AbstractCardiovascular adjustments during heat stress are generally attenuated in healthy aged humans, which could be due to lower increases in sympathetic activity compared to the young. We compared muscle sympathetic nerve activity (MSNA) between 11 young (Y: 28 ± 4 years) and 10 aged (A: 70 ± 5 years) subjects prior to and during passive heating. Furthermore, MSNA responses were compared when a cold pressor test (CPT) and lower body negative pressure (LBNP) were superimposed upon heating. Baseline MSNA burst frequency (Y: 15 ± 4 vs. A: 31 ± 3 bursts min−1, P ≤ 0.01) and burst incidence (Y: 26 ± 8 vs. A: 50 ± 7 bursts (100 cardiac cycles (CC))−1, P ≤ 0.01) were greater in the aged. Heat stress increased core temperature to a similar extent in both groups (Y: +1.2 ± 0.1 vs. A: +1.2 ± 0.0°C, P = 0.99). Absolute levels of MSNA remained greater in the aged during heat stress (burst frequency: Y: 47 ± 6 vs. A: 63 ± 11 bursts min−1, P ≤ 0.01; burst incidence: Y: 48 ± 8 vs. A: 67 ± 9 bursts (100 CC)−1, P ≤ 0.01); however, the increase in both variables was similar between groups (both P ≥ 0.1). The CPT and LBNP further increased MSNA burst frequency and burst incidence, although the magnitude of increase was similar between groups (both P ≥ 0.07). These results suggest that increases in sympathetic activity during heat stress are not attenuated in healthy aged humans.
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机译：摘要热应激期间的心血管调节通常在健康的老年人中减弱，这可能是由于与年轻人相比，交感神经活动的增加较低。我们比较了被动加热之前和期间的11位年轻（Y：28±4岁）和10岁（A：70±5岁）受试者之间的肌肉交感神经活动（MSNA）。此外，在加热时叠加冷压试验（CPT）和下身负压（LBNP）时，比较了MSNA响应。基线MSNA突发频率（Y：15±4 vs.A：31±3突发min -1 ，P≤0.01）和突发发生率（Y：26±8 vs.A：50±7突发（100个心动周期（CC）） -1 ，P≤0.01）在老年人中更大。两组的热应力使核心温度升高的程度相似（Y：+ 1.2±0.1 vs. A：+ 1.2±0.0°C，P = 0.99）。在高温下，老年人的MSNA绝对水平仍然更高（爆发频率：Y：47±6 vs. A：63±11 burst min -1 ，P≤0.01;突发发生率：Y：48 ±8 vs. A：67±9爆发（100 CC） -1 ，P≤0.01）;但是，两组之间两个变量的增加相似（均为P≥0.1）。 CPT和LBNP进一步增加了MSNA爆发频率和爆发发生率，尽管两组之间的增加幅度相似（均为P≥0.07）。这些结果表明，在健康的老年人中，热应激期间交感神经活动的增加并未减弱。
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