Thermal Loading and Subsequent Adaptation in Response to Simulated Solar Radiant Heat Exposure and Influences of Sunscreen Use on Thermoregulation

• Main Authors: Shih-Yin Chang, 張詩吟
• Other Authors: 陳振菶
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/41336909250410665460

碩士 === 中國醫藥大學 === 職業安全與衛生學系碩士班 === 101 === Solar radiant heat is amongst the most significant meteorological factors affecting metabolic heat load when people remain outdoors. In recent years, the frequent appearance of high ambient temperature in association with global climate change presents an increasing challenge to the physiological capacity of heat load and to that of thermoregulation. Among the affected, those who live and/or work in the urban areas are of particular concern—the thermal transient developed between the entrance of an air-conditioned building and the ambient environment often increases the thermal stress imposed on human body when people enter/leave the building. To prevent injury from over-exposure to solar radiation, the sunscreens are commonly adopted as a strategy of self protection. This study aimed to, by means of a series of experiments conducted in dual microclimatic chambers simulating different combinations of solar radiation, environmental temperature, and non-climatic factors including the use of sunscreens and the sex, investigate the physiological/psychological responses of human body to and the balance with thermal stress when the body is confronted with a thermal environment of either a steady state or a transient state due to a drop in environmental temperature following loss of solar radiant heat. The physiological indicators selected in the study were those of body core and of skin physiology involved in the dissipation of metabolic heat. The core indicators consisted of metabolic rate and core temperature, while the dermal physiological indicators included skin capillary blood flow, skin moisture, transepidermal water loss, and skin temperature. The subjective thermal sensation and thermal comfort were also gauged, using a standardized questionnaire developed by the American Society of Heating, Refrigerating, and Air-conditioning Engineers Standard 55. The study findings were analyzed to interpret the progress of heat acclimation (thermal adaptation), the time course of physiological responses as driven by thermoregulatory requirement, the relationship of dose (thermal exposure) and response for each individual event of thermoregulation, and the roles of the radiant heat as well as of using sunscreens in the aforementioned relationships. As the results show, the metabolic heat load and thermoregulation occurring in response to radiant heat exposure was greater and required a longer period to acclimatize compared to those resulting from exposure to the air temperature. These physiological changes in feedback to thermal pressure were particularly pronounced for males, as manifested in the alteration of skin moisture and transepidermal water loss, when not using sunscreens and thermally challenged at a globe temperature of 32oC. Upon entering the thermal transient developing from the sudden loss of radiant heat, the skin capillary blood flow and skin temperature required a longer period to re-equilibrate with the ambient environment compared to the requirements observed when the transient arose entirely as a result of air temperature step, suggesting a potential residual effect of radiant heat in delaying the thermoregulation occurring in response to the transient thermal environment. Using sunscreens reduced the burning sensation on the skin following exposure to solar radiation. In addition, the cooling effect of sunscreens significantly alleviated the metabolic heat load and thermoregulation resulting from exposure to radiant heat and from exposure to the thermal transient developing from a disappearance of solar raidation. The thermal comfort of females was more associated with the thermal sensation compare to that of males. These findings provide insights on how the current indices of thermal stress may be improved and promote a better understanding on the effects of using sunscreens in hot-and-humid areas such as Taiwan, protecting people from being thermally stressed from being exposed to solar radiation, particularly in hot summer days.