Intensive cardiovascular routines may reduce the harmful effects of being in a low-gravity environment for long periods of time.
PROBLEM: Previous studies have shown that astronauts who stay in a low-gravity environment may experience dizziness when standing up, have impaired muscle function, and lose considerable bone mass. Little is known, however, about the effects of long-term space flight on their heart and vascular systems.
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METHODOLOGY: Researchers led by Richard Hughson asked six astronauts, 41 to 55 years of age, who were aboard the International Space Station for 52 to 199 days to allot 2.5 hours a day to prepare and exercise on a cycle, treadmill, or using resistance training. They collected data on each subject's cardiovascular health during spontaneous and paced breathing, and measured various factors, including finger arterial blood pressure, heart rate, left ventricular ejection time, and cardiac output. The astronauts repeated these measures independently a few weeks after they arrived at the space station, then a few weeks before they returned. A final assessment was conducted soon after they landed on Earth.
RESULTS: The astronauts' heart rate, blood pressure, and arterial baroreflex response (the body's way of regulating heart rate and blood pressure) were unchanged from pre-flight to in-flight. Left ventricular ejection times and cardiac output both increased in-flight, while time between heartbeats, arterial pulse pressure, and the amount of blood pumped from the heart decreased. Compared to pre-flight measures, the post-flight testing showed slight increases in heart rate and cardiac output and a decrease in arterial baroreflex response by about a third when measured in the seated position.
CONCLUSION: Despite the potentially harmful effects of a low-gravity environment, intensive exercise sessions appear to keep astronauts relatively healthy and prepared for return to Earth.
SOURCE: The full study, "Cardiovascular Regulation During Long-Duration Spaceflights to the International Space Station," is published in the Journal of Applied Physiology.
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