Sandler H, Popp R L, Harrison D C
National Aeronautics and Space Administration, Cardiovascular Research Office, Ames Research Center, Moffett Field, CA.
Aviat Space Environ Med. 1988 Nov;59(11 Pt 1):1047-54.
Hemodynamic changes were measured during stepwise exposure to lower-body negative pressure (LBNP) (5 min, -20, -30, and -40 mm Hg) in a group of seven physically active subjects before and after consecutive exposure to three 2-week bed rest periods. Bed rest exposures were separated by 3-week periods of ambulatory recovery. Dynamic exercise (68% max O2, 30 min each day) and isometric exercise (21% max leg extension, 30 min each day) performed during bed rest and reambulation failed to prevent deconditioning or accelerate the recovery process between bed rest exposures. Heart rate (HR) and end-diastolic volume index (EDVI) proved to be parameters showing greatest changes during LBNP. Heart rate increases at -40 mm Hg LBNP (compared to respective pre-LBNP levels) were 13.3%, 35.1%, and 51.0% for each of the pre-bed rest exposures, while respective changes after bed rest were 57.8%, 57.2%, and 75.5%. The significantly elevated HR responses during subsequent pre-bed rest (control) periods indicated incomplete recovery despite mild exercise and ambulation. Comparison of EDVI and HR revealed a similar linear regression relationship during LBNP before and after bed rest so that EDVI = 112.5-0.85 x HR, r = -0.97. We conclude from these findings that cardiovascular deconditioning for physically active individuals involves factors other than simple loss of plasma volume, requires at least 3 weeks or longer to return to the pre-bed rest state, and is not counteracted by the levels of aerobic and/or isometric exercise used in the present study.
在一组七名身体活跃的受试者中，在连续经历三个为期2周的卧床休息期之前和之后，逐步暴露于下体负压（LBNP）（5分钟，-20、-30和-40毫米汞柱）期间测量血流动力学变化。卧床休息期之间通过为期3周的动态恢复阶段隔开。在卧床休息和恢复活动期间进行的动态运动（最大摄氧量的68%，每天30分钟）和等长运动（最大腿部伸展的21%，每天30分钟）未能预防身体机能下降或加速卧床休息期之间的恢复过程。心率（HR）和舒张末期容积指数（EDVI）被证明是在LBNP期间变化最大的参数。对于每次卧床休息前的暴露，在-40毫米汞柱LBNP时心率增加（与各自的LBNP前水平相比）分别为13.3%、35.1%和51.0%，而卧床休息后的相应变化分别为57.8%、57.2%和75.5%。在随后的卧床休息前（对照）期，心率反应显著升高，表明尽管进行了轻度运动和活动，但恢复不完全。EDVI和HR的比较显示，卧床休息前后LBNP期间存在相似的线性回归关系，即EDVI = 112.5 - 0.85×HR，r = -0.97。我们从这些发现中得出结论，对于身体活跃的个体，心血管机能下降涉及除血浆量简单减少之外的因素，需要至少3周或更长时间才能恢复到卧床休息前的状态，并且本研究中使用的有氧运动和/或等长运动水平无法抵消这种下降。
