[Central circulation in the healthy human being during 7 days of head-down tilt and decompression of different body areas].

The effect of 7-day head-down tilt (-15 degrees) and decompression of various body parts (lower body-LBNP, upper body in the area of the hydrostatically indifferent point-UBNP, and local negative pressure applied to both calves-LNP) on central circulation was investigated on eight healthy test subjects who, for 10 days, had catheters (Swan-Ganz) implanted into the pulmonary and radial arteries. It was shown that, when calculated by square centimeter of the decompression area, the effect of UBNP on central venous pressure (CVP) and pulmonary artery pressure (PAP) was 3-4 times greater than that of LBNP or LNP. This indicates a high sensitivity of this body part to the exposure. During the 7-day study, CVP and PAP showed the most distinct changes. By the 7th hour of the head-down tilt study, CVP remained unchanged and systolic PAP increased by 5.5 mm Hg (27%) (p less than 0.05). This was paralleled by a decrease of plasma aldosterone and renin. By the 2nd day of the study, CVP and PAP were close to the pretest level; on the 3rd day, they began to decline and remained about 3 mm Hg lower than the pretest values to the end of the study (p less than 0.05). During this same period, the contractility of the right heart (the mean rate of right ventricular pressure increment) decreased by 34% (p less than 0.05) and its work by 27% (p less than 0.05). By the 24th hour after the study (the recovery period), CVP and PAP were close to the pretest values, whereas heart rate, cardiac index and oxygen tension in the mixed venous blood were significantly higher than the pretest values (p less than 0.05). The factors responsible for these changes and the potential application of the catheterization technique in biomedical investigations during real space flight are discussed.