteriosclerosis obliterans (ASO).The initial success rate of the laser angioplasty was 88.5%. Clinical success was defined as an improvement in symptoms and increase in the ankle pressure index in all of these patients. There was no perforation of arterial wall caused by thermal ablation with a hot tip heated by repeat pulses under a power condition of 10 watts of argon laser energy for 5 seconds. Additional flexible fiber optic angioscopy is one of the effective adjuncts for obtaining an accurate location of a hot tip in the arterial occlusive region.Re-stenosis or occlusion of the arteries was observed in 2 of 13 patients followed up to 6 months after angioplasty.Because of limited luminal diameter dilated by thermal ablation alone, additional balloon angioplasty was necessary in all cases. No significant complications were observed during laser angioplasty without local dissection of the arterial wall after balloon dilatation. Further investigation on patency rate of the arteries is required for long follow-up period.

Thermodynamic correlates of hot tip laser angioplasty.

Surface temperatures of normal human cadaver arteries and polytetrofluoroethylene grafts were measured in vitro using thermography to assess vascular wall heating from the metal-capped ("hot tip") laser probe. Laser pulse duration, vessel diameter, blood flow, and saline infusion were varied; power from an Argon laser was constant at 10 watts. The surface temperatures resulting in perforation were 76.2 +/- 2.2 degrees C for arteries and 90.4 +/- 2.1 degrees C for grafts. Blood flow provided an effective heat sink reducing artery and graft wall peak temperatures from 10 watt/5 sec pulses by 12.2 +/- 1.7 and 14.1 +/- 6.1 degrees C at 100 mL/min, and by 16.3 +/- 2.4 and 22.4 +/- 4.9 degrees C at 500 mL/min, respectively. In the occluded conduit, inflow of saline proximal to the probe tip reduced peak temperatures (degrees C) from 10 watt/5 sec pulses as follows: 14.0 +/- 3.2 (artery) and 23.2 +/- 8.5 (graft) at 50 mL/min, and 19.0 +/- 0.6 (artery) and 26.6 +/- 8.5 (graft) at 100 mL/min. Radial heating by the hot tip probe can cause thermal perforation. Blood flow or saline infusion modifies nontarget heating and may offer significant protection to the vasculature.

A Hot Tip for the Treatment of Deep and Superficial Burns

A Hot Tip for the Treatment of Deep and Superficial Burns

In vitro effects of argon laser radiation on blood: Quantitative and morphologic analysis

Use of the argon laser to recanalize stenosed arteries may require delivery of the beam through blood. To assess the degree of hemolysis and debris formation, 84 samples of citrated whole blood were exposed to argon laser radiation with varying power (1, 2 and 3 watts) and duration (5, 10, 20 and 40 seconds). Compared with control samples, only blood samples exposed to a power of 3 watts for 40 seconds showed a marked decrease in hematocrit (from 37 +/- 1.3 to 33 +/- 1.4%, p less than 0.01) and a marked increase in both free hemoglobin concentration (from 0.2 +/- 0.2 to 1.3 +/- 0.5 g/100 ml, p less than 0.01) and debris weight (from 0.9 +/- 0.3 to 2.8 +/- 0.5 mg, p less than 0.01). Scanning electron microscopy of debris from samples of whole blood, washed erythrocytes and platelet-rich plasma lased at 3 watts for 40 seconds documented the presence of membrane denaturation of blood elements, resulting in their fusion to form complex mesh-like conglomerates. Similar morphologic changes were observed in whole blood samples exposed to a "hot tip" rather than laser radiation. These data indicate that: 1) argon laser radiation with a power of 3 watts does not produce apparent hemolysis or debris formation for exposure periods up to 20 seconds, and 2) the effects of laser radiation on blood are probably mediated by thermal denaturation of cell membranes, as suggested by the same morphologic changes produced by thermal injury from a "hot tip."

"Hot tip": another method of laser vascular recanalization.

This study is a preliminary report evaluating the use of laser radiation to heat a metal-capped fiber for arterial recanalization. The method was compared to the currently used bare-ended fiber for recanalization of occluded vessels. The model used was a human coronary artery xenograft transplanted in the femoral artery of the dog. At 4 weeks following the transplantation, laser recanalization was attempted using the heated metal probe ("hot tip") in five arteries and the bare fiber in another five arteries. 1) Angiography demonstrated recanalization in all five arteries treated with the "hot tip" and three of the five arteries treated with the bare fiber. 2) Only one perforation occurred with the "hot tip," whereas three perforations occurred with the bare fiber. 3) The larger metal cap was capable of creating a wider channel in the occluded arterial segment. Although the trend favored the heated metal cap in terms of recanalization and less perforation than the bare fiber, the total number of experiments were not adequate to demonstrate statistical significance. Microscopic examination of the vessels recanalized by either technique was similar. Characteristic charring at the recanalization site was seen regardless of the technique used. These observations suggest that the effect of direct laser radiation on plaques is predominantly a thermal effect. Although these results would suggest utilization of a metal-capped fiber for vascular recanalization, more studies need to be done to confirm these preliminary findings.

