Spaceflight poses various risks to the human body as it is displaced from the Earth’s life-supporting environment to the less benign conditions encountered in space.
These conditions include radiation; confinement in small, enclosed spaces with associated physical and psychological stressors; disrupted circadian rhythms; and, of course, microgravity. They take a toll on the human body, affecting vision, the musculoskeletal system, and the immune system.
Scientists at NASA are researching the risks associated with short and long duration space missions, such as spending more than six months on the ISS or – the next giant leap – a mission to Mars. A recent discovery by a team at NASA Johnson Space center suggests that one of these risks may not be as much of a problem as previously assumed.
Space flight anemia – the reduction of circulating red blood cells (RBCs) during time spent in space – is a generally accepted phenomenon. However, the majority of the studies examining changes to concentrations of red blood cells during spaceflight have been limited to evaluations of short-duration missions after astronauts had returned to earth.
The few evaluations made while astronauts were still in space have been conducted during short-duration flights, before the astronauts’ bodies had fully adapted to microgravity. Their findings may not accurately reflect what happens to red blood cells during long-duration flight.
Dr Richard Simpson, associate professor at The University of Arizona and the University of Houston, a co-author of the study explained: “This unique sample allowed us to track hematological parameters – such as concentrations of red blood cells (RBCs), hemoglobin or hematocrit – in astronauts on board the International Space Station during flight.”
This is the first study to show that RBC concentrations and hematocrit remain at higher levels even after astronauts’ bodies have adapted to microgravity
The samples were collected from 31 astronauts (six women and 25 men) who spent up to six months on the ISS. Blood was drawn at various time points before, during and after the astronauts’ time in space: at 180 and 45 days before they flew to the ISS, during their first two weeks in space, and approximately three and six months into the mission. The samples were sent to Earth within 48 hours of collection for analysis either in Houston or at Star City, Russia. Post-flight samples were collected three to eight hours after landing and 30 days after the mission had ended.
The researchers found that during space flight, concentrations of RBCs, platelets and the oxygen-carrying protein hemoglobin were higher compared to pre-flight levels. Hematocrit (the ratio of RBCs to the total volume of blood) also increased during space flight. While previous studies had shown this to be the case during the first few days of flight, this is the first study to show that RBC concentrations and hematocrit remain at higher levels even after astronauts’ bodies have adapted to microgravity.
Some of the changes observed in the in-flight blood samples were to be expected due to the 48-hour processing delay between sample collection and analysis (delays affect the concentration of various components of collected blood samples), but the changes in hematocrit during spaceflight were striking, according to the researchers.
Hematocrit had increased by 12.2%, 12.2% and 10.0% at early, mid, and late time points during space flight compared to pre-flight levels. However, only a 4.7% increase in hematocrit was observed in reference samples taken on earth from non-astronauts after the 48-hour processing delay. This suggests that the increases observed in the ISS samples are partly due to a true in-flight increase in RBC count. After the astronauts examined in this study returned to Earth, all blood parameters returned to pre-flight levels within 30 days.
The findings have to be interpreted within the context of the effects that microgravity has on body fluids, according to the study. For example, without the constant gravitational force that is present on Earth, fluids shift towards the head, resulting in a “puffy” face and a reduced leg volume.
Dr Simpson said: “Although the data does not indicate that significant anemia is present, it must be interpreted in the context of crew plasma volume during flight. Overall plasma volume has been shown to be reduced during spaceflight, but this has not been assessed during long-duration missions. In order to fully interpret the changes to RBC, hematocrit and other parameters observed in this study, further research into plasma volume during long space missions is needed.”