Objective: To investigate the long-term in vivo effect of laser dosimetry on rabbit septal cartilage integrity, viability, and mechanical behavior.Methods: Nasal septal cartilage specimens ( control and irradiated pairs) were harvested from 18 rabbits. Specimens were mechanically deformed and irradiated with an Nd:YAG laser across a broad dosimetry range (4-8 W and 6-16 seconds). Treated specimens and controls were autologously implanted into a subperichondrial auricular pocket. Specimens were harvested an average +/- SD of 208 +/- 35 days later. Tissue integrity, histology, chondrocyte viability, and mechanical property evaluations were performed. Tissue damage results were compared with Monte Carlo simulation models.Results: All laser-irradiated specimens demonstrated variable tissue resorption and calcification, which increased with increased dosimetry. Elastic moduli of the specimens were significantly either lower or higher than controls (all P <.05). Viability assays illustrated a total loss of viable chondrocytes within the laser-irradiated zones in all treated specimens. Histologic examination confirmed these findings. Experimental results were consistent with damage profiles determined using numerical simulations.Conclusion: The loss of structural integrity and chondrocyte viability observed across a broad dosimetry range underscores the importance of spatially selective heating methods prior to initiating application in human subjects.

In this study, laser reshaping of porcine septal cartilage was performed using an Nd:YAG laser (/spl lambda/=1.32 /spl mu/m), while changes in acoustic waves were observed, in an attempt to develop technique to monitor the reshaping process. Concurrent measurements of strain (during tensile compression and tension, as well as flexure), temperature, and a 5-MHz ultrasonic signal were recorded during laser irradiation (/spl lambda/=1.32 /spl mu/m, 4 W, 13 s). The sample was set up in a water bath to enhance acoustic coupling. From the ultrasonic signal, both time of flight (TOF) and signal amplitude as reflected from the back wall of the cartilage were extracted and correlated with temperature and strain measurements. The onset of stress relaxation of the cartilage generally occurred between 50/spl deg/C and 60/spl deg/C. While TOF measurements indicated a generally constant increase in the speed of sound of the cartilage during the irradiation period, the amplitude of the reflected acoustic signal correlated directly with the stress relaxation of the cartilage. At the point of stress relaxation, the amplitude of the acoustic signal consistently attenuated to roughly 50% of its original magnitude.

Background and Objectives: The process of altering the shape of cartilage using heat has been referred to as thermoforming, and presents certain clinical benefits in reconstructive surgical procedures within the head and neck. Thermoforming allows cartilage in the upper airway and face to be reshaped without the use of classic surgical maneuvers such as carving, morselizing, or suturing. The goal of this study was to determine the dependence of cartilage shape change on both temperature and laser dosimetry using two thermoforming methods: saline bath immersion and laser irradiation.Study Design/Materials and Methods: Ex-vivo rabbit and porcine nasal septal cartilages were mechanically deformed and reshaped using the two thermoforming methods. With saline bath immersion using rabbit cartilage, each specimen was deformed by securing it to a small copper tube (outer diameter 8 mm) using dental bands. For porcine cartilage immersed in a saline bath, each sample was mechanically deformed between two pieces of wire mesh attached to a semicircular acrylic block. With both porcine and rabbit cartilage, the specimen and apparatus were then immersed in a hot saline bath for time intervals varying from 20 and 320 seconds and at constant temperatures between 62 and 74 degrees C. In laser reshaping, the cartilage specimens were mechanically deformed on a jig and consecutively irradiated with an Nd:YAG laser (lambda = 1.32 mu m) in several spots for 6-16 seconds and irradiances of 10.2-40.7 W/cm(2) per spot. After either saline bath heating or irradiation, cartilage specimens were immersed in room temperature saline for 15 minutes, then upon removal from the jig the length between the ends of each specimen was measured in order to calculate the resulting bend angle.Results: The transition zone for cartilage reshaping was defined as where a significant increase in bend angle was observed between consecutive times of immersion/ irradiation at the same temperature/irradiance. For the saline bath experiments, the transition zone was observed between 59-68 degrees C and 62-68 degrees C for porcine and rabbit cartilage, respectively. Similar transition zones occurred with laser irradiation below irradiances of 20.4 W/cm(2) for both porcine and rabbit cartilage. In addition, the dosimetry pairs in the transition zones produce peak temperatures below the thresholds determined from the saline bath immersion studies.Conclusions: The critical transition temperature region was determined by the sharp increase in bend angle at consecutive times of immersion at the same temperature. This range was determined to be 59-68 degrees C and 62-68 degrees C for porcine and rabbit cartilage, respectively. Similar transition zones for dosimetry occurred below 20.4 W/cm(2) during cartilage irradiation in both species.

