Central circulation of a normal man during 7-day head-down tilt and decompression of various body parts

The effect of 7-d 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 d, 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-d 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).(ABSTRACT TRUNCATED AT 250 WORDS)