Edgell Heather, Grinberg Anna, Beavers Keith R, Gagné Nathalie, Hughson Richard L
Faculty of Applied Health Sciences, University of Waterloo, Waterloo, Ontario, Canada.
School of Kinesiology and Health Sciences, York University, Toronto, Ontario, Canada.
Physiol Rep. 2018 Sep;6(19):e13874. doi: 10.14814/phy2.13874.
After exposure to microgravity, or head-down bed rest (HDBR), fluid loading is often used with the intent of increasing plasma volume and maintaining mean arterial pressure during orthostatic stress. Nine men (aged 18-32 years) underwent three randomized trials with lower body negative pressure (LBNP) before and after: (1) 4-h of sitting with fluid loading (1 g sodium chloride/125 mL of water starting 2.5-h before LBNP), (2) 28-h of 6-degree HDBR without fluid loading, and (3) 28-h of 6-degree HDBR with fluid loading. LBNP was progressive from 0 to -40 mmHg. After 28-h HDBR, fluid loading did not protect against the loss of plasma volume (-280 ± 64 mL without fluid loading, -207 ± 86 with fluid loading, P = 0.472) nor did it protect against a drop of mean arterial pressure (P = 0.017) during LBNP (Post-28 h HDBR response from 0 to -40 mmHg LBNP: 88 ± 4 to 85 ± 4 mmHg without fluid loading and 93 ± 4 to 88 ± 5 mmHg with fluid loading, P = 0.557 between trials). However, fluid loading did protect against the loss of stroke volume index and central venous pressure observed after 28-h HDBR. Fluid loading also attenuated the increase of angiotensin II seen after 28-h HDBR and throughout the LBNP protocol (Post-28 h HDBR response from 0 to -40 mmHg LBNP: 16.6 ± 3.4 to 23.7 ± 5.0 pg/mL without fluid loading and 6.1 ± 0.8 to 12.2 ± 2.3 pg/mL with fluid loading, P < 0.001 between trials). Our results indicate that fluid loading did not protect against plasma volume loss due to HDBR or change blood pressure responses to LBNP. However, changes in central venous pressure, stroke volume and fluid regulatory hormones could potentially influence longer duration studies and those with more severe orthostatic stress.
在经历微重力环境或头低位卧床休息（HDBR）后，常采用补液的方法，目的是在体位性应激期间增加血浆量并维持平均动脉压。9名男性（年龄18 - 32岁）在以下情况前后分别进行了三项关于下体负压（LBNP）的随机试验：（1）在LBNP前2.5小时开始坐立4小时并补液（1克氯化钠/125毫升水）；（2）6度头低位卧床休息28小时且不补液；（3）6度头低位卧床休息28小时并补液。下体负压从0逐渐增加至 - 40 mmHg。在28小时头低位卧床休息后，补液并不能防止血浆量的减少（不补液时血浆量减少 - 280 ± 64毫升，补液时减少 - 207 ± 86毫升，P = 0.472），在进行下体负压试验期间也不能防止平均动脉压的下降（P = 0.017）（28小时头低位卧床休息后下体负压从0至 - 40 mmHg时的反应：不补液时从88 ± 4 mmHg降至85 ± 4 mmHg，补液时从93 ± 4 mmHg降至88 ± 5 mmHg，试验间P = 0.557）。然而，补液确实可以防止在28小时头低位卧床休息后观察到的每搏输出量指数和中心静脉压的下降。补液还减弱了在28小时头低位卧床休息后以及整个下体负压试验过程中血管紧张素II的增加（28小时头低位卧床休息后下体负压从0至 - 40 mmHg时的反应：不补液时从16.6 ± 3.4 pg/mL增至23.7 ± 5.0 pg/mL，补液时从6.1 ± 0.8 pg/mL增至12.2 ± 2.3 pg/mL，试验间P < 0.001）。我们的结果表明，补液不能防止头低位卧床休息导致的血浆量减少，也不能改变下体负压试验时的血压反应。然而，中心静脉压、每搏输出量和液体调节激素的变化可能会对更长时间的研究以及那些体位性应激更严重的研究产生潜在影响。
