Journal of Applied Physiology, Vol 63, Issue 3 1003-1007, Copyright © 1987 by American Physiological Society
Continuous monitoring of blood volume changes in humans
H. Hinghofer-Szalkay and J. E. Greenleaf
Laboratory for Human Environmental Physiology, National Aeronautics and Space Administration Ames Research Center, Moffett Field, California 94035.
The mass density of antecubital venous blood was measured continuously for
80 min/session with 0.1 g/l precision at a flow rate of 1.5 ml/min in six
male subjects. Each person participated in two different sessions with the
same protocol. To induce transvascular fluid shifts, the subjects changed
from sitting to standing and from standing to supine positions. There was
transient blood density shifts immediately after postural changes, followed
by an asymptotic approach to a new steady-state blood density level.
Additional deviations from a simple time course were regularly observed.
Blood density increased by 3.5 +/- 1.4 (SD) g/l when standing after sitting
and decreased by 5.0 +/- 1.2 g/l while supine after standing. The
corresponding half time of the blood density increase was 5.6 +/- 1.4 min
(standing after sitting) and 6.9 +/- 3.1 min (supine after standing) of the
blood density decrease. Erythrocyte density was calculated and did not
change with body position. Whole-body blood density was calculated from
plasma density, hematocrit, and erythrocyte density, assuming an F-cell
ratio of 0.91. Volume shifts were computed from the density data; the
subject's blood volume density decreased by 6.2 +/- 1.2% from sitting to
standing and increased by 8.5 +/- 2.1% from standing to supine. Additional
discrete plasma density and hematocrit measurements gave linear relations
(P less than 0.001) between all possible combinations of blood density,
plasma density, and hematocrit.(ABSTRACT TRUNCATED AT 250 WORDS)
