Blood Density

link.springer.com/article/10.1007%2FBF01907921
​Interesting that blood density rises during traditional flat bed rest, yet falls when upright during the day. I suspect it remains lower using IBT

Ventilatory changes of pulmonary capillary blood volume assessed by arterial density
Journal of Applied Physiology, Vol 61, Issue 5 1724-1731, Copyright © 1986 by American Physiological Society

ARTICLES
Ventilatory changes of pulmonary capillary blood volume assessed by arterial density
J. S. Lee and L. P. Lee

By use of an improved density measuring system, we found that the gravimetric density of arterial blood of dogs fluctuates at the same frequency as the spontaneous or mechanical ventilation. Similar density fluctuations were observed in the blood leaving isolated, perfused lobes of dogs that were ventilated cyclicly. Employing an analysis that balanced the erythrocyte and plasma flows through distensible capillaries containing blood with a tube hematocrit lower than the hematocrit in large blood vessels, we derived a relationship to estimate from the density fluctuation the change in pulmonary capillary blood volume (Vc). For mechanical ventilation, the maximum change in density over one ventilation cycle increased from 0.084 +/- 0.01 to 0.47 +/- 0.05 (SE) g/l as the frequency decreased from 29 to 6 cycles/min. These density changes were estimated to be the result of an 1-16% change in Vc. A larger tidal volume for the mechanical ventilation led to a larger density fluctuation. The maximum density change of spontaneous respiration of 6 cycles/min was one-sixth of the mechanical case, indicating a much smaller change in Vc during spontaneous respiration. When the airway flow resistance was increased for spontaneous respiration, larger density fluctuations were observed.