Kenney W Larry
The Pennsylvania State University, University Park, Pennsylvania.
J Appl Physiol (1985). 2020 Aug 1;129(2):263-271. doi: 10.1152/japplphysiol.00345.2020. Epub 2020 Jun 18.
Critical environmental limits are those above which human heat balance cannot be maintained for a given metabolic heat production. These limits, and associated critical evaporative coefficients (') that can be used to model responses in hot environments, have not been determined for older subjects. The present paper graphically characterizes psychrometric limits and environmental isotherms and derives ' values for a group of unacclimated older ( = 10; age 62 - 80 yr) women exercising at 30% V̇o. Uniquely, we compare and contrast these data with published data from young, unacclimated and young, heat-acclimated women tested across a four-decade span using the same protocol in the same environmental chamber. These loci are presented graphically on a psychrometric chart (with confidence intervals). Isotherms constructed from biophysical modeling and sweating capacity closely fit the data but underestimated empirically derived data points in hotter, drier environments. Compared with the young (age 19-26 yr) women previously tested, the older women had significantly constrained (lower) critical environmental limits, in part due to lower sweating rates. Age-specific values of the critical evaporative coefficient, ', derived by partial calorimetry in the more humid environments (in which skin wettedness approached 1), were likewise lower for the older women (overall mean = 9.1 W·m·mmHg; < 0.05) vs. unacclimated (15.4 W·m·mmHg) and acclimated (17.0 W·m·mmHg) young women. Constrained psychrometric limits and lower critical evaporative coefficients lend biophysical clarity to decreased abilities of older women for prolonged exercise in the heat. This study is the first to describe, graphically and quantitatively, critical environmental limits for women between the ages of 62 and 80 yr based on the biophysics of heat exchange. These psychrometric limit lines define combinations of ambient temperature and humidity above which human heat balance cannot be maintained for a given metabolic heat production. These limits, and associated critical evaporative coefficients ('), can be used to model low- to moderate-intensity exercise responses in hot environments and have directly translatable data that can be used for evidence-based policy decisions, to prepare for impending heat events, and for implementation of other safety interventions.
关键环境限值是指在给定代谢产热情况下，人体热平衡无法维持的限值。这些限值以及可用于模拟热环境中反应的相关关键蒸发系数（'），尚未针对老年受试者确定。本文以图形方式描述了湿度计限值和环境等温线，并得出了一组未适应环境的老年女性（n = 10；年龄62 - 80岁）在以30% V̇o₂运动时的'值。独特的是，我们将这些数据与在同一环境舱中使用相同方案在四十年间测试的年轻、未适应环境和年轻、热适应女性的已发表数据进行了比较和对比。这些位点在湿度计图表上以图形方式呈现（并带有置信区间）。由生物物理模型和出汗能力构建的等温线与数据拟合良好，但在更热、更干燥的环境中低估了经验得出的数据点。与之前测试的年轻女性（年龄19 - 26岁）相比，老年女性的关键环境限值显著受限（更低），部分原因是出汗率较低。在湿度较高的环境中（皮肤湿润度接近1）通过部分量热法得出的老年女性关键蒸发系数'的年龄特异性值同样较低（总体平均值 = 9.1 W·m⁻²·mmHg⁻¹；P < 0.05），而未适应环境的年轻女性为（15.4 W·m⁻²·mmHg⁻¹），热适应的年轻女性为（17.0 W·m⁻²·mmHg⁻¹）。受限的湿度计限值和较低的关键蒸发系数从生物物理角度明确了老年女性在热环境中进行长时间运动能力下降的情况。本研究首次基于热交换生物物理学，以图形和定量方式描述了62至80岁女性的关键环境限值。这些湿度计限值线定义了环境温度和湿度的组合，在该组合之上，对于给定的代谢产热，人体热平衡无法维持。这些限值以及相关的关键蒸发系数（'）可用于模拟热环境中低至中等强度运动的反应，并具有可直接转化的数据，可用于基于证据的政策决策、为即将到来的热事件做准备以及实施其他安全干预措施。
