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Biomedical subjects

J H Torres

Publications and source records attributed to J H Torres.

At least 19 recordsLinked to original sources
PubMed2001

Indication of superconductivity at 35 K in graphite-sulfur composites.

We report magnetization measurements performed on graphite-sulfur composites which demonstrate a clear superconducting behavior below the critical temperature T(c0) = 35 K. The Meissner-Ochsenfeld effect, screening supercurrents, and magnetization hysteresis loops characteristic of type-II superconductors were measured. The results indicate that the superconductivity occurs in a small sample fraction, possibly related to the sample surface.

Journal Article↗
PubMed2001

Cryogen spray cooling: Effects of droplet size and spray density on heat removal.

BACKGROUND AND OBJECTIVE: Cryogen spray cooling (CSC) is an effective method to reduce or eliminate non-specific injury to the epidermis during laser treatment of various dermatological disorders. In previous CSC investigations, fuel injectors have been used to deliver the cryogen onto the skin surface. The objective of this study was to examine cryogen atomization and heat removal characteristics of various cryogen delivery devices. STUDY DESIGN/MATERIALS AND METHODS: Various cryogen delivery device types including fuel injectors, atomizers, and a device currently used in clinical settings were investigated. Cryogen mass was measured at the delivery device output orifice. Cryogen droplet size profiling for various cryogen delivery devices was estimated by optically imaging the droplets in flight. Heat removal for various cryogen delivery devices was estimated over a range of spraying distances by temperature measurements in an skin phantom used in conjunction with an inverse heat conduction model. RESULTS: A substantial range of mass outputs were measured for the cryogen delivery devices while heat removal varied by less than a factor of two. Droplet profiling demonstrated differences in droplet size and spray density. CONCLUSIONS: Results of this study show that variation in heat removal by different cryogen delivery devices is modest despite the relatively large difference in cryogen mass output and droplet size. A non-linear relationship between heat removal by various devices and droplet size and spray density was observed.

Administration, Topical↗
PubMed2001

An analysis of heat removal during cryogen spray cooling and effects of simultaneous airflow application.

BACKGROUND AND OBJECTIVE: Cryogen spray cooling (CSC) is a method used to protect the epidermis from non-specific thermal injury that may occur as a result of various dermatological laser procedures. However, better understanding of cryogen deposition and skin thermal response to CSC is needed to optimize the technique. STUDY DESIGN/MATERIALS AND METHODS: Temperature measurements and video imaging were carried out on an epoxy phantom as well as human skin during CSC with and without simultaneous application of airflow which was intended to accelerate cryogen evaporation from the substrate surface. An inverse thermal conduction model was used to estimate heat flux and total heat removed. RESULTS: Lifetime of the cryogen film deposited on the surface of skin and epoxy phantom lasted several hundred milliseconds beyond the spurt, but could be reduced to the spurt duration by application of airflow. Values over 100 J/cm(3) were estimated for volumetric heat removed from the epidermis using CSC. CONCLUSIONS: "Film cooling" instead of "evaporative cooling" appears to be the dominant mode of CSC on skin. Estimated values of heat removed from the epidermis suggest that a cryogen spurt as long as 200 milliseconds is required to counteract heat generated by high laser fluences (e.g., in treatment of port wine stains) in patients with high concentration of epidermal melanin. Additional cooling beyond spurt termination can be avoided by simultaneous application of airflow, although it is unclear at the moment if avoiding the additional cooling would be beneficial in the actual clinical situation.

Aerosol Propellants↗
PubMed2000

Epidermal protection with cryogen spray cooling during high fluence pulsed dye laser irradiation: an ex vivo study.