Objectives: This study describes the process of tissue electroforming and how shape changes in cartilage can be produced by the application of direct current (DC). The dependence of shape change on voltage and application time is explored. Study Design: Basic investigation using ex vivo porcine septal cartilage grafts and electromechanical cartilage deformation focused on development of a new surgical technique. Methods: Uniform flat porcine nasal septal cartilage specimens were mechanically deformed between two semicircular aluminum electrodes. DC current was applied to establish charge separation and electrical streaming potential. Voltage (0–3.5 V) and application time (0–5 minutes) were varied. Shape change was measured, and shape retention was calculated using analytic representation. The effect of the direction of applied current on shape change was evaluated by switching the polarities of electrodes and using parameters of 0 to 5.5 V and 5 minutes. Temperature during reshaping was monitored with a thermocouple, and surface features were evaluated using light microscopy. Results: Reshaped specimen demonstrated mechanical stability similar to native cartilage tissue. Shape retention strongly correlated with increasing voltage and application time. Only a small current (<0.1 A) through the tissue was measured. Temperature change was less than 2°C during electroforming, suggesting that electroforming likely results from some nonthermal mechanisms. Surface features indicated that electrodeposition may occur depending on electrode material and magnitude of the applied voltage. Conclusions: These findings demonstrate that cartilage can be reshaped through the process we have described as “electroforming” by generating intrinsic differences in charge separation with negligible heat production.

The optimization of electrosurgical procedures requires a rigorous understanding of the electrical, thermal, mechanical and chemical events accompanying the ablation process. Modeling is indispensable and is needed to further advance this technology. This study introduces a novel tissue electrosurgical ablation model based on interstitial vapor nucleation and expansion. The model describes interstitial vapor nucleation and bubble growth using a homogeneous nucleation theory and Rayleigh equation. Electrosurgical incisions were made on beef muscle while equivalent electrical circuit parameters were monitored as a function of power settings and scalpel geometries. Thermal damage was measured using light and polarization microscopy. Results were compared with predictions produced by a numerical simulation, which modeled the tissue and electrosurgical scalpel interaction as a function of power settings and scalpel geometry.

Dielectric properties of cartilage have received comparatively little interest and few studies have examined the effect of the applying electric currents to mechanically deformed cartilages. The objective of this study was to determine the dependence of shape change on electrode composition during a process we have described as “electroforming.” Porcine nasal septal cartilage specimens (16 x 5 x 2 mm) were mechanically deformed between two semicircular electrodes. Direct current (DC) current was applied to establish charge separation and electrical streaming potential. Voltage (<10 V) and application time (0-6 minutes) were varied, and shape change was measured using analytic representation. Surface features were evaluated using light microscopy. While shape change strongly correlated with voltage and time for all electrode materials, the voltage and application time that produced maximum shape change (curvature of the jig, ~ 160°) varied for each material. Aluminum is more effective for electroforming than gold as it yields the lowest set of plateau values. Surface features indicated that electrodeposition occurs depending upon the voltage and the standard reduction potential of electrodes. The results from this study provide insight into the dependence of shape change on the external electrical environment of cartilage and how optimal shape change can be produced with nominal electrodeposition.

We developed a 3D thermo-electrical model of RF tissue cutting that takes into account variations in electrical and thermal properties with temperature and water content, dynamics of water evaporation and thermal and electrical processes at the tissue-scalpel interface. The model predicts measurable parameters of the electric circuit (tissue impedance, ESU output RMS voltage and current) and tissue cutting rate. Results of numerical simulations suggest that high circuit impedance during electrosurgical cutting can result not only from tissue dehydration but from the configuration of the electric field as well. It appears that the area of tissue-scalpel electric contact is significantly smaller than the area of the scalpel itself but is large enough to rule out electric sparks as a major mechanism of electrosurgical cutting.

We investigated anomalies in the reflectance change of retinal lesions resulting from laser photocoagulation, These anomalies deviate from the predicted pattern and could cause misleading postoperative assessment of lesion depth and problems with proposed automated lesion control algorithms. We found that for certain irradiation parameters which produce super-threshold lesions, lesions exhibiting annular reflectance patterns are induced in an albumen eye phantom, The correlation between central reflectance and actual lesion depth thus becomes invalid for these anomalous lesions, Evidence of anomalous lesions in vivo was also found. Assumptions regarding retinal lesion formation must consider annular reflectance patterns, These patterns are produced by vaporization in the albumen eye phantom; vaporization may also play a role in anomalous retinal lesions along with the well known effect of minor retinal hemorrhage.