Investigations of the mechanisms by which lower body negative pressure (LBNP) improves orthostatic responsesSaline ingestion during LBNP is a counter measure proposed to improve orthostatic function during space flight. To understand the mechanism(s) responsible for this effect, body fluid, endocrine, and orthostatic responses (graded LBNP tests) were measured during bed rest (BR) and after 2 hr and 4 hr LBNP/saline treatments (-30 mm Hg and 1 liter of isotonic saline). PV (from I-125 and hematocrit measurements) decreased during BR but was restored to the pre-bed rest level (3157 +/- 161 ml) 20 hrs after both 2 hr (3109 +/- 146 ml) and 4 hr (3144 +/- 173 ml) LBNP. The heart rate response to graded LBNP tests was significantly improved after the 4 hr, but not after the 2 hr treatment. These results suggest PV expansion may be responsible for some improvement in orthostatic responses, but other mechanisms also must contribute.
Document ID
19920073077
Acquisition Source
Legacy CDMS
Document Type
Conference Paper
Authors
Fortney, S. M. (NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Steinmann, L. (NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Dussack, L. (NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Wood, M. (NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Cintron, N. (NASA Lyndon B. Johnson Space Center Houston, TX, United States)
Whitson, P. (NASA Johnson Space Center; Krug International Corp. Houston, TX, United States)