BACKGROUND AND OBJECTIVE: Higher laser fluences than currently used in therapy (5-10 J/cm(2)) are expected to result in more effective treatment of port wine stain (PWS) birthmarks. However, higher incident fluences increase the risk of epidermal damage caused by absorption of light by melanin. Cryogen spray cooling offers an effective method to reduce epidermal injury during laser irradiation. The objective of this study was to determine whether high laser incident fluences (15-30 J/cm(2)) could be used while still protecting the epidermis in ex vivo human skin samples. STUDY DESIGN/MATERIALS AND METHODS: Non-PWS skin from a human cadaver was irradiated with a Candela ScleroPlus Laser (lambda = 585 nm; pulse duration = 1.5 msec) by using various incident fluences (8-30 J/cm(2)) without and with cryogen spray cooling (refrigerant R-134a; spurt durations: 40-250 msec). Assessment of epidermal damage was based on histologic analysis. RESULTS: Relatively short spurt durations (40-100 msec) protected the epidermis for laser incident fluences comparable to current therapeutic levels (8-10 J/cm(2)). However, longer spurt durations (100-250 msec) increased the fluence threshold for epidermal damage by a factor of three (up to 30 J/cm(2)) in these ex vivo samples. CONCLUSION: Results of this ex vivo study show that epidermal protection from high laser incident fluences can be achieved by increasing the cryogen spurt duration immediately before pulsed laser exposure.

Aerosol Propellants↗
PubMed1996

Optical characterization and coagulation performance of side-emitting fiber delivery systems for laser therapy of benign prostatic hyperplasia: a comparative study.

OBJECTIVES: Currently, various side-emitting optical fibers with different tip geometry are used transurethrally to deliver laser radiation for treatment of benign prostatic hyperplasia (BPH). Since fiber tip design could profoundly affect the size and profile of the emitted laser beam, and consequently the tissue response and the extent of tissue coagulation, we evaluted commercially available fibers in regard to their optical characteristics and their ability to coagulate tissue in a controlled experimental setting. METHODS: Thirteen fibers manufactured by different companies and clinically used at the present time were tested using a surgical neodymium: yttrium-aluminum-garnet laser. The profile of the laser beam delivered via each fiber was imaged on a CCD camera at various distances and evaluated by means of a laser beam analyzer. Beam divergence angle was then calculated for each tip. Tissue coagulation effects were assessed by irradiating samples of beef muscle immersed in water at 37 degrees C. The fiber tip was kept 2.5 mm away from the tissue and irrigation was maintained at flow rate of 350 to 400 cc/min during irradation. Laser powers of 20, 40, and 60 W were used for 180, 90, and 60 seconds, respectively, delivering a total energy of 3600 J. RESULTS: The results of the optical evaluation divided the fibers into two major groups: broad beam with large divergence angle and narrow beam with small divergence angle. Statistical analysis of the data (using analysis of variance) showed that volumes of coagulated tissue were significantly larger for broad beam fibers than for narrow beam fibers (1.15 +/- 0.32 versus 0.89 +/- 0.34 cm 3; P < 0.05). Also, significantly larger volumes were obtained for 20 W when compared with 60 W (1.08 +/- 0.43 versus 0.88 +/- 0.27 cm 3; P < 0.05). CONCLUSIONS: The laser power density delivered by individual fibers to the prostate tissue may vary significantly, thus greatly affecting the extent of tissue coagulation. Therefore, irradiation parameters must be optimized for each fiber type.

Animals↗
PubMed1995

Lifetime testing of sapphire and sculpted silica fiber scalpels.

BACKGROUND AND OBJECTIVE: Sapphire and sculpted silica fiber scalpels were evaluated for performance as they aged. Performance was determined by measuring their useful lifetime, forward transmission, incision depth, and the thermal coagulation thickness at the sides and bottom of the incision. STUDY DESIGN/MATERIALS, AND METHODS: Aging was performed with a chicken breast model. Performance measurements were made at periodic intervals. Sapphire scalpels were cooled with air or saline. RESULTS: The air-cooled, frosted sapphire scalpels had the longest useful lifetime, whereas the saline-cooled, frosted sapphire scalpels had the shortest. Aging deteriorated the forward transmission of the sculpted silica fiber scalpels the most. Little difference was found between the averages of all incision measurements. Two of the saline-cooled, frosted sapphire scalpels fractured during the aging process. CONCLUSION: Aging influences the scalpel lifetime, but there was no evidence that the aging process significantly affected the incision size.

