Department of Physical Therapy, Loma Linda University, Loma Linda, CA 92350, USA.
Med Sci Monit. 2011 Jan;17(1):CR1-8. doi: 10.12659/msm.881315.
When heat is applied to the skin, it is dissipated due to conductive heat flow in the tissue and the blood. While heat flow has been studied after applying a single heat exposure, the physiology of repeated exposures to local heat has not been well investigated.
MATERIAL/METHODS: Twenty male and female subjects in the age range of 20-65 years old participated in a series of experiments during which a thermode was placed on their leg above the quadriceps muscle for 20 minutes, and on 3 sequential days, to see the effect of repeated local heat on skin blood flow, skin temperature, and on caloric transfer from a thermode used to raise skin temperature.
The results of the experiment showed that, for young subjects, to raise skin temperature to 40 degrees C required more than double the calories required in older subjects. Further, in the younger subjects, the blood flow response in the first 20 minutes of heat exposure was over 30% higher than that seen in the older subjects. However, on the 2nd and 3rd day, the blood flow response of the younger subjects, was not significantly different between day 2 and 3, but was significantly less than day 1. There was no statistical difference in the blood flow response between day 1, 2 and 3 in the older subjects. In the younger subjects, in the 2 and 3rd day, the number of calories needed to warm the skin was also significantly less than that seen in the first day.
In younger subjects but not older subjects, there appears to be some degree of acclimatization with an enhanced blood flow response in the first day that was protective to the skin which was not seen in repeated heat exposure.
当热量施加于皮肤时，由于组织和血液中的传导热流，热量会被散发。虽然已经研究了单次热暴露后热量的流动情况，但对局部热的重复暴露的生理学尚未得到很好的研究。
材料/方法：20 名年龄在 20-65 岁之间的男性和女性受试者参加了一系列实验，在这些实验中，一个热模放置在他们的腿部上方的四头肌上 20 分钟，在连续 3 天内，观察重复局部热对皮肤血流、皮肤温度以及用于升高皮肤温度的热模的热量传递的影响。
实验结果表明，对于年轻受试者，要将皮肤温度升高到 40 度，需要的热量比老年受试者多一倍以上。此外，在年轻受试者中，在热暴露的前 20 分钟内，血流反应比老年受试者高 30%以上。然而，在第 2 天和第 3 天，年轻受试者的血流反应没有显著差异，但明显低于第 1 天。在第 1 天、第 2 天和第 3 天之间，老年受试者的血流反应没有统计学差异。在年轻受试者中，在第 2 天和第 3 天，加热皮肤所需的热量也明显少于第 1 天。
在年轻受试者中，但在老年受试者中没有，似乎存在一定程度的适应性，第 1 天的血流反应增强，对皮肤具有保护作用，而在重复热暴露中则没有观察到这种作用。