“Hot tip”: Another method of laser vascular recanalization

AbstractThis study is a preliminary report evaluating the use of laser radiation to heat a metal‐capped fiber for arterial recanalization. The method was compared to the currently used bare‐ended fiber for recanalization of occluded vessels. The model used was a human coronary artery xenograft transplanted in the femoral artery of the dog. At 4 weeks following the transplantation, laser recanalization was attempted using the heated metal probe (“hot tip”) in five arteries and the bare fiber in another five arteries. Results: 1) Angiography demonstrated recanalization in all five arteries treated with the “hot tip” and three of the five arteries treated with the bare fiber. 2) Only one perforation occurred with the “hot tip,” whereas three perforations occurred with the bare fiber. 3) The larger metal cap was capable of creating a wider channel in the occluded arterial segment. Although the trend favored the heated metal cap in terms of recanalization and less perforation than the bare fiber, the total number of experiments were not adequate to demonstrate statistical significance. Microscopic examination of the vessels recanalized by either technique was similar. Characteristic charring at the recanalization site was seen regardless of the technique used. These observations suggest that the effect of direct laser radiation on plaques is predominantly a thermal effect. Although these results would suggest utilization of a metal‐capped fiber for vascular recanalization, more studies need to be done to confirm these preliminary findings.

Morphological Phase Transition Measured by "Surface Kinetic Dimension" of Growing Random Patterns

"Surface kinetic dimension" was defined as a quantity to measure the logarithmic derivative of the surface with respect to the volume of growing patterns. This quantity for the growing pattern based on the "hot tip model" was found to show two kinks when the tip priority factor was increased. They were found to correspond to a microscopic roughening transition and a macroscopic morphological transition from a compact to a dendritic growth pattern, respectively. The result of the simulation based on the triangular pixel was also reported. A possible mechanism of the transition was discussed. It was pointed out that the surface kinetic dimension plays the role of a potential in the growing pattern dynamics.

A heat transfer study for a partially immersed refractory rod in a plasma

The thermal behavior of a tungsten rod partially immersed in a plasma flame is analyzed. The longitudinal temperature profiles are obtained by numerical solution of the heat balance equation. Results show that a heat transfer model consisting of pure natural convection up to the plasma outer edge and forced convection inside the plasma, fails to predict temperatures at the hot tip of the rod. In order to make the experimental and calculated profiles to converge, one has to consider modifications in the mechanical and thermal conditions of the surrounding medium due to the presence of the rod in the plasma. This leads to the use, in the “cold” gas zone, of particular values of heat transfer coefficient h and of a parameter T x which is defined only at the immediate boundary of the rod. The latter are given in the form of variations along the axis of the rod. This perturbation effect decreases with the rod diameter. Allowance is made for the variation of the thermal properties of the solid.

Untersuchungen zur Therapie virusinfizierten Hopfens (Humulus lupulus L) durch Wärmebehandlung von Fechsern und Triebspitzen

Summary Hot water treatment of dormant hop cuttings at temperatures ranging from 35°C to 65°C in intervals of 5 min. to 4 h. proved to be inadequate for the inactivation of hop viruses. In comparable research works different types of heat chambers have been tested for use in hot air treatments of hop plants. Relatively most satisfying was a stationary chamber in which plants after a period of heat adaptation grew under artificial light conditions in temperatures between 37°C to 40 °C, in relative air humidities between 60 to 80 per cent and in soil temperature of 28°C sufficiently survived a treatment of at least 25 days. From more than 1000 about 2 to 3 cm. long shoot tips of 25 to 118 days heat treated hop plants belonging to 15 varieties, 3 clones and 2 breeding lines, 7401 young hop plants could be developed. RMV (rose mosaic virus), NRSV ( Prunus necrotic ringspot virus), AMV ( arabis mosaic virus), and hop mosaic virus in an extend of 34.0, 27.3, 16.7, and 24.3 per cent have been eliminated. However, elimination of the latent rod shaped hop virus (656 nm) only in 2 varieties extreme rarely succeeded even if the longest heat periods have been used. In order to increase the curing rate the combination of hot air treatment and tip meristem culture techniques is recommended. Healthy or virus-poor hop material has been selected on the basis of 2 to 8 times repeated indexings on test plants, partly repeated agar gel double diffusion tests, using antiseras against RMV, NRSV, and AMV and by the reaction of indicators and electron-microscopical tests in course of several years.

A Field Ion Investigation of Oxygen on Tungsten

The adsorption of oxygen on tungsten was investigated with a field ion microscope. Two experimental procedures were followed. In the first, a tungsten tip previously annealed to 973 or 1173 °K was held at 78 °K while exposed to oxygen. Coverages ranged from less than a monolayer to saturation. After the ambient oxygen was removed, the tip was heated to the annealing temperature. In the second, oxygen adsorption occurred on a hot tip held at 973 °K. Estimated coverages were significantly less than a monolayer.Results reveal a dramatic difference in the extent of surface diffusion, rearrangement, disruption, and oxygen penetration for the two procedures, the latter producing more extensive effects. Possible explanations for these differences are considered.

Synthesis and dome properties of BeTe, BeSe and BeS

The Seebeck coefficient of a material is dependent on its composition and microstructure and is consequently sensitive to service related material degradation; of particular interest is the sensitivity to thermal and irradiation embrittlement which may be exploited for the material characterisation of in service components. Conventionally, thermoelectric measurements are taken using a two-point contact technique which introduces a temperature differential in the test component through a heated ‘hot tip’ electrode; it is argued that measurements using this methodology are sensitive to the thermal contact resistance between the component and the electrodes. An alternative three- or four-point technique is proposed where heat is introduced to the component remotely which leads to much less sensitivity to contact condition. An experiment is presented that compares the two techniques and demonstrates the improved performance of the four-point technique. Aside from the improved accuracy, the modified technique also facilitates a ‘passive’ implementation that could be used from continuous monitoring of components in service.