Aluminum Oxide↗
PubMed1995

Laser photocoagulation of prostate: influence of dosimetry.

BACKGROUND AND OBJECTIVE: Recently, increasing enthusiasm has been shown for application of lasers for the treatment of benign prostate hyperplasia (BPH). However, little is known about the thermodynamics of prostatic tissue response during laser irradiation and how the treatment outcome can be optimized. Our objective was to conduct a systematic study of the influence of exposure parameters on the extent of tissue coagulation and to determine the effects of rate of tissue heating on lesion size by comparing the tissue response to high laser power rapid heating vs. low laser power slow heating. STUDY DESIGN/MATERIALS AND METHODS: Nd:YAG laser irradiation of prostate was performed in 15 mongrel canines, using an incident power of 15, 30, or 50 Watts (at the fiber tip) and an exposure time varying from 30 to 300 seconds. The laser beam was delivered via a Urolase side-emitting catheter. The tissue response was compared based on gross as well as histological evaluations of thermal lesions. RESULTS: The depth of coagulation necrosis increased as the laser power was reduced from 50 W to 30 W and further to 15 W while the total delivered energy was kept constant at 2,700 J by adjusting the exposure time. The difference between the three heating rates was more dramatic when the estimated volume of coagulated tissue was considered. Increasing the irradiation time for the low power (15 W) from 180 to 300 seconds resulted in enlarging the coagulated volume by a factor of 1.6. However, for high power (50 W), increasing the exposure time from 54 to 90 seconds resulted in increasing the coagulated volume by a factor of 1.2. CONCLUSION: This study suggests that a slow heating regimen yields larger volumes of coagulation necrosis than the currently used rapid heating approach.

Aluminum Silicates↗
PubMed1995

Comparison of thermocoagulation effects of low power, slow heating versus high power, rapid heating Nd: YAG laser regimens in a canine prostate model.

We compared the thermocoagulation effects of low power, slow heating (15 W x 180 seconds) versus high power, rapid heating (50 W x 60 seconds) laser regimens in the canine prostate. The study was performed in 20 mongrel canines. On each prostate, the low power regimen was delivered at the 2 and 4 o'clock positions, and the high power at the 8 and 10 o'clock positions. The laser power was measured at the fiber tip. Seven dogs (acute group) were sacrificed 1 hour after the procedure. The other 13 dogs (chronic group) were sacrificed at different time intervals from 3 days to 9 weeks after the procedure. The average depth of coagulation was significantly greater in lesions treated at low power (acute: 10.7 mm., chronic: 13.3 mm.) than in those treated at high power (acute: 8.5 mm., chronic: 11.6 mm.). Another potential benefit of the low power regimen observed in the study was preservation of the integrity and efficiency of the laser probe.

Animals↗
PubMed1994

Comparison of the thermal tissue effects produced by aged sapphire and silica hemispherical tips.

This study evaluated the performance of sapphire and fused silica hemispherical tips under the same exposure conditions. Lesions produced in the chicken breast and a blood field were sectioned for light and transmission polarizing microscopy. Lesion size and thermal damage area were recorded as a function of the tips accumulated exposure. The tips transmission was measured after every 1,000 J of exposure. Fused silica tips lasted for approximately 5,000 J and experienced significant surface and transmission deterioration. The sapphire hemispherical tips lasted for > 12,000 J with no surface and transmission deterioration. Lesions produced with the fused silica tips generally increased in depth with use, and depths of 6 mm were common. Lesions produced by the sapphire tips were subsurface spherical areas of coagulation with the tissue surface relatively intact. This difference in resulting lesions may be attributed to the higher thermal conductivity of sapphire.

