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Biomedical subjects

J A Pearce

Publications and source records attributed to J A Pearce.

32 records · Page 2Linked to original sources
PubMed1987

Laser probe ablation of normal and atherosclerotic human aorta in vitro: a first thermographic and histologic analysis.

The metal-tipped optical fiber or "laser probe" has been extensively studied in animal preparations in vivo and in human clinical trials of revascularization. The aim of this study was to evaluate the thermal characteristics of laser probe tissue ablation and to contrast the vascular tissue response to exposure to the laser probe and bare optical fiber. A 2 mm laser probe was heated with up to 4 W of argon-ion laser irradiation and applied to six postmortem strips of human nonatherosclerotic aorta as well as to five atherosclerotic aortic specimens. Surface temperature maps of the laser probe and of the vascular tissue in air were obtained via 8 to 12 micron thermographic imaging. Laser probe temperature was additionally monitored via thermocouples. Two strips each of normal and diseased aorta were irradiated directly with the bare optical fiber. Thus a total of 43 laser probe application sites and 19 bare fiberoptic laser irradiation sites on a total of 15 aortic strips were analyzed both thermographically and histologically. Based on measured temperature rises and histologic findings, the following observations were made: (1) The laser probe heats initially at its tip and attains a uniform surface temperature distribution within 5 sec. The steady-state temperature attained by the probe is inversely related to the thermal conductivity of the surrounding media. In all media studied, probe temperature increases linearly with applied laser energy. (2) Tissue ablation starts at temperatures greater than 100 degrees C, and ablation temperatures typically exceed 180 degrees C. Adventitial temperatures during laser probe application may reach 70 degrees C. Tissue ablation is enhanced both by greater laser energy deposition in the probe and by higher force at which the probe is applied to tissue. (3) Ablation of fibrofatty atheromata is more extensive than of nonatherosclerotic aortic tissue. This may be due to the lower thermal conductivity of atheromatous tissue. (4) In contrast to direct argon-ion laser ablation of aortic tissue, laser probe-mediated ablation occurs in a controlled fashion, is not associated with extensive subintimal dissections, and allows uniform conduction of heat to tissue as reflected by essentially "isothermal" injury lines.

Aorta↗
PubMed1987

Laser applications in clinical medicine.

Laser energy sources have been used in a wide range of clinical applications over the last decade to obtain cutting, coagulation, and denaturization of tissue. The therapeutic effect depends on complex interaction among the optical and thermal properties of tissue and damage accumulation. In applications where localized white coagulum is required, there are trade-offs between continuous activation using a large spot size and repetitive pulses with a small spot size as well as between a highly scattered, deep penetration source and a highly absorbed, shallow penetration laser source. For applications involving ablation of tissue, high intensity, pulsed, shallow penetration sources have many advantages over continuously activated penetrating sources. In this article, the range of applications is reviewed with particular attention to the underlying physical phenomena that influence the choice of treatment parameters.

Humans↗
PubMed1985

Effect of laser radiation on tissue during laser angioplasty.

The thermal properties of adipose and ceramic atherosclerotic plaque deposits and normal arterial vessel wall were measured in the temperature range of 25-95 degrees C. In general, the data indicate that fatty plaques exhibit the lowest thermal conductivity and thermal diffusivity of the three types, whereas calcified plaques seem to have the highest values. By using a video scanning thermograph, temperature rise was recorded in normal vessel wall and plaque during ablation of tissue. Theoretical analysis suggested that realistic modeling of laser angioplasty should account for scattering of light, water content, and ablation. This paper is a preliminary report of these results.

Arteriosclerosis↗
PubMed1983

Thermographic evaluation of horses with podotrochlosis.

