Effects of Four Weeks of Absolute Bed Rest on Circulatory Functions in Man.

Various effects of 4 weeks of absolute bed rest on the circulatory system were studied in 12 healthy male volunteers. Postural tolerance varied from day to day before and after bed rest. Repeated tilt table testing allowed a more accurate appraisal of changes in postural tolerance caused by bed rest. Postural syncope on the tilt table was more frequent after bed rest. Forty-two percent of the subjects, however, did not faint during repeated testing after bed rest. A comparison of the highest orthostatic heart rates recorded during each tilt table test without an antigravity suit before and after bed rest showed a distinctly higher range of orthostatic heart rates after bed rest in each subject studied. When an antigravity suit was worn during tilt table testing after bed rest, postural syncope occurred on one occasion only. The relation of these studies to proposed flights in the Manned Orbiting Laboratory is discussed. p R O L O N G E D SPACE F L I G H T and prolonged bed rest are sufficiently analogous to justify concern that the tendency to faint upon standing observed in normal subjects after prolonged bed rest may also be present in crew members reexposed to the earth's gravity after a 30 day flight in the Manned Orbiting Laboratory. In both environments the need for physical activity is greatly diminished and significant positional changes in hydrostatic pressure in the body fluids are absent. This paper presents a study of various effects of 4 weeks of absolute bed rest on the circulatory system of man. Its purpose is: (1) to provide data useful in the prediction of cardiovascular tolerance to gravity after landing from a 30 day mission in the Manned Orbiting Laboratory; (2) to provide a model for later use to compare the cardiovascular effects of 4 weeks of space flight to 4 weeks of bed rest; (3) to evaluate the efficiency of an antigravity garment in preventing postural intolerance after 4 weeks of bed rest, and by analogy, 4 weeks of space flight; (4) to determine the suitability of this period of bed rest for future studies 1194 Aerospace Medicine 9 December 1964 seeking effective cardiovascular maintenance procedures adaptable to space flight.