Asthmatx Inc., Sunnyvale, CA 94089 USA.
Biomed Eng Online. 2010 Nov 27;9:81. doi: 10.1186/1475-925X-9-81.
Bronchial thermoplasty is a novel technique designed to reduce an airway's ability to contract by reducing the amount of airway smooth muscle through controlled heating of the airway wall. This method has been examined in animal models and as a treatment for asthma in human subjects. At the present time, there has been little research published about how radiofrequency (RF) energy and heat is transferred to the airways of the lung during bronchial thermoplasty procedures. In this manuscript we describe a computational, theoretical model of the delivery of RF energy to the airway wall.
An electro-thermal finite-element-analysis model was designed to simulate the delivery of temperature controlled RF energy to airway walls of the in vivo lung. The model includes predictions of heat generation due to RF joule heating and transfer of heat within an airway wall due to thermal conduction. To implement the model, we use known physical characteristics and dimensions of the airway and lung tissues. The model predictions were tested with measurements of temperature, impedance, energy, and power in an experimental canine model.
Model predictions of electrode temperature, voltage, and current, along with tissue impedance and delivered energy were compared to experiment measurements and were within ± 5% of experimental averages taken over 157 sample activations.The experimental results show remarkable agreement with the model predictions, and thus validate the use of this model to predict the heat generation and transfer within the airway wall following bronchial thermoplasty.
The model also demonstrated the importance of evaporation as a loss term that affected both electrical measurements and heat distribution. The model predictions showed excellent agreement with the empirical results, and thus support using the model to develop the next generation of devices for bronchial thermoplasty. Our results suggest that comparing model results to RF generator electrical measurements may be a useful tool in the early evaluation of a model.
支气管热成形术是一种通过控制气道壁的加热来减少气道平滑肌的数量，从而降低气道收缩能力的新型技术。该方法已在动物模型中进行了研究，并已在人类哮喘患者中进行了治疗。目前，关于支气管热成形术过程中射频（RF）能量和热量如何传递到肺气道的研究甚少。在本文中，我们描述了一种用于模拟气道壁射频能量传递的计算理论模型。
设计了一个电热有限元分析模型，以模拟在体肺气道壁受控 RF 能量的传递。该模型包括由于 RF 焦耳加热而产生的热量以及由于热传导而在气道壁内传递的热量。为了实现该模型，我们使用气道和肺组织的已知物理特性和尺寸。该模型的预测结果通过在实验犬模型中测量温度、阻抗、能量和功率进行了测试。
模型对电极温度、电压和电流的预测值，以及组织阻抗和传递的能量与实验测量值进行了比较，结果在 157 次激活的实验平均值的±5%以内。实验结果与模型预测值非常吻合，从而验证了该模型在预测支气管热成形术后气道壁内热产生和传递方面的应用。
该模型还表明，蒸发作为一个损失项，会影响电测量和热分布，这一点非常重要。模型预测值与经验结果非常吻合，因此支持使用该模型开发下一代支气管热成形术设备。我们的结果表明，将模型结果与 RF 发生器电测量值进行比较可能是早期评估模型的有用工具。
