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Surgeons badigned to the first astronauts to go into space during NASA's Mercury program noticed very few changes when they monitored heart rate, blood pressure and body temperature.
"But what changed was when they came back to Earth," said Bill Carpentier, flight surgeon at Apollo 11. "The heart rate increased after the flight and the blood pressure was reduced. Last Mercury flight, which lasted 34 hours, when Gordon Cooper got off the shuttle and got up, his heart rate became very high., 180. And his blood pressure dropped, he had the impression But once he started moving, the situation improved and he was able to cross the bridge. "
It was feared that this would become progressive with longer missions in the Apollo program lasting up to 14 days.
Orthostatic hypotension occurs when blood rushes to the feet and away from the brain when someone gets up after sitting or lying down. This causes a temporary drop in blood pressure, which can result in dizziness or fainting.
"One of the biggest problems since the launch of the manned space program has been the fainting of astronauts after their descent to Earth.The more time spent in a non-gravity environment is high, the greater the risk is." said Dr. Benjamin. Levine, lead author of studies and director of the Institute of Exercise and Environmental Medicine at Texas Health Presbyterian Hospital in Dallas. "This problem has long tarnished the space program, but this condition is also what ordinary people often feel."
People suffering from certain health problems or using bed rest to recover from an injury may also feel this sensation.
The study involved 12 astronauts, eight men and four women aged 43 to 56 years. They spent six months in space aboard the International Space Station between 2009 and 2013.
As is common practice for astronauts of space stations, they exercised for two hours each day of their mission. This included endurance and strength training exercises. Astronauts at the station regularly exercise to prevent bone and muscle loss, including the loss of cardiovascular muscle.
This exercise countermeasure has evolved over time based on studies, said Levine.
And on their return to Earth, the astronauts received saline intravenous solutions.
"The space causes a loss of plasma volume that is accentuated by the re-entry process," Levine said. "Exercise keeps the size and function of the heart intact and the fluid fills it in preparation for the gravity of the Earth."
Before, during and after their missions, the astronauts' heart rate and blood pressure were recorded over a 24-hour period.
Their blood pressure was little changed and none of them fainted or felt dizzy after landing and performing activities over a 24 hour period.
Levine stated that it was the first study to show that astronauts did not experience these symptoms after landing, as long as they exercised in flight and received an infusion of saline solution. at their return.
"What surprised me the most is how much the astronauts have managed after six months in space," Levine said. "I thought that there would be frequent bouts of fainting when they would come back to Earth, but they did not have any.This is an irrefutable proof of the effectiveness of the counter -measures – the program of exercises and the fluid reconstitution. "
The study takes into account a few considerations, including the small size of its samples and the fact that researchers do not know if blood pressure readings occurred when astronauts were awake or asleep. They also do not know what would have happened if the astronauts had not done IV exercises at the return because they had all done so.
But the results could also help people on Earth.
"Understanding the physiology of spaceflight can be helpful in understanding many of the conditions experienced by non-astronauts, for example, the exercise program developed by our laboratory for the space program is already helping people with mental health problems. a fainting called postural orthostatic tachycardia syndrome (POTS), "said Levine. "As we prepare to celebrate the 50th anniversary of the Apollo 11 lunar landing, it is exciting to think about how our exploration in and in space can lead to d & # 39; important medical advances here on Earth. "
Next, researchers are studying ways to mitigate other effects of spaceflight on the human body.
"We are currently testing strategies to unload the heart and brain at night with the help of a sleeping bag connected to a vacuum pump," said Levine. "We hope that this will prevent the remodeling behind the eye that causes vision loss of some astronauts.We have just submitted 2 grants to NASA to review longer stays on the ISS, up to the end. We are particularly interested in atria (and the risk of atrial fibrillation) and the potential for space flight in general, and space radiation in particular, to accelerate atherosclerosis. "
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