Summary: Astronauts do not feel dizzy or faint during post-flight exercise, so long as they participate in certain types of exercise in space and receive IV fluids when they return to earth. The findings could have implications for people postural orthostatic tachycardia syndrome (POTS).
Source: American Heart Association
Nearly 50 years after man’s first steps on the moon, researchers have discovered a way that may help astronauts spending prolonged time in space come back to Earth on more stable footing, according to new research in the American Heart Association’s journal Circulation.
“One of the biggest problems since the inception of the manned space program has been that astronauts have fainted when they came down to Earth. The longer the time in a gravity-free environment space, the greater the risk appeared,” said Benjamin Levine, M.D., the study’s senior author who is a professor of Exercise Sciences at UT Southwestern Medical Center and director of the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital in Dallas. “This problem has bedeviled the space program for a long time, but this condition is something ordinary people often experience as well.”
Orthostatic hypotension is the technical term for a temporary drop in blood pressure when a person stands up after sitting or lying down because blood rushes to the feet, away from the brain. Dizziness or fainting due to changes in blood flow can occur after lengthy bed rest, among people with certain health disorders or, in the case of astronauts, being in a low-gravity environment.
The study included 12 astronauts (eight men and four women age 43-56) who spent about six months in space. All performed individualized endurance and resistance exercise training for up to two hours daily during space flight to prevent cardiovascular, bone and muscle deconditioning. They also received a saline infusion upon landing.
The astronauts’ blood pressure was recorded with every heartbeat over each 24-hour period before, during and after their time in space. The researchers found that there was minimal impact on their blood pressure during all phases of measurement and none of the astronauts in the study experienced dizziness or fainting during routine activities 24 hours after landing.
This is the first study to demonstrate that astronauts do not experience dizziness or fainting during routine activity after landing, as long as they participate in certain types of exercise training while in flight and receive IV fluids when they return to earth, said Levine
“What surprised me the most was how well the astronauts did after spending six months in space. I thought there would be frequent episodes of fainting when they returned to Earth, but they didn’t have any. It’s compelling evidence of the effectiveness of the countermeasures–the exercise regimen and fluid replenishment,” he said.
The researchers note that the sample size was small. Also, they could not clearly distinguish whether specific in-flight blood pressure readings occurred while the astronauts were awake or asleep, so the data were combined and examined over 24-hour periods. Since all the astronauts participated in the exercise regimen and received a saline fluid infusion upon landing, researchers do not know the blood pressure stabilization would have occurred without those measures.
Next, the researchers would like to study larger numbers of astronauts and those who spend longer than six months in space.
“Understanding the physiology of space flight can be helpful for understanding many conditions experienced by non-astronauts. For example, the exercise program our lab developed for the space program is already helping people with a fainting condition known as postural orthostatic tachycardia syndrome (POTS),” Levine said. “As we prepare to celebrate the 50th anniversary of the Apollo 11 moon landing, it’s exciting to think of how our exploration in and of space can lead to important medical advances here on Earth.”
Co-authors are Qi Fu, M.D., Ph.D.; Shigeki Shibata, M.D. Ph.D.; Jeffrey L. Hastings, M.D.; Steven H. Platts, Ph.D.; Douglas M. Hamilton, M.D.; Michael W. Bungo, Ph.D.; Michael B. Stenger, Ph.D.; Christine Ribeiro, J.D., M.S., and Beverly Adams-Huet, M.S.
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Source: American Heart Association Media Contacts: Karen Astle – American Heart Association Image Source: The image is in the public domain.
Impact of Prolonged Spaceflight on Orthostatic Tolerance During Ambulation, and Blood Pressure Profiles in Astronauts
Background: Astronauts returning to Earth usually demonstrate reduced orthostatic tolerance when assessed on a tilt table or quiet standing. But no studies have evaluated post-flight orthostatic tolerance during activities of daily living (ADL) 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 ADLs, especially when measured on a beat-to-beat basis. We evaluated the impact of prolonged spaceflight on orthostatic tolerance and BP profiles in astronauts.
Methods: 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 (SD) yrs]. BP variability in the time domain was calculated as the standard deviation. Systolic BP distribution was characterized by skewness and kurtosis.
Results: In contrast to previous studies which employed the use of tilt tables or stand tests, no astronaut experienced orthostatic intolerance/hypotension during ADLs before or after spaceflight. Twenty-four-hour systolic BP decreased in space (120±10 pre- vs. 106±9 mmHg inflight; P<0.01), but it returned to normal upon landing (122±13 mmHg). Diastolic BP was unchanged during and following 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 vs. 1.43±1.00; P=0.001), indicating that signal fluctuations became asymmetrical; however, it returned to pre-flight levels after landing (0.51±0.42). The kurtosis increased in space (5.01±7.67 vs. 11.10±11.79; P=0.010), suggesting that fluctuations concentrated around the mean with a narrow distribution, however, it also returned to pre-flight levels (2.21±2.56) after return to earth.
Conclusions: Given current countermeasures including exercise training in-flight 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, though the latter showed a transient change in space (accompanied by mild relative hypotension) all of which returned to preflight values after return to earth.