The head-down tilt and adaptability for aerospace flight.

A L T H O U G H tilt table procedures have been used extensively in the study of the circulatory system, most studies have been with subjects in the feet-down position. 1,2 The tilt table provides a means of studying the influence of g force upon the circulatory system. When an individual is strapped to the tilt table, feet down, in the vertical position r he is exposed to + 1 g. When tilted to the recumbent or horizontal position, the subject is exposed to a transverse force of 1 g. If the individual is tilted vertically, head down, he is exposed to negative 1 g. Thus, the tilt table offers a laboratory procedure for evaluating the response of the circulatory system over prolonged periods of time to different types of g force stimulation. It provides certain obvious advantage over more complex procedures. Many centrifuges do not permit sudden change from positive to negative g as can be accomplished on the simple tilt table. With the advent of the space age, considerable interest has been expressed in circulatory response during weightless conditions. 4 The type of circulatory response to weightlessness will be somewhere between + 1 g and I g. Whether or not weightlessness has a major influence upon