Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas, USA.
Clin Auton Res. 2011 Dec;21(6):381-7. doi: 10.1007/s10286-011-0126-6. Epub 2011 Jun 18.
Whole-body heat stress compromises the control of blood pressure during an orthostatic challenge, although the extent to which this occurs can vary greatly between individuals. The mechanism(s) responsible for these varying responses remain unclear. This study tested the hypothesis that the individuals who are best able to tolerate an orthostatic challenge while heat stressed are the ones with the largest increase in sympathetic activity during orthostasis, indexed from recordings of muscle sympathetic nerve activity (MSNA).
MSNA, arterial blood pressure, and heart rate were recorded from 11 healthy volunteers throughout passive whole-body heating and during 15 min of 60° head-up tilt (HUT) or until the onset of pre-syncopal symptoms.
Whole-body heating significantly increased core temperature (~0.9°C), supine heart rate and MSNA. Eight of 11 subjects developed pre-syncopal symptoms resulting in early termination of HUT. The HUT tolerance time was positively correlated (R = 0.82, P = 0.01) with the increase in MSNA by HUT.
These data suggest that the individuals with the largest increase in MSNA during upright tilt have the greatest capacity to withstand the orthostatic challenge while heat stressed.
全身热应激会影响直立倾斜试验期间的血压控制，尽管个体之间的影响程度可能存在很大差异。导致这种不同反应的机制尚不清楚。本研究假设，在热应激时最能耐受直立倾斜试验的个体，是那些在直立倾斜期间交感神经活动增加最多的个体，用肌间神经活动（MSNA）记录来衡量。
11 名健康志愿者在被动全身加热期间和 60°头高位倾斜（HUT）期间的 15 分钟内或出现先兆晕厥症状前，记录 MSNA、动脉血压和心率。
全身加热显著升高核心体温（约 0.9°C）、仰卧位心率和 MSNA。11 名受试者中有 8 名出现先兆晕厥症状，导致 HUT 提前终止。HUT 耐受时间与 HUT 期间 MSNA 的增加呈正相关（R=0.82，P=0.01）。
这些数据表明，在直立倾斜期间 MSNA 增加最大的个体，在热应激时承受直立挑战的能力最强。
