Esophagus histological analysis after hyperthermia-induced injury: implications for cardiac ablation.

PURPOSE: To evaluate and numerically score histological alterations observed in the acute phase in the esophagus after being exposed to a hyperthermic dosage and subsequently to correlate the scores obtained with the hyperthermic treatment parameters (i.e. temperature (T) and time (t)). MATERIAL AND METHODS: Esophagus samples obtained from New Zealand white rabbits were immersed in a temperature-controlled saline bath at 40, 50, 60 and 70 degrees C for 30, 60 and 90 s. Samples were then processed for histological analysis (Masson Trichrome technique), and evaluated by searching for objective heat-damage signs. A numerical value was assigned to each sample for each finding. RESULTS: In general, all the layers were affected by the treatment, however, the greatest alterations were found in the epithelium and deeper muscular layers (circular and longitudinal). We found no damage (i.e. no differences to control) in all of the samples treated at 40 degrees C, and severe damage in treatments at 60 and 70 degrees C, regardless of exposure time. On the other hand, samples treated at 50 degrees C did show different results related to time: no damage for 30 s, light damage for 60 s, and moderate damage for 90 s. We assigned a score value to each hyperthermic dosage, and obtained the fitted equation based on a logarithmic transformation of the Arrhenius equation: Score = 130.7 - 40,851/(T + 273) + log t, (R(2) = 0.9326, P < 0.0001). CONCLUSIONS: Hyperthermic treatment mainly affects the epithelium and deeper muscular layers. The results suggest a damage threshold of 50 degrees C for treatments of 30-90 s. The proposed scoring system provides a good fit with the hyperthermic parameters.

Research and development of a new RF-assisted device for bloodless rapid transection of the liver: computational modeling and in vivo experiments.

BACKGROUND: Efficient and safe transection of biological tissue in liver surgery is strongly dependent on the ability to address both parenchymal division and hemostasis simultaneously. In addition to the conventional clamp crushing or finger fracture methods other techniques based on radiofrequency (RF) currents have been extensively employed to reduce intraoperative blood loss. In this paper we present our broad research plan for a new RF-assisted device for bloodless, rapid resection of the liver. METHODS: Our research plan includes computer modeling and in vivo studies. Computer modeling was based on the Finite Element Method (FEM) and allowed us to estimate the distribution of electrical power deposited in the tissue, along with assessing the effect of the characteristics of the device on the temperature profiles. Studies based on in vivo pig liver models provided a comparison of the performance of the new device with other techniques (saline-linked technology) currently employed in clinical practice. Finally, the plan includes a pilot clinical trial, in which both the new device and the accessory equipment are seen to comply with all safety requirements. RESULTS: The FEM results showed a high electrical gradient around the tip of the blade, responsible for the maximal increase of temperature at that point, where temperature reached 100 degrees C in only 3.85 s. Other hot points with lower temperatures were located at the proximal edge of the device. Additional simulations with an electrically insulated blade produced more uniform and larger lesions (assessed as the 55 degrees C isotherm) than the electrically conducting blade. The in vivo study, in turn, showed greater transection speed (3 +/- 0 and 3 +/- 1 cm2/min for the new device in the open and laparoscopic approaches respectively) and also lower blood loss (70 +/- 74 and 26 +/- 34 mL) during transection of the liver, as compared to saline-linked technology (2 +/- 1 cm2/min with P = 0.002, and 527 +/- 273 mL with P = 0.001). CONCLUSION: A new RF-assisted device for bloodless, rapid liver resection was designed, built and tested. The results demonstrate the potential advantages of this device over others currently employed.

Assessment of hyperbolic heat transfer equation in theoretical modeling for radiofrequency heating techniques.

Theoretical modeling is a technique widely used to study the electrical-thermal performance of different surgical procedures based on tissue heating by use of radiofrequency (RF) currents. Most models employ a parabolic heat transfer equation (PHTE) based on Fourier's theory, which assumes an infinite propagation speed of thermal energy. We recently proposed a one-dimensional model in which the electrical-thermal coupled problem was analytically solved by using a hyperbolic heat transfer equation (HHTE), i.e. by considering a non zero thermal relaxation time. In this study, we particularized this solution to three typical examples of RF heating of biological tissues: heating of the cornea for refractive surgery, cardiac ablation for eliminating arrhythmias, and hepatic ablation for destroying tumors. A comparison was made of the PHTE and HHTE solutions. The differences between their temperature profiles were found to be higher for lower times and shorter distances from the electrode surface. Our results therefore suggest that HHTE should be considered for RF heating of the cornea (which requires very small electrodes and a heating time of 0.6 s), and for rapid ablations in cardiac tissue (less than 30 s).

Formation of cartilage in vivo with immobilized autologous rabbit auricular cultured chondrocytes in collagen matrices.

BACKGROUND: The availability of generated cartilage de novo is one of the needs of reconstructive surgery. In this study, the authors constructed a matrix formed by autologous immobilized chondrocytes using collagen gel as a scaffold. Furthermore, the ability of these matrices to engraft and generate new cartilage was examined. METHODS: Biopsy specimens of elastic cartilage were surgically obtained from the ears of eight New Zealand White rabbits. After collagenase II digestion of cartilage, chondrocytes were isolated and propagated in culture medium. Chondrocytes were immobilized into bovine collagen lattices and implanted, replacing pieces of removed native cartilage. Five weeks after implantation, the rabbits were killed and the ears were examined macroscopically and analyzed by means of histochemical methods. RESULTS: The results show the formation of new cartilage from implanted lattices with chondrocytes. Gross analysis of the ears shows similarities in appearance, consistency, texture, and histology between native and new cartilage. Fluorescence of the nucleus from bisbenzimide-labeled chondrocytes was detected in newly formed tissue, pointing out its in vitro culture origin. No signs of an inflammatory reaction attributable to implants were found in either the control or the chondrocyte lattices. CONCLUSION: The authors suggest that this approach is of value for future clinical use.