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Pros and Cons of Using Water Immersion to Simulate Physiological Responses to MicrogravityHead-out water immersion (HOI) has been employed as a remedial treatment for various ills and ailments for many millennia, and total body immersion even longer as protective encapsulation for the mammalian fetus. Two discrete differences between stimuli induced by true microgravity (10(exp -4) g) and HOI are readily apparent. External water pressure on the skin and accompanying negative pressure breathing cause blood to shift headward. Secondly, the gravitational force is ever present during immersion and microgravity, but its effect is essentially neutralized during Earth orbital flight. Thus, the physiological responses to immersion should not be expected to match those during microgravity. Immersion has been used mainly to study and understand kidney function and associated cardiovascular responses for control of body fluid volume and osmotic content, with some application to and simulation of microgravity responses. There is a plethora of data from human HOI studies, but relatively few controlled data from microgravity studies. In general, it appears that physiological responses occur more quickly with water immersion than in microgravity, but this may be due to less rigorous control (voluntary and involuntary) of the preflight state of crew members. The central venous pressure-vasopressin (Gauer-Henry) reflex control for fluid balance may not be of prime importance in microgravity. Gross functions such as reduced body weight and water, level of hypovolemia, decreased isokinetic strength, and lower nitrogen balance found during immersion are qualitatively similar in microgravity, but the mechanisms controlling these and other functions are, for the most part, unclear. Only acquisition of data from well-controlled microgravity experiments will resolve this discrepancy.
Document ID
20020038411
Acquisition Source
Ames Research Center
Document Type
Conference Paper
Authors
Greenleaf, J. E.
(NASA Ames Research Center Moffett Field, CA United States)
Tomko, David L.
Date Acquired
August 20, 2013
Publication Date
January 1, 1995
Subject Category
Aerospace Medicine
Meeting Information
Meeting: Third International Head-Out Water Immersion Symposium
Location: Copenhagen
Country: Denmark
Start Date: August 25, 1995
End Date: September 6, 1995
Funding Number(s)
PROJECT: RTOP 199-18-12-07
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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