[Respiration and cardiovascular mechanisms of hypobaric correction of the head-down redistribution of local blood volumes].

The focus was placed on the physiological mechanisms of correction of the blood redistribution during the head-down tilt (HDT) with a discrete or complex use of the methods of negative pressure respiration (NPR) and lower body negative pressure (LBNP). It was evidenced that rise in the intracranial hydrostatic pressure in HDT (-6 degrees) can be compensated by NPR within a range of -10 to -15 cm of water column causing decrease in the intrasternal pressure from -5.04 to -7.74 cm w.c. Bioimpedance and ultrasonic investigations led to the conclusion that the decreased transpulmonary pressure is responsible for blood outflow from the intracranial venous system till the level adequate to the horizontal position of the body. The results were verified in experiments with unconscious cats: pressure in the exterior jugular vein and v. cava superior during HDT (-30 degrees) with NRP at -5 cm w.c. decreased by 3.2. and 4.3. w.c., respectively. Experiments with human subjects also demonstrated that the complex use of NPR and LBNP produces an additive hemodynamic effect and can be considered a new method for correcting the adverse consequences of redistribution of the local blood volumes toward the head end.