Department of Medicine, Hunter Holmes McGuire Department of Veterans Affairs Medical Center and Medical College of Virginia at Virginia Commonwealth University, Richmond, VA, USA.
J Physiol. 2010 Apr 1;588(Pt 7):1129-38. doi: 10.1113/jphysiol.2009.186650. Epub 2010 Feb 15.
Although astronauts' cardiovascular function is normal while they are in space, many have altered haemodynamic responses to standing after they return to Earth, including inordinate tachycardia, orthostatic hypotension, and uncommonly, syncope. Simulated microgravity impairs vagal baroreceptor-cardiac reflex function and causes orthostatic hypotension. Actual microgravity, however, has been shown to either increase, or not change vagal baroreflex gain. In this study, we tested the null hypothesis that spaceflight does not impair human baroreflex mechanisms. We studied 11 American and two German astronauts before, during (flight days 2-8), and after two, 9- and 10-day space shuttle missions, with graded neck pressure and suction, to elicit sigmoid, vagally mediated carotid baroreflex R-R interval responses. Baseline systolic pressures tended to be higher in space than on Earth (P = 0.015, repeated measures analysis of variance), and baseline R-R intervals tended to be lower (P = 0.049). Baroreceptor-cardiac reflex relations were displaced downward on the R-R interval axis in space. The average range of R-R interval responses to neck pressure changes declined from preflight levels by 37% on flight day 8 (P = 0.051), maximum R-R intervals declined by 14% (P = 0.003), and vagal baroreflex gain by 9% (P = 0.009). These measures returned to preflight levels by 7-10 days after astronauts returned to Earth. This study documents significant increases of arterial pressure and impairment of vagal baroreflex function in space. These results and results published earlier indicate that microgravity exposure augments sympathetic, and diminishes vagal cardiovascular influences.
虽然宇航员在太空中的心血管功能正常，但许多人在返回地球后对站立的血液动力学反应发生了改变，包括异常的心动过速、直立性低血压，以及不常见的晕厥。模拟微重力会损害迷走神经压力感受器-心脏反射功能，并导致直立性低血压。然而，实际的微重力已经被证明会增加或不改变迷走神经压力反射增益。在这项研究中，我们检验了一个零假设，即太空飞行不会损害人类的压力反射机制。我们研究了 11 名美国宇航员和 2 名德国宇航员，在两次、9 天和 10 天的航天飞机任务前、期间（飞行第 2-8 天）和之后，进行了分级颈压和抽吸，以引出斜型、迷走介导的颈动脉压力感受器反射 R-R 间期反应。基础收缩压在太空中比在地球上更高（P = 0.015，重复测量方差分析），基础 R-R 间期更低（P = 0.049）。在太空中，压力感受器-心脏反射关系在 R-R 间期轴上向下移位。R-R 间期对颈压变化的反应范围从飞行第 8 天开始平均下降了 37%（P = 0.051），最大 R-R 间期下降了 14%（P = 0.003），迷走神经压力反射增益下降了 9%（P = 0.009）。这些指标在宇航员返回地球后 7-10 天内恢复到飞行前的水平。这项研究记录了太空中动脉压的显著升高和迷走神经压力反射功能的损害。这些结果和之前发表的结果表明，微重力暴露增强了交感神经的作用，同时减弱了迷走神经对心血管的影响。
