Mordon Serge R, Wassmer Benjamin, Reynaud Jean Pascal, Zemmouri Jaouad
INSERM U 703 - IFR 114, Lille University Hospital, 59037 Lille, France.
Biomed Eng Online. 2008 Feb 29;7:10. doi: 10.1186/1475-925X-7-10.
Liposuction continues to be one of the most popular procedures performed in cosmetic surgery. As the public's demand for body contouring continues, laser lipolysis has been proposed to improve results, minimize risk, optimize patient comfort, and reduce the recovery period. Mathematical modeling of laser lipolysis could provide a better understanding of the laser lipolysis process and could determine the optimal dosage as a function of fat volume to be removed.
STUDY DESIGN/MATERIALS AND METHODS: An Optical-Thermal-Damage Model was formulated using finite-element modeling software (Femlab 3.1, Comsol Inc). The general model simulated light distribution using the diffusion approximation of the transport theory, temperature rise using the bioheat equation and laser-induced injury using the Arrhenius damage model. Biological tissue was represented by two homogenous regions (dermis and fat layer) with a nonlinear air-tissue boundary condition including free convection. Video recordings were used to gain a better understanding of the back and forth movement of the cannula during laser lipolysis in order to consider them in our mathematical model. Infrared video recordings were also performed in order to compare the actual surface temperatures to our calculations. The reduction in fat volume was determined as a function of the total applied energy and subsequently compared to clinical data reported in the literature.
In patients, when using cooled tumescent anesthesia, 1064 nm Nd:YAG laser or 980 nm diode laser: (6 W, back and forth motion: 100 mm/s) give similar skin surface temperature (max: 41 degrees C). These measurements are in accordance with those obtained by mathematical modeling performed with a 1 mm cannula inserted inside the hypodermis layer at 0.8 cm below the surface. Similarly, the fat volume reduction observed in patients at 6-month follow up can be determined by mathematical modeling. This fat reduction depends on the applied energy, typically 5 cm3 for 3000 J. At last, skin retraction was observed in patients at 6-month follow up. This observation can be easily explained by mathematical modeling showing that the temperature increase inside the lower dermis is sufficient (48-50 degrees C) to induce skin tightening
Laser lipolysis can be described by a theoretical model. Fat volume reduction observed in patients is in accordance with model calculations. Due to heat diffusion, temperature elevation is also produced inside the lower reticular dermis. This interesting observation can explain remodeling of the collagenous tissue, with clinically evident skin tightening. In conclusion, while the heat generated by interstitial laser irradiation provides stimulate lipolysis of the fat cells, the collagen and elastin are also stimulated resulting in a tightening in the skin. This mathematical model should serve as a useful tool to simulate and better understand the mechanism of action of the laser lipolysis.
抽脂术仍是整形外科中最常见的手术之一。随着公众对身体塑形需求的持续增长，激光溶脂术被提出以改善效果、降低风险、优化患者舒适度并缩短恢复期。激光溶脂术的数学建模可以更好地理解激光溶脂过程，并能根据待去除的脂肪量确定最佳剂量。
研究设计/材料与方法：使用有限元建模软件（Femlab 3.1，Comsol公司）建立了光热损伤模型。通用模型使用传输理论的扩散近似来模拟光分布，使用生物热方程来模拟温度升高，并使用阿伦尼乌斯损伤模型来模拟激光诱导的损伤。生物组织由两个均匀区域（真皮和脂肪层）表示，具有包括自由对流的非线性空气 - 组织边界条件。使用视频记录来更好地理解激光溶脂过程中套管的来回运动，以便在数学模型中加以考虑。还进行了红外视频记录，以将实际表面温度与我们的计算结果进行比较。脂肪量的减少被确定为总施加能量的函数，并随后与文献中报道的临床数据进行比较。
在患者中，当使用冷却的肿胀麻醉时，1064 nm Nd:YAG激光或980 nm二极管激光：（6 W，来回运动速度：100 mm/s）产生相似的皮肤表面温度（最高：41摄氏度）。这些测量结果与在皮下层表面以下0.8 cm处插入1 mm套管进行数学建模得到的结果一致。同样，在患者6个月随访时观察到的脂肪量减少可以通过数学建模来确定。这种脂肪减少取决于施加的能量，通常3000 J可减少5 cm³。最后，在患者6个月随访时观察到皮肤回缩。通过数学建模很容易解释这一现象，即真皮下层内部的温度升高足以（48 - 50摄氏度）引起皮肤收紧。
激光溶脂术可以用理论模型来描述。患者中观察到的脂肪量减少与模型计算结果一致。由于热扩散，真皮网状下层内部也会产生温度升高。这一有趣的观察结果可以解释胶原组织的重塑，临床上表现为明显的皮肤收紧。总之，虽然间质激光照射产生的热量可刺激脂肪细胞的溶脂作用，但也会刺激胶原蛋白和弹性蛋白，并导致皮肤收紧。这个数学模型应作为一个有用的工具，用于模拟和更好地理解激光溶脂术的作用机制。
