Photo by Graham Colm
Blood samples
Previous research has suggested that astronauts develop anemia during space flight, but a new study indicates this is not the case for astronauts on long space missions.
“There is an idea of ‘space anemia’ that is associated with space flight,” said Richard Simpson, PhD, of the University of Houston in Texas.
“However, this is based on blood samples from astronauts collected after flight, which may be influenced by various factors—for example, the stress of landing and re-adaptation to conditions on Earth.”
“For this study . . ., living, whole blood samples were collected during space flight and returned to Earth for analysis. This unique sample allowed us to track hematological parameters—such as concentrations of red blood cells, hemoglobin, or hematocrit—in astronauts on board the International Space Station during flight.”
Dr Simpson and his colleagues reported their findings in BMC Hematology.
The researchers found that, during space flight, concentrations of red blood cells (RBCs), platelets, and hemoglobin were higher compared to pre-flight levels. Hematocrit also increased significantly 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.
To find out how the blood of astronauts may change if they spend a long time in space, the researchers collected blood samples from 31 astronauts who spent up to 6 months on the International Space Station (ISS). There were 6 female and 25 male subjects, and their mean age was 52 (range, 38–61).
Samples were collected at 180 days and 45 days before the astronauts flew to the ISS. Blood was also collected while they were in space—during the first 2 weeks (early time point), between 2 and 4 months (mid time point), and about 6 months into the mission (late time point).
Samples were returned to Earth for analysis either in Houston or at Star City, Russia, within 48 hours of collection. Post-flight samples were collected 3 to 8 hours after landing and 30 days after the mission had ended.
Results
The researchers said 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.
However, the team found that RBC concentration was significantly elevated at all 3 in-flight time points, when compared to the 180-day pre-mission time point (baseline). And RBC counts returned to baseline levels upon Earth landing.
The mean RBC concentrations (x 106 cells/μL) were:
- 4.4 ± 0.4 (range, 3.5–5.1) at baseline
- 4.8 ± 0.5 (range, 3.9–5.7) at the early time point (P<0.05)
- 4.7 ± 0.4 (range, 3.9–5.4) at the mid time point (P<0.05)
- 4.7 ± 0.4 (range, 4.1–5.6) at the late time point (P<0.05).
Hemoglobin was elevated early in flight but returned to pre-flight levels during the mission and fell below baseline levels on landing day. The mean hemoglobin (g/dL) levels were:
- 14.1 ± 1.4 (range, 11.0–17.8) at baseline
- 15.0 ± 1.9 (range, 10.7–17.5) at the early time point (P<0.05)
- 13.5 ± 1.4 (range, 10.1–15.9) on landing day (P<0.05).
Mean corpuscular hemoglobin (MCH) decreased during the mission and was significantly lower than baseline at the late time point. However, MCH returned to pre-flight values upon landing. The mean MCH (pg) was:
- 31.7 ± 1.6 (range, 28.8–36.4) at baseline
- 31.3 ± 1.9 (range 26.3–34.0) at the late time point (P<0.05).
The researchers said they observed significant increases in mean corpuscular volume (MCV) during space flight. However, these reflect the changes observed following the 48-hour processing delay. So there were no variations in MCV attributable to space flight.
The changes observed in hematocrit during space flight were “striking,” according to the researchers. The mean hematocrit levels were:
- 40.9 ± 3.9 (range, 33.1–48.0) at baseline
- 45.9 ± 4.7 (range 38.2–52.1) at the early time point (P<0.05)
- 45.9 ± 5.5 (range 38.9–58.3) at the mid time point (P<0.05)
- 45.0 ± 2.5 (range 38.9–49.9) at the late time point (P<0.05).
Compared to pre-flight levels, hematocrit increased by 12.2% at early, 12.2% at mid, and 10.0% at late time points. In comparison, there was a 4.7% increase in hematocrit in reference samples from non-astronauts after the 48-hour processing delay.
Finally, the researchers found that platelet concentrations were elevated in flight, at the early and mid time points. However, platelets were not significantly elevated at the late time point, and they were stable upon landing.
For all of the astronauts, all blood parameters returned to pre-flight levels within 30 days of landing on Earth.
The researchers said these results are susceptible to the possible influence of dehydration or plasma volume alterations. However, the findings do suggest the increases observed in the ISS samples are partly due to a true in-flight increase in RBC count.
“Although the data does not indicate that significant anemia is present, it must be interpreted in the context of crew plasma volume during flight,” Dr Simpson said. “Overall plasma volume has been shown to be reduced during space flight, 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. This will be addressed in a separate, ongoing NASA investigation.”
