University of Ottawa , Faculty of Health Sciences, Human and Environmental Physiology Research Unit, Ottawa, Canada.
J Occup Environ Hyg. 2012;9(4):269-79. doi: 10.1080/15459624.2012.666467.
Blood marker concentrations such as cortisol (COR) and interleukin (IL)-6 are commonly used to evaluate the physiological strain associated with work in the heat. It is unclear, however, if hot environments of an equivalent thermal stress, as defined by a similar wet bulb globe temperature (WBGT), result in similar response patterns. This study examined markers of neuroendocrine (COR) and immune (IL-6) responses, as well as the cardiovascular and thermal responses, relative to changes in body heat content measured by whole-body direct calorimetry during work in two different hot environments with equivalent WBGT. Eight males performed a 2-hr heavy intermittent exercise protocol (six 15-min bouts of cycling at a constant rate of metabolic heat production (360W) interspersed by 5-min rest periods) in Hot/Dry (46°C, 10% relative humidity [RH]) and Warm/Humid (33°C, 60% RH) conditions (WBGT ∼ 29°C). Whole-body evaporative and dry heat exchange, change in body heat content (ΔH(b)), rectal temperature (T(re)), and heart rate were measured continuously. Venous blood was obtained at rest (PRE) and the end of each exercise bout for the measurement of changes in plasma volume (PV), plasma protein (an estimate of plasma water changes), COR, and IL-6. Ratings of perceived exertion and thermal sensation were measured during the last minute of each exercise bout. No differences existed for ΔH(b), heart rate, T(re),%ΔPV, plasma protein concentration, perceptual strain (thermal sensation, perceived exertion), and COR between the Hot/Dry and Warm/Humid conditions. IL-6 exhibited an interaction effect (p = 0.041), such that greater increases were observed in the Hot/Dry (Δ = 1.61 pg·mL(-1)) compared with the Warm/Humid (Δ = 0.64 pg·mL(-1)) environment. These findings indicate that work performed in two different hot environments with equivalent WBGT resulted in similar levels of thermal, cardiovascular, and perceptual strain, which support the use of the WBGT stress index. However, the greater IL-6 response in the Hot/Dry requires further research to elucidate the effects of different hot environments and work intensities.
血液标志物浓度，如皮质醇（COR）和白细胞介素（IL）-6，通常用于评估与热环境相关的生理应激。然而，热环境是否会导致与类似湿球黑球温度（WBGT）定义的热应激相同的反应模式尚不清楚。本研究通过全身直接量热法测量全身热量含量的变化，比较了两种不同热环境（WBGT 约为 29°C）中相同热应激下神经内分泌（COR）和免疫（IL-6）反应以及心血管和热反应标志物。8 名男性在热干（46°C，10%相对湿度[RH]）和温湿（33°C，60%RH）条件下进行了 2 小时的重间歇性运动方案（6 次 15 分钟的自行车运动，恒定代谢热产生率（360W），间隔 5 分钟休息期）。全身蒸发和干热交换、体热含量变化（ΔH(b)）、直肠温度（T(re)）和心率连续测量。在休息（PRE）和每次运动结束时采集静脉血，用于测量血浆体积（PV）变化、血浆蛋白（血浆水变化的估计）、COR 和 IL-6 的变化。在每次运动的最后一分钟测量感觉用力和热感觉。在热干和温湿条件下，ΔH(b)、心率、T(re)、%ΔPV、血浆蛋白浓度、感知应变（热感觉、感觉用力）和 COR 无差异。IL-6 表现出交互作用（p = 0.041），在热干（Δ=1.61 pg·mL(-1))中观察到的增加大于温湿（Δ=0.64 pg·mL(-1))环境。这些发现表明，在具有相同 WBGT 的两个不同热环境中进行的工作导致了相似水平的热、心血管和感知应激，这支持了 WBGT 应激指数的使用。然而，在热干环境中更大的 IL-6 反应需要进一步研究，以阐明不同热环境和工作强度的影响。