Aluminum Oxide↗
PubMed1994

Tissue optical property measurements: overestimation of absorption coefficient with spectrophotometric techniques.

This study examines the validity of optical property measurements by comparing surface temperatures rises predicted by a well-tested mathematical model with temperatures measured experimentally during laser irradiation. Analysis is based on the early temperature response that is proportional to the absorption coefficient. The results of the investigation suggest that values for tissue absorption coefficient can be greatly overestimated when current spectrophotometric techniques are used. This seems especially true when a broad light beam and a low port-to-beam-size ratio are used for transmission and reflection measurements with an integrating sphere.

Absorption↗
PubMed1994

Effects of surface irrigation on the thermal response of tissue during laser irradiation.

Effects of surface irrigation on the thermal response of tissue during laser irradiation are investigated. In particular, influence of temperature and flow rate of the irrigation fluid on the resulting temperature distributions and coagulation depths are studied. Intraluminal Nd:YAG laser irradiation of bovine muscle is performed in vitro for a fixed value of the irrigation flow rate while the irrigation temperature is varied, and for a fixed irrigation temperature while the irrigation flow rate is kept constant. Thermocouples are used to measure the temperatures within the tissue for various irradiation and irrigation conditions. Higher temperatures and deeper coagulation depths are achieved as the temperature of the irrigation fluid is increased. For sufficiently low values of irradiance and exposure time, the use of cold irrigation is shown to prevent or delay tissue carbonization. Beyond a critical irradiance and an exposure time, use of cold irrigation does not prevent tissue carbonization. Coagulation depths and temperature distributions are not affected by a change in the flow rate of laminar irrigation. Application of stagnant irrigation, however, results in an increase in coagulation depth. Results of this study suggest that the dominating mechanism of heat transfer during application of laminar irrigation is thermal diffusion as compared to the bulk motion of the fluid.

Animals↗
PubMed1991

[Localization of the mandibular canal: experimental comparison of four types of radiological examination].

This investigation, involves eight dry mandibles, and compares four of radiological examinations to allow the measurement of the depth of the mandibular canal in relation to the alveolar crest. It showed that their (ability to detect the mandibular canal) differed significantly: coronal tomography: 64% retro-alveolar X-ray: 83% orthopantomography: 85% coronal tomodensitometry: 100% The retro-alveolar X-ray appears to have the best cost/information ratio, while the coronal tomography must be left aside.

Humans↗
PubMed1990

TCP shortens the latency of onset of isoelectricity in hypoglycaemia and fails to protect striatal neurones and dentate gyrus granule cells from hypoglycaemic injury in rats.

Competitive N-methyl-D-aspartate (NMDA) receptor antagonists are known to protect neurones against hypoglycaemic damage. We tested N-[1-(2-thienyl)cyclohexyl]piperidine (TCP), a non-competitive NMDA antagonist, in a recovery model of hypoglycaemic coma in the rat. Administered concomitantly with insulin, TCP shortened the latency of onset of electrocerebral silence, and failed to prevent striatal and dentate gyrus hypoglycaemia-induced injury. This effect is probably related to an increase in glucose consumption of neurones: TCP enhances energy metabolism in several brain structures, which could facilitate, at low blood glucose levels, the onset of isoelectricity, and hamper a putative neuro-protective effect of the drug.

Animals↗
PubMed1990

Disparate absorption of argon laser radiation by fibrous versus fatty plaque: implications for laser angioplasty.

