Role of previous simulated G-force exposure and AGSM on tolerance to orthostatic stress (LBNP)

J. M. Serrador, M. G. Chambers, R. W. Brock, J. A. Hawley, R. L. Bondar, R. L. Hughson

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Research has demonstrated that exposure to -Gz fores increases the BP drop upon exposure to +Gz (Banks et al, 1994). This study further examined the cardiovascular response to simulated +Gz with or without previous -Gz exposure. All subjects participated in two conditions: Control (CON) in which they were placed in 45° Head Up Tilt (HUT) in a seated position inside an LBNP box for 5 min followed by 5 min of -80 mmHg LBNP and 5 min of recovery; Experimental (EXP) in which the test began with 3 min 45° followed by 10 cycles of alternating 30 sec 30° Head Down Tilt and 30 sec 85° HUT with -40 mmHg LBNP while performing the Anti-G Straining Maneuver (AGSM). At the completion of the ten cycles the subjects were placed in 45° HUT with -80 mmHg LBNP for 5 min followed by 5 min recovery. Subjects demonstrated a greater increase in Heart Rate during the EXP LBNP (+30% 1st min, +39% 5th min) than CON (+21% 1st min, +18% 5th min) and drop in SBP-EXP (-9% 1st min,-18% 5th min) than CON (-1% 1st min,-5% 5th rain). Stroke Volume initially decreased more in CON (-22% 1st min, -34% 5th min) than EXP (-15% 1st min, -31% 5th min). TPR increased significantly in CON (+5% 1st min,+16% 5th min) over EXP (-11% 1st min, 5% 5th min). These data suggest that subjects with previous -Gz exposure and AGSM were unable to vasoconstrict to the same degree during LBNP to maintain their BP and Cardiac Output, thus having to increase their HR to compensate. This may be due to competition from metabolically induced vasodilation post-AGSM. Ability to maintain SV in the face of lower TPR may be the result of redistribution of blood volume due to the AGSM.

Original languageEnglish (US)
Pages (from-to)A96
JournalFASEB Journal
Issue number3
StatePublished - 1997
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Biotechnology
  • Biochemistry
  • Molecular Biology
  • Genetics

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