Blood coagulability changes in females exposed to dry immersion: examining a mechanism for the development of venous thromboembolism in microgravity

The recent report of a blood clot in the internal jugular vein (IJV) of an astronaut aboard the International Space Station (ISS) has prompted the need of the international scientific community to investigate the potential underlying pathophysiology. Current published research on this topic is male-centred, despite known clotting sex-differences and heightened risk for females on Earth. In this study, we assessed the hemostatic responses of female participants exposed to dry immersion simulated microgravity. Based on previous evidence from studies of males in simulated microgravity (head-down tilt bedrest), we hypothesized an initial increase in pro-coagulation activity along with increased anticoagulation activity. Eighteen healthy female participants (28.2 ± 4.1 years, 59.4 ± 6.4 kg, 64.7 ± 6.0 cm) took part in the ESA- sponsored VIVALDI I five-day dry immersion study. Coagulation risk was assessed with rotational thromboelastometry and thrombin-antithrombin tests. The results showed a significant increase from baseline for coagulation and maximum clot firmness measurements, and a decrease in clot formation time by the last day of dry immersion. Thrombin-antithrombin levels were unchanged in response to dry immersion. These data present evidence of significant changes in hemostatic responses for females exposed to five days of dry immersion and suggest a possibility for increased clotting risks during flight. • A jugular vein clot in a female astronaut on the ISS has raised health concerns • Females are underrepresented in spaceflight research • Eighteen females took part in a 5-day dry immersion study of venous thromboembolism • Female hemostatic equilibrium was sub-clinically disrupted by 5-day dry immersion • Coagulation time and maximum clot firmness increased. Clot formation time decreased