(CNN) The lack of gravity astronauts encounter during spaceflight makes returning to the force of Earth's gravity a little disorienting. And when they return to Earth, they faint.
A new study published Friday in Circulation, the American Heart Association's journal, has identified a way to avoid that.
Surgeons assigned to some of 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 returned to Earth," said Bill Carpentier, Apollo 11 flight surgeon. "The heart rate was increased post-flight and blood pressure was seen to be lower. And on the last Mercury flight, which was 34 hours, when Gordon Cooper got out of the spacecraft and stood up, his heart rate went really high, 170, 180. And his blood pressure dropped, he felt like he was going to faint. But once he started moving, things got better and he was able to walk across the deck."
There was concern that this could become progressive with longer missions in the Apollo program that could last up to 14 days.
Orthostatic hypotension occurs when the blood rushes to the feet and away from the brain as someone stands up after sitting or lying down. This causes a temporary drop in blood pressure, which can lead to dizziness or fainting.
"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 Dr. Benjamin Levine, senior study author and a professor of Internal Medicine at UT Southwestern Medical Center and Director of the Institute for Exercise and Environmental Medicine, a collaboration between UT Southwestern and Texas Health Presbyterian Hospital Dallas. "This problem has bedeviled the space program for a long time, but this condition is something ordinary people often experience as well."
People with certain health conditions or using bed rest to recover from an injury can also experience this sensation.
The study involved 12 astronauts, eight men and four women between the ages of 43 and 56. They spent six months in space aboard the International Space Station between 2009 and 2013.
As is standard practice for space station astronauts, they exercised for two hours each day of their mission. This included endurance and resistance training. Astronauts on the station regularly exercise to prevent the loss of bone mass and muscle, including cardiovascular muscle loss.
This exercise countermeasure evolved over time based on studies, Levine said.
And upon returning to Earth, the astronauts received saline IV fluids.
"Space causes a loss of plasma volume that is accentuated by the re-entry process," Levine said. "Exercise keeps the heart size and function intact and fluid fills it in preparation for Earth's gravity."
Before, during and after their missions, the astronauts heart rate and blood pressure was recorded over a 24-hour period.
Their blood pressure only shifted minimally and none of them fainted or experienced dizziness after landing and performing activities over a 24-hour period.
Levine said this is the first study to show that astronauts aren't experiencing these symptoms after landing as long as they exercise in flight and receive a saline infusion when they return.
"What surprised me the most was how well the astronauts did after spending six months in space," Levine said. "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."
There are a few considerations for the study, including its small samples size and the fact that the researchers don't know if the blood pressure readings happened when the astronauts were awake or asleep. They also don't know what would have happened if the astronauts didn't exercise or receive IVs upon return because all of them did.
But the findings could help people on Earth as well.
"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."
Next, the 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 using a sleeping sac hooked up to a vacuum pump," Levine said. "We hope that this will prevent the remodeling behind the eye that is causing some astronauts to have diminished vision. We just submitted 2 grants to NASA to examine longer durations stays on the ISS, through 1 year. We are particularly interested in the atria (and risk of atrial fibrillation) and the possibility that spaceflight in general, and space radiation in particular could accelerate atherosclerosis."