Penn State Heart and Vascular Institute, Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
J Appl Physiol (1985). 2022 Jul 1;133(1):234-245. doi: 10.1152/japplphysiol.00684.2021. Epub 2022 Jun 23.
Acute whole body heat stress evokes sympathetic activation. However, the chronic effects of repeated moderate heat exposure (RMHE) on muscle sympathetic nerve activity (MSNA) in healthy individuals remain unclear. We performed RMHE with 4 wk (5 days/wk) of warm baths (∼40°C, for 30 min) in nine healthy older (59 ± 2 yr) volunteers. Hemodynamic variables and MSNA were examined before, 1 day after, and 1 wk following 4 wk of RMHE in a laboratory at ∼23°C. Cold pressor test (CPT) and handgrip (HG) exercise were performed during the tests. Under normothermic condition, the resting MSNA burst rate (prior, post, post 1-wk: 31.6 ± 2.0, 25.2 ± 2.0, and 27.7 ± 1.7 bursts/min; < 0.001) and burst incidence ( < 0.001) significantly decreased after RMHE. Moreover, the resting heart rate significantly decreased after RMHE (62 ± 2, 60 ± 2, and 58 ± 2 beats/min, = 0.031). The sensitivity of baroreflex control of MSNA and heart rate were not altered by RMHE, although the operating points were reset. The MSNA and hemodynamic responses (i.e., changes) to handgrip exercise or cold pressor test were not significantly altered. These data suggest that the RMHE evoked by warm baths decreases resting sympathetic activity and heart rate, which can be considered beneficial effects. The mechanism(s) should be examined in future studies. To our knowledge, this is the first study to observe the effects of repeated warm baths on sympathetic nerve activity during rest and stress in healthy middle age and older individuals. The data suggest that the repeated warm baths decreased resting sympathetic activity and heart rate, which can be considered beneficial effects. This study also provides the first evidence that the repeated warm baths did not alter the baroreflex sensitivity and the sympathetic responses to stress.
急性全身热应激会引起交感神经激活。然而，反复适度热暴露（RMHE）对健康个体肌肉交感神经活动（MSNA）的慢性影响尚不清楚。我们对 9 名健康老年人（59 ± 2 岁）志愿者进行了 4 周（每周 5 天）的温水浴（约 40°C，30 分钟）的 RMHE。在实验室中于约 23°C 下，在 RMHE 前、1 天后和 1 周后检查血流动力学变量和 MSNA。在测试期间进行冷加压试验（CPT）和握力（HG）运动。在正常体温条件下，RMHE 后静息 MSNA 爆发率（前、后、后 1 周：31.6 ± 2.0、25.2 ± 2.0 和 27.7 ± 1.7 次/分钟；<0.001）和爆发频率（<0.001）显著降低。此外，RMHE 后静息心率也明显降低（62 ± 2、60 ± 2 和 58 ± 2 次/分钟， = 0.031）。RMHE 并未改变 MSNA 和心率的压力反射控制敏感性，尽管操作点已重置。HG 或 CPT 引起的 MSNA 和血液动力学反应（即变化）没有明显改变。这些数据表明，温水浴引起的 RMHE 降低了静息交感神经活动和心率，可以认为是有益的影响。未来的研究应检查其机制。据我们所知，这是第一项观察反复温水浴对健康中年和老年人休息和应激时交感神经活动影响的研究。数据表明，反复温水浴降低了静息交感神经活动和心率，可以认为是有益的影响。本研究还首次证明，反复温水浴不会改变压力反射敏感性和对压力的交感神经反应。