The thermal response of white fibrous atheromatous plaque to argon laser irradiation was compared with the thermal response of yellow fatty plaque and normal aortic wall to the same type of radiation. Samples of normal aorta, fibrous, and fatty plaque were irradiated in air with 3.5 Watts of laser power on a 2 mm spot for 5 and 10 seconds. Heterogeneous foci, each covering normal aorta and either fibrous or fatty plaque, were additionally irradiated with 7 Watts on a 1 cm spot for 30 seconds to 2.5 minutes. Tissue surface temperature was monitored during laser irradiation via a 3-5 micron infrared camera. For the 2 mm spot and 5 second exposure time, argon laser irradiation of normal aorta produced popping and surface tearing at a peak temperature of 145 +/- 10 degrees C. Irradiation of fatty plaque produced popping and crater formation at a peak temperature of 200 +/- 10 degrees C. However, fibrous plaque was nonablatively discolored by the same dose of laser radiation with a peak temperature of only 85 +/- 10 degrees C. Irradiation for 10 seconds caused crater formation and carbonization in the fatty plaque but failed to produce ablation in the fibrous plaque. Irradiation of the heterogeneous foci confirmed the disparity in the temperature attained by these two types of plaque and their degree of damage. Therefore, this study suggests that the ablation threshold for soft atheroma is strongly dependent on the optical properties of the particular type of tissue. Yellow fatty plaque preferentially absorbs argon laser radiation, but white fibrous plaque absorbs this radiation less readily than normal aortic wall.

Angioplasty, Balloon↗
PubMed1990

Limitations of a thermal camera in measuring surface temperature of laser-irradiated tissues.

Thermal cameras are used in research laboratories to measure tissue temperature during laser irradiation. This study was an evaluation of the accuracy of a 3-5 microns thermal camera and two 8-12 microns cameras in detecting the maximum temperatures of small targets. The size of the targets was within the range of laser spot diameters which are used for vessel welding, angioplasty, and dermatology. The response to a sharp thermal edge was measured and analyzed for the three cameras, which had a scanning rate of 30 frames per second. The response of the 3-5 microns camera to reference black body targets of different sizes was also studied. It was found that the detector system required an average of 2.44 microseconds to reach 90% of maximum step response for the 8-12 microns system and 5.85 microseconds for the 3-5 microns system. With a 3 x telescope and a 9.5 inch focal distance close-up lens, the 3-5 microns camera underestimated the temperature of targets smaller than 2.0 mm because of its slow detector response. Although the 8-12 microns camera provides more accurate measurements due to its faster detector response, it still underestimates the temperature of targets smaller than 900 microns, when similar magnification and focal distance are used. Methods to compensate for the inaccuracies are discussed, including empirical correction factors and the inverse filtering technique.

Calibration↗
PubMed1990

Laser probe temperature control by measuring the returning infra-red radiation.

The metal-tipped fibre or 'laser probe' developed for angioplasty comprises a metallic probe at the end of an optical fibre. The probe is heated by an argon or Nd:YAG laser and applied against the tissue to be vapourized. The heated probe generates infra-red radiation which is proportional to the temperature of the probe. The paper investigates the feasibility of a feedback control system that measures the temperature of the probe by detecting the infra-red radiation transmitted back through the fibre. The probe was initially heated by physical contact with a hot surface, and then by an argon laser via the optical fibre. The returning IR radiation was sensed by a lead sulphide detector, while probe temperature was simultaneously measured by a thermocouple. Temperatures as low as 200 degrees C were measured through a 5 m long fibre during the laser heating of the probe. The detector signal increased in an exponential fashion as the probe temperature increased. A resolution of 1 degree C was obtained at a probe temperature of 400 degrees C. It can be concluded that, for the laser probe, it is feasible to use a feedback control system which measures the infra-red radiation transmitted back through the same fibre that carries the heating laser light.

Feasibility Studies↗
PubMed1990

[Drug interactions in dentistry].

The authors describe the various interactions which may exist between the medical treatments followed by patients and various groups of substances used in odonto-stomatology: non-steroid anti-inflammatory drugs, antibiotics, antifungicides, vasoconstrictors and local anaesthetics. They clarify the clinical risk relating to each of these medicament interactions.

Analgesics↗