Influence of 21-Day Head-Down Bed Rest on the Hemostasis System of a Healthy Human

The bed rest experiment involved six healthy men aged 24 to 41 years. The subjects were in the supine position for 21 days, the angle of inclination in the cranial direction was –6°. In citrated blood plasma on days 2, 5, 8, and 21 of exposure, as well as 7 days after its end, the following hemostasis parameters were determined: thrombin time, prothrombin time, activated partial thromboplastin time, fibrinogen, and D-dimer concentrations, as well as activity of protein C. In comparison with the background, there was slight elongation in prothrombin time on days 2 and 5 of the experiment, as well as on day 7 of the recovery period, a slight shortening of the thrombin time on days 8 and 21 of the experiment and day 7 of the recovery period, moderately elongated activated partial thromboplastine time on days 5 and 21. The concentration of D-dimer was significantly reduced relative to the background in all periods of the survey, except for day 21, approaching the background values on day 7 after the end of exposure. The activity of protein C did not change significantly during the entire experiment and was significantly lower than the background values only on day 7 after the end of the experiment. The concentration of fibrinogen did not change significantly during all periods of the examination. The results of the study indicate minor changes in the parameters of the plasma component of the hemostatic system, indicating a decrease in procoagulant potential in the early stages of exposure and its increase in the later stages of hypokinesia and in the recovery period.