Changes of blood volume distribution by postural changes in rats.

During a space flight the human body responds to many different gravities. The launching of the rocket, the weightlessness, the re-entry of the spacecraft, and other factors influence the astronaut's body. The fluid shifts and the effect on the cardiovascular system arising from these gravitational changes have been frequently studied in space medicine by using body tilting, lower body negative pressure (LBNP) and centrifugal accelerators. There exist, however, few reports about the changes in whole body blood volume distribution caused by body tilting. These changes can be measured using radioisotopes: scintigraphy using 99mTechnetium-labeled human serum albumin (99mTc-HSA), etc. In humans, however, because the visual field of the scintillation camera is so small, the simultaneous measurement of whole body blood volume distribution cannot be done during body tilting. We therefore used rats, whose whole bodies can be encompassed within the visual field of the camera, and we discussed the changes in blood volume distribution induced by body tilting. We also measured the blood concentrations in each organ by using whole body autoradiography in mice, and discussed the effect of postural changes on some abdominal organs.