Abstract：
The frequency, duration, and severity of extreme heat events have increased and are projected to continue to increase throughout the next century. As a result, there is an increased risk of excessive heat- and cardiovascular-related morbidity and mortality during these extreme heat events. Therefore, the purposes of this investigation were to establish 1) critical environmental core temperature (Tc) limits for middle-aged adults (MA), 2) environmental thresholds that cause heart rate (HR) to progressively rise in MA and older (O) adults, and 3) examine critical environmental Tc limits and HR environmental thresholds across the adult age span. Thirty-three young (Y) (15 F; 23 ± 3 yr), 28 MA (17 F; 51 ± 6 yr), and 31 O (16 F; 70 ± 3 yr) subjects were exposed to progressive heat stress in an environmental chamber in a warm-humid (WH, 34-36°C, 50-90% rh) and a hot-dry (HD, 38°C-52°C, <30% rh) environment while exercising at a low metabolic rate reflecting activities of daily living (∼1.8 METs). In both environments, there was a main effect of age on the critical environmental Tc limit and environmental HR thresholds (main effect of age all P < 0.001). Across the lifespan, critical environmental Tc and HR thresholds decline linearly with age in HD environments (R2 ≥ 0.3) and curvilinearly in WH environments (R2 ≥ 0.4). These data support an age-associated shift in critical environmental Tc limits and HR thresholds toward lower environmental conditions and can be used to develop evidence-based safety guidelines to minimize future heat-related morbidity and mortality across the adult age span.NEW & NOTEWORTHY This study is the first to identify critical environmental core temperature and heart rate thresholds across the adult age spectrum. In addition, our data demonstrate that the rate of decline in Tc and HR limits with age is environmental-dependent. These findings provide strong empirical data for the development of safety guidelines and policy decisions to mitigate excessive heat- and cardiovascular-related morbidity and mortality for impending heat events.
摘要：
频率,持续时间,极端高温事件的严重程度有所增加，预计在下个世纪将继续增加。因此,在这些极端高温事件期间,过度高温和心血管相关的发病率和死亡率的风险增加.因此,这项调查的目的是建立(1)中年人(MA)的临界环境核心温度(Tc)限值，（2）导致心率（HR）逐渐上升的MA和老年人（O）的环境阈值，（3）检查整个成年年龄范围内的关键环境Tc限制和HR环境阈值。33名青年（Y）（15F；23±3年），28MA（17F；51±6年），和31O（16F；70±3年）受试者在温暖潮湿的环境室中暴露于进行性热应激（WH，34-36°C,50-90%Rh)和干热(HD,38°C-52°C,<30％rh）环境，同时以低代谢率运动，反映日常生活活动（〜1.8METS）。在这两种环境中,年龄对临界环境Tc限值和环境HR阈值有主要影响（年龄的主要影响均p<0.001）。在整个生命周期中，在HD环境中，临界环境Tc和HR阈值随年龄线性下降(R2≥0.3)，并且在WH环境中曲线早期(R2≥0.4)。这些数据支持关键环境Tc限值和HR阈值向较低环境条件的年龄相关转变，并可用于制定基于证据的安全指南，以最大程度地减少整个成人年龄范围内未来与热相关的发病率和死亡率。
