Jia Wangcun, Svaasand Lars O, Nguyen Thang B, Nelson J Stuart
Beckman Laser Institute, University of California-Irvine, 1002 Health Sciences Road East, Irvine, CA 92612, USA.
Lasers Surg Med. 2007 Dec;39(10):776-81. doi: 10.1002/lsm.20582.
Cryogen spray cooling with tetrafluoroethane (R134a) has been used to enhance epidermal protection during dermatologic laser surgery. However, R134a has a very high global warming potential (GWP = 1300). Our objective was to evaluate the cooling effectiveness of an alternative cryogen with a much lower GWP, namely liquid carbon dioxide (CO(2), GWP = 1).
STUDY DESIGN/MATERIALS AND METHODS: A thin-film thermocouple deposited on an epoxy skin phantom was used to measure surface temperature (T(s)) variations induced by R134a or CO(2) sprays. The temperature distribution in the skin phantom was estimated using T(s) and Duhamel's method. Impact pressure and noise level of both cryogen sprays were measured with a dynamic sensor and sound meter, respectively. Consumption of both cryogens was also evaluated.
For R134a sprays, T(s) was kept almost constant after 15 milliseconds. For CO(2) sprays, T(s) decreased continuously during the entire spurt of 50 milliseconds. The minimum T(s) induced by the CO(2) sprays was lower than that induced by R134a when the spurt duration was longer than 35 milliseconds. Numerical simulation shows that CO(2) sprays were able to induce very similar temperature reductions in the skin phantom as compared to R134a sprays when the spurt duration and delay time were selected appropriately. R134a sprays induced an impact pressure of 3.6 kPa, as compared to 43.1 kPa for CO(2) sprays. The maximum noise level for R134a sprays was 109 dBA as compared to 135 dBA for the CO(2) sprays. The R134a consumption for a 50 milliseconds spurt is 67 mg as compared to 225 mg for a CO(2) spurt of the same duration.
CO(2) sprays are expected to have similar skin cooling efficacy as R134a sprays. Although the CO(2) consumption is higher than R134a, its contribution to global warming is still much less than R134a. The effects of varying spurt durations on in vivo human skin and the impact on cutaneous blood flow require further investigation.
在皮肤科激光手术中，用四氟乙烷（R134a）进行低温喷雾冷却可增强表皮保护。然而，R134a具有很高的全球变暖潜能值（GWP = 1300）。我们的目的是评估一种全球变暖潜能值低得多的替代制冷剂——液态二氧化碳（CO₂，GWP = 1）的冷却效果。
研究设计/材料与方法：使用沉积在环氧树脂皮肤模型上的薄膜热电偶来测量由R134a或CO₂喷雾引起的表面温度（T(s)）变化。利用T(s)和杜哈梅尔方法估算皮肤模型中的温度分布。分别用动态传感器和噪声计测量两种制冷剂喷雾的冲击压力和噪声水平。还评估了两种制冷剂的消耗量。
对于R134a喷雾，15毫秒后T(s)几乎保持恒定。对于CO₂喷雾，在整个50毫秒的喷射过程中T(s)持续下降。当喷射持续时间超过35毫秒时，CO₂喷雾引起的最低T(s)低于R134a引起的最低T(s)。数值模拟表明，当适当选择喷射持续时间和延迟时间时，与R134a喷雾相比，CO₂喷雾能够在皮肤模型中引起非常相似的温度降低。R134a喷雾引起的冲击压力为3.6 kPa，而CO₂喷雾为43.1 kPa。R134a喷雾的最大噪声水平为109 dBA，而CO₂喷雾为135 dBA。50毫秒喷射的R134a消耗量为67毫克，而相同持续时间的CO₂喷射为225毫克。
预计CO₂喷雾与R134a喷雾具有相似的皮肤冷却效果。虽然CO₂的消耗量高于R134a，但其对全球变暖的贡献仍远小于R134a。不同喷射持续时间对人体活体皮肤的影响以及对皮肤血流的影响需要进一步研究。
