Institute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital, Dallas (Q.F., S.S., B.D.L.).
The University of Texas Southwestern Medical Center, Dallas (Q.F., S.S., J.L.H., B.A.-H., B.D.L.).
Circulation. 2019 Aug 27;140(9):729-738. doi: 10.1161/CIRCULATIONAHA.119.041050. Epub 2019 Jul 19.
Astronauts returning to earth usually demonstrate reduced orthostatic tolerance when assessed on a tilt table or quiet standing, but no studies have evaluated postflight orthostatic tolerance during activities of daily living, when it is most clinically relevant. Ambulatory blood pressure (BP) variability also is associated with orthostatic intolerance in certain patient populations and can capture clinically significant orthostatic hypotension during activities of daily living, especially when measured on a beat-to-beat basis. We evaluated the impact of prolonged spaceflight on orthostatic tolerance and BP profiles in astronauts.
Ambulatory beat-to-beat BP was recorded using a portable device for multiple 24-hour time periods before, during, and after 6 months of spaceflight in 12 astronauts (4 women; age 48±5 [mean±SD] years). BP variability in the time domain was calculated as the SD. Systolic BP distribution during activities of daily living was characterized by skewness and kurtosis.
In contrast with results from previous studies that used tilt tables or stand tests, no astronaut experienced orthostatic intolerance/hypotension during activities of daily living before or after spaceflight. Also, 24-hour systolic BP decreased in space (120±10 mm Hg before spaceflight versus 106±9 mm Hg during spaceflight; P<0.01), but it returned to normal upon landing (122±13 mm Hg). Diastolic BP was unchanged during and after spaceflight. Systolic and diastolic BP variability remained the same before, during, and after spaceflight (both P>0.05). The skewness of systolic BP increased in space (0.74±0.51 versus 1.43±1.00; P=0.001), indicating that signal fluctuations became asymmetrical; however, it returned to preflight levels after landing (0.51±0.42). The kurtosis increased in space (5.01±7.67 versus 11.10±11.79; P=0.010), suggesting that fluctuations concentrated around the mean with a narrow distribution; however, it also returned to preflight levels (2.21±2.56) after return to earth.
Given current countermeasures including in-flight exercise training and volume resuscitation on return, no astronauts experienced orthostatic hypotension or intolerance during routine (for landing day) activities in the initial 24 hours after landing following 6 months in space. Prolonged exposure to spaceflight had little impact on systolic BP variability and its distribution, although the latter showed a transient change in space (accompanied by mild relative hypotension), all of which returned to preflight values after return to earth.
在倾斜台或安静站立时评估时，返回地球的宇航员通常表现出直立耐受力降低，但尚无研究评估过日常生活活动中的飞行后直立耐受力，而这在临床上最为相关。在某些患者群体中，动态血压（BP）变异性也与直立不耐受有关，并且可以在日常生活活动中检测到具有临床意义的直立性低血压，尤其是在逐拍测量时。我们评估了长期太空飞行对宇航员直立耐受力和 BP 谱的影响。
使用便携式设备在 12 名宇航员（4 名女性；年龄 48±5[均值±标准差]岁）进行为期 6 个月的太空飞行之前、期间和之后的多个 24 小时时间段内记录动态逐拍 BP。通过标准差计算时域中的 BP 变异性。日常生活活动中的收缩压分布通过偏度和峰度来描述。
与使用倾斜台或站立测试的先前研究结果相反，在太空飞行之前或之后，没有宇航员在日常生活活动中经历直立不耐受/低血压。此外，24 小时收缩压在太空中下降（太空飞行前为 120±10mmHg，太空飞行期间为 106±9mmHg；P<0.01），但着陆后恢复正常（122±13mmHg）。太空飞行期间和之后舒张压不变。太空飞行之前、期间和之后，收缩压和舒张压变异性均相同（均 P>0.05）。太空飞行时收缩压的偏度增加（0.74±0.51 对 1.43±1.00；P=0.001），表明信号波动变得不对称；然而，着陆后恢复到飞行前水平（0.51±0.42）。太空飞行时峰度增加（5.01±7.67 对 11.10±11.79；P=0.010），表明波动集中在均值附近，分布较窄；然而，返回地球后也恢复到飞行前水平（2.21±2.56）。
鉴于当前的对策，包括飞行中运动训练和返回后的容量复苏，在返回后的最初 24 小时内，在着陆日进行的日常活动中，没有宇航员经历过直立性低血压或不耐受。长时间暴露于太空对收缩压变异性及其分布几乎没有影响，尽管后者在太空中表现出短暂的变化（伴有轻度相对低血压），但所有这些变化在返回地球后均恢复到飞行前水平。
