Astronauts tolerate simulated Mars gravity after 6 months in space

Northwestern University researchers tracked 13 astronauts for about 6 months on the International Space Station, according to an Oct. 21 ScienceDaily report on a Circulation study.

Evidence grade: Moderate (consistent observational data or small trials). The observational study matters for Mars planning because Mars gravity is roughly 38% of Earth’s, a major comparison for crews leaving microgravity.

The researchers, from Northwestern Medicine, UT Southwestern and UT Houston, used echocardiograms before, during and after the astronauts’ missions. Echocardiograms are ultrasound scans that show heart structure and pumping function.

“With our findings, there is now reason to think that we would be able to traverse to Mars, get there and actually work on the surface of Mars,” said James Thomas, the study’s senior author and a professor of medicine at Northwestern University Feinberg School of Medicine.

The study found early declines in cardiac filling, stroke volume and other measures during the first 2 weeks in space. Cardiac filling is the amount of blood entering the heart between beats, while stroke volume is the amount pumped out with each contraction.

Those measures later improved toward preflight levels, ScienceDaily reported. After return to Earth, the astronauts underwent a 22-degree tilt test, designed to shift blood toward the lower body and approximate some circulatory effects of Martian gravity.

The astronauts showed no significant signs of cardiovascular strain during that simulated Martian gravity test, according to the report. Their heart performance under the test was described as comparable to standing upright on Earth before their missions.

Exercise was a central part of the missions. Under NASA’s Exercise Countermeasures program, astronauts exercised for up to 2 hours a day, including 30 to 45 minutes of endurance training and 60 to 75 minutes of resistance training.

“You lose muscle mass and cardiac mass when you're in a weightless environment because you are working less up there,” Thomas said. “To counter that, exercise is crucial when you're in space,” he added.

The study cannot show that all astronauts would respond the same way, or that an actual Mars landing would produce the same cardiovascular effects as a tilt test on Earth.

The findings apply most directly to highly selected astronauts who completed long-duration International Space Station missions and structured daily exercise. They do not establish recommendations for the general public, patients with cardiovascular disease or people training outside spaceflight.

Funding came from the National Space Biomedical Research Institute, NASA, the IDP Foundation, Sandra Helton and the National Heart Foundation of Australia. The study is titled “Impact of Prolonged Spaceflight on Cardiac Structure and Function: An Exploratory Longitudinal Observational Study.”

Source: ScienceDaily Health report on Northwestern University materials and Circulation study, Oct. 21.

Atlas360 reports health research and does not provide medical advice.