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.

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.

Reliability assessment of a cooled intraesophageal balloon to prevent thermal injury during RF cardiac ablation: an agar phantom study.

UNLABELLED: Cooled Balloon Prevents Thermal Injury During RF Ablation. INTRODUCTION: The use of a cooled intraesophageal balloon has recently been proposed to minimize the risk of thermal injury in the esophagus during radiofrequency (RF) ablation of the left atrium. However, the capacity of this device to adequately protect the esophagus under different procedural and anatomical conditions remains unknown. METHODS AND RESULTS: An agar phantom-based model was built that provided temperature readings not only on the cooled balloon (T(b)) but also at a hypothetical point between the esophageal lumen and myocardium at a distance of 2 mm (T(2-mm)). The RF ablations were conducted considering two anatomical factors (total distance between the electrode and balloon and flow rate around the electrode) and two procedural factors (angle and pressure between the electrode and agar surface). The results show that most of the parameters studied have no significant influence on the temperature measured on the cooled balloon (T(b)), the exception being a variation in the flow rate, which was found to influence the temperature. On the other hand, T(2-mm) was affected to a great extent by all the factors considered, the smallest influence being that of the contact pressure. The results also suggest that when an intraesophageal balloon is employed, the applied power is not a good predictor either of the temperature on the balloon or of the temperature measured at a distance 2 mm away. CONCLUSION: The results suggest that a cooled intraesophageal balloon provides effective thermal protection of the esophageal lumen. However, under certain circumstances, the temperature reached at a distance 2 mm away could possibly put at risk the integrity of the inner layers of the esophagus.

A cooled water-irrigated intraesophageal balloon to prevent thermal injury during cardiac ablation: experimental study based on an agar phantom.

A great deal of current research is directed to finding a way to minimize thermal injury in the esophagus during radiofrequency catheter ablation of the atrium. A recent clinical study employing a cooling intraesophageal balloon reported a reduction of the temperature in the esophageal lumen. However, it could not be determined whether the deeper muscular layer of the esophagus was cooled enough to prevent injury. We built a model based on an agar phantom in order to experimentally study the thermal behavior of this balloon by measuring the temperature not only on the balloon, but also at a hypothetical point between the esophageal lumen and myocardium (2 mm distant). Controlled temperature (55 degrees C) ablations were conducted for 120 s. The results showed that (1) the cooling balloon provides a reduction in the final temperature reached, both on the balloon surface and at a distance of 2 mm; (2) coolant temperature has a significant effect on the temperature measured at 2 mm from the esophageal lumen (it has a less effect on the temperature measured on the balloon surface) and (3) the pre-cooling period has a significant effect on the temperature measured on the balloon surface (the effect on the temperature measured 2 mm away is small). The results were in good agreement with those obtained in a previous clinical study. The study suggests that the cooling balloon gives thermal protection to the esophagus when a minimum pre-cooling period of 2 min is programmed at a coolant temperature of 5 degrees C or less.

Esophageal temperature monitoring during radiofrequency catheter ablation: experimental study based on an agar phantom model.

Although previous studies have established the feasibility of monitoring esophageal temperature during radiofrequency cardiac ablation using an esophageal temperature probe (ETP), some questions remain regarding its efficacy. The aims of this study were to study the effect of the location of the ETP on the temperature reached, and to test the characteristics of ETP as used in clinical practice. We constructed an agar phantom to model the thermal and electrical characteristics of the biological tissues (left atrium, esophagus and connective tissue). The ETP was positioned at 6.5 mm from an ablation electrode and at distances of 0, 5, 10, 15, 20 mm from the catheter axis. A thermocouple was located on the probe to measure the actual temperature of the external esophageal layer during the ablations (55 degrees C, 60 s). The mean temperatures reached at the thermocouple were significantly higher than those measured by the ETP (48.3 +/- 1.9 degrees C versus 39.6 +/- 1.1 degrees C). The temperature values measured with the ETP were significantly lower when the probe was located further from the catheter axis (up to 2.5 degrees C lower when the distance from the probe-catheter axis was 2 cm). The dynamic calibration of the ETP showed a mean value for the time constant of 8 s. In conclusion, the temperature measured by the ETP always underestimates the temperature reached in the thermocouple. This fact can be explained by the distance gap between the thermocouple and probe and by the dynamic response of the ETP. The longer the distance between the ETP and catheter axis, the higher is the temperature difference.

Black-box modeling to estimate tissue temperature during radiofrequency catheter cardiac ablation: Feasibility study on an agar phantom model.

The aim of this work was to study linear deterministic models to predict tissue temperature during radiofrequency cardiac ablation (RFCA) by measuring magnitudes such as electrode temperature, power and impedance between active and dispersive electrodes. The concept involves autoregressive models with exogenous input (ARX), which is a particular case of the autoregressive moving average model with exogenous input (ARMAX). The values of the mode parameters were determined from a least-squares fit of experimental data. The data were obtained from radiofrequency ablations conducted on agar models with different contact pressure conditions between electrode and agar (0 and 20 g) and different flow rates around the electrode (1, 1.5 and 2 L min(-1)). Half of all the ablations were chosen randomly to be used for identification (i.e. determination of model parameters) and the other half were used for model validation. The results suggest that (1) a linear model can be developed to predict tissue temperature at a depth of 4.5 mm during RF cardiac ablation by using the variables applied power, impedance and electrode temperature; (2) the best model provides a reasonably accurate estimate of tissue temperature with a 60% probability of achieving average errors better than 5 degrees C; (3) substantial errors (larger than 15 degrees C) were found only in 6.6% of cases and were associated with abnormal experiments (e.g. those involving the displacement of the ablation electrode) and (4) the impact of measuring impedance on the overall estimate is negligible (around 1 degrees C).

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.

Flow cytometric kinetic assay of the activity of Na+/H+ antiporter in mammalian cells.

BACKGROUND: The Na(+)/H(+) exchanger (NHE) of mammalian cells is an integral membrane protein that extrudes H(+) ion in exchange for extracellular Na(+) and plays a crucial role in the regulation of intracellular pH (pHi). Thus, when pHi is lowered, NHE extrudes protons at a rate depending of pHi that can be expressed as pH units/s. METHODS: To abolish the activity of other cellular pH-restoring systems, cells were incubated in bicarbonate-free Dulbecco's modified Eagle's medium buffered with HEPES. Flow cytometry was used to determine pHi with 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein acetoxymethyl ester or 5-(and-6)-carboxy SNARF-1 acetoxymethyl ester acetate, and the appropriate fluorescence ratios were measured. The calibration of fluorescence ratios versus pHi was established by using ionophore nigericin. The activity of NHE was calculated by a kinetic flow cytometric assay as the slope at time 0 of the best-fit curve of pHi recovery versus time after intracellular acidification with a pulse of exogenous sodium propionate. RESULTS: The kinetic method allowed determination of the pHi-dependent activity of NHE in cell lines and primary cell cultures. NHE activity values were demonstrated to be up to 0.016 pH units/s within the pHi range of 7.3 to 6.3. The inhibition of NHE activity by the specific inhibitor ethyl isopropyl amiloride was easily detected by this method. CONCLUSIONS: The assay conditions can be used to relate variations in pHi with the activity of NHE and provide a standardized method to compare between different cells, inhibitors, models of ischemia by acidification, and other relevant experimental or clinical situations.