Journal of Hematology & Thromboembolic Diseases
Open Access

Hematological Changes in Astronauts During Spaceflight

Beverley Makris^{* *}Correspondence: Beverley Makris, Department of Experimental Haematology, University of Cairo, Cairo, Egypt, Email:

Author info »

Description

Space exploration has captured human imagination for decades, and the advancements in space missions have led to a deeper understanding of the human body's response to spaceflight. As astronauts venture into space, they are subjected to unique conditions that alter various physiological systems, including the hematological system. The absence of gravity, exposure to cosmic radiation, and the confined environment aboard spacecraft can lead to significant changes in blood composition and function. These hematological alterations are critical to understanding the health risks astronauts face during long-duration missions and to developing countermeasures to mitigate these effects.

Red Blood Cells and Hemoglobin in Space

One of the most prominent hematological changes during spaceflight is the alteration in Red Blood Cell (RBC) mass and hemoglobin levels. Studies have shown that astronauts experience a decrease in total red blood cell count and a reduction in hemoglobin concentration during and after space missions. These changes are primarily due to a combination of factors related to fluid shifts, bone marrow suppression, and changes in erythropoiesis.

Decreased red blood cell mass: During spaceflight, the redistribution of body fluids due to the absence of gravity can lead to a transient increase in plasma volume, which results in a dilution of red blood cells and hemoglobin (a condition known as "space anemia"). This process, also known as hemodilution, can cause a temporary reduction in hematocrit levels .

Suppressed erythropoiesis: The production of RBCs is regulated by erythropoietin (EPO), a hormone primarily produced in the kidneys in response to low oxygen levels (hypoxia). On Earth, gravity and the body's typical daily activities can stimulate EPO production to maintain appropriate oxygen-carrying capacity in the blood. In space, however, the absence of gravity and altered environmental conditions may lead to changes in the EPO response .

White Blood Cells and Immunity in Space

The immune system undergoes significant alterations during spaceflight, and changes in White Blood Cell (WBC) count and function are central to these shifts. The reduction in WBCs, particularly neutrophils and lymphocytes, is commonly observed in astronauts, which may affect the body’s ability to respond to infections and stress .

Leukopenia and lymphocytopenia: Leukopenia (a reduction in the total number of white blood cells) is a common observation during spaceflight. The number of circulating lymphocytes, particularly T-cells and B-cells, is significantly reduced during space missions. This decline in immune cell numbers may be attributed to several factors, including stress-induced apoptosis (cell death) of immune cells, alterations in bone marrow function, and changes in the production and release of cytokines .

Altered immune function: The reduction in WBC count during space missions does not necessarily correlate with an immediate increase in infection rates, but it does affect the overall immune system's functionality .

Mechanisms behind hematological changes in space

The exact mechanisms behind these hematological alterations are not fully understood, but several factors are thought to contribute to the changes observed in astronauts' blood profiles during spaceflight .

Microgravity: The absence of gravity in space leads to fluid shifts within the body, with blood and other fluids being redistributed toward the upper body and head. This can affect the volume of plasma and blood cells, leading to dilutional effects on hemoglobin and RBC mass.

Cosmic radiation: Space radiation, particularly cosmic rays and solar radiation, contributes to oxidative stress, which can damage blood cells, including red blood cells and white blood cells. This radiation-induced damage may increase hemolysis, leukopenia, and platelet dysfunction .

Conclusion

Hematological changes in astronauts during spaceflight are complex and multifactorial, involving alterations in red blood cells, white blood cells, platelets, and coagulation factors. These changes are primarily caused by the unique conditions of space, including microgravity, radiation exposure, psychological stress, and altered physical activity. While most of these changes are transient and do not lead to clinically significant health issues, understanding and mitigating the risks associated with hematological alterations are crucial for the health and performance of astronauts on long-duration missions.