Journal of Applied Physiology, Vol 73, Issue 4 1366-1369, Copyright © 1992 by American Physiological Society
Effects of simulated microgravity (HDT) on blood fluidity
L. Lampe, K. Wienhold, G. Meyer, F. Baisch, H. Maass, W. Hollmann and R. Rost
Institute for Cardiology and Sports Medicine, German Sports University, Cologne.
Exposures to microgravity and head-down tilt (HDT) produce similar changes
in body fluid. This causes an increase in hematocrit that significantly
affects hemorheological values. Lack of physical stimulation under bed rest
conditions and the relative immobility of the crew during spaceflight also
affects the blood fluidity. A group of six healthy male subjects
participated as volunteers, and blood samples were collected 10 days
before, on day 2 and day 9, and 2 days after the HDT phase. Blood rheology
was quantified by plasma viscometry, red cell aggregability, and red cell
deformability. A reduced red cell deformability, an indication of the
diminished quality of the red blood cells, was measured under HDT
conditions that finally led to the so-called "space flight anemia."
Enhanced red cell membrane fragility induced by diminished physical
activity and an increase in hemoglobin concentration are responsible for
this effect. Plasma viscosity is reduced as a result of diminished plasma
proteins. However, despite the reduction in plasma proteins, including
fibrinogen, alpha 2-macroglobulin, and immunoglobulin M, red cell
aggregation was enhanced, principally because of the increase in
hematocrit. Our results of hemorheological alterations under HDT conditions
may help to elucidate the formerly documented hematologic changes during
spaceflight.
