[Changes in several indicators of blood rheology in experiments simulating weightlessness]

Changes in blood rheological parameters of 21 male volunteers, aged 25-37 years, were studied. The test subjects were subdivided into three groups. Nine subjects of Group 1 were exposed to head-down tilting (-8 degrees) for 14 days, six subjects of Group 2 were exposed to 7-day continuous immersion, and six subjects of Group 3 to intermittent immersion. During head-down tilting the apparent viscosity and hematocrit and then caisson viscosity increased. By day 7 the coefficient of red blood cell aggregation decreased significantly. These changes persisted till the end of the tilt study. The above rheological parameters returned to normal three days after the exposure. During continuous immersion the apparent viscosity showed the largest changes. Other specific changes included a moderate decrease of hematocrit, lack of significant changes in the yield limit of blood and a tendency towards an increase in the erythrocyte aggregation coefficient. Three days after the exposure the blood viscosity was much higher than before the study. During intermittent immersion rheological changes were induced by the first 36-hour exposure when shifts in blood viscosity and other parameters were most significant. It should be noted that following this exposure 72 hours of normal motor activity did not result in the normalization of the above rheological parameters.