Cui Jian, Wilson Thad E, Crandall Craig G
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas, 7232 Greenville Ave., Dallas, TX 75231, USA.
J Appl Physiol (1985). 2004 Jun;96(6):2103-8. doi: 10.1152/japplphysiol.00717.2003. Epub 2004 Feb 20.
The purpose of this project was to test the hypothesis that increases in muscle sympathetic nerve activity (MSNA) during an orthostatic challenge is attenuated in heat-stressed individuals. To accomplish this objective, MSNA was measured during graded lower body negative pressure (LBNP) in nine subjects under normothermic and heat-stressed conditions. Progressive LBNP was applied at -3, -6, -9, -12, -15, -18, -21, and -40 mmHg for 2 min per stage. Whole body heating caused significant increases in sublingual temperature, skin blood flow, sweat rate, heart rate, and MSNA (all P < 0.05) but not in mean arterial blood pressure (P > 0.05). Progressive LBNP induced significant increases in MSNA in both thermal conditions. However, during the heat stress trial, increases in MSNA at LBNP levels higher than -9 mmHg were greater compared with during the same LBNP levels in normothermia (all P < 0.05). These data suggest that the increase in MSNA to orthostatic stress is not attenuated but rather accentuated in heat-stressed humans.
在体位性应激期间，热应激个体的肌肉交感神经活动（MSNA）增加会减弱。为实现这一目标，在九名受试者处于常温及热应激条件下进行分级下肢负压（LBNP）时，测量了MSNA。每个阶段以-3、-6、-9、-12、-15、-18、-21和-40 mmHg施加渐进式LBNP，持续2分钟。全身加热导致舌下温度、皮肤血流量、出汗率、心率和MSNA显著增加（均P < 0.05），但平均动脉血压未增加（P > 0.05）。在两种热状态下，渐进式LBNP均导致MSNA显著增加。然而，在热应激试验期间，与常温下相同LBNP水平相比，LBNP水平高于-9 mmHg时MSNA的增加更大（均P < 0.05）。这些数据表明，热应激个体对体位性应激的MSNA增加并未减弱，反而增强。
