Abstract:

Noninvasive or minimally invasive laser lipolysis has great potential to reduce obesity, but the absorption of near infrared laser by water may cause thermal damage of dermis. At present, there is no effective cooling method to protect normal skin tissue from thermal injury, which restricts the development of laser lipolysis. A novel multi-pulsed cryogen spray cooling for laser lipolysis was proposed to protect epidermis and dermis. Numerical simulation based on multi-layer uniform skin tissue model and Pennes biological heat transfer equation was conducted to investigate the cooling effect of continuous and multi-pulsed R134a cryogen spray cooling. It was found that continuous spray cannot meet the requirement of laser lipolysis both in temperature and skin depth. Under the same accumulative spray time, the cooling depth of multi-pulsed spray is greater than that of continuous spray. The lowest temperature at 1 mm below skin surface after multi-pulsed cryogen spray can reach to 11℃ with pulse width of 10 ms, interval time of 2500 ms, spray times of 10 and duty cycle of 0.004, and the simulation cooling depth achieves 5000 μm, which can satisfy the cooling depth requirement of laser lipolysis.

Key words: laser lipolysis, R134a, multi-pulsed cryogen spray cooling, numerical simulation, heat transfer, biomedical engineering

摘要：

无创激光溶脂发展潜力巨大，但水对近红外激光的吸收可能导致真皮热损伤。目前尚无有效的正常组织冷保护措施，制约了激光溶脂的发展。提出采用多脉冲喷雾冷却的方式对人体皮肤进行冷保护，建立皮肤组织多层均匀模型，结合Pennes生物传热方程数值模拟制冷剂R134a连续和脉冲式喷雾对皮肤深层组织的冷却效果。发现相同累计喷雾时间下多脉冲喷雾的冷却深度大于连续式喷雾，从冷却温度和冷却深度上更适合于激光溶脂的皮肤冷却。在单次喷雾时间10 ms、间隔时间2500 ms、喷雾次数10次、占空比0.004的条件下，冷却深度达到5000 μm，1 mm深度的皮肤组织喷雾中心温度最低能达到11℃，可以有效满足激光溶脂对皮肤冷却深度的要求。

关键词: 激光溶脂, R134a, 多脉冲喷雾冷却, 数值模拟, 传热, 生物医学工程