THE RESPONSES OF CARDIOVASCULAR DURING HEAD-UP TILT PLUS LOWER BODY NEGATIVE PRESSURE

A method of head-up tilt plus lower body negative pressure (LBNP-HUT) is used in simulating the stress of gravity upon crewman after returing to the earth from spaceflight, in order to study the regulatory function of cardiovascular system. The subjects are 20 healthy young men. The examination consisted of a simple head-up tilt (HUT, 75°) experiment for twice, each lasting 20 min and two times of LBNT-HUT, of the latter -5333 Pa LBNP is acted with subjects in supine position on a tilt table for 2 min then the subjects are turned to HUT (75°) for 20 min while the LBNP is maintained. Four types of regulation are found, according to the responses of the subjects in heart rate, perpheral resistance and tolerance time during LBNP-HUT, which are vessel-type (VT), mixture-type (MT), heart-type (HT) and under regulation-type (URT). The cardiovascular regulative capacity during LBNP-HUTis in the order of VT>MT>HT>URT. The results show that the method of LBNP-HUT is an effective approach to examine the regulatory function of cardiovascular system, as it con provide larger stress upon the subjects than the simple method does, when only HUT or LBNP alone is applied. It can be used in the selection of cardiovascular function of astronauts.