Levine Benjamin D, Pawelczyk James A, Ertl Andrew C, Cox James F, Zuckerman Julie H, Diedrich André, Biaggioni Italo, Ray Chester A, Smith Michael L, Iwase Satoshi, Saito Mitsuru, Sugiyama Yoshiki, Mano Tadaaki, Zhang Rong, Iwasaki Kenichi, Lane Lynda D, Buckey Jay C, Cooke William H, Baisch Friedhelm J, Eckberg Dwain L, Blomqvist C Gunnar
Institute for Exercise and Environmental Medicine, Presbyterian Hospital of Dallas and the University of Texas Southwestern Medical Center at Dallas, Dallas, TX 75231, USA.
J Physiol. 2002 Jan 1;538(Pt 1):331-40. doi: 10.1113/jphysiol.2001.012575.
Orthostatic intolerance is common when astronauts return to Earth: after brief spaceflight, up to two-thirds are unable to remain standing for 10 min. Previous research suggests that susceptible individuals are unable to increase their systemic vascular resistance and plasma noradrenaline concentrations above pre-flight upright levels. In this study, we tested the hypothesis that adaptation to the microgravity of space impairs sympathetic neural responses to upright posture on Earth. We studied six astronauts approximately 72 and 23 days before and on landing day after the 16 day Neurolab space shuttle mission. We measured heart rate, arterial pressure and cardiac output, and calculated stroke volume and total peripheral resistance, during supine rest and 10 min of 60 deg upright tilt. Muscle sympathetic nerve activity was recorded in five subjects, as a direct measure of sympathetic nervous system responses. As in previous studies, mean (+/- S.E.M.) stroke volume was lower (46 +/- 5 vs. 76 +/- 3 ml, P = 0.017) and heart rate was higher (93 +/- 1 vs. 74 +/- 4 beats min(-1), P = 0.002) during tilt after spaceflight than before spaceflight. Total peripheral resistance during tilt post flight was higher in some, but not all astronauts (1674 +/- 256 vs. 1372 +/- 62 dynes s cm(-5), P = 0.32). No crew member exhibited orthostatic hypotension or presyncopal symptoms during the 10 min of postflight tilting. Muscle sympathetic nerve activity was higher post flight in all subjects, in supine (27 +/- 4 vs. 17 +/- 2 bursts min(-1), P = 0.04) and tilted (46 +/- 4 vs. 38 +/- 3 bursts min(-1), P = 0.01) positions. A strong (r(2) = 0.91-1.00) linear correlation between left ventricular stroke volume and muscle sympathetic nerve activity suggested that sympathetic responses were appropriate for the haemodynamic challenge of upright tilt and were unaffected by spaceflight. We conclude that after 16 days of spaceflight, muscle sympathetic nerve responses to upright tilt are normal.
宇航员返回地球后，体位性不耐受很常见：经过短暂的太空飞行，多达三分之二的人无法站立10分钟。先前的研究表明，易感个体无法将其全身血管阻力和血浆去甲肾上腺素浓度提高到飞行前直立水平以上。在本研究中，我们检验了以下假设：对太空微重力的适应会损害在地球上对直立姿势的交感神经反应。我们研究了6名宇航员，分别在16天的神经实验室航天飞机任务前约72天和23天以及着陆当天进行研究。我们在仰卧休息时以及60度直立倾斜10分钟期间测量了心率、动脉压和心输出量，并计算了每搏输出量和总外周阻力。在5名受试者中记录了肌肉交感神经活动，并将其作为交感神经系统反应的直接指标。与先前的研究一样，太空飞行后倾斜期间的平均（±标准误）每搏输出量低于飞行前（46±5对76±3 ml，P = 0.017），心率高于飞行前（93±1对74±4次/分钟，P = 0.002）。飞行后倾斜期间的总外周阻力在部分但并非所有宇航员中较高（1674±256对1372±62达因·秒·厘米⁻⁵，P = 0.32）。在飞行后倾斜的10分钟内，没有机组人员出现体位性低血压或晕厥前症状。所有受试者在飞行后仰卧（27±4对17±2次/分钟，P = 0.04）和倾斜（46±4对38±3次/分钟，P = 0.01）体位时的肌肉交感神经活动均较高。左心室每搏输出量与肌肉交感神经活动之间存在强线性相关性（r² = 0.91 - 1.00），这表明交感神经反应适合直立倾斜的血流动力学挑战，且不受太空飞行影响。我们得出结论，经过16天的太空飞行后，肌肉交感神经对直立倾斜的反应是正常的。
