[Dynamics of the redistribution of human blood in response to lower body negative pressure].

During exposure to LBNP of -10 to -60 mm Hg variations in the blood filling of body segments were measured, using 59Fe labelled erythrocytes. The study was performed on 10 healthy volunteers each of which was exposed to six LBNP sessions (in recumbency). The data obtained were related to changes in the blood filling of various body segments (head, thorax, abdomen, pelvis, legs) which were most pronounced at LBNP -20 to -30 mm Hg. As the LBNP level increased, the changes in the blood filling of the pelvis and legs, head and thorax decreased. In the abdominal area this parameter remained essentially unaltered. The distinct variations in the thoracic blood filling were probably dependent on the amount of blood shifted to the decompressed area which may be related not only to the venous capacity in this area but also to the venous- arterial reflexes and possibly to the specific transfer of reduced pressure in tissues.