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Impact of Spaceflight on Blood Pressure
Study Questions:
What is the impact of prolonged spaceflight on orthostatic tolerance and blood pressure (BP) profile in astronauts?
Methods:
An ambulatory beat-to-beat BP monitor was used to record 24-hour time periods twice before, four-times during, and once after 6 months of spaceflight in 12 astronauts (four women, mean age 48 [standard deviation 5] years). Data were averaged over a 24-hour period given the inability to tell day from night while in space. BP standard deviation was used to define BP variability. The distribution of 24-hour systolic BP was described using the skewness (higher values representing asymmetrical systolic BP distribution) and kurtosis (how narrow/broad the distribution of systolic BP values around the mean).
Results:
No astronaut experienced orthostatic intolerance/hypotension during activities of daily living before or after spaceflight. Twenty-four–hour systolic BP decreased during the 6 months in space (120 ± 10 mm Hg pre- vs. 106 ± 9 mm Hg in-flight, p < 0.01), but it returned to normal after landing back on earth (122 ± 13 mm Hg). BP variability remained the same before, during, and after spaceflight. The skewness (asymmetry) of systolic BP increased in space (0.74 ± 0.51 vs. 1.43 ± 1.00, p = 0.001), but then returned to normal after landing back on earth (0.51 ± 0.42). The kurtosis (broad/narrow distribution) also increased in space (5.01 ± 0.51 vs. 11.10 ± 11.79, p = 0.010), but then returned to normal after landing back on earth (2.21 ± 2.56).
Conclusions:
The authors concluded that current in-flight activities were associated with no orthostatic hypotension or intolerances during spaceflight. They also concluded that 6 months of spaceflight had limited impact on BP variability and BP distribution once the astronauts returned to earth.
Perspective:
Prior studies have demonstrated that many astronauts experience orthostatic intolerance and this has been a major challenge both in-flight and following return to earth. As countermeasures, the astronauts regularly perform in-flight exercises and receive volume expansion upon landing back on earth. However, prior studies have been limited by standing or upright tilting rather than 24-hour BP measurements, including during activities of daily living. This report highlights that while in-flight BP measures do change from baseline, that the current countermeasures likely help mitigate these changes. While these data are helpful for future astronauts, they may also provide early insight into methods used to manage patients with chronic orthostatic symptoms and BP variability.
Keywords: Activities of Daily Living, Astronauts, Blood Pressure, Blood Pressure Determination, Hypotension, Hypotension, Orthostatic, Orthostatic Intolerance, Primary Prevention, Space Flight, Vascular Diseases
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