title: Cardiovascular studies during and following simulation and weightlessness.
abstract: Two major characteristics of space flight may be simulated to some degree by bed rest and by water immersion. These are inactivity and the lack of the hydrostatic stress on the systematic circulation. Studies prior to the advent of space flight led to the prediction of orthostatic intolerance, muscular weakness, and calcium loss. Prolonged space flight has heightened the interest in these simulations to provide information concerning the temporal cause of the "deconditioning" or disuse syndrome and the value of simulation for testing the effectiveness of remedial measures. This report will evaluate the extent to which the simulation appears valid. In its gross effects, orthostatic intolerance can be studied with respect to its temporal course, etiology and effectiveness of remedial measures. The intolerance develops more rapidly during water immersion with respect to cause as well as effect. The short term of immersion studies does not allow study of the secondary change in blood volume due to red cell mass changes, Remedial measures seem clearly defined in water immersion simulation and less clear in bed rest. Measures of venous pooling following water immersion appear different than those obtained following weightlessness. There also appear to be differences in the results of evaluation of protective devices and measures and in the time course of development and recovery of orthostatic intolerance. Correlates of the cardiovascular responses such as muscle tone, skeletal strength, and endocrine change (catecholamines, vasopressin and aldosterone) suggest a marked alteration in physiology during hypodynamic status. To date, work on exposure to increased G force has provided only extrapolated data concerning metabolic requirements.
authors.affiliation: Department of Physiology and Biophysics, University of Kentucky, USA.
authors.forename: L D
authors.initials: LD
authors.lastname: Carlson
mesh_terms: D001510:Bed Rest; D001794:Blood Pressure; D001810:Blood Volume; D018493:Cardiovascular Deconditioning; D006339:Heart Rate; D006801:Humans; D007024:Hypotension, Orthostatic; D007101:Immersion; D008297:Male; D018667:Tilt-Table Test; D014867:Water; D014893:Weightlessness; D018544:Weightlessness Countermeasures; D018474:Weightlessness Simulation
chemical_list: D014867:Water