Cardiovascular Deconditioning from Space Cabin Simulator Confinement.

D IFFICULTIES ENCOUNTERED in assessing the influence of weightlessness on the circulatory system have previously been discussed, s Problems other than weightlessness which profoundly influence the cardiovascular system must also be considered. One of these in confinement or inactivity resulting in cardiovascular deconditioning. Simulated hypogravic studies done to date all include inactivity as a major factor in the experiments.i, ',, a. r. s, 9 The supine position, whether it be in a body cast, water immersion, or bed rest, is perpendicular to the vertical g field (perpendicular to +Gz and-Gz) . Whether or not this has any particular physiological influence cannot be judged with certainty in the presence of a significant decrease in physical activity. The original studies of Dietrick 6 and Taylor 14, 1'~ were principally designed to study the influence of inactivity or bed rest. They were not intended to study the influences of weightlessness. Data obtained during manned orbital flight from the Mercury Project suggesting decreased orthostatie tolerance must also be regarded from the point of view of confinement, inactivity, or deconditioning, as opposed to the influences of weightlessness.4, 5 Data obtained from future manned space flights cannot provide a significant answer relative to the problem of weightlessness unless adequate consideration of deconditioning due to inactivity is given. As long as the vehicle provides limited opportunity for activity the problems of deconditioning will complicate the picture. Since previous reported studies of inactivity are complicated by the supine position or absence of vertical g, it has not been possible on these studies to separate the influence of inactivity versus absence of vertical g stimulation. To understand what might be seen in a space vehicle related to weightlessness one should first study the results of an environment exactly similar to the space capsule within the laboratory with normal g force application. The opportunity to do this occurred as the result of the preand post-examinations of subjects who were being studied for space cabin simulator flights. Since these individuals were either seated or moved about within a small confined area they presented the problem of confinement with inactivity during normal g force application. Such studies provide the beginnings of a method of controlled evaluation to which comparison of observations during space flight may be made. In a sense, studies designed in this man-