Background: Tracheal cartilage deformities due to trauma, prolonged endotracheal intubation or infection are difficult to correct. Current treatment options such as dilation, laser ablation, stent placement, and segmental resection are only temporary or carry significant risks. The objectives of this project were to design and test a laser activated endotracheal stent system that can actively modify the geometry of tracheal cartilage, leading to permanent retention of a new and desirable tracheal geometry.
Methods: Ex vivo rabbit tracheal cartilage (simulating human neonate trachea) were irradiated with an Er: Glass laser, (λ= 1.54um, 0.5W-2.5W, 1 sec to 5 sec). Shape change and gross thermal injury were assessed visually to determine the best laser power parameters for reshaping. A rigid endoscopic telescope and hollow bronchoscope were used to record endoscopic images. The stent was constructed from nitinol wire, shaped into a zigzag configuration. An ex vivo testing apparatus was also constructed.
Results: The best laser power parameter to produce shape change was 1 W for 6-7 seconds. At this setting, there was significant shape change with only minimal thermal injury to the tracheal mucosa, as assessed by visual inspection. The bronchoscopy system functioned adequately during testing in the ex vivo testing apparatus.
Conclusion: We have successfully designed instrumentation and created the capability to endoscopically reshape tracheal cartilage in an ex vivo rabbit model. The results obtained in ex vivo tracheal cartilage indicated that reshaping using Er: Glass laser can be accomplished.
Identification of proliferating chondrocytes along the periphery of laser ablation sites in irradiated cartilage has led to interest in studying the use of laser heating alone to stimulate chondrocyte growth. However, excessive heat produced by a laser can also cause chondrocyte necrosis and apoptosis. The objective of this study was to evaluate acute injury to cartilage following irradiation by an Nd:YAG (λ=1.32μm) laser in intact ex-vivo tissue specimens. Rabbit nasal septal cartilage was irradiated using an Nd:YAG laser using pulse durations (4, 6, and 8 seconds) and power (4, 6, and 8 watts) settings previously determined to produce cell division. Immediately after laser irradiation, the extent of thermal injury to the cartilage samples was evaluated using a Live/Dead cell viability assay combined with confocal microscopy. Thermal injury was assessed with respect to distribution of live and dead cells surrounding the laser spot where regeneration was previously observed. The cell viability assay identified necrotic tissue within and immediately around the laser spot. Moving away from the center of the laser spot, a mixed population of necrotic and live chondrocytes was observed. As expected, a correlation between irradiation time, power and degree of injury was found. The results of this experiment will be used to determine the threshold required to produce regeneration while minimizing thermal injury.
Stenotic, collapsed, and flow-restricted tracheal airways may result from blunt trauma, chronic infection, and the prolonged endotracheal intubation. This pilot investigation characterizes the degree of shape change produced by Ho:YAG laser (λ=2.12 μm) irradiation of rabbit and pig trachea tissue as a function of laser dosimetry and application protocol. Force displacement curves were generated using fresh lagomorph and porcine tracheal cartilage rings secured in a modified single beam cantilever geometry. These specimens were then irradiated for varying amounts of time and power with the objective of straightening these curved specimens. The degree of shape change was documented photographically. Force and surface temperature were monitored. Confocal microscopy was then used in combination a vital staine (“live-dead assay”) to determine the level of viability of straightened cartilage for selected exposure time-power pairs. Laser Cartilage Reshaping of the trachea may provide a new method to treat severe tracheal injuries without the need for classic open surgical techniques. This pilot investigation is the first step toward demonstrating the feasibility of this technique. Long-term, the design of stents combined with laser irradiation may provide a means to alter tracheal shape.
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