Human and Environmental Physiology Research Unit, School of Human Kinetics, University of Ottawa, Ottawa, ON, Canada.
Faculty of Physical Activity Sciences, University of Sherbrooke, Sherbrooke, QC, Canada.
Appl Physiol Nutr Metab. 2024 Dec 1;49(12):1773-1782. doi: 10.1139/apnm-2024-0126. Epub 2024 Aug 13.
Foot immersion and neck cooling are recommended cooling strategies for protecting heat-vulnerable persons during heat waves. While we recently showed that these strategies do not limit core temperature increases in older adults during prolonged heat exposure, we did observe small reductions in heart rate. Expanding on these findings, we examined the effects of foot immersion with and without neck cooling on cardiac autonomic function. Seventeen adults (9 females; 65-81 years) underwent 3 randomized, 6 h exposures to 38 °C and 35% relative humidity with: no cooling (control), foot immersion (20 °C water), or foot immersion with a wet towel (20 °C) around the neck. Cardiac autonomic responses were measured at baseline and end-exposure. These included heart rate variability, cardiac and systolic blood pressure responses to standing, indexed via the 30:15 ratio and supine-to-standing systolic pressure change, respectively, and baroreflex sensitivity during repeated sit-to-stand maneuvers. The 30:15 ratio was 0.04 [95% CI: 0.01, 0.07] greater with foot immersion and neck cooling (1.08 (SD: 0.04)) relative to control (1.04 (0.06); = 0.018). Similarly, standing systolic blood pressure was elevated 9 [0, 17] mmHg with foot immersion and neck cooling ( = 0.043). That said, neither difference remained statistically significant after adjusting for multiplicity (≥ 0.054). No differences in 30:15 ratio or standing systolic blood pressure were observed with foot immersion alone, while heart rate variability and baroreflex sensitivity were unaffected by either cooling intervention. While foot immersion with neck cooling potentially improved cardiac autonomic responses in older adults exposed to simulated indoor overheating, these effects were small and of questionable clinical importance.
足部浸泡和颈部冷却被推荐为在热浪期间保护易受热影响人群的冷却策略。虽然我们最近表明，这些策略不会限制老年人在长时间暴露于高温下核心温度的升高，但我们确实观察到心率略有降低。在此基础上，我们研究了足部浸泡和颈部冷却对心脏自主功能的影响。17 名成年人（9 名女性；65-81 岁）接受了 3 次随机、6 小时暴露于 38°C 和 35%相对湿度的实验，分别为：无冷却（对照）、足部浸泡（20°C 水）或颈部周围用湿毛巾包裹的足部浸泡（20°C）。在基线和暴露结束时测量心脏自主反应。这些反应包括心率变异性、心脏和收缩压对站立的反应，分别通过 30:15 比值和仰卧位到站立位收缩压变化来表示，以及重复坐立起运动期间的血压反射敏感性。与对照（1.04（0.06））相比，足部浸泡和颈部冷却时 30:15 比值更大（0.04 [95%CI：0.01，0.07]；1.08（SD：0.04）；=0.018）。同样，站立时收缩压升高 9 [0，17]mmHg，足部浸泡和颈部冷却（=0.043）。也就是说，在进行多重调整后（≥0.054），这两个差异均不再具有统计学意义。单独进行足部浸泡时，30:15 比值或站立收缩压没有差异，而心率变异性和血压反射敏感性不受任何冷却干预的影响。虽然在模拟室内过热情况下，颈部冷却的足部浸泡可能改善了老年人的心脏自主反应，但这些影响很小，临床意义值得怀疑。
