The effects of the tilt test (at 60-70 degrees for 20 min) and LBNP test (at -30 and -60 mm Hg for 20 min each) on the basic parameters of central circulation (15 test subjects) and coronary circulation (11 test subjects) were investigated. The study was performed using thermistor-equipped catheters implanted into the pulmonary artery and coronary sinus and Teflon catheters implanted into the brachial artery. In the study, the basic parameters of central circulation (pressure in the right atrium and pulmonary artery, transmural pressure in these compartments, cardiac index, stroke index, etc.) and coronary circulation (blood flow in the coronary sinus, left ventricle oxygen consumption, coronary resistance, etc.) were measured. Correlation between circulation variations and metabolic requirements was assessed (with respect to changes in acid-base equilibrium of blood). The effect of the tilt test and LBNP test on the basic parameters of central and coronary circulation, blood acid-base equilibrium and oxygenation was compared.

Experiments were performed to study the effect of leg decompression in the head-down position at -15 degrees. The method of chronic catheterization was used, pressure was measured in different areas of the cardiovascular system, blood was withdrawn for biochemical analysis. The effect of leg decompression was compared with that of lower body negative pressure. Decompression produced changes in PAP and CVP that were similar in sign but different in magnitude. The decompression-induced changes in PAP and CVP were primarily determined by the area of exposure. Using previous data, a monograph was constructed to evaluate PAP and CVP variations as a function of the decompression mode and site.

The effect of tilt (head-up and head-down) tests, LBNP tests, and 7-d head-down tilt (at -15 degrees) on coronary circulation was investigated in healthy male volunteers. Catheters were implanted into the coronary sinus and brachial artery. The Ganz catheter in the coronary sinus was used to measure volume flow in the area (constant thermodilution), pressure, and to withdraw samples of outflowing blood for biochemical analysis (acid-base equilibrium and oxygenation). Transfer from supine to upright body position, lower body negative pressure (-30 mm Hg for 20 min), as well as 15 degrees head-down (by day 5-6) produced similar changes in the basic parameters of coronary circulation-reduction of blood flow and oxygen consumption, decrease of pressure in the coronary sinus, and increase of coronary resistance. Transfer from head-up to head-down position caused opposite changes of the above parameters. The changes in coronary circulation were adequate for myocardial metabolic requirements since the biochemical composition of the outflowing blood remained essentially constant during the gravitational exposures described.

Eleven healthy male test subjects performed exercises of 600 kgm/min (98 W) for 20 min in the head-down position (-15 degrees). A day before exercises they were catheterized, with catheters implanted into the internal jugular vein and brachial artery. It was shown that exercises in the head-down position led to an increase in cerebral circulation, a decrease in oxygen utilization and a decrease in jugular pressure. CO2 tension in arterial blood and blood outflowing from the brain remained comparatively stable, while base deficiency and buffer capacity decreased by a similar value.