Florian John P, Baisch Friedhelm J, Heer Martina, Pawelczyk James A
Navy Experimental Diving Unit, Panama City, Florida, United States of America.
DLR-Institute of Aerospace Medicine, Cologne, Germany.
PLoS One. 2015 Apr 27;10(4):e0118812. doi: 10.1371/journal.pone.0118812. eCollection 2015.
Astronauts consume fewer calories during spaceflight and return to earth with an increased risk of orthostatic intolerance. Whether a caloric deficiency modifies orthostatic responses is not understood. Thus, we determined the effects of a hypocaloric diet (25% caloric restriction) during 6° head down bedrest (an analog of spaceflight) on autonomic neural control during lower body negative pressure (LBNP). Nine healthy young men completed a randomized crossover bedrest study, consisting of four (2 weeks each) interventions (normocaloric bedrest, normocaloric ambulatory, hypocaloric bedrest, hypocaloric ambulatory), each separated by 5 months. Muscle sympathetic nerve activity (MSNA) was recorded at baseline following normocaloric and hypocaloric interventions. Heart rate (HR) and arterial pressure were recorded before, during, and after 3 consecutive stages (7 min each) of LBNP (-15, -30, -45 mmHg). Caloric and posture effects during LBNP were compared using two-way ANOVA with repeated measures. There was a strong trend toward reduced basal MSNA following caloric restriction alone (normcaloric vs. hypocaloric: 22±3 vs. 14±4 burst/min, p = 0.06). Compared to the normocaloric ambulatory, both bedrest and caloric restriction were associated with lower systolic blood pressure during LBNP (p<0.01); however, HR responses were directionally opposite (i.e., increase with bedrest, decrease with caloric restriction). Survival analysis revealed a significant reduction in orthostatic tolerance following caloric restriction (normocaloric finishers: 12/16; hypocaloric finishers: 6/16; χ2, p = 0.03). Caloric restriction modifies autonomic responses to LBNP, which may decrease orthostatic tolerance after spaceflight.
宇航员在太空飞行期间消耗的卡路里较少，返回地球后发生体位性不耐受的风险增加。热量不足是否会改变体位反应尚不清楚。因此，我们确定了在6°头低位卧床休息（模拟太空飞行）期间低热量饮食（热量限制25%）对下体负压（LBNP）期间自主神经控制的影响。九名健康的年轻男性完成了一项随机交叉卧床休息研究，该研究包括四种（每种2周）干预措施（正常热量卧床休息、正常热量走动、低热量卧床休息、低热量走动），每次干预间隔5个月。在正常热量和低热量干预后的基线记录肌肉交感神经活动（MSNA）。在连续3个阶段（每个阶段7分钟）的LBNP（-15、-30、-45 mmHg）之前、期间和之后记录心率（HR）和动脉压。使用重复测量的双向方差分析比较LBNP期间的热量和体位影响。仅热量限制后基础MSNA有强烈的降低趋势（正常热量与低热量：22±3次/分钟与14±4次/分钟，p = 0.06）。与正常热量走动相比，卧床休息和热量限制均与LBNP期间较低的收缩压相关（p<0.01）；然而，HR反应方向相反（即卧床休息时增加，热量限制时降低）。生存分析显示热量限制后体位耐受性显著降低（正常热量完成者：12/16；低热量完成者：6/16；χ2，p = 0.03）。热量限制会改变对LBNP的自主反应，这可能会降低太空飞行后的体位耐受性。