The distal forelimbs of 10 clinically normal horses with hair clipped on 1 limb were thermographically scanned before and after exercise. The thermal patterns, temperature distribution, and temperature changes after exercise were determined and compared with those of 8 horses with podotrochlosis. Clipping the hair did not cause changes in the thermal patterns, but the clipped limbs were warmer than the unclipped limbs. The temperature of the limbs of horses with podotrochlosis did not increase as much after exercise as did the limbs of normal horses. The failure of skin temperature increase correlated with the radiographic evidence of enlarged vascular foramina in the navicular bone. Because the failure to increase skin temperature after exercise is the result of low blood flow, the enlarged vascular foramen can be related to a state of low blood flow.

Animals↗
PubMed1982

Myocardial stimulation with ultrashort duration current pulses.

In order to identify a practical short-duration limit for stimulating myocardium, theoretical and experimental studies were carried out using dog and turtle hearts. The strength-duration curves for current, charge and energy were derived from the standard excitable membrane model which employs a parallel resistance and capacitance. From these derivations, the predicted duration for minimum energy was identified. The experimentally measured strength-duration curves for two types of myocardium followed the predicted values closely. The duration for minimum energy was calculated to be 1.25 times the membrane time constant. The practical short-duration limit for a pacemaking stimulus is about 10% of the membrane time constant. For dog myocardium the average time constant was 2.4 ms. Therefore, a practical stimulus duration for minimum charge in the dog should be no longer than about two-tenths of a millisecond, although shorter duration stimuli are equally effective. This minimum charge criterion provides the minimum drain on the stimulator power supply.

Animals↗
PubMed1982

The effect of gelled-pad design on the performance of electrosurgical dispersive electrodes.

A two-dimensional model of a simplified configuration of the gelled-pad electrode applied to human tissue was developed. As a consequence of the boundary discontinuity near the edge of the pad, the model predicted high peripheral and low central surface temperature rises. By comparison with base conditions, increased gelled-pad area and gel electrical resistivity and decreased initial pad temperature reduce the temperature rise across the pad surface. Temperature distributions measured on the thighs of human subjects were shown to have similar characteristics to those predicted by the model. Even though three-dimensional and blood flow effects were not considered, the model is satisfactory for evaluating the effect of electrode design changes on thermal performance.

Electrodes↗
PubMedDate not supplied

Prediction of transient temperature fields and cumulative tissue destruction for radio frequency heating of a tumor.

A therapeutic hyperthermia protocol using a radio frequency (rf) electrode placed adjacent to a bronchial wall tumor has been modeled using the finite element technique. Variable physical properties and variable blood perfusion have been assigned to the tumor and to the surrounding normal lung tissue. The Laplace equation was solved on a curvilinear grid for a single rf source electrode to determine the steady-state electric field, which in turn governs the energy deposition function. The heat generation in the tumor and in the lung tissue is then calculated from the energy deposition profile, and the bioheat equation is solved on the same finite element mesh to determine the transient temperature history. The temperatures are displayed as isothermal contours at designated times during the protocol and as temperature histories at selected points. In addition, an Arrhenius-type injury model has been implemented to predict thermally induced damage, from which equal total amounts of energy are deposited into the tissue using a constant power density for an appropriate time or using a cyclic heating pattern. The cyclic heating pattern consisted of a series of equal duration time periods during which the rf current source is alternately turned on and off (50% duty cycle). This study illustrates how a finite element model could be used to evaluate alternative protocols for heating a tumor of a specific geometry and to evaluate thermally induced damage to surrounding normal tissue.

Humans↗
PubMedDate not supplied

What's new in electrosurgical instrumentation?

A 1976 report of the use of radiofrequency current to devitalize carcinomas in man stimulated this review of the historical background, the presently used techniques, and the problems associated with electrosurgery. Difficulties in electrosurgical techniques requiring further research are identified--i.e., the high heating and variable performance of dry dispersive electrodes, the hazards of tissue stimulation, high-frequency interference, and the potential impact of government regulation.

Animals↗
PubMedDate not supplied

A proposed method for quantitative performance evaluation of electrosurgical dispersive electrodes.

The measurement of thermal performance of electrosurgical dispersive electrodes presents special problems since it is necessary to determine the spatial distribution of transient temperature fields in the presence of high-energy, high-frequency, electric fields. Contact sensors are contraindicated. high-speed video-scanning thermographic systems solve the problem and, additionally, provide a permanent record of the temperature-time history of experiments on videotape. The overall uncertainty in temperature rise determination using this method is on the order of 0.4 degrees C. This measurement approach, which has been used in experiments on human subjects, yields repeatable, quantitative determinations of the thermal performance of dispersive electrodes.

Data Display↗
PubMedDate not supplied

The thermal behavior of electrolyte-coated metal-foil dispersive electrodes.

The thermal properties of electrolyte-coated aluminum (Al) and copper (Cu) foil dispersive electrodes carrying 700 mA of electrosurgical current for 1 min were studied on seven human subjects ranging in weight from 46 to 84 kg. Calibrated thermographic imaging was used for data analyses. The mean skin temperature rise for the Al-foil electrode was 1 degrees C and for the Cu-foil electrode was 0.5 degrees C. The maximum temperatures occurred at the perimeter of both electrode types and were 3.5 degrees C for the Al-foil and 2.5 degrees C for the Cu-foil electrode. Both electrodes performed adequately under these severe test conditions.

Adult↗
PubMedDate not supplied

Skin burns from electrosurgical current.

At 34 skin sites on anesthetized pigs, graded levels of average electrosurgical current density, J (A/cm2), at 500 kHz were delivered for specified times (t sec) to cause thermal injury. The severity of cutaneous response was determined by gross and microscopic study 56 hours later. The product J2t has been defined as the relative energy density factor, and is proportional to the delivered energy that determines skin heating. Nine of 10 sites that received low energy density factor exposure (J2t = 0.20-0.70 A2/cm4.sec-1) exhibited maximum skin temperatures of 38-47 degrees C beneath the electrodes, and subsequently has either no damage or as mild second-degree burn lying just beyond the electrode contact zone. At 9 of 11 sites exposed to a medium energy density factor (J2t = 0.70-1.60), the maximum skin temperatures below the electrodes were between 49 and 55 degrees C, with single or multiple rings of second-degree burns located just inside or beyond the rim of the electrode. At all 13 sites exposed to high energy density (J2t = 1.60-7.50), the maximum skin temperatures beneath the electrodes were 55-81 degrees C, and severe burns were produced with white to brownish, dry, firm, third-degree burns surrounded by peripheral rings of second-degree burns. No significant skin damage was produced with skin temperatures less than 45 degrees C (an energy density factor of 0.75). These data identify the temperature and energy density factor necessary to produce lesions on porcine skin.

Animals↗
PubMedDate not supplied

Equipment for local hyperthermia therapy of cancer.

Technology for local heat therapy of cancer is evolving rapidly at a number of technologically diverse and geographically scattered institutions and companies. No single technology is superior to others in all applications, and no single company, laboratory, or research group has all the answers. An ideal system would provide focused heating at depth in a predictable fashion, with little probability of generating undesired hot spots in normal tissues and little interference with monitoring equipment. Existing systems approximate this ideal to different degrees, depending on the anatomy and geometry of the tumor and its surrounding tissues. In the foregoing discussion the important problem of measuring temperatures in tumors and normal tissues has been slighted. At the present time, all thermometry is necessarily invasive, and there are limitations to the number of points at which temperatures can be measured utilizing percutaneously placed catheters as conduits for thermometers. However, further advances in the art, the science, and the technology of local heat therapy are likely to be forthcoming in the next few years from a diverse community of investigators and young companies who are following an interesting variety of approaches. Continued research and development in the spirit of constructive, rather than destructive, competition will certainly advance the field substantially--much to the benefit of patients. At present, however, clinical engineers should realize that hyperthermia therapy for cancer is still experimental. Despite the flurry of commercial activity, considerable caution should be exercised in the purchase and use of hyperthermia equipment.

Equipment and Supplies